Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The formation of Fe-colloids resulting from the chemical weathering of chlorite (Mg5.5Al2.48Fe2+3.02Fe3+0.94)(Si5.33Al2.66)O20 was studied in batch experiments. The chemistry of the detected colloids was determined by SEM/EDS measurements on separated agglomerated colloids fixed on filter membranes. The results show that the Fe-colloids exist as aqueous colloids as well as sorbed colloids forming iron coatings on the chlorite platelets. It was also observed that the newly-formed Fe-colloids are preferentially attached to the {hk0} edge surfaces and only to a minor extent as isolated Fe-colloids to the {001} basal plane surfaces. The average surface coverage of sorbed Fe-colloids on the {hk0} edge surfaces was found to be 0,276 žm2 of sorbed Fe-colloids per 1 žm2 of {hk0} chlorite surface, i.e. 27,6 % of the {hk0} surfaces is covered with adsorbed Fe-colloids. This value is significantly higher than the surface coverage found on the {001} basal plane surfaces. Here, the average surface coverage of Fe-colloids on the {001} basal plane surfaces was determined to be 0,030 žm2 of sorbed Fe-colloids per 1 žm2 of {001} chlorite surface, i.e. 3,0 % of the {001} surface area is covered with sorbed Fe-colloids. This shows that there are nine times more Fe-colloids adsorbed onto the edge surfaces than on the basal plane surfaces.
The detected colloids were, based on their chemistry, their spherical character and small particles sizes, identified as ferrihydrite. In addition, Mössbauer spectroscopy measurements were used to quantify the increase of ferric iron which formed during the batch experiment. This detected increase in ferric iron in the chlorite from 14.0 to 15.3 % š 1% was attributed to the formation of ferrihydrite.
The assumption that the edge surfaces of sheet silicates show a much higher affinity for adsorption reactions was so far not conclusively proven. However, the results of this study clearly show that colloid adsorption on the sheet silicate chlorite preferentially takes place on the {hk0} edge surfaces indicating that the edge surfaces of sheet silicates are by far more reactive in regard to sorption reactions than the distinctively less reactive {001} basal plane surfaces. In addition, the influence of Fe-phases as weathering products on sorption processes in nature is discussed.

Es ist ein Zeichen einer guten Sicherheitskultur, wenn Hersteller, Betreiber und Gutachter gleichermassen das Sicherheitsniveau von Kernkraftwerken stetig anheben wollen. Derzeit bietet sich die Gelegenheit, ueber fruehere, aktuelle und zukuenftige Konzepte nachzudenken. Ziel ist es, zukuenftige Anlagen zu optimieren, durch Systemvereinfachungen die Uebersichtlichkeit zu erhoehen und somit ihre Zuverlaessigkeit zu verbessern. Ferner sollen Effektivitaet und Wirtschaftlichkeit gesteigert werden. Hierzu wird seit Mitte der 90er Jahre an verschiedenen Stellen weltweit die Effektivitaet und das Betriebsverhalten passiver Sicherheitssysteme untersucht.
Im Beitrag wird auf die Geschichte des NOKO-Versuchsstandes zurueckgeblickt. Ferner werden ausgewaehlte Hoehpunkte der experimentellen Untersuchungen (u. a. der experimentelle Nachweis der thermohydraulischen Wirksamkeit des Notkondensators, des Gebaeudekondensators sowie des passiven Impulsgebers) beschrieben.

The ferric oxide schwertmannite is commonly formed in acid mine drainage waters (pH-range from 2.8 to 4.5) in the presence of high sulfate concentrations. Because of its large specific surface area its may influence the migration of uranium(VI) by sorption processes. The aim of this study were structural informations for uranium(VI) surface complexes given by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. We include Goethite in our investigations as a reference to compare and interpret the schwertmannite data.

Samples for EXAFS analysis were prepared under N₂ atmosphere using 200 mg of schwertmannite or goethite with initial uranium(VI) concentrations of 1x10^-5 (pH 6.5) to 5x10^-5 M (pH 4.2). The ionic strength was adjusted using 0.01 M Na₂SO₄ or NaClO₄ respectively. EXAFS spectra were recorded at room temperature in fluorescence mode at the Rossendorf beamline (ROBL) at the ESRF in Grenoble. The measured EXAFS oscillations were fitted using EXAFSPAK procedure. The theoretical phase shifts and backscattering amplitudes were calculated with FEFF8.

All distances of the equatorial oxygens are about 2.37 Å. These are significantly shorter than typical values of 2.41 Å for the aquatic UO₂ ²⁺ ion, which indicates strong interactions. An iron backscatterer is clearly found for uranium(VI) sorbed onto goethite at pH 4.2 and 6.5 in sulfate-rich solution as well as for schwertmannite at pH 4.2 in perchloric solution. Such a uranium - iron distance indicates a bidentate inner sphere complexation. In contrast, the EXAFS of uranium(VI) sorbed onto schwertmannite at pH 4.2 in sulfate-rich solutions shows only a sulfur backscatterer at a distance of 3.66 Å, indicating the formation of a ternary surface complex.

Tetrahedral amorphous carbon (ta-C) is an amorphous form of carbon with a high content of sp3 bonded atoms, which can be deposited as thin films by energetic carbon ions or neutral atoms. As-grown ta-C films possess a high level of intrinsic compressive stresses (~10 GPa) inhibiting the use of this very promising material. The stress is due to a specific growth mechanism (subplantation), resulting from a competition between the densification of subsurface layers by incoming ions and the thermally activated diffusion of subplanted atoms to the surface. In agreement with experiment, we demonstrate using atomic scale simulation that low-temperature annealing can induce a considerable stress reduction in as-grown ta-C with minor
changes in its atomic structure and density. Simulating annealing by means of empirical molecular-dynamics with the interatomic Brenner potential for carbon and realistic boundary conditions, the dependence of the residual stress on the annealing temperature was investigated. It is found that a complete stress relief in ta-C is not accompanied by a change in the short-range order. The average atomic coordination remains nearly constant up to 1400 K. The stress relaxation mechanism discussed involves only structural optimization within the sp3 bonded constituent of ta-C and does not require clustering of sp2 bonded atoms.

The uptake of heavy metals into plants is commonly quantified by the soil-plant transfer factor. Up to now little is known about the chemical speciation of actinides in plants. To compare the obtained spectroscopic data of uranium complexes in plants with model compounds, we investigate the complexation of uranium with relevant bioligands of various functionalities. A very important class of ligands are phosphate esters, which serve as phosphate group and energy transmitters as well as energy storage mediums in biological systems.
Therefore, in our study we present the results of uranium complexation with glucose-1-phosphate (G1P) obtained by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and potentiometric titration. The TRLFS-experiments were performed at a fixed uranyl concentration (10^-5 M) as a function of the ligand concentrations (10^-5 to 10^-3 M) in a pH range from 2 to 4.5. The potentiometric titrations were performed at fixed uranyl (10^-4 M) and ligand (10^-3 M) concentrations in a pH range from 3 to 10.
The TRLFS-measurements show a decrease in the fluorescence intensities with increasing ligand concentrations, and no shift of the emission bands. The TRLFS spectra indicate the presence of only one species with fluorescence properties. This species has a lifetime of 1.50 µs and was identified as the free uranyl ion. Therefore we conclude that the complexed uranyl glucose phosphate species shows no fluorescence.
From quantitative evaluation of the TRLFS spectra we conclude, that 1:1 uranyl glucose phosphate species UO₂(G1P) has formed. The complex formation constant was calculated to be log beta=5.60.
The results of the potentiometric titration show the same type of complex with a stability constant of log beta=5.37.

The influence of deposition conditions on the sp3 content, intrinsic stress, and elastic modulus in hard amorphous carbon (a-C) films was studied at the atomic scale. Simulation of ion beam deposition of carbon films was performed by the molecular-dynamics method with a modified analytical hydrocarbon potential of Brenner. Deposition of films with a thickness of up to 10 nm was computed for ion energies E = 10-80 eV, and for substrate temperatures ranging from 100 to 900 K. The dependence of the sp3 content and the intrinsic stress on substrate temperature was found to be in qualitative agreement with experiment. At low substrate temperatures and low ion energies, the sp3 fraction increases with ion energy, giving at E > 30 eV a highly sp3 bonded tetrahedral amorphous carbon (ta-C) with a high level of intrinsic compressive stress. This trend also remains at room emperature, however with lower values of sp3 content, whereas at T > 200 °C a transition to graphite-like a-C with dominating sp2 bonding was found.

A model of thermochemical polishing, namely the conversion of diamond into non-diamond carbon at elevated temperatures and the subsequent dissolution of the non-diamond carbon into a transition metal polishing plate is investigated. Equations of the conversion rate k1, the dissolution rate k2, the diffusion constant of carbon in steel D, and the concentration profile of carbon in steel N(x,t)are derived. The rate constants are calculated for four diamond films polished at varying temperatures. Elastic recoil detection analysis (ERDA) measured carbon depth profiles in steel agree well with theoretical calculations. However, the calculated value of D = 1,16 x 10-14 cm2/s is far below the value of D = 1,19 x 10-7 cm2/s for gamma-iron. The discrepancy between the two values is related to oxygen-enhanced segregation of carbon in the near surface region of steel and to the incorporation of elements which act as trap centers of carbon in steel.

The volatility of plutonium oxides in the O₂-H₂O_(g)/SiO_2(s) system has been studied by thermochromatography in the temperature range 1475 to 600 K. Oxides of uranium and neptunium have been studied for comparison. Oxide samples containing 10¹⁵ - 10¹⁶ actinide atoms were heated in the starting position of the thermochromatographic silica columns. Mixtures of helium, oxygen and water vapor were applied as reactive mobile gas phase. Resulting from thermochromatography the volatile actinide species are deposited in the column downstream, thus creating inner chromatograms along a temperature gradient. At the end of each experiment the actinide chromatograms were measured by alpha spectrometry.
Plutonium was found to be volatile in humid oxygen at temperatures above 1250 K. The Pu volatility is lower than that of uranium, but higher as one would expect for stable Pu(IV) which is nonvolatile under the applied experimental conditions. The Pu volatility is assigned to PuO₂(OH)_2(g). The experimental results give further evidence that water can oxidize plutonium dioxide.

This paper reports the synthesis, biological evaluation and in vitro autoradiography of a new technetium-99m radioligand with high affinity for the 5-HT_1A receptor. The neutral complex combines an N₂S₂ diamine dithiol (DADT) ligand as complexing moiety for oxotechnetium(V) and a 2-(1-piperazino)phenol via a 6-carbon alkyl chain, derived from desmethyl-WAY-100635 (DWAY). The complex displays an IC₅₀ value for the 5-HT_1A receptor of 1.29 nM against the selective 5-HT_1A agonist [³H]8-OH-DPAT, a moderate selectivity towards the alpha₁-adrenergic receptor (IC₅₀ of 8.1 nM against [³H]prazosin) and a good selectivity for the D₂ receptor (IC₅₀ of 192 nM against [³H]spiperone) and the 5-HT_2A receptor (IC₅₀ of 922 nM against [³H]ketanserin). Biodistribution studies in rats show an initial brain uptake of 0.65%±0.07% ID 2.5 min p.i. In vitro autoradiographic studies of the ^99mTc complex in rat brains indicate a strong specific accumulation of the radioactivity in 5-HT_1A receptor-rich brain regions.

The remediation of former uranium mining and milling sites of Saxony and Thuringia requires the purification of uranium contaminated seepage and mine waters. The separation of uranium(VI) from aqueous solution by calixarenes by means of solvent extraction is described in the literature (e.g., [1,2]). Calixarenes are macrocyclic molecules formed by 4, 6 or 8 parasubstituted phenolic units linked by methylene bridges ortho to the OH functions. Thus, molecules of various ring sizes are formed. The substitution of calix[6]arenes on the hydroxyl group by carboxylic and hydroxamic groups, respectively, leads to ligands that are able to bind uranium(VI) selectively.
The present work represents an innovative method for the separation of uranium(VI) from aqueous solution using uranophile calix[6]arenes that are fixed on textile substrates such as polyester fabric. For this, the calix[6]arenes are statistically functionalized by spacer groups (n-alkyl groups) that enable their fixation onto polyester fabric.
The complex formation of the textile bound calixarenes, e.g., carboxymethoxy-p-mono-nonyl-penta-tert-butyl-calix[6]arene, and their selectivity towards uranium(VI) ions is studied as a function of pH value, ionic strength and competing ions by means of batch experiments. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is used to determine complex formation constants. The reaction mechanisms are discussed. As competing ions, Na⁺, Ca²⁺, Mg²⁺ and Fe³⁺ as well as SO₄ ^2- are studied, that occur typically in mine waters. Furthermore, the reversibility of the uranium binding is evaluated. The results are compared with those obtained for the corresponding non-fixed calixarenes [3].
The new technique for the remediation of uranium contaminated waters is also applicable for lower contamination levels ([UO₂ ²⁺] < 1x10^-6 M) and is especially suitable for smaller remediation objects. The applicability of this separation principle to further actinides is expected.

[1] Shinkai, S., Koreishi, H., Ueda, K., Arimura, T., Manabe, O.: Molecular Design of Calixarene-Based Uranophiles which Exhibit Remarkably High Stability and Selectivity. J. Am. Chem. Soc. 109, 6371 (1987).
[2] Nagasaki, T., Shinkai, S.: Synthesis and Solvent Extraction Studies of Novel Calixarene-based Uranophiles Bearing Hydroxamic Groups. J. Chem. Soc., Perkin Trans. 2 (7), 1063 (1991).
[3] Schmeide, K., Barz, B., Heise, K.H., Bernhard, G., Gloe, K.: Solvent Extraction of Uranium(VI) by Calix[6]arene. In: FZR-318, Annual Report 2000 (Th. Fanghänel, ed.). Forschungszentrum Rossendorf, Institute of Radiochemistry, Rossendorf 2001, p. 17.

There is ample evidence from groundwaters, river waters, lakes or seawater that colloids influence the transport behavior of contaminants such as As, Pb, Cu, Zn, actinides, fission products, hydrophobic organics etc. Little efforts have been made to elucidate the role of colloids in mine waters. We studied mine waters of very different nature for their colloid-chemistry.
Very stable Fe(III) oxyhydroxy sulfate colloids were found in acid rock drainage (oxic acidic pore waters, pH < 3). The particle size was < 5 nm, the colloid concentration reached the g/l range. Mineralogically, the particles were a mixture of hydronium jarosite and schwertmannite. As and Pb showed a high tendency to adsorb onto these particles. Quite a different type of colloids was found in the oxic "bulk waters" of mines as for instance in tunnel waters (near-neutral pH). The particles were composed of oxyhydroxides of Fe(III) and Al, the particle size was 100 to 300 nm, the particle concentration was about 1 mg/l, the colloids were unstable, i.e. they tended to aggregate. Important colloid-borne contaminants were As, Cu, Zn, Pb, Po. Uranium(VI) adsorption is normally supressed due to the formation of uranyl carbonato complexes in such "bulk waters". The flooding of mines can be regarded as the dilution of acidic pore waters to form "bulk waters". Huge amounts of iron(III) particles with a size of 100 to 300 nm are formed under such conditions. The adsorption of trace elements rises drastically when the pH reaches the near-neutral region. Uranyl adsorption to the iron(III) particles is neither supressed by acidity nor by uranyl carbonate complexation in the pH region 4 to 6. Therefore most of the uranium(VI) is colloid-borne in waters of the transition type; scavenging, colloid aggregation and sedimentation can result in the immobilization of uranium in such waters ("natural attenuation").

Inorganic colloids in mine waters are able to influence trace heavy metal transport. In oxic waters they mainly result from the formation of oxyhydroxides and oxyhydroxy sulfates of Fe(III) and Al due to the oxidation of Fe2+ and the hydrolysis of Fe3+ and Al3+. However, the colloid inventories and the colloid properties depend on the mine wa-ter type. Acidic pore waters (pH < 3) contain large amounts (g/l range) of relatively stable ultrafine (< 5 nm) iron(III) oxyhydroxy sulfate particles which most probably consist of a mixture of hydronium jaro-site (HFe3(SO4)2(OH)6) and schwertmannite (Fe8O8(OH)6SO4). Arse-nic and lead tend to be adsorbed onto these colloids. Waters of higher pH (pH > 4) contain smaller amounts (mg/l range) of Fe- and Al-rich colloids of 100 to 300 nm that are unstable. They carry elements such as As, Pb, Zn, Cu, Po, Th, Ac. These trace heavy metals can be scavenged by the colloids and can be immobilized due to colloid coagulation and sedimentation ("natural attenuation"). In the pH range from 4 to 6 (flooding waters) also U(VI) is adsorbed onto the colloidal particles since their adsorption is neither prevented by high acidity nor by the formation of uranyl carbonato complexes. Also U(VI) can be scavenged and immobilized in this pH range. However, in "bulk wa-ters" of pH > 6 such as tunnel waters the adsorption of U(VI) to the colloids is normally prevented by carbonate complexation

The OECD Main Steam Line Break (MSLB) Benchmark was defined to validate the thermal-hydraulic system codes coupled with three-dimensional neutron kinetic codes. The reference problem is a MSLB in a pressurized water reactor (PWR) at end of cycle (EOC). The analyses were performed with the three-dimensional core model DYN3D, the thermal-hydraulic system code ATHLET and the coupled code DYN3D/ATHLET. The results of the DYN3D and ATHLET simulations based on the specification are compared with the results of other participants in the final OECD reports. The effect of the thermal-hydraulic nodalisation of the core, i.e. the number of coolant channels, and the influence of the coolant mixing inside the pressure vessel are studied in the paper. Calculations with a reduced number of coolant channels are performed often in coupled calculations for saving
computational time. Results of a 25-channel model were compared with the 177-channel calculation (1 channel/assembly). The results for global parameters like nuclear power show only small differences for the two models, however the prediction of local parameters such as maximum fuel temperatures requires a detailed thermal-hydraulic modeling. The effect of different coolant mixing within the reactor pressure vessel is investigated. It is shown that the influence of coolant mixing mitigates the accident
consequences when three-dimensional neutron kinetics is applied. In case of point kinetics, coolant mixing leads to an opposite effect. To profit from the three-dimensional core model, a realistic description of the coolant mixing in the coupled codes is a topic of further investigations.

Ex-vessel neutron dosimetry at NPP with VVER was used for validation of 3D absolute neutron fluence calculations. As second step of the VVER-1000 Balakovo-3 Ex-vessel Exercise, an analysis of calculational results has been performed. The reference experimental data - End-Of-Irradiation activities AEOI - were used as criteria of validation. The purpose of the research was to perform an intercomparison of independent calculational results and comparison with reference data of the full-scale VVER-1000 ex-vessel experiment. New and improved results of calculations analysed in the paper were run with codes and applied libraries DORT/BUGLE-96, DORT/EURLIB-6, DORT/ABBN-93 (and ABBN-93 modifications), TRAMO/ENDF/B-VI, MCNP/ENDF/B-VI. Calculated pure 3D or 3D synthesis multigroup neutron fluence rates in positions of experimental capsules provided by every calculator were used as basic calculational information. As first step of their comparative analysis a study was done of the used calculation input data prepared on the base of the same reactor information. For example, a difference of neutron source model details may be a reason of some discrepancy of results obtained by similar calculational procedures. Aspects of the influence of different dosimetry cross sections and local power history on the calculation of AEOI from calculated spectra were investigated. The analysed dosimetry cross section libraries were IRDF-90v2, JENDL-D99, RRDF-98 and ENDF/B-VI based BUGLE-96 responses. Final C/E values were based on AEOI. The C/E values for threshold dosimetry reactions 237Np(n,f), 93Nb(n,n'), 238U(n,f), 58Ni(n,p), 54Fe(n,p), 46Ti(n,p) and 63Cu(n,a), which are widely used in reactor pressure vessel dosimetry for fast neutron fluence evaluation, showed on the whole the expected agreement (better 20 %). It was found that the C/E data for the Balakovo-3 exercise in application to the 237Np(n,f) and 93Nb(n,n') reactions may be improved in case of using JENDL-D99 library. Another new aspect of the Balakovo-3 research is an analysis and intercomparison of calculational and experimental results for (n,g) dosimetry reactions. Different type (n,g) detectors were irradiated in cadmium. The obtained reaction rates characterize the distribution of epithermal neutrons. A comparison of the reaction rates, for example, for reactions 93Nb(n,g), 69Co(n,g) and 103Ag(n,g) in case of DORT/BUGLE-96 calculations has shown a coincidence of experiment and calculation data within ± 11 %. For one ex-vessel position where bare (n,g) detectors were irradiated thermal neutron parameters were evaluated and compared.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was used to study the properties of uranium complexes (emission spectra and fluorescence lifetimes) formed by the cells of the three recently described eco-types of Acidithiobacillus ferrooxidans. The results demonstrated that these complexes have different lifetimes which increase in the same order as the capability of the strains to accumulate uranium. The complexes built by the cells of the eco-type II were the strongest, whereas, those of the eco-types I and III were significantly weaker. The emission spectra of all A. ferrooxidans complexes were almost identical to those of the uranyl organic phosphate compounds. The latter funding was confirmed by infrared spectroscopic analysis.

Material of a mine waste dump of Kupferschiefer mining was investigated in column and equilibrium experiments in closed vessels over 64 days and 90 days, respectively. The de-ployed solids are composed of silicate phases, calcite, dolomite, gypsum, and a few percent of residual sulfides, already indicating a depletion of the karstifyable material and in particular a dedolomitization. The development of the solution composition at the columns outflow is characterized by a steady increase of alkalinity with a striking transient maximum, succeed-ing draw back and equilibration. In connection with an increasing mole fraction of magnesium in solution this phenomenon is interpreted as consequence of dedolomitization and depicted in abinary solubility diagram according to Lippmann (1980). In calcium rich pore waters (due to gypsum dissolution) dolomite dissolves incongruently precipitating calcite. Such compli-cated reaction paths are usually not identified by "crude" batch experiments. Moreover it could be shown that the formation of preferred flow paths may even affect the solution com-position in particular cases. In these experiments an estimation of transport parameters was not yet carried out, but is planned for the future to apply reactive transport codes for model-ing these processes.

The ability of transport codes ANISN, DORT, ROZ-6, MCNP and TRAMO, as well as nuclear data libraries BUGLE-96, ABBN-93, VITAMIN-B6 and ENDF/B-6 to deliver consistent gamma and neutron flux results was tested in calculation of an one-dimensional cylindrical model consisting of a homogeneous core and an outer zone with a single material. Model variants with H2O, Fe, Cr and Ni in the outer zones were investigated. The results are compared with MCNP-ENDF/B-6 results. Discrepancies are discussed. The specified test model is proposed as a computational benchmark for testing calculation codes and data libraries.

Radiation embrittlement of pressure vessel steel in mixed neutron-gamma fields is mostly determined by neutrons, but in some cases also by gamma-radiation. Depending on the reactor type, gamma radiation can influence evaluations of lead factors of surveillance specimens, effect the interpretation of results of irradiation experiments and finally, it can result in changed pressure vessel lifetime evaluations. This work aims to facilitate for some reactor types the evaluation of the importance of gamma radiation for embrittlement studies. Absolute neutron and gamma fluence spectra had been calculated for two core loading variants of the Russian PWR type VVER-1000, for a German PWR of Konvoi-Type and for a German BWR. Based on the calculated spectra several fluence integrals and radiation damage parameters were derived for the region of the midplane azimuthal flux maximum for different radial positions between the core and the biological shield, particularly, the inner and outer PV walls, the ¼ PV thickness and the surveillance positions. The relative contributions of gamma radiation to the sums of gamma and neutron contributions are of special interest. As damage parameters the displacements per atom of iron are given separately for neutrons and gammas as well as some rough estimations of the numbers of freely migrating defects. To get some notion about the uncertainty of the obtained dpa, the calculations were performed using different dpa cross section evaluations. Additionally, gamma produced dpa were calculated by means of the Monte Carlo code EGS.
Another parameter of practical interest for pressure vessel dosimetry, the contribution of photofission to the total number fissions, was calculated for the detector reactions 237Np(n,f) and 238U(n,f).
Most of the calculations were performed using a 3D synthesis of 2D/1D-flux distributions obtained by the DORT code with the BUGLE-96 library. To increase the reliability of the evaluations some of the calculations were repeated by different laboratories. For two reactors the influence of the group approximation on the calculation results was investigated by parallel calculations with the continuous energy Monte Carlo code MCNP using nuclear data from the library ENDF/B-VI.
The results were compared and the reasons of found discrepancies were discussed.

The Forschungszentrum Rossendorf (FZR) e.V. is building a new large-scale test facility for thermal hydraulic single effect tests, named TOPFLOW. The acronym stands for Transient Two Phase Flow Test Facility. It will mainly be used for the investigation of generic and applied steady state and transient two phase flow phenomena in power- and process industries. Main research activities are the investigation of:

· transient flow regimes in horizontal, vertical and inclined tubes,
· the dynamic behaviour of interphase areas in gas-liquid flows,
· critical mass flows and oscillations during depressurization of chemical reactors,
· natural convection in large pools with local heating,
· natural convection in parallel channels and feed pipes and
· condensation phenomena (e.g. in emergency and isolation condensers, WWER steam generators).
It is FZR strategy to use TOPFLOW as a central experimental basis for the nuclear competence centre, rejoining FZR, the Technical University of Dresden (TUD) and the University of Applied Sciences Zittau-Görlitz (HTW) and to offer it to working groups throughout Europe. They will be invited to come to Rossendorf with their ideas and to perform their experiments here making use of the parameters (power, water and steam mass flow, pressure range, measuring instrumentation) and the multipurpose character of the test facility.

Depth profiling measurements of tritium at carbon samples have been performed during the past seven years at the AMS facility installed at the Rossendorf 3 MV tandetron. The samples have been cut from the inner wall of the fusion experiments ASDEX-upgrade/Garching and JET/Culham. The increasing amounts of tritium inside the samples from JET have been required a dedicated AMS facility to prevent any contamination of the versatile 3 MV tandetron. On base of an air-insulated 100 kV tandem accelerator equipped with a gas stripper a small dedicated AMS facility for tritium depth profiling was installed, tested and used for routinely measurements. After successful tests of diamond-like carbon (DLC) stripper foils at this accelerator a small and compact SF6-insulated 100 kV tandem accelerator with a DLC-stripper has been installed at the AMS facility. Results measured with the different tandem accelerators are presented.

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In order to validate Monte Carlo calculations for coupled neutron/gamma problems in reactor dosimetry an experimental benchmark programme at two low power reactors was started to measure both, neutron and gamma flux spectra behind and inside of transmission modules consisting of variable iron and water slabs. The comparison of the first series of experiments with MCNP calculations is presented.

The processes of sulfide oxidation, water acidification and water mineralization in abandoned ore mines is closely associated with the existence of gangue fissures in the host rock that contain clay minerals and finely-divided sulfide ores. These fis-sures release highly mineralized, red-colored acid rock drainage (ARD) solutions which can easily be collected from pools in front of the fissures. ARD solution from an abandoned Zn-Pb-Ag mine at Freiberg, Germany, (pH 2.7, sulfate concentration 411 mmol/l, Fe concentration 93,5 mmol/l) was investigated by photon correlation spec-troscopy, centrifugation, filtration, ultrafiltration, scanning electron microscopy, ICP-MS, AAS, ion chromatography, TOC analysis, and X-ray absorption fine structure (EXAFS) spectroscopy. The question was if this ARD solution contains colloidal par-ticles of the lower nanometer range or if it is particle-free after the common filtration through a 450-nm filter. We found that the solution contains a small amount (about 20 mg/l) of submicron particles of about 100 nm in size. However, the major colloidal component was shown to be a population of ultrafine particles of less than 5 nm. The concentration of these particles is about 1 g/l. They consist of Fe, As and Pb com-pounds. According to EXAFS spectroscopy, the most probable mineralogical compo-sition of these particles is a mixture of hydronium jarosite (HFe3(SO4)2(OH)6) and schwertmannite (ideally Fe8O8(OH)6SO4). We also observed the formation of a rela-tively coarse precipitate of a similar mineralogy in the colloidal solution over a time span of months. The ultrafine colloids are obviously an intermediate in the formation process of the long-term precipitate. The arsenic is probably bound onto the ultrafine colloidal particles as a bidentate binuclear arsenate surface complex (inner-sphere complex). However, the transformation of the colloids to the more aggregated long-term precipitate leads to the incorporation of the arsenic into the interior of the iron hydroxy sulfate structures. The mechanism of this incorporation could be the substi-tution of arsenate for sulfate in the jarosite structure and/or the formation of very small scorodite clusters as occlusions within the oxyhydroxysulfate structures. The lead might occur as anglesite (PbSO4).

Two novel five-coordinate cis-dioxorhenium(V) complexes of the general formula ReO₂[R₂NCH₂CH₂S][PPh₃] (R₂N=Et₂N, complex 1 and R₂N=(o-CH₃O-C₆H₄N(CH₂CH₂)₂N, complex 2) have been synthesized by reacting ReOCl₃(PPh₃)₂ with the respective bidentate ligands R₂NCH₂CH₂SH. The complexes have been characterized by elemental analysis, IR, NMR spectroscopies and X-ray crystallography. X-ray crystallographic studies showed that the coordination geometry around rhenium is distorted trigonal bipyramidal. the basal plane is defined by the two doubly bonded oxygen atoms and the sulfur of the bidentate ligand, while the nitrogen of the ligand and the phosphorus occupy the apical positions.

Results of two surge line break experiments, which were conducted at the PMK-2 test facility, are presented. The thermo-hydraulic computer code ATHLET, which was developed by GRS (Gesellschaft für Anlagen- und Reaktorsicherheit) mbH, was used for post-test calculations. The experiments simulate a break of the pressurizer surge line in the hot leg of a VVER-440-type reactor with different injection modes from the ECC systems. The main phenomena of the experiments are discussed and in case of selected events a more detailed interpretation with help of the measured void fraction, obtained with a special measurement device, is given. The results of the experiments and the ATHLET calculations are compared. In both experiments natural circulation instabilities could be observed. The physical mechanisms of the instabilities are discussed and it could be shown, that ATHLET can calculate the instabilities in good agreement with the experimental data.

A new method for the thermal-hydraulic calculations in the reactor core using a porous media approach is presented in this paper.
The Core Crossflow Experimental Facility (CCEF) was built for the validation of this method.
The comparison of the calculations using this method with the experimental data from CCEF are also presented.

High-spin states in 90Y were populated in the 82Se(11B,3n)
reaction at a beam energy of 37 MeV. Gamma rays were detected with the spectrometer GASP. The level scheme of 90Y was extended up to J^\pi = (18^+) at 9.6 MeV. Mean lifetimes of four levels were determined using the Doppler-shift-attenuation method. The structure of 90Y was
interpreted in terms of the shell model. The calculations were performed in the model space \pi(0f_{5/2},1p_{3/2},1p_{1/2},0g_{9/2})
\nu(1p_{1/2},0g_{9/2},1d_{5/2}) and in an extended space including the \nu(0g_{7/2})$ orbital as well. The calculations in the extended model space reveal a correspondence between states in ^{90}Y and ^{89}Y. Moreover, a combination of the predicted states with J^\pi \geq 14^(+) can be found
that reproduces the large B(M1) values of up to about 1 W.u.

The present work gives a detailed overview about our motivation for the synthesis of humic acid model substances. Exemplary for one synthetic humic acid (type M42), which is synthesized from xylose, glutamic acid and water [1], the synthesis, 14C-labeling ([14C]M42) and modification (M42-PB) of humic acids are described. We will discuss the characterization of these synthetic humic acids in comparison to natural humic acids from the literature as well as to natural humic acid Kranichsee [2]. This humic acid was isolated from surface water of the mountain bog "Kleiner Kranichsee" (Johanngeorgenstadt, Western Saxony, Germany) applying standard isolation techniques for humic acids.
The application of synthetic humic acid model substances will be presented with two examples. First, we will demonstrate the use of humic acid type M42 and humic acid type M42 with blocked phenolic and other blocked acidic OH groups (M42-PB) as model substances for the investigation of the neptunium(V) complexation by humic acids.
Secondly, we will discuss the application of 14C-labeled synthetic humic acid type M42 in batch and column experiments. The intend of these investigations is to improve the knowledge about the influence of humic acids on the mobilization or immobilization of actinides under natural conditions.
In addition to humic acid-like melanoidins, we synthesize humic acid model substances with distinct redox functionalities. Applying these model substances, detailed investigations with regard to the redox behavior of humic acids as well as to the redox stability of actinide humate complexes can be performed. In the present work we will give an brief overview about the synthesis, characterization and application of humic acids with pronounced redox functionalities.

[1] S. Pompe (Sachs), M. Bubner, K. Schmeide, K.H. Heise, G. Bernhard, H. Nitsche, 'Influence of Humic Acids on the Migration Behavior of Radioactive and Non-radioactive Substances under Conditions Close to Nature. Synthesis, Radiometric Determination of Functional Groups, Complexation', Report FZR-290, Rossendorf, 2000.
[2] K. Schmeide, H. Zänker, K.H. Heise, H. Nitsche, in Report FZKA 6124, G. Buckau (ed.), Karlsruhe, 1998, p. 161.

Polyelectrolytic organic macromolecules, like humic substances, are important complexing agents towards actinide metal ions. Due to these properties humic substances are possible carriers for the migration of actinides in the environment. The study of the high molecular compounds is very complex. Therefore the investigation of simple model ligands would give a more detailed description of the binding behavior of humic substances. Especially the different bonding of carboxylic and phenolic group and the discrimination between them is of interest to get more detailed information about the complex formation. The various hydroxy benzoic acids allow the investigation of these differences.
To study the complex formation of actinides with such organic ligands we used the new, recently developed tool of femtosecond laser-induced time-resolved fluorescence spectroscopy. The method uses the fluorescence properties of organic ligands with p-electron systems and their change by interaction with metal ions to study the complex formation of these systems.
The method was validated by study of the deprotonation of 2,3 dihydroxybenzoic acid. Within the error limits a very good agreement of the third protonation constant was found.
The studies of the complex formation of uranium(VI) with 2,3 dihydroxybenzoic acid in the pH range from 3.0 to 4.5 showed an one to one complex. The dependence of the complex formation on pH leads to the conclusion that besides the carboxylic group one of the two phenolic OH-groups contributes to the complex formation. The formation constant was determined to be log K(I=0.1M) = - 3.02 ± 0.09.
Studies of the complex formation in the system neptunium(V)-2,3 dihydroxybenzoic acid showed a completely different behavior. At low pH values also an one to one complex formation was found. This complex formation was not dependent on pH. That means complexes with the deprotonated carboxylic group were formed.
The formation constant was determined to be log K(I=0.1M) = 0.11 ± 0.04. With increasing pH the complex reaction changes. An intermediate complex can be observed by its own fluorescence properties. At pH values higher then six an one to two complex will be formed. The complex formation constants and the stoichiometry of the complex reaction will presented.

Summary. The surface sorption process of Eu(III) onto smectite and kaolinite was investigated by time-resolved laser fluorescence spectroscopy (TRLFS) in the trace concentration range. The experiments were performed in 0.025 M and 0.45 M NaClO4. The sorption process of Eu(III) onto smectite was obtained by TRLFS under atmospheric conditions and in absence of CO2. The pH was varied between 3.5 and 9 at a fixed metal ion concentration of 3.3x10-6 mol/L Eu(III). At low pH (< 4) the metal ion keeps its complete hydration sphere indicating outer-sphere complexation. With increasing pH the formation of an inner-sphere Eu(III) surface complex was observed. The differences in the spectra and the fluorescence emission lifetimes of the surface sorbed Eu(III) in presence and absence of carbonate indicate the formation of ternary clay/Eu(III)/carbonate complexes. The different europium/clay surface complexes were characterized by their fluorescence emission spectra (5D0®7F1/5D0®7F2 intensity ratio) and their fluorescence emission lifetime.

Das Verhalten eines Reaktordruckbehälters bei Kernschmelzunfällen ist von hoher sicherheitstechnischer Bedeutung für die Beherrschung derartiger Störfälle. An der Königlich-Technischen Hochschule Stockholm werden in einem umfangreichen Programm (FOREVER - Failure Of REactor VEssel Retention) die Verformung und das Versagenverhalten des Druckbehälters unter der thermischen Belastung einer oxidischen Schmelze untersucht. Die Experimente werden begleitet durch Finite-Element-Modell-Vorausrechnungen und durch metallografische Nachuntersuchungen. Die Gefügeänderungen geben Hinweise auf die aufgetretenen Maximaltemperaturen und Temperaturgradienten, auf die Wechselwirkungen mit der Schmelze und der umgebenden Atmosphäre sowie auf den Versagensmechanismus. Am Beispiel eines FOREVER-Experimentes werden die Ergebnisse der Nachtestuntersuchungen mit den FE-Modellrechnungen verglichen. Die metallografischen Befunde bestätigen die FEM-Vorausrechnungen.

The use of electromagnetic forces to control the flow of electrically
conducting fluids is mostly associated with highly conducting liquids
like liquid metals and semiconductor melts. Only recently,
Electro-magnetic Flow Control for fluids of low electrical
conductivity like seawater has gained increasing interest. Most of the
published experimental and numerical work in this emerging field is
dedicated to skin friction reduction in turbulent boundary layers.

The present paper is focused on utilizing the accelerating effect of a
streamwise Lorentz force to prevent flow separation at the suction
side of a NACA 0015 hydrofoil. While the basic effects of
separation suppression and circulation enhancement have been
shown in [1], we will concentrate on the comparison of the
experimental results with such of separation control by steady
blowing. For this purpose, the Lorentz force strength will be given in
terms of an electromagnetic momentum coefficient C_EMHD, describing
the ratio of the total electromagnetic force imposed on the flow to
the product of dynamic pressure and wing area. Force measurements in
the Reynolds number range 2.9 10E4 < Re < 3.7 10E5, obtained with 3
different hydrofoils will be used to give a first approximation of the
maximum lift gain in dependence upon Reynolds number and Lorentz
force. Again, the electromagnetic momentum coefficient seems to be an
acceptable correlation factor to describe the control effect of the
Lorentz force in different flow configurations.

Es wurde gezeigt, daß das Lettenwasser eine kleine Menge (ca. 20 mg/l) an Submicronpartiklen von etwa 100 nm Größe enthält. Die kolloidale Hauptkomponente sind jedoch ultrafeine Partikel einer Größe von weniger als 5 nm. Sie weisen eine Konzentration von ca. 1 g/l auf. Diese Partikel bestehen wahrscheinlich aus einem Gemisch von H-Jarosit und Schwertmannit und sind ein Zwischenprodukt bei der Ausscheidung gröberkristalliner Präzipitate. Außerdem tragen sie Arsen und Blei. Das As ist offensichtlich als Arsenat-Oberflächenkomplex an die ultrafeinen Partikel gebunden. Bei der Ausscheidung von gröberkristallinen Fe-Oxyhydroxisulfatpräzipitaten scheint dann auch Arsenateinbau in das Innere der Oxyhydroxisulfatstrukturen eine Rolle zu spielen.

Monte-Carlo estimates of the subthreshold Phi meson production are performed for the reaction ¹²C + ¹²C at 2 AGeV assuming the Phi's to be emitted isotropically and distributed thermally in the center-of-mass system of the colliding nuclei. Different scenarios involving the detector installations FOPI and HADES at SIS/GSI are considered to determine the expected yields of Phi(1020) mesons identified via the K⁺K^- and e⁺e^- decay channels.

The preliminary experimental data on phi production in the reaction Ni(1.93 AGeV) + Ni point to a puzzling high phi yield which can not be reproduced with present transport codes. We survey the experimental situation and present prospects for dedicated measurements of the phi multiplicities with the $K^+ K^-$ and $e^+ e^-$ channels at HADES and FOPI.

Crystalline and amorphous GaSb surfaces are compared concerning their response
to sputter erosion with low-energy Ar$^+$-ions under normal incidence. We show
that the formation of regular nanostructures on GaSb is basically independent
on whether the initial material is crystalline or amorphous. The similarity in
the temporal and spatial evolution demonstrates that the dynamics of the
morphology evolution is entirely controlled by a thin amorphous
nonstoichiometric surface layer.

We have investigated the temperature dependence of the optical reflectivity on
a femtosecond scale in a near-optimally doped YBa$_2$Cu$_3$O$_{7-x}$
superconductor. The combined study of the lattice and carrier dynamics at
temperatures above T$_c$ allows us to identify two crossover temperatures in
the normal state giving evidence for an inhomogeneity of the pseudogap regime.
These crossovers exhibit a clear hysteresis behavior depending on the direction
of temperature change. The carrier and lattice dynamics within the crossover
regimes show distinct differences from and similarities to the superconducting
state, which may help in choosing between the competing theories for the
pseudogap state.

Background:

Intraluminal beta-irradiation has been shown to decrease neointimal proliferation after angioplasty in experimental models. The purpose of this study was to test the technical feasibility and biological effects of ¹⁸⁶Re-labeled stents.

Methods and results:

Thirty-four New Zealand White rabbits were fed a 0.5% cholesterol diet before balloon angioplasty and insertion of Palmaz stents in the infrarenal aorta. The animals were killed 7 weeks after stent implantation. Two of 34 animals died prematurely (aortic leak, pneumonia). Control stents (n=7) were compared with ¹⁸⁶Re stents (2.6 MBq [n=6], 8.1 MBq [n=5], 16 MBq [n=6], and 25.3 MBq [n=8]). Stent application was successful in all cases. No thrombus occlusion was observed. After 7 weeks, neointima formation was 2.2±0.2 mm² in the control group. In the treatment groups, a dose-dependent neointima reduction was detectable (0.5±0.5 mm² [2.6 MBq], 0.4±0.4 mm² [8.1 MBq], and 0 mm² [16.0 MBq, 25.3 MBq]). No induction of neointimal formation was observed at the edges of the stents. Radiation resulted in delayed reendothelialization.

Conclusions:

¹⁸⁶Re stents were capable of reducing neointima formation in a dose-dependent fashion. ¹⁸⁶Re stents did not cause late thrombosis or neointimal induction at the stent margins in the observation period of 7 weeks.

Excited states of the nucleus 79Br were investigated via the reaction
76Ge(7Li,4n) at 35 MeV. Coincidence data of emitted gamma rays
were measured with an arrangement of six EUROBALL CLUSTER detectors.
The E2 bands built on the 9/2+ and 3/2- states were extended up to
J = 37/2 at E \approx 8.8 MeV. The M1 band starting with a 15/2-
state at 2.6 MeV was extended to J = (29/2) at E = 6.4 MeV. Cross-over
E2 transitions within this band were observed for the first time. Mean
lifetimes of 17 levels were deduced using the Doppler-shift-attenuation method.
The M1 band can be described within theTilted-Axis-Cranking model on the
basis of the tilted three-quasiparticle configuration
pi(g9/2) nu (g9/2) nu (fp) which has a triaxial shape. This band
appears as a mixed case including contributions of both, magnetic and
collective rotation.

Parabolic potential profiles are commonly used in ion sheaths as it simplifies the mathematical formulation and is observed in limited experimental observations, where measurement uncertainties justify it. However, before using the parabolic potential profile assumption in all cases, there are other factors that needs to be concerned. The article highlights these factors for collisionless and collisional ion sheaths.

In existing NPPs water hammers can occur in case of an inflow of sub-cooled water into pipes or other parts of the equipment, which are filled with steam or steam-water mixture. They also may appear as the consequence of valve closing or opening actions or of breaks in pipelines, with single phase or two-phase flow. The influence of the fluid-structure interaction on the magnitude of the loads on pipe walls and support structures is not yet completely understood. The lack of experimental data obtained at well defined geometric boundary conditions is a significant obstacle for the validation of codes which consider fluid-structure interaction. Furthermore, up to now the feedback from structural deformations to the fluid mechanics is not fully implemented in existing calculation software codes. Therefore, at FZR a cold water hammer test facility (CWHTF) was designed and built up.

Dipole excitations in the semimagic N=50 nucleus ^{87}Rb were investigated at the Stuttgart Dynamitron
facility using bremsstrahlung with an endpoint energy of 4.0 MeV. The widths Gamma or the reduced excitation probabilities B(Pi 1)uparrow of 19 states were determined for the first time. The magnetic dipole excitations
are well reproduced in the framework of the shell model, however, these calculations cannot describe the observed electric dipole excitations.The 1/2^+ state at 3060 keV is proposedto be the weak coupling of an f_{5/2} proton hole to the 3^- octupole vibrational state in the N=50 core ^{88}Sr. The relatively strong E1 transition from that state to the ground state is explained as mainly the neutron h_{11/2} \rightarrow g_{9/2} transition. The breakup of the N=50 core and neutron excitations into the h_{11/2} shell are essential to describe electric dipole excitations, but neutron-core excitations do not play an important role for the structure of magnetic dipole excitations.

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 are currently underway at the Division of Nuclear Power Safety of the Royal Institute of Technology Stockholm. 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.
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 a Finite Element model is developed based on a multi-purpose code. After post-test calculations for the FOREVER-C2 experiment, pre-test calculations for the forthcoming experiments are performed. Additionally metallographic post test investigations of the experiments are conducted to improve the numerical damage model and to adjust the correlation between the metallographic observations and the calculated damage. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.
After analysing the calculations, it seems to be advantageous to introduce a vessel support which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it is possible to install an absolutely passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down.

Scaled coupled melt pool convection and vessel creep failure experiments are being performed in the FOREVER program at the Royal Institute of Technology, Stockholm. These experiments are simulating the lower head of a pressurized reactor vessel under the thermal load of a melt pool with internal heat sources [1]. Due to the multi axial creep deformation of the three-dimensional vessel with a highly non-uniform temperature field these experiments offer an excellent opportunity to validate numerical creep models. A Finite Element model is developed and using the Computational Fluid Dynamic module, the melt pool convection is simulated and the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a new creep modeling procedure. Additionally, the material damage is evaluated considering the creep deformation as well as the prompt plasticity [2, 3].
Pre- and post-test calculations of at least 4 FOREVER experiments have been performed successfully [4]. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.
After analyzing the calculations, it seems to be advantageous to introduce a vessel support which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it is possible to install an absolutely passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down.

By using the fusion-evaporation reaction 28Si(36Ar,p3n) and spectroscopy of beta-delayed gamma rays and charged particles on mass-separated sources, beta-decay properties of the neutron-deficient isotope 60Ga were studied for the first time. The half-life of 60Ga was determined to be 70(15) ms, and, based on gamma-gamma coincidences, the isobaric-analogue state in 60Zn was identified at 4851.9(7) keV. A semiempirical proton separation energy value of 40(70) keV was deduced for 60Ga. The experimental results on half-life, mass excess, proton separation energy, and structure of the 60Zn daughter states are discussed in comparison with various model predictions, including large scale shell model calculations.

6H-SiC n-type wafers were implanted with Al+ and N+ ions in two steps: first N+ double implantation (65 keV, 5x1016 cm-2 , 120 keV, 1.3x1017 cm-2 ) followed by Al+ double implantation (100 keV, 5x1016 cm-2 and 160 keV, 1.3x1017 cm-2 ). The implantation was carried out at a substrate temperature of 800 0C in order to avoid amorphisation. In this way a buried SiC1-x(AlN)x layer could be created. Variable-energy positron Doppler broadening measurements were performed at room temperature using a magnetic transport beam system in order to characterize the vacancy-type defects created by ion implantation. Depth profiles could be evaluated from the measured Doppler broadening profiles. The defect distribution and the defect size after the complete co-implantation are discussed and the contribution of the different implantation steps to the evolution of this defect structure is shown.

An epitaxial n-type 6H-SiC layer has been fourfold implanted with Al+ ions at temperatures ranging from room temperature to 1200 oC in order to create a buried p-doped layer from 200 nm to 600 nm below the surface. The defects induced by the ion implantation at different temperatures have been investigated by Slow Positron Implantation Spectroscopy. Higher substrate temperatures were found to lead to a significant reduction in the depth of the damage. However, this is accompanied by the formation of vacancy clusters of sizes up to seven Si-C divacancies. Only at 1200 ºC does the vacancy agglomeration disappear in the implanted region, and larger agglomerates are formed immediately below the surface. Furnace annealing at 1650 ºC was found to be insufficient to remove all damage.

Single crystal 6H-SiC samples were irradiated at room temperature with 200 keV Al+ ions at fluences ranging from 3.5x1013 to 2.8x1014 ion/cm2. Depth profiles of crystal defects both in the C and Si sublattices were measured by Backscattering Spectrometry combined with channeling technique (BS/C) at 3550 keV 4He+ ion beam energy along the <0001> axial channeling direction. Damage in the carbon sublattice was found to be higher than in the silicon one. Moreover, C/Si damage ratio decreased with increasing fluence. The crystal defect profiles can be well simulated both by full-cascade SRIM and Crystal-TRIM programs. Effective displacement energies for carbon and silicon sublattices in the applied fluence range of Al implantation were determined by comparing SRIM simulations to BS/C results.

Niedriglegierte ferritische Stähle gelten ebenso wie die hochlegierten austentischen Stähle als anfällig gegen Wasserstoffversprödung. Im Kernreaktor können Korrosion oder Radiolyse zur Bildung von atomaren Wasserstoff an der inneren Oberfläche des Reaktordruckbehälters und folglich zur Wasserstoffaufnahme während des Reaktorbetriebes führen. Der Beitrag stellt Ergebnisse zum Wasserstoffdiffusionsverhalten, zur Wasserstofflöslichkeit und zum Einfluss des Wasserstoffs auf die mechanischen Eigenschaften vor. Sie wurden an unbestrahlten Druckbehälterstählen unterschiedlicher Art gewonnen und beziehen sich auf solche Bedingungen, die denen im DWR nahe kommen.

During emergency core cooling (ECC) injection into the cold leg of a PWR an incomplete mixing of the injected water with the natural circulation flow in the loop takes place. Due to the higher density of the ECC water a streak of cold water is flowing downwards the downcomer. This causes thermal loads on the reactor pressure vessel wall. Furthermore, the core behaviour is determined by the resulting parameter distributions at the core inlet.
An experimental study was carried out at the ROCOM test facility, a fluid dynamic model of a German type PWR (KONVOI 1300 MWe) in the scale of 1:5. Natural circulation conditions in one loop were approximated by running the corresponding pump at low rotation speed by means of a frequency transformer system. The higher density of the injected water was simulated by adding sugar. The evolution of the spatial distribution of the ECC water was measured by tracering with sodium chloride. Conductivity distributions reflecting the share of ECC water present at given time and location were measured by electrode mesh sensors, one close to the reactor inlet nozzle (16 x 16 measuring points), two sensors in the upper and lower part of the downcomer (2D grids of 4 radial and 64 angular measuring positions) and one sensor at the core entrance (inlets of each of 193 fuel elements).
The paper presents visualisations of the streak effect in the downcomer. The transition from momentum driven flow in the downcomer to a density driven regime was identified (critical Froude number). In the experiments the relative density difference was varied between 0 and 10 % and the loop flow rate between 0 and 15 % of the nominal. The streak effect is more pronounced at higher density differences.

In an attempt to develop new technetium-based radiopharmaceuticals for the non-invasive diagnosis of myocardial metabolism, we have synthesized three examples of novel metal-containing fatty acid derivatives according to the '3+1' mixed-ligand and the Schiff Base/tricarbonyl design. The chelates contain the metal core in the oxidation states +5 and +1 respectively, and were attached to the ending position of a fatty acid chain. The complex formation was accomplished by ligand exchange reactions using three different rhenium precursors, whereas the inactive rhenium metal was utilized as surrogate of the technetium radionuclide. The molecular structures of the fatty acid complexes 7, 10 and 14 were determined by single-crystal X-ray diffraction analyses and show impressively a general problem in technetium tracer research, namely the significant structural alterations of bioactive molecules by coordination even to small-sized metal chelates.

The instability of a rotating magnetic field driven liquid metal flow in a finite cylinder with respect to infinitesimal azimuthally periodic
perturbations is studied numerically. This instability is observed to set in prior to its axisymmetric counterpart with relatively low frequency at diameter-to-height ratios between 0.5 and 2. The both, axisymmetric and three-dimensional instabilities have similar characteristic features. The instability originates in the cross-section of the horizontal and vertical rotating boundary layers and excites inertial waves in the inviscid core.

Renal cell carcinoma (RCC) belongs to the 12 most frequent tumors in Germany. Its incidence increases worldwide. 30% to 40% of patients already have metastases when the tumor is diagnosed and further 50% develop metastases after tumor resection. Radiotherapy or chemotherapy have no therapeutic effect against RCC. Systematic therapy of RCC with immunostimulatory cytokines is limited by dose due to serious side effects. A tumor targeting antibody offers the possibility to achieve efficient local doses of cytotoxic or immunostimulating reagents within the tumor without high systemic burden.

Our approach is to treat metastatic RCC with immunoactive agents coupled to our mAb 138H11 specific for human GGT (gamma-glutamyltransferase) which has the ability to target human clear cell and papillary RCC. In extracorporeal transfusion experiments with human RCC-bearing kidney 99m-Tc-labeled 138H11 was enriched up to 20-fold in the tumor. Treatment of nude mice bearing human RCC xenografts with a highly cytotoxic drug (Calicheamicin theta) conjugated to mAb 138H11 led to a significant shrinkage of tumor mass (Cancer Res. 2000, 60, 6089-6094). However, these nude mice are not useful for evaluating ADCC of naked 138H11 or immunoactive conjugates.

For creating a syngeneic 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-analyses 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-labeled 138H11 in the GGT positive RENCA tumors compared to the wild type tumors.

Nowadays, the majority of radiopharmaceuticals used in routine nuclear medicine imaging procedures are ^99mTc labelled compounds, and intensive research is in progress to design new ^99mTc radiopharmaceuticals. Investigation of Tc and Re carbonyl chemistry has led to an organometallic M(I) aqua ion, M(CO)₃(H₂O)₃]⁺
(M = Tc, Re), as a precursor for the preparation of complexes containing the small [M(CO)₃]⁺ moiety. Tc(I) and Re(I) tricarbonyl complexes represent a new and promising approach to low-valent, non-polar and inert compounds. Complexes with N-donor or S-donor chelating ligands coordinated to the M(I) tricarbonyl moiety with high stability in aqueous solution may serve in the design of radiopharmaceuticals [1, 2].

The aim of this work was to investigate the stability of a model Tc(I) dithioether-tricarbonyl complex, Tc1, in aqueous solution and to estimate structural
parameters for the dissolved compounds. Owing to the extremely small concentration of the radionuclide present in the radiopharmaceutical preparation (10^­6 ­ 10^­8 M), XAS studies as well as most other chemical investigations employ the long-lived isotope ⁹⁹Tc (K-edge at 21.044 keV). We found that the complex Tc1 is reversibly transformed into the complex Tc1a in aqueous solution (Figure 24).

Fig. 24: Reversible transformation of the complex Tc1 in aqueous solution.

Chemical investigations were performed both at the ⁹⁹Tc and ^99mTc levels. The change of charge of the complexes was determined by electrophoresis. Mass-spectrometric analyses and EXAFS measurements confirmed the composition of the compounds. EXAFS analyses were carried out at BM20 (Rossendorf CRG beamline, ROBL) [3]. ⁹⁹Tc solutions of Tc1 and Tc1a were prepared by dissolving solid Tc1 in water/methanol and adding chloride or Ag⁺, respectively. With an excess of sodium chloride the equilibrium (Figure 24) is on the side of the Tc1 complex. If chloride is removed from the equilibrium by precipitation as AgCl, Tc1a is the species in solution. To obtain a satisfactory evaluation of the EXAFS spectra and the Fourier transforms, single-scattering paths including the C, O and S/Cl coordination shells and multiple-scattering paths to model the oxygen atom of the carbonyl group were taken into account (Figure 25). The estimated atomic distances are 1.92 Å (Tc­C), 2.49 Å (Tc­S or Tc­Cl), 2.19 Å (Tc­O_aq) and 3.06 Å (Tc­O_CO). The coordination numbers agree with the molecular structure represented in Figure 24. EXAFS analysis of Tc1a shows the same structural parameters for the C, S/Cl and CO coordination shells as Tc1 except that the coordination number for the S/Cl coordination shell is lowered by approximately one. In addition, the detection of 1.2 ± 0.3 oxygen atoms at 2.19 Å proves the substitution of chlorine by water. This can be seen in Figure 25 as a reduction of the magnitude of the second peak in the Fourier transform since electron back-scattering from the oxygen atom is weaker than from the chlorine atom.

Fig. 25: Tc K-edge k3-weighted EXAFS spectra and the corresponding Fourier transforms of Tc1 and Tc1a (solid line: experimental data, dotted line: fit), transmission mode, sample concentration 3.5 x 10-2 M, sample thickness 1 cm, room temperature.

EXAFS analyses were successfully used to determine structural parameters of Tc(I) tricarbonyl complexes in solution. In connection with chromatographic,
electrophoretic and mass-spectrometric methods, it was found that Tc(I) tricarbonyl complexes containing a bidentate thioether ligand are able to react with water by
exchange of chlorine.

References
[1] R. Alberto et al., Coordination Chem. Rev., 190-192, 901 (1999).
[2] H.-J. Pietzsch et al., Bioconj. Chem., 11, 414 (2000).
[3] W. Matz et al., J. Synchrotron Rad., 6, 1076 (...

Die Erfindung betrifft Materialuntersuchungen mit Hilfe der Tomographie.
Der Erfindung liegt die Aufgabe zugrunde, auch dann eine quantitative Bildrekonstruktion durchführen zu können, wenn im zu untersuchenden Objekt kein Gebiet bekannter Absorption vorhanden ist.

Der Erfindung liegt die Aufgabe zugrunde, ein neues Schichtmaterial für optische Informationsträger und Lichtmasken sowie ähnlich gelagerte Anwendungen vorzuschlagen. Außerdem wird ein einfaches Verfahren zur lokalen Veränderung der optischen Absorption in diesem Schichtmaterial angegeben, mit dem Strukturgrößen erreichbar sind, wie sie die fortgeschrittene Halbleiterindustrie fordert.
Das Schichtmaterial besteht aus amorphem, hydroxierten Siliciumkarbid der Form a-SiC:H, die Schichtbereiche hoher optischer Absorption enthalten Metallatome, vorzugsweise Gallium oder Zinn.

Die Erfindung betrifft ein Biomaterial und ein Verfahren zu dessen Herstellung. Potentielle Anwendungen sind medizinische Implantologie, Gewebezüchtung, Biotechnologie und Pharmazeutik.
Der Erfindung liegt die Aufgabe zugrunde, ein Biomaterial für Anwendungen in medizinischer Implantologie, Gewebezüchtung, Biotechnologie und Pharmazeutik zu schaffen, das eine gute Strukturbildung und Haftfestigkeit aufweist sowie die zellbiologischen Aspekte berücksichtigt.
Der Erfindung obliegt auch die Aufgabe, ein einfaches und anwendungswirksames Verfahren zur Herstellung des genannten Biomaterials vorzuschlagen.

Aufgabe der Erfindung ist es Substanzen vorzuschlagen, die zur Diagnose und Therapie von Tumoren in der Nuklearmedizin geeignet sind und ein Verfahren zur Herstellung der Substanzen anzugeben.

Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren und eine Schaltungsanordnung vorzuschlagen, mit denen der Extremwert einer Größe, oft als Gütegröße bezeichnet, auch bei sehr kleinen Stellbewegungen zu finden und zu halten ist und bei denen der Suchverlust durch die Suchbewegungen konstant gehalten werden kann.

Die Erfindung betrifft ein Verfahren zur Behandlung heteroepitaktisch auf Siliziumsubstraten abgeschiedener Halbleiterschichten. Die Erfindung soll insbesondere für die Herstellung elektronischer Bauelemente eingesetzt werden.

Die Erfindung betrifft ein Verfahren zur Behandlung heteroepitaktisch auf SOI-Substraten abgeschiedener Halbleiterschichten. Die Erfindung soll insbesondere für die Herstellung elektronischer Bauelemente eingesetzt werden.

Der Erfindung liegt die Aufgabe zugrunde, dass bei Auftreten von Fluid-Gas-Gemischen (2-Phasen-Gemischen) für das Rekonstruktionsobjektbild die Fehler verringert oder vermieden werden.

Die Anwendung ist insbesondere als tomographische Anordnung zur Erzeugung von Schnittbildern von Objekten gegeben, deren Gestalt beziehungsweise Zusammensetzung schnellen Änderungen unterworfen ist, und zwar für den Fall, dass die Änderungen sich zeitlich periodisch wiederholen.
Aufgabe der Erfindung ist es, eine Anordnung vorzuschlagen, die auch bei Objekten, deren Gestalt beziehungsweise Zusammensetzung schnellen, sich periodisch wiederholenden Änderungen unterworfen sind, die Ermittlung von Projektionen gestattet, die einen Momentanzustand oder eine Abfolge von Momentanzuständen der periodisch veränderlichen Verteilung des Absorptionsverhaltens repräsentieren und aus denen sich die Verteilungen selbst rekonstruieren lassen und die dabei mit einer kontinuierlich Strahlung aussendenden Gammaquelle auskommt.

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The experimental investigations of the emergency condenser of the SWR1000 done at Forschungszentrum Jülich is described in detail. After the description of the emergency condenser operation mode and the NOKO Test facility the performance and the evaluation of several bundle tests are presented. From the bundle tests a thermal and a hydraulic condition are developed. Single tube test results are remarked at the end of the presentation.

In the presentation the modeling of condensation inside horizontal tubes is described. The differences between condensation in vertical tubes and in horizontal tubes is explained in detail. The development of the improvement KONWAR for the German thermohydraulic program system ATHLET is decribed in detail. Afterwards the validation of this improvement with the two different experiments NOKO (Forschungszentrum Jülich GmbH) and HORUS (Universität Zittau/Görlitz) is presented.

In the presentation a description of the investigations concerning flowmaps for vertical pipes done at the institute of safety research are given. That means, the test facility MTLOOP of the institute with its measurement techniques and the test matrix is described in detail. From these experiments a new criterium for the bubble to slug flow transition is presented. Afterwards, the comparison of this criterium to existing flow maps is done.

In the presentation a description of the new multipurpose thermohydraulic test facility TOPFLOW is given including the construction phase and the main working fields. Then, after the details about flow diagram and facility loayout as well as the building layout the chosen documentatin form via internet and intranet is presented. Ideas concerning possible CAREM system tests in TOPFLOW are summarized, too.

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We have studied the isotopes 82Rb45, 83Rb46, and 84Rb47 to search for magnetic rotation which is predicted in the tilted-axis cranking model for a certain mass region around A = 80. Excited states in these nuclei were populated via the reaction 11B + 76Ge with E = 50 MeV at the XTU tandem accelerator of the LNL Legnaro. Based on a -coincidence experiment using the spectrometer GASP we have found magnetic dipole bands in each studied nuclide. The regular M1 bands observed in the odd-odd nuclei 82Rb and 84Rb include B(M1)/B(E2) ratios decreasing smoothly with increasing spin in a range of 13^-≤J^π≤16^-. These bands are interpreted in the tilted-axis cranking model on the basis of four-quasiparticle configurations of the type π(fp) πg_9/2 ² vg_9/2. This is the first evidence of magnetic rotation in the A ≈ 80 region. In contrast, the M1 sequences in the odd-even nucleus 83Rb are not regular, and the B(M1)/B(E2) ratios show a pronounced staggering.

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We report the results of recent measurements of the spectroscopic quadrupole moments of high-spin isomers. For the K-pi = 35/2(-) five-quasiparticle isomer in W-179 we measured Q(B) =4.00 ((+0.83)(-1.06)) eb. It corresponds to a smaller deformation compaxed to the ground states of the W isotopes and is in disagreement with the current theoretical predictions. We also measuredthe quadrupole moment of the I-pi = 11(-) isomer in Pb-196, Q(s) = (-)3.41(66) eb. It has the same proton (s(1/2)(-2)h(9)/(2)i(13/2)) configuration as the one suggested for the 11 = 16(-) magneticbandhead which allows to deduce the quadrupole moment of the 16(-) state as Q(s) = -0.316(97) eb. This small value proves the near sphericity of the bandhead.

Tc(III) and Re(III) complexes [M(NS₃)(CNR)] (M = Re, ^99mTc, NS₃ = 2,2',2''-nitrilotris(ethanethiol), CNR = functionalized isocyanide bearing a derivative of WAY 100635) have been synthesized and characterized. Re was used as Tc surrogate for chemical characterization and in vitro receptor-binding studies. For two representatives subnanomolar affinities for the 5-HT_1A as well as for the alpha1-adrenergic receptor were reached. Biodistribution studies in rats of the ^99mTc complexes showed brain uptakes between 0.3 and 0.5 % ID/organ (5 min p.i.). In vitro autoradiography of one ^99mTc representative in sections of post mortem human brain indicate its accumulation in 5-HT_1A receptor-rich brain regions. However, addition of the specific 5-HT_1A receptor agonist 8-OH-DPAT as well as the alpha1-adrenoceptor antagonist prazosin could not substantially block this tracer accumulation. A preliminary SPET study in a monkey showed negligible brain uptake.

Ziel des Vorhabens war die analytische und numerische Simulation der Kühlmittelvermischung im Ringraum und unteren Plenum von Druckwasserreaktoren. Generell ist die Kühlmittelvermischung relevant für zwei große Störfallgruppen - Borsäureverdünnungsstörfälle und Kaltwassertransienten. Zur Untersuchung der Vermischungsphänomene aus diesen Störfallszenarien wurde die Rossendorfer Versuchsanlage ROCOM konzipiert, die ein 1:5 skaliertes Plexiglasmodell des DWR Konvoi darstellt, in dem auch Geschwindigkeitsmessungen mit Hilfe von LDA-Technik möglich sind. Konstruktion, Errichtung und meßtechnische Ausstattung von ROCOM erfolgten in einem 2. Teil des Vorhabens. Im Vorfeld der Errichtung des ROCOM-Versuchsstandes wurden mit Hilfe des dreidimensionalen Strömungsberechnungsprogrammes CFX-4 Skalierungseffekte untersucht. Die Vergleichsrechnungen belegten, daß eine 1:5 Skalierung ausreichend ist. Nach dem Aufbau des Versuchsstandes und der Inbetriebnahme im 2. Teil des Vorhabens wurden die Vorausberechnungen anhand von experimentellen Ergebnissen bestätigt. Es wurde weiterhin ein Verfahren zur vereinfachten analytischen 2D-Beschreibung des Strömungsfeldes im Ringraum von Druckwasserreaktoren aufgestellt. Es beruht auf der Potentialtheorie, wobei Quellen an den Kühlmitteleintrittspositionen und Wirbel unter Beachtung der Randbedingungen der typischen Ringspaltgeometrie von DWR überlagert wurden. Der Schwerpunkt des Projektes lag jedoch in der numerischen Simulation der Kühlmittelvermischung unterschiedlicher Reaktoranlagen mit CFX-4 und der Validierung des Rechenprogramms anhand von Vermischungsexperimenten. Dabei wurden sowohl stationäre Schleifendurchsätze bei Nominalbetrieb und Teilschleifenbetrieb bzw. transiente Strömungsbedingungen der Reaktortypen DWR Konvoi und WWER-440 untersucht. Die Ergebnisse der CFX-4 Rechnungen im Vergleich mit den Leitfähigkeits- bzw. LDA-Messungen sind im Abschlußbericht dokumentiert. Grundlage für diesen Abschlußbericht ist eine Promotionsarbeit von T. Höhne zum gleichnamigen Thema im Rahmen des Kompetenzerhaltungsprogrammes Kerntechnik.

A short review of our investigations devoted to the use of ion beam synthesized nanoclusters for silicon based light emission and nonvolatile memory effects is presented. Blue-violet light emission is demonstrated basing on Ge-implanted silicon dioxide layers thermally grown on silicon substrates. This version of silicon-based light emission relies on Ge-related defects in the amorphous -Si-O-Si- network. The photo (PL) - and electroluminescence (EL) is excited by a singlett S0-S1 transition of neutral oxygen vacancy and by electron injection from the silicon substrate into the silicon dioxide layer, respectively. Whereas the PL excitation is a well-known mechanism, for the case of electroluminescence an interpretation was performed for the first time in the course of our studies. It is found that the most probable way to excite luminescence centers is the impact excitation by hot electrons. Whereas the injection is explained by trap assisted tunneling of electrons from the substrate into the oxide, the electrons will be transported via traps or in the SiO2 conduction band. The application of the silicon-based light emitting devices for an optocoupler arrangement are described. Another application of nanoclusters is basing on the investigation of thin Si-implanted silicon dioxide layers for nonvolatile memory applications. First promising results demonstrated that the observed programming window can reach several volts and the devices exhibit excellent retention behavior. A 256k-nv-SRAM is demonstrated showing a programming window >1V for write pulses of 12V/8ms.

Der Stofftransport über Flüssig-Flüssig-Phasengrenzen führt sehr oft zu hydrodynamischen Instabilitäten und zur Bildung von dissipativen, d. h. konvektiven Strukturen. Zwei Mechanismen liegen diesen Instabilitäten zurunde. Der erste ist mit dem Wirken von Grenzflächenspannungsgradienten in Systemen mit flüssigen oder flüssig-gasförmigen Grenzflächen verbunden und wird als Marangoniinstabilität bezeichnet. Der zweite, als Rayleigh-Bénard-Instabilität bezeichnete Mechanismus wird durch Auftriebskräfte aufgrund lokaler Dichteunterschiede verursacht. In diesem Beitrag soll über experimentelle und numerische Untersuchungen berichtet werden, die an Systemen vorgenommen wurden, bei denen die übergehende Komponente eine chemischen Reaktion an der Grenzfläche eingeht und Auftriebskräfte bei der Ausbildung der Instabilität dominieren.

The proton-rich isotope 56Cu was produced at the GSI On-Line Mass Separator by means of the 28Si(32S, p3n)
fusion¯evaporation reaction. Its -decay properties were studied by detecting -delayed rays and protons. A half-life of
93±3 ms was determined for 56Cu. Compared to the previous work, six new rays and three new levels were assigned to the
daughter nucleus 56Ni. The measured Gamow¯Teller strength values for five 56Ni levels are compared to shell-model
predictions

Mass transfer across interfaces in liquid-liquid systems may give rise to hydrodynamic instability and the formation of various dissipative, i. e. convective, structures. There are two basic mechanisms leading to instability. The first one is related to the action of surface tension gradients in systems with free interfaces and is referred to as Marangoni effect while the second one is related to buoyancy forces and is referred to as Rayleigh-B'enard instability. Convection at the interface and in the bulk of the liquids greatly enhances mass transfer rates. This paper reports on experimental and numerical studies which have been carried out on systems where the transferred species undergoes a chemical reaction at the interface and buoyancy forces predominate.

Transient boiling is examined for conditions related to the hypothetical heating of liquids in a storage tank by an external fire, with the potential for evaporation of the liquids and the release of toxic gases into the environment. Temperature and void fraction distribution data were obtained from an experiment on water heated in a tank. Numerical simulations were also performed. These generally agreed reasonably well with measurements.

Bericht über Dienste und Weiterentwicklung der IT-Infrastruktur des FZR im Zeitraum 1999 bis 2000 in den Tätigkeitsbereichen Zentrale Server, Datennetz und Benutzerservice.

The most prominent back-reaction effects observed in the Riga dynamo experiment are presented and a preliminary interpretation of them is given.

Color centers have been generated on [100] surfaces of LiF crystals by irradiation with a focussed beam of 35 keV Ga+ ions at room temperature and at 240 K. The luminescence of two centers at 655 and 540 nm, ascribed to F2 and F3+ centers, respectively, has been detected and spatially resolved, with spatial resolution in the range of 1 µm, by imaging microscopy, as well as by laser scanning confocal microscopy. Diffusion and pinning of color centers have been observed directly in this way. Due to the high intensity in the focal spot of the confocal microscope nonlinear photophysical and photochemical processes are observed. For example an additional emission at 775 nm could be detected at high excitation density. The luminescence band is tentatively ascribed to radiative triplet-triplet emissions of F2 centers after recombination of F2+ centers with an electron.

The uptake of heavy metals into plants is commonly quantified by the soil-plant transfer factor. Up to now little is known about the chemical speciation of actinides in plants. To compare the obtained spectroscopic data of uranium complexes in plants with model compounds, we investigate the complexation of uranium with relevant bioligands of various functionalities. A very important class of ligands are phosphate esters, which serve as phosphate group and energy transmitters as well as energy storage mediums in biological systems. Heavy metal ions bound to the phosphate esters can be transported into living cells and than deposited.
Therefore, in our study we present the results of uranium complexation with glucose-6-phosphate (G6P), and fructose-6-phosphate (F6P) obtained by time-resolved laser-induced fluorescence spectroscopy (TRLFS). The experiments were performed at a fixed uranyl concentration (10^-5 M) as a function of the ligand concentrations (10^-5 to 10^-3 M) in a pH range from 2 to 4.5.
For the glucose phosphate system we observed, using increasing ligand concentrations, a decreased fluorescence intensity and a small red shift of the emission bands. From this we conclude that the complexed uranyl glucose phosphate species either show only minor or no fluorescence properties. The TRLFS spectra of the glucose phosphate samples indicated the presence of only one species with fluorescence properties. This species has a lifetime of approximately 1.5µs and was identified as the free uranyl ion.
An opposite phenomenon was observed for the fructose phosphate system: There was no decrease of fluorescence intensity. However, a strong red shift of the spectra was observed illustrating the fluorescence properties of the uranyl fructose phosphate complex. The TRLFS spectra of the fructose phosphate system showed a second lifetime (<1µs) belonging to the complexed species.
The concentration of the free uranyl ion was determined on the basis of the measured fluorescence spectra. These data were used to calculate the corresponding concentrations of the uranyl sugar phosphate complexes and the non complexed ligands. The complex formation reaction is assumed to be:
x lig + UO₂ ²⁺ <==> UO₂(lig)_x ^(2-y)+ + y H⁺ (lig = sugar phosphate)
Applying the mass action law and transformation to the logarithmic scale, we obtain:
log {[UO₂(lig)_x ^(2-y)+] / [UO₂ ²⁺]} = x log[lig_nonkomplexed] - y log[H⁺] + logK

From this we conclude, that 1:1 uranyl sugar phosphate species UO₂(ROPO₃) (R is either glucose or fructose) has formed. Using these data complex formation constants for the complexes were calculated to be in the range of logK=3.7 for G6P and 3.2 for F6P.

Bei einer Vielzahl von natürlichen und technischen Strömungsvorgängen besteht das strömende Medium aus mehreren Phasen. Bei der Förderung derartiger Medien mit Kreiselpumpen führen bislang nicht genügend bekannte Vorgänge bei bestimmten Betriebsbedingungen zu einer starken Verringerung der Förderleistung und einem Anstieg des Leistungsbedarfs. Bei der Förderung von gasbeladenen Flüssigkeiten kann ein zu hoher Gasanteil zum vollständigen Zusammenbruch der Förderung führen. Zusätzlich führt die erosive Wirkung von Kavitation zu einer starken Minderung der Lebensdauer der Pumpe.

Diese Arbeit beschreibt ein neuartiges Verfahren, das es erstmals gestattet, die Methode der Gamma-Tomographie zur Bestimmung der örtlichen Phasenverteilung innerhalb von rotierenden Pumpenläufern und ähnlichen Bauteilen anzuwenden. Dabei wird eine Zeitauflösung von ca. 100 µs erreicht, mit der die Gasverteilung wesentlich genauer als bisher erfaßt werden kann. Mit dem Tomographen wurden die Vorgänge innerhalb des Läufers einer Axialpumpe bei Förderung eines Luft-Wasser-Gemischs visualisiert. Es wird gezeigt, wie sich die Änderung äußerer Strömungsparameter und die Variation des Arbeitspunktes auf die räumliche Phasenverteilung innerhalb des Läufers auswirkt.

The nuclei $^{91}$Sr and $^{92}$Sr were produced at high spin as fission fragments following the fusion reaction $^{36}$S + $^{159}$Tb at 165 MeV. Gamma rays were detected with the Gammasphere array. The level schemes of
$^{91}$Sr and $^{92}$Sr were extended up to $E \approx$ 6 MeV and $E \approx$ 8 MeV, respectively. Level structures in $^{91}$Sr and $^{92}$Sr were interpreted in terms of the shell model. The calculations were performed in the configuration space $(0f_{5/2}, 1p_{3/2}, 1p_{1/2}, 0g_{9/2})$ for the
protons and $(1p_{1/2}, 0g_{9/2}, 1d_{5/2})$ for the neutrons. Negative-parity states in the yrast sequences are described in these calculations by coupling $3^-$ proton excitations to the unpaired $1d_{5/2}$ neutrons. A possible reduction of the gap between the proton $1p_{3/2}$ and $1p_{1/2}$ orbitals in
$^{92}$Sr is discussed.

The Forschunszentrum Rossendorf (FZR) e.V. is constructing a new large-scale test facility, TOPFLOW, for thermalhydraulic single effect tests. The acronym stands for Transient Two Phase Flow Test Facility. It will mainly be used for the investigation of generic and applied steady state and transient two phase flow phenomena and the development and validation of models of Computational Fluid Dynamic (CFD) Codes.

The ATHLET code has been improved and validated for the safety analysis of high flux research reactors against experimental data of the Thermalhydraulic Test Loop of Oak Ridge National Laboratory (ORNL). Therefore, an extensive series of "stiff mode" experiments were recalculated. The comparison between experiments and ATHLET posttest calculations shows that the extended code simulates accurately the thermalhydraulic conditions and the flow instabilities in a wide range of inlet velocity, head and mass flux.

The 6th dynamic benchmark is a logical continuation of the work to validate systematically coupled neutron kinetics / thermohydraulics code systems for the estimation of the transient behaviour of VVER type nuclear power plant which was started in the 5th dynamic benchmark. This benchmark concerns a double ended break of one main steam line (asymmetrical MSLB) in a VVER-440 plant. The core is at the end of first cycle in full power conditions. The asymmetric leak causes a different depressurization of all steam generators. New features in comparison to the 5th dynamic benchmark were included: asymmetric operation of the feed water system, consideration of incomplete coolant mixing in the reactor vessel, and the definition of a fixed isothermal recriticality temperature for normalising the nuclear data.

The solution of this benchmark was obtained by means of coupled code system DYN3D/ATHLET. There, the whole core including neutron kinetics and thermohydraulics processes was calculated by three dimensional neutron kinetics core model DYN3D. The thermal hydraulics behaviour of primary and secondary circuit was modelled by the system code ATHLET.
For the purpose of realisation of the fixed isothermal recriticality temperature Trecrit = 210°C the cross section data of absorber were adapted.

During the transient calculation of MSLB scenario, the reactor scram was initiated with the assumption that two of the most reactive control rods in the sector of highest overcooling are stuck at their fully withdrawn position. Accordingly, the power is decreased due to reactor scram. Thereafter, the reactivity feedback caused by the decrease of coolant temperature entailed the increase of the reactor power. Based on an assumed delayed start of the high pressure safety injection, the recriticality of the shut-off reactor is achieved. The value of total power in the second maximum is about 80 MW.

In this paper the behaviour of the main thermohydraulic and neutron kinetic parameters is presented.

Seepage and mine waters of the abandoned uranium mining and milling sites in Saxony and Thuringia are contaminated by uranium and its decay products. Therefore, efficient water purification technologies are necessary.
The separation of uranium(VI) from aqueous solution by calixarenes by means of solvent extraction is described in the literature. Calixarenes are macrocyclic molecules formed by 4, 6 or 8 para-substituted phenolic units linked by methylene bridges ortho to the OH functions. Thus, molecules of different ring sizes are formed. Especially calix[6]arenes functionalized with carboxylic or hydroxamic groups on the lower rim are suitable to separate uranium from aqueous solution.
In the present work, the extraction efficiency of various carboxylate derivatives of calix[6]arene, e.g., carboxymethoxy-p-tert-octyl-calix[6]arene, including their selectivity towards uranium(VI) is studied in a two phases solvent extraction system in dependence on pH value and the amount of competing ions in aqueous solution as well as in dependence on ligand concentration and solvent. The complex formation between uranium(VI) and calix[6]arenes is further studied by means of time-resolved laser-induced fluorescence spectroscopy (TRLFS). Uranium species are identified, complex formation constants are determined, and reaction mechanisms are discussed. The suitability of the calix[6]arenes as efficient reagents for selective separation of uranium from aqueous solution, even in the acidic pH region, is shown.

In einem gemeinsamen Vorhaben mit dem Diagnosezentrum für russische Kernkraftwerke (DIAPROM Moskau) wurde ein Beitrag zur verbesserten Beurteilung der mechanischen Integrität von Reaktoren der russischen WWER-Baureihen, insbesondere zur empfindlichen Früherkennung und Lokalisation mechanischer Schädigungen an Reaktorkomponenten mit Hilfe schwingungsdiagnostischer Methoden geleistet. Zu diesem Zweck wurde für den WWER-440 und WWER-1000 das mechanische Schwingungsverhalten aller Primärkreiskomponenten mit finiten Elementen (FE) modelliert. Dafür wurde das Programmpaket ANSYS® genutzt.
Der Einfluss des strömenden Kühlmittels auf die schwingenden mechanischen Strukturen ist im Rahmen der Fluid-Struktur-Interaktion (FSI) berücksichtigt worden. Die Berechnungsmodelle wurden mit Ergebnissen experimenteller Schwingungsuntersuchungen justiert. Zum Teil konnte auf aktuelle Messungen zurückgegriffen werden. Die Modelle können als weitgehend verifiziert gelten. Diese wurden in der Hauptsache genutzt, um zu klären, wie sich unterstellte mechanische Defekte von Reaktoreinbauten auf die Schwingungen der Gesamtanlage auswirken. Diese Schadenssimulation ist besonders geeignet, empfindliche Messpositionen für die on-line Überwachung zu finden und physikalisch fundierte Grenzwerte zu definieren.
Die entwickelten Modelle sind grundsätzlich auch geeignet, um Lastabschätzung für die Reaktorkomponenten bei Einwirkung von außen (Explosion, Erdbeben) vorzunehmen.

Charge storage properties of 20-30 nm gate oxides implanted with Si+ ions are investigated using MOS capacitors, single transistor structures and a non-volatile memory. The observed programming window can reach several volts for programming with electric fields of about 4-7 MV/cm. The structures exhibit good retention (250°C, 280h) and the endurance (>106 w/e-cycles) considerably exceeds the typical values of present EEPROM technologies. The capability of Si implanted SiO2 films as gate dielectrics for a real non-volatile memory is demonstrated for the first time by a 256k - nvSRAM showing a programming window of larger than 1 volt.

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The wire-mesh sensor developed by the Forschungszentrum Rossendorf produces measuring sequences of instantaneous gas fraction distributions in a cross section at a rate of up to 10 000 frames per second and a spatial resolution of about 2-3 mm. This sensor was applied to an upwards air-liquid flow in a vertical channel. After a brief introduction of the functioning of the sensor, the paper presents results obtained at a rate of 1200 frames per second, which were used to study the evolution of bubble size distributions and radial gas fraction profiles along the pipe, starting at a relative distance of L/D=0.6 above the gas injection and ending at L/D=60. The developed 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. Furthermore, the paper presents results of a flow visualisation at the rate of 10 000 frames per second, showing details of the flow structure in the region of transition to annular flow.

For studies on the characteristics of bubble flow in a rectangular channel (20x100mm) an electrode-mesh tomograph has been applied. The measuring principle is based on local conductivity measurement. The applied sensor scans the local void fraction distribution in 2 parallel planes, separated 1.5mm in flow direction, with a resolution of 6.1x2.2mm and an overall sampling rate of 1200Hz (all 256 points). Algorithms for the calculation of the local instantaneous void fraction distribution and the true gas velocity are presented. Based on these values the approximate shape of bubbles has been reconstructed and the gas volume flow through the sensor evaluated. The superficial gas velocity as well as the local distribution of the gas volume flux was
calculated. Finally, bubble diameter spectra have been obtained and the statistical behavior of the bubble rising velocity in its dependency from bubble diameter in a turbulent flow of high void fraction has been investigated. An extensive sensitivity study illustrating the applicability and accuracy is presented, based on experimental observations as well as theoretical considerations. The evaluated results are compared with high-speed video observations of the flow field as well as data comparing the reconstructed volume flow with measurements by a laminar flow meter. Good agreement can be stated.

We summarize the history and the results of the first successful hydromagnetic dynamo experiment which was prepared and run at the Institute of Physics in Riga, Latvia.

The electronic confinement in semiconductor quantum wells gives rise to the formation of electronic subbands within the conduction or valence band. Due to the same curvature of initial and final subband, intersubband optical transitions (within one band) exhibit a quasi-zero-dimensional joint density of states and therefore resemble atomic transitions in some way. The typical energy spacing from 10 to a few 100 meV corresponds to the far- and mid infrared spectral range. Thus, for the study of nonlinear or time resolved phenomena in these structures, IR free-electron lasers are among the most – or the only – suitable light sources.

As an example, I will review some experiments on the energy relaxation of electrons in wide GaAs/AlGaAs quantum wells, performed with FELIX.

Transitions between minibands in strongly coupled superlattices exhibit a one-dimensional joint density of states, and I will show how the dispersion along the growth axis can be employed to study the electron distribution function.

Finally I will present the status of the ELBE project at the Forschungszentrum Rossendorf near Dresden. This project comprises a superconducting electron accelerator, providing the electron beam for two undulators. The latter form the heart of the FELs, which are planned to operate from 5 to 25 microns and 20 to 100 (or 150) microns, respectively. First lasing is expected for early 2002.