Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

It is demonstrated that the intrinsic stress in cubic boron nitride films can be significantly relaxed during growth by simultaneous medium energy ion implantation. The stress in the growing film has been studied in-situ using cantilever curvature measurements and has been reduced to below 2 GPa by simultaneous Ar+ or N+ ion implantation with an energy of 70 keV and 35 keV, respectively. The resulting cubic boron nitride films show an increased long term stability. The results reveal that the stress in cBN is not reduced due to segregation of boron at grain boundaries.

The interaction of uranium with cells of three recently described eco-types of Acidithiobacillus ferrooxidans recovered from uranium mining wastes was studied. The uranium sorption studies demonstrated that the strains from these types possess different capability to accumulate and tolerate uranium. The amount of uranium biosorbed by all A. ferrooxidans strains increased with increasing the concentration of uranium. We have found that the representatives of type II accumulate significantly higher amounts of uranium in comparison to the other A. ferrooxidans strains. The investigations of the tolerance to uranium showed that the types I and III are resistant to 8 and 9 mM of uranium respectively, whereas the type II does not tolerate more than 2 mM of uranium. The recovery of the accumulated uranium by desorption was investigated using various desorbing agents as sodium carbonate, sodium citrate and EDTA at different concentrations. Sodium carbonate was the most efficient desorbing agent, removing 97% of the uranium sorbed from the cells of A. ferrooxidans type III, and 88.33 and 88.50% from the cells of the types I and II, respectively.

Mobilization of heavy metals in the environment due to industrial activities is of serious concern due to the toxicity of these metals in humans and other forms of life. Uranium is an example of these metals, and is considered one of the most seriously threatening heavy metals mainly because of its high toxicity, not so much radioactivity. Activities associated with the nuclear industry, mining and wastewater treatment have brought excessive amounts of uranium into the environment. In uranium deposits a number of acidophilic chemolithoautotrophic ( Acidithiobacillus ferrooxidans, for instance) bacteria have been identified which are able to oxidise sulphide minerals, elemental sulfur, ferrous iron. Sequence analysis of the 16S rRNA genes of several reference strains and uranium mining waste pile isolates of A. ferrooxidans revealed specific signatures which distinguish three types within the species. These types differ in their capability to accumulate and tolerate uranium /1/.
Uranium (VI) complexes formation at cell surfaces of A. ferrooxidans types was studied using uranium LIII-edge Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. In all samples uranium is coordinated by two axial oxygen atoms (Oax) at distance of 1.77-1.78 Å. The average distance between uranium and the equatorial oxygen atoms (Oeq) is 2.35 Å. The coordination number for Oeq is 5-6.
Using U-C and U-P phase and amplitude functions, the third and the fourth peak in the FT of A. ferrooxidans give a distance of 2.91 and 3.58 ± 0.02Å, respectively. The latter is the same U-P bond distance as for the organic uranyl phosphate (U(VI)-ATP complex). But we do not exclude the possibility of implication of sulfur because these 2 elements (P and S) are close each other in the periodic system of elements and EXAFS can not distinguish between them. In addition, the P (or S) is bonded in a monodentate mode to the uranyl ion. A bidentate bounding would give a atomic distance of approximately 3.2 Å.
Moreover, no structural differences were observed between the uranium complexes formed by the 3 types of A. ferrooxidans. However, the EXAFS spectra are indicating a formation of uranium complexes which are different from those formed by Bacilli /2/.

/1/ M. Merroun et al., Interaction of three types of Acidithiobacillus ferrooxidans with uranium, Biometals (in preparation).
/2/ C. Hennig et al., EXAFS investigation of uranium(VI) complexes formed at Bacillus cereus and Bacillus sphaericus surfaces, Radiochim. Acta (in press).

In den vergangenen Jahren wurde grundsätzlich akzeptiert, dass Kolloide unter bestimmten Randbedingungen einen erheblichen Beitrag zum Transport von Stoffen in aquatischen Systemen leisten können. Nach wie vor ist jedoch umstritten, welche Relevanz der kolloidale Transport bei einer Vielzahl von Fragestellungen hat.

Plasma immersion ion implantation (PIII) from a chlorine containing plasma has been used in order to improve the high temperature oxidation behavior of titanium aluminide alloys. This process is promising since the subsurface Cl concentration, which is needed for optimum protection against oxidation, can be quickly obtained (approx. fluence 1·1016 Cl/cm-2) in a PIII process.
A PIII system being resistant against the strongly etching Cl2 plasma is presented. Plasma diagnostics of the Cl2 plasma sustained by an ICP source using Langmuir probe measurements is discussed. For the electro-negative Cl plasma, the measurements are examined regarding the influence of negative ions. The implantation of Cl is correlated to the plasma parameters using AES depth profiling of the surface after implantation. The high temperature oxidation behavior is tested using thermogravimetrical analysis (TGA) in air at 900 °C and microstructural investigations of the oxide scale. PIII implantations of Cl2 with 30 kV HV pulses (effective energy 15 keV) show a strong reduction of the oxidation at 900 °C in air, which is comparable to conventional beam line im-plantations of Cl at 15 keV.

Due to the spontaneous heat release during the initiation of the strongly exothermic Grignard reaction, these reactions dispose of considerable harzard potentials. Therefore, the knowledge of thermody-namic and thermokinetic parameters is one of the prerequisites for safe formation of Grignard rea-gents in production plants. To obtain more accurate results, these studies on the formation of Grignard reagents were carried out in a closed reaction calorimeter by dosing the pure bromobenzene deriva-tive for the first time. The molar reaction enthalpy per mole bromobenzene derivative was determined with a standard deviation of about 5%.

We show that coherent optical phonons in GaAs multiple quantum wells are generated in a completely different way compared to bulk GaAs. Unlike in GaAs where the ultrafast screening of electric fields by photogenerated charge carriers is known to be dominant, three distinctive generation mechanisms contribute simoultaneously in multiple quantum wells.

Natural convection is a basic principle for a lot of industrial processes. As an example for the investigation of natural convection phenomena, the paper describes investigations of a passive heat removal system in advanced designs of nuclear power plants. The SWR1000 concept of Siemens AG includes emergency condensers. In the Research Centre Jülich at the NOKO test facility experiments were performed, to investigate the heat transfer capability under different operation modes. In the last time the heating up phenomena on the secondary side were investigated in detail. The paper describes simulations performed in the Forschungszentrum Rossendorf using the CFD-code CFX-4 of AEA-Technology and comparisons to the experiments. Performing additional calculations, measures to avoid undesired temperature stratification were investigated.

The irradiation sensibility and the annealing behaviour were studied on seven different heats from VVER 440 and VVER 1000-type reactor pressure vessel steels. The specimens were irradiated at the Rheinsberg prototype VVER 2 reactor to mean neutron fluences between 43 - 127.6A1018 n/cm² [E > 0.5 MeV] and afterwards toughness and strength properties were determined. In addition the microstructure was analysed using SANS technique. There is an obvious trend regarding the correlations between the irradiation-induced changes of transition temperature, hardness and volume fraction of microstructural features of the radius near of approx. 0 to 2 nm. The main parameters of influence are the neutron fluence and the nickel content. The nickel-containing VVER 1000-type pressure vessel steel is more sensible against irradiation than the VVER 440-type steel which has a low content of nickel. For the last one the sensibility against radiation embrittlement depends on content of copper and phosphorus. Annealing at 475 °C (100 h) reduces the irradiation effect but not completely in every case.

Experiments with 3 MW deuterium injection have been carried out in the Gas Dynamic Trap (GDT) to simulate the axial profile of the fusion reaction intensity in the proposed neutron source based on the GDT. Quite narrow angular distribution function of the fast ions produced by an oblique neutral beam injection results in a peaked axial profile of the fusion yield. This strong peaking is essential to produce an intense neutron flux in the testing zones of the GDT-based neutron source.
The scintillation counters were installed in the central cell of the device to monitor the DD fusion reaction products: neutrons (2.45 MeV) and protons (3,02 MeV). They were closely located to the plasma column inside of the vacuum chamber in oreder to avoid contribution from the scattered neutrons and to improve the spatial resolution of the measurements. The axial profiles of the fusion neutrons and protons have been measured in the high-beta regime of the GDT operation.
In the paper the experimental data are compared with the results of numerical simulations. The conclusion may be drawn that the kinetics of the fast ion relaxation and scattering is determined by classical Coulomb collisions.

Laser induced spectroscopic methods are an excellent tool for the study of complex formation of actinides with various ligands at relatively low concentrations. Laser-induced Photoacoustic spectroscopy and Time-resolved Laser-induced Fluorescence spectroscopy are well-known methods. These methods are inappropriate for metal ions which show no change in their spectroscopic properties with complexation. In the case of organic actinide complexes it is possible to use the dependence of fluorescence of the organic ligands on actinide concentration in order to determine complex formation constants. The fluorescence lifetimes of organic ligands in aqueous solution at room temperature are below 20 ns. To study fluorescence properties of theses organic substances laser systems with ultrashort pulses are inevitable. We, therefore, have installed a femtosecond-laser-induced fluorescence spectroscopy system in our laboratory.
The lasersystem provides femtosecond laserpulses in the wavelength range from 250 nm to 10 µm and a pulse duration of 130 fs. The repetition rate is 1 kHz. The emitted fluorescence signal is detected with an intensified CCD camera, with gate width between 80 ps and 6 ns. The delay for time resolved spectra can be adjusted between 0 and 20 ns after the laser pulse with stepwidth down to 25 ps.
We validated this time-resolved laser-induced fluorescence system by studying the fluorescence behavior of salicylic acid and 5-sulfosalicylic acid at pH 4.0 as function of the uranium(VI) concentration. Using a static quenching mechanism the complex formation constants are calculated to be log KI=0.1M= -1.12 ± 0.03 for salicylic acid and log KI=0.1M= -0.67 ± 0.08 for 5-sulfosalicylic acid, respectively, assuming a 1:1 complex formation. The data from the NIST database /1/ are log KI=0.1M= -1.0 and log KI=0.1M= -0.72, respectively. For the actinides neptunium and plutonium much less data are available. Complex formation constants of various substituted benzoic acids with these actinide elements are reported.

/1/ A.E. Martel, R.M. Smith and R.J. Motekaitis: NIST Critically Selected Stability Constants of Metal
Complexes Database Version 5.0; 1998

The effect of plasma immersion ion implantation of chlorine on the high temperature oxidation of titanium aluminides alloys was investigated. PIII implantations of Cl2 at 30 kV (effective energy 15 keV) show a strong reduction of the oxidation at 900°C in air, which is comparable to conventional beam line im-plantations of Cl at 15 keV. A specialized PI³ system for the strongly etching Cl2 plasma was set up. The chamber is coated inside with aluminum foil, in order to protect the chamber and to avoid contamination of the plasma except with Al. The pumping system is chemically resistant. First implantations and plasma diagnostic of an ICP source sustained Cl2 plasma are discussed. The effect on the high temperature oxidation behavior is tested using thermogravimetrical analysis and microstructural investigations

The Paks Nuclear Power Plant is equipped with VVER-440/V213-type pressurised water reactors. As known, these reactors have a number of special features, therefore the transient behaviour should be different from PWRs of usual design.
To study the transient behaviour of this type of NPPs an integral-type facility called PMK-2, a scaled-down model of the Paks NPP was designed and constructed in the middle of 1980s and several experiments of different types have been performed.
In the framework of a European Union financed Phare project an upgrading of PMK-2 was performed. Equipments installed are as follows: needle-shaped void-probes for local void measurements, full-flow turbines for velocity measurements, micro-turbines for two-phase flow measurements, three beam gamma densitometer to measure coolant density and to identify flow patterns, and in addition a new data acquisition system has been installed.
This paper deals with the application of void probes for the evaluation of the results of a loss of coolant accident.

The paper presents a method to prevent the water hammer by an adaptive control of the valve closing process. For this purpose, the valve is equipped with a brake system that acts onto the rotation axis of the valve flap. The brake cylinder of the applied hydraulic disk brake is connected to the pipeline just upstream the valve, so that the fluid pressure may activate the brake. By this means the closing is interrupted when the pressure of the fluid increases due to the water hammer. The pressure peak is limited to a maximum pressure given by the user.
The described system does not need any external energy source. Furthermore, it adapts to changes of the pipe system parameters, such as varying pipeline length (e.g. liquid supplied from tanks with a different distance from the valve), fluid velocity or physical properties of the fluid. These are major advantages compared to traditional damping systems, which delay valve closing in a fixed manner.

The paper presents a new wire-mesh sensor for the fast visualisation of gas-liquid flows with a rate of 10 000 frames per second based on the measurement of the local instantaneous conductivity of the two-phase mixture. With this resolution it is now possible to visualise and quantify individual bubbles at mixture velocities of about 10 m/s. The sensor consists of two electrode grids with 16 electrodes each, placed at a small axial distance behind each other. The conductivity is measured at the crossing points of the wires of the two grids. The high measuring rate was achieved by applying an integrated digital signal processor for the control of the signal acquisition process. For the link to the data acquisition PC an ETHERNET interface is used. The internal memory is sufficient to store 170,000 frames, i.e. a continuous measurement over 17 s is possible. In the paper, results obtained in a vertical two-phase air-water flow are presented.

The void fraction produced in an adiabatic section (riser) during flashing-induced instabilities in a natural-circulation steam/water loop is measured by means of a wire-mesh sensor and two gamma-transmission set-ups located just above and below the wire-mesh sensor respectively. In this paper a comparison between the two different measuring techniques is given. The wire-mesh sensor is capable of measuring the time-dependent two-dimensional void-fraction distribution on a grid of 16x16 points equally distributed over a cross section of the riser, while the gamma-transmission set-ups measure the chordal void fraction along a collimated beam through the riser at a certain height.
The high sampling rate of the wire-mesh sensor (up to 1200 Hz) allows to detect both the frequencies characteristic of the flashing process (between 2 and 4 Hz) and the frequencies characteristic of the flashing-induced flow oscillation (below 0.05 Hz). The former frequencies are less visible in the spectrum of the gamma-transmission signal due to the lower signal-to-noise ratio.
The effect of the wire-mesh sensor on the triggering of void production due to the provision of extra nucleation sites is also studied; no significant differences are observed in the main parameters of the instability if the wire-mesh sensor is removed from the experimental loop.

The high intrinsic stresses in cBN films after deposition are reduced significantly employing thermal treatment and ion implantation. In-situ stress measurement and ex-situ polarized infrared reflection spectroscopy are utilized to study stress relaxation and the phase stability. Argon ion implantation into cBN films at room temperature and at 340°C reveals that the critical fluence for amorphization increases with increasing temperature. The fraction of cBN transformed into sp2 bonded BN by Ar ion implantation decreases with increasing substrate temperature for the same amount of stress release.

Damage has been observed in MeV-ion-implanted Si away from the maximum of the nuclear energy deposition profile, mainly around the half of the projected ion range, Rp/2, after annealing at temperatures between 700°C ad 1000°C. This damage is primarily created by the implanted ions and consists of intrinsic defects remaining so small that they have not been observed by techniques sensitive to the lattice structure (RBS/C, TEM). The only way to detect this damage is to decorate it with metals and to measure the metal distribution. In this study the formation and disappearance of the Rp/2 damage has been investigated by Cu gettering in Si +-ion implanted Si versus temperature and time of the annealing cycle. The defects undergo a defect evolution during annealing which results in a decrease of the width of the damage layer with increasing temperature and prolonged time of the annealing. It is mostly believed that an excess of vacancies around Rp/2 getter metal impurities. Nevertheless, by means of positron annihilation spectroscopy no vacancy defects have been observed. In contrast in our XTEM investigation we found small (20-30nm) interstitial loops in the Rp/2 region. The creation of these loops is triggered by injected interstitials resulting from the ion milling procedure used during TEM specimen preparation. The ion bombardment of Si give rise to self-interstitials that diffuse extensively at room temperature and may modify the existing interstitial clusters to bigger agglomerates which can be observed by XTEM.

The formation of crystalline SiC by implantation of C ions into silicon is not a single-step process. The implantation results in an elastic distortion of the Si matrix lattice and in a formation of crystalline SiC particles depending on ion fluence and thermal conditions at implantation and post-annealing.
The growth of the SiC particles in the Si matrix was studied with different x-ray scattering techniques and high-resolution transmission electron microscopy. Crystallites of the 3C-SiC polytype are formed in a buried layer. Three groups of crystallites with different orientation relation to the Si matrix are found: with a random orientation like a powder material, with a fibre texture axis parallel to the surface normal, and completely aligned to the Si matrix lattice due to a partially coherent growth of SiC in the Si matrix. The thermal treatment favours the growth of highly oriented material: a higher implantation temperature is more efficient than a post-implantation treatment even at higher temperatures.

4-([¹⁸F]fluoro)benzoyl-neurotensin(8-13) (¹⁸FB-Arg⁸-Arg⁹-Pro¹⁰-Tyr¹¹- Ile¹²-Leu¹³-OH, 1) and three analogues stabilized in one, two and three positions (¹⁸FB-Arg⁸Psi(CH₂NH)Arg⁹-Pro¹⁰-Tyr¹¹- Ile¹²-Leu¹³-OH, 2, ¹⁸FB-Arg⁸Psi(CH₂NH)Arg⁹-Pro¹⁰-Tyr¹¹-Tle¹²-Leu¹³-OH, 3, ¹⁸FB-Arg⁸Psi(CH₂NH)Arg⁹-Pro¹⁰-DmTyr¹¹-Tle¹²-Leu¹³-OH, 4) were synthesized in a radiochemical yield of 25 - 36% and a specific activity of 5 - 15 GBq/mmol. The peptides were evaluated in vitro and in vivo for their potential to image tumours, overexpressing neurotensin receptor 1 (NTR1) by positron emission tomography (PET). The analogues exhibited in vitro binding affinity in the low nanomolar range to NTR1-expressing human tumours, measured by quantitative receptor autoradiography (IC₅₀: 1 0.42±0.05 nM, 2 0.91±0.20 nM, 3 4.1±0.60 nM) , HT-29 (IC₅₀: 24.0±4.2 nM) and WiDr cells and to sections of tumours derived from these cell lines in mice. The radiotracers were internalised in the cells in vitro, and the fluorinated peptides were able to mobilize intracellular Ca²⁺ of WiDr cells. In in vivo studies in rats and in mice bearing HT-29 cell tumours, only a moderate uptake of the radioligands into the studied tumours was observed, presumingly due to degradation in vivo and fast elimination by the kidneys of rats and by the liver of mice. The pathway of the fast enzymatic degradation of the non-stabilized or not sufficiently stabilized ¹⁸F-labeled peptides was elucidated. The main catabolic product is the ¹⁸FB-Arg⁸Psi(CH₂NH)Arg⁹-Pro¹⁰. In vivo, in comparison with the other analogues, the specific tumour uptake expressed as tumour-to-muscle relation was highest for the radioligands 3 and 4. The blood clearance of the analogues was reduced by co-injection of peptidase inhibitors.
The 4-[¹⁸F]fluorobenzoyl label on the N-terminal arginine, the introduction of one reduced peptide bond and two bulky amino acid residues (Tle, DmTyr), are tolerable for a high in vitro affinity to the neurotensin receptor 1 (NTR1) and the ability to be internalised in receptor-positive tumour cells. Only the double and threefold-stabilized (3, 4) exhibited a remarkable specific tumour uptake which was, however, not sufficient for tumour imaging in the abdomen. Additional efforts are required to improve molecule stabilization against enzymatic attack and to enable receptor-based tumour imaging.
This work was partially supported by the BIOMED grant BMH4-CT98-3198 of the EC.

Dipole excitations in the spherical nucleus 88Sr, observed in the energy region 4.5 MeV < E_x < 5.5 MeV,
are proposed to be scissors-like excitations on top of the dynamically deformed quadrupole vibrational state.

no abstract

Die Wechselwirkung von Cm(III) (9E-8 mol/L) mit einer Calcit Suspension (1 g/L) wurde mit Hilfe der zeitaufgelösten Laserfluoreszenzspektroskopie untersucht. Dabei konnte ein Cm(III)/Calcit Oberflächenkomplex nachgewiesen und charakterisiert werden. Das Maximum der Fluoreszenzemission dieser Curium Spezies liegt bei 607.5 nm und entspricht damit dem des Tetracarbonatokomplexes Cm(CO3)45- in Lösung. Während das freie Cm-Aquoion von 9 Wassermolekülen umgeben ist, läßt die für den Oberflächenkomplex ermittelte Fluoreszenzlebensdauer von 314 ± 6 ms auf ein Wassermolekül in der ersten Koordinationssphäre des Curiums schließen. Mit zunehmender Cm(III)/Calcit Kontaktzeit nimmt die Stärke des Signals mit einem Emissionsmaximum bei 607.5 nm sukzessive ab und ein sehr weit rot verschobenes Signal wird sichtbar. Die gemessene extreme Verschiebung zu einem Wert von 619 nm ist bisher einmalig und deutet auf eine starke Veränderung des Cm-Ligandenfeldes hin. Für diese Spezies wurde eine Fluoreszenzlebensdauer von 1302 ± 75 ms gemessen. Das entspricht dem theoretisch bestimmten Wert für wasserfreies Curium. Die ermittelte Fluoreszenzlebensdauer und die starke Verschiebung des Cm-Spektrums mit der Dauer der Kontaktzeit ist der spektroskopische Beweis für den Einbau des Curiums in das Calcitgitter.

Lecture (Conference): GDCh Jahrestagung der Fachgruppe Nuklearchemie 2001 in Würzburg, Sept. 2001 (submitted)

Radionuklidkontaminationen können über den Belastungspfad Boden-Pflanze-Nahrungskette deutlich zur Strahlenbelastung des Menschen beitragen. Für zuverlässige Abschätzungen der Radionuklidmigrationen in das geologische und biologische Umfeld ist ausgehend von der Verteilung der Nuklide die chemische Charakterisierung der Radionuklidspezies unbedingt erforderlich, um den summarischen Transferfaktor durch chemisch eindeutig identifizierte Parameter zu ersetzen. In verschiedenen Versuchsreihen wurde mit der Bestimmung der chemischen Speziation von U(VI) in Pflanzen begonnen. Durch Untersuchungen mittels zeitaufgelöster Laser-induzierten Fluoreszenzspektroskopie und Röntgenabsorptionsspektroskopie wurde deutlich, daß Uran in der Oxidationsstufe +6 in der Pflanze vorliegt und es Unterschiede zwischen der Angebotsspeziation im Porenwasser des Bodens bzw. in der Hydrokulturlösung und der Akkumulationsspeziation in der Pflanze gibt. Es zeigte sich, daß der chemische Zustand des Urans im Gleichgewicht in der Wurzel, Sproßachse und im Blatt identisch und unabhängig von der Art der Pflanze, den Wachstumsbedingungen und der Angebotsspeziation ist. Die bisherigen spektroskopischen Resultate deuten auf die Bildung von Uranyl-Phophato-Komplexe als Hauptspezies hin. Neben der Phosphatanbindung müssen aber auch carboxylische Bindungen zum Uran in den Pflanzenproben in Betracht gezogen werden.[1]
Ausgehend von diesen Ergebnissen, wurden Modellkomplexierungen von U(VI) mit ausgewählten organischen Liganden durchgeführt, die im Aufbau und Stoffwechsel der Pflanzen eine große Rolle spielen. In Anlehnung an das Verhalten von Schwermetallen im pflanzlichen System wurden Vertreter aus den Substanzklassen Carbonsäuren, Aminosäuren und Peptide, Kohlenhydrate, Lipoide und aus der Gruppe der freien und polymergebundenen Nukleobasen für die Modellkomplexierungen ausgewählt. Für die Untersuchungen des Reaktionsverhaltens von U(VI) gegenüber den ausgewählten Bioliganden werden neben der UV-Vis Spektroskopie insbesondere die zeitaufgelöste Laser-induzierte Fluoreszenzspektroskopie genutzt. Erste Ergebnisse werden hier vorgestellt. Ziel ist es, die erhaltenen spektroskopischen Datensätze mit Daten von kontaminierten Pflanzenproben zu vergleichen, um auf diese Weise U(VI)-Spezies in Pflanzen eindeutig zu charakterisieren.

[1] A. Günther, Zwischenbericht DFG-BE 2234/1-1

Das Uranbergwerk Königstein (Sachsen) befindet sich zur Zeit in der Flutungsphase. Es wurde Flutungswasser kolloidchemisch untersucht (pH 5,6; Eh 450 mV; CCa 0,9 mM, CFe 0,3 mM, CU 0,05 mM, CSulfat 1,2 mM, CHydrogenkarbonat 1,0 mM). Nahezu 90% des Fe waren zweiwertig. Auf Grund des Eh-Wertes erwarten wir, daß das Uran sechswertig vorlag. Die Kolloidkonzentration betrug 2 bis 3 mg/l, die Partikelgröße war 100 bis 300 nm. Die Partikel bestanden vor allem aus Fe, Al, S und U.
Grubenwässer können kolloidchemisch zwischen zwei Extreme eingeordnet werden:
(a) Hochmineralisierte Porenwässer mit pH-Werten von 1 bis 3, die ultrafeine Fe(III)-
Partikel im g/l-Bereich enthalten (Partikelgröße <5 nm) und
(b) "Bulk"-Wässer mit pH-Werten um 7, die Fe(III)/Al-Submicronpartikel im Konzen-
trationsbereich von wenigen mg/l enthalten (Partikelgröße 100 bis 300 nm) [1].
Die pH-Abhängigkeit der Schwermetallsorption an Oxyhydroxysulfaten und Oxyhy-droxiden des Fe(III) und Al kann durch sigmoide Kurven mit einem steilen Anstieg bei mittleren pH-Werten ("Adsorption Edge") beschrieben werden. Bei Wässern des Typs (a) findet kaum Adsorption statt (Ausnahmen: 210Pb, Ra-Isotope). Bei Wässern des Typs (b) werden viele radiotoxische Schwermetalle stark sorbiert und sind somit fil-trierbar (210Po, 230Th, 227Ac, 210 Pb). Bemerkenswert ist das Verhalten von U(VI). In karbonatfreien Lösungen zeigt es an Fe(III)-Partikeln eine starke Adsorption bei pH-Werten >4 [2]. In realen "Bulk"-Wässern aus Bergwerken wird die U-Adsorption durch die Bildung von Uranylkarbonatokomplexen jedoch deutlich unterdrückt [1].
Flutungswässer repräsentieren den Übergang von Wässern des Typs (a) in Wässer des Typs (b). In unseren Proben waren stark adsorbierende Nuklide wie 210Po und 210Pb zum größten Teil an Kolloidpartikel gebundenen (filtrierbar). In-teressanterweise erwiesen sich aber auch 60 bis 90% des Urans als kolloidgetragen. Offensichtlich wird bei dem vorliegenden pH-Wert von 5,6 die Uranadsorption weder durch hohe Azidität noch durch Karbonatkomplexierung verhindert.
Der Zutritt von Sauerstoff löst eine Vielfalt von chemischen Reaktionen in den Proben aus. Durch die Oxidation des Fe2+ steigt der Gehalt an Fe(III)-Partikeln (Faktor 10). Trotz der höheren Trägerkolloidkonzentration sinkt der filtrierbare Uranylanteil zunächst. Grund ist der pH-Abfall (bis auf etwa 4,5), den die Fe-Oxidation verursacht. Mit einiger Verzögerung steigt der pH-Wert wieder weil die Ge-samtkarbonatkonzentration durch CO2-Entgasung sinkt; der Hydrogenkarbonatgehalt fällt bis auf <0,05 mMol/l. Beides bewirkt einen Anstieg des filtrierbaren Urananteils auf fast 100%. Alle diese Vorgänge (O2-Zutritt, pH-Variationen, CO2-Entgasung) spielen auch im Bergwerk eine Rolle.
Die oft getroffene Annahme einer ungehinderten Migration von Uranyl in gelö-ster Form ist für pH-Werte von 4 bis 6 "überkonservativ". Scavenging durch Fe(III)-Partikel und Kolloidkoagulation plus Sedimentation kann in diesem pH-Bereich das U(VI) in erheblichem Maße immobilisieren.

[1] Zänker, H. et al.; Radiochim. Acta 88, 619 (2000)
[2] Hsi, C.D. and Langmuir, D.; Geochim. Cosmochim. Acta 49, 1931 (1985)

Spherical silica colloids with a diameter of 1.0 µm, made by wet chemical synthesis, were irradiated with 2–16 MeV Au ions at fluences in the range (2–11)×1014 cm–2. The irradiation induces an anisotropic plastic deformation turning the spherical colloids into ellipsoidal oblates. After 16 MeV Au irradiation to a fluence of 11×1014 cm–2, a size aspect ratio of 5.0 was achieved. The size polydispersity (~3%) remains unaffected by the irradiation. The transverse diameter increases exponentially with ion fluence. By performing measurements as a function of ion energy at a fixed fluence, it is concluded that the transverse diameter increases linearly with the average electronic energy loss above a threshold value of ~0.6 keV/nm. Nonellipsoidal colloids are observed in the case where the projected ion range is smaller than the colloid diameter. The data provide strong support for the thermal spike model of anisotropic deformation.

For further informations, please contact the author (M.Posselt@fz-rossendorf.de).

Ion beam deposition of carbon films was studied by molecular-dynamics simulations. Using a slightly modified version¹ of the 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 following properties of the calculated films were analysed: (i) sp³ content versus mass density in inner film regions, (ii) binding energies of 3- and 4-fold coordinated carbon atoms in films of different mass densities, (iii) probability distributions for the number of sp³ atoms generated (or annihilated) per deposited ion, and (iv) structure and width of the graphite-like surface regions. As a result, an atomistic picture is provided which shows how the formation of tetrahedral amorphous carbon (ta-C) films is affected by both ion energy and substrate temperature.

¹ H.U. Jäger and K. Albe, J. Appl. Phys. 88, 1129 (2000).

Bei der Freimessung von Bauschutt aus dem Abriß von Nuklearanlagen ist eine direkte Messung der alpha-aktiven Nuklide im stehenden Gebäude auf Grund ihrer geringen Reichweite und ihrer Absorption im Beton nicht möglich. Die im Rahmen von BMBF-Projekten entwickelte Methode der direkten Alpha-Spektrometrie von großflächigen dünnen Meßpräparaten nach nur mechanischer Präparation des Betons ermöglicht eine Bestimmung der Actinide bis zu 0,02Bq/g in Multielementspektren [1,2]. Durch die große Fläche wird eine hohe Impulsrate und durch die dünne Schicht eine geringe Selbstabsorption der Alpha-Strahlung und damit eine gute Auflösung der Spektren erreicht. In einem aus zwei Schritten bestehendem Zerkleinerungsprozeß wurden mittlere Partikeldurchmesser von 0,5µm erreicht. Die Grobzerkleinerung erfolgt mit einem Backenbrecher (reiner Beton) oder mit einer Tischfragmentierungsanlage (Trennung von Beton und Armierungseisen), die Feinzerkleinerung durch Naßmahlen mit Spezialmahlkugeln. Die Meßproben mit einem Durchmesser von 20cm und Schichtdicken zwischen 0,6 und 5µm entstanden durch Sprühen mit einer Zweistoffdüse aus der Betonsuspension auf Probenträger und anschließendes Trocknen. Die Suspensionsstabilität konnte durch verschiedene Peptisatoren erhöht werden. Die Alpha-Spektren der Meßproben wurden in einer Gitterionisationskammer aufgenommen. Durch die Verwendung von Standardbeton mit zugefügten Actiniden konnten die Selbstabsorption der Alpha-Strahlung und die Peakform in Abhängigkeit der Probendicke ermittelt werden. Somit konnten die Spektren unbekannter Betonproben gleicher Geometrie entfaltet werden. Das für diese Arbeit entwickelte Programm WINKRUM basiert auf einem geometrischen Modell für Partikelgröße, Partikelverteilung und Packungsdichte. Mit Strahlungstransportberechnungen [3] können Spektren simuliert werden, die ebenfalls eine Peakentfaltung von Mul-tielementspektren ermöglichen.

Das diesem Bericht zugrundeliegende Vorhaben wurde mit Mitteln des Bundesministeriums für Bildung und Forschung unter dem Förderkennzeichen 02 S 7768 gefördert. Die Verantwortung für den Inhalt liegt bei den Autoren.

Literatur
[1] Nebelung, C.; Nitsche, H., Henniger, J.
"Stillegung und Rückbau: Direktmessung alpha-aktiver Nuklide in Bauschutt zur Freigabe-entscheidung Schlußbericht" BMBF 02S 7655 /02S7655A, 1999
[2] Nebelung, C.; Henniger, J.
Schlußbericht zum Fördervorhaben BMBF 02 S 7768 in Vorbereitung
[3] Henniger, J.
"AMOS - ein multivalent nutzbares Programmsystem zur Berechnung von Strahlungstrans-portproblemen", Strahlenschutz : Physik und Messtechnik, Band 1, 26. Jahrestagung des Fachverbandes für Strahlenschutz e.V., Karlsruhe, 24.-26. Mai 1994; Verlag TÜV Rhein-land.

At present the scaled core melt down experiments FOREVER are underway. These experiments are simulating the lower head of a reactor pressure vessel under the load of a melt pool with internal heat sources. Due to the multiaxial creep deformation of the three-dimensional vessel with a highly non-uniform temperature field these experiments are an excellent possibility to validate numerical creep models. A Finite Element model is developed and using the Computational Fluid Dynamic module the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a new creep model procedure. Additionally the material damage is evaluated considering the creep deformation as well as the prompt plasticity.
After post-test calculations for the FOREVER-C2 experiment, pre-test calculations for the experiments to come are performed. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios. Analysing the calculations it seems to be advantageous to introduce a vessel support which can disburden the vessel from a part of the mechanical load and therefore avoid the vessel failure or at least prolongate the failure time as a possible accident mitigation strategy. Additionally, it seems to be possible to install an absolutely passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in case of a core melt down.

In spite of the fact that a great deal of research has been carried out on liquid metal ion sources, suprisingly few results exist on the temperature dependence of their emission characteristics. In this article we study two liquid metal alloy ion sources (LMAISs), namely Co₃₆Nd₆₄ and Au₇₇Ge₁₄Si₉. While the results of the former source were as expected, the latter displayed an entirely different dependence of its emission characteristics on temperature. The unusual results of the Au₇₇Ge₁₄Si₉ LMAIS are explained in terms of the abnormal behavior of the surface tension of the alloy with temperature.

Vertical two-phase flow is normally classified into the four basic flow regimes bubble, slug, churn and annular flow. The transition between the different flow regimes does not occur suddenly and many extensions of this classification can be found in literature. For the prediction of flow patterns empirical and theoretical flow pattern maps have been developed.

This paper presents a digitized version of a thermodynamic sorption database, implemented as a relational database under MS Access. The data are required for the parametrization of Surface Complexation Models (SCM). It is mineral-specific and can therefore also be used for additive models of more complex solid phases such as rocks or soils. An integrated user interface helps users to access selected mineral and sorption data, to convert parameter units, to extract internally consistent data sets for sorption modeling, and to export them into formats suitable for other modeling software. Data records comprise of mineral properties, specific surface area values, characteristics of surface binding sites and their protolysis, sorption ligand information, and surface complexation reactions. The following submodels are already implemented, extensions to other variants are straightforward: the Non-Electrostatic Model, the Diffuse Double Layer Model, the Constant Capacitance Model, the Triple Layer Model, and the Basic Stern Model. For every SCM type (where applicable), also the concept of strong and weak binding sites, and the 1-pK approach is included. Surface species composed from up to three different ligands can be incorporated.
An extensive bibliography is also included, providing links not only to the above listed data items, but also to background information concerning surface complexation model theories, related software for data processing and modeling, and sorption experiment techniques. Only very few of the abundant surface complexes proposed in the literature (mostly resulting just from best-fit considerations) are actually validated by spectroscopic evidence or supported by theoretical (quantum-chemical) calculations. If such information is available it is also stored in the database.
The database will help to substitute the at present in risk assessment studies most often applied simplistic distribution coefficients (Kd-values) by the more realistic description of sorption phenomena with SCM. It assists the identification of critical data gaps, the evaluation of existing parameter sets, consistency tests and the establishment of selected reference data sets. As to the knowledge of the authors, so far there is no such digital thermodynamic database for surface complexation equilibria existent world-wide, despite the vast amount of available data.

kein Abstract vorgesehen

Chlorite is a common accessory mineral, commonly found in sedimentary and low grade metamorphic rocks like the phyllite in the former uranium mining area of Saxony (Germany). The cur-rent flooding of the mines leads to an interaction be-tween the uranium containing flooding water and the surfaces of the wall rock. During the weathering of phyllite a secondary mineral is formed, which in further investigations [1] was described as ferrihydrite. The source of this secondary mineral is the iron-rich chlo-rite of the phyllite.
Chlorite is a phyllosilicate with a trioctahedral structure, consisting of negatively charged 2:1 layers that alternate regularly with positively charged interlayer sheets [2]. During the weathering of chlorite the main constituents of the octahedral sheets, Mg2+, Fe2+, Fe3+ and Al3+, are released into the aqueous solu-tions. In laboratory experiments the dissolution of chlo-rite was studied with a continuous flow-through reactor and in batch experiments. In this study we will lay em-phasis on the released iron because of its ability to form secondary minerals and colloids.
Experiments: Batch experiments were carried out on an iron-rich chlorite from Flagstaff Hill, California, with a grain size of 63-200 µm. Half a gram of the samples were added to 40 ml deionized water, which was previously adjusted to an ionic strength of 0.1 M with NaClO4. The suspension was aged during 2 months without any pH adjustment. A pH value of 7 was found at the end of the experiment. The freshly formed iron hydroxide particles were separated from the large excess of the micron-size chlorite powder particles by well-defined centrifugations (2500 x g, 1h and 3500 x g, 1h). A defined volume of the centrifugate was filtered through a 50 nm and 15 nm Nuclepore filter in order to fix the ultrafine iron particles on a substrate. The filter membranes were prepared for scanning electron microscopy (SEM).
Results: In SEM investigations spherical particles are detected on the Nuclepore filter. The size of these colloids ranges from 30 to 80 nm. The colloids are mainly arranged as agglomerates, while individual colloids are rarely observed. On several large agglom-erates energy-dispersive X-ray analysis (EDS) were taken in order to get information about the chemistry of these colloids. With this method we were able to detect directly iron colloids of a chlorite suspension at pH 7. The process leading to the formation of colloids can be explained as a consequence of the iron release during the dissolution of chlorite. The dissolved iron oxidizes to ferric iron which subsequently hydrolyses, precipi-tates and forms secondary minerals and iron colloids. The detection of iron colloids was previously described in a suspension of ground phyllite [3], where a com-bined technique of centrifugation at varying centrifugal speed and ICP-MS and AAS of the centrifugates was used. The formation of iron colloids was prevented in the acid region of pH = 4 due to the higher solubility of Fe in this pH region. With decreasing solubility in the neutral and alkaline medium, the released Fe forms iron colloids or precipitates as secondary iron mineral coatings. The formation of iron colloids during the dissolu-tion of chlorite must be taken into consideration in the assessment of contaminant behavior in the nature. Though contributing only little to the mass balance of a water body, iron colloids can show significant adsorp-tion of trace elements because of their high specific surface area and their affinity to heavy metals.
The formation of secondary iron mineral coatings is also of importance for the behavior of contaminants in the nature since coatings significantly change the sur-face properties of the weathering chlorite. The most common secondary iron mineral is ferrihydrite, a poorly crystallized iron mineral with a chemical for-mula of 5Fe2O3 . 9H2O [4] and a large specific surface area. Sorption experiments which were carried out with ur...

Complexation processes of Cm(III) and Eu(III) by glycolic acid are studied by time-resolved laser fluorescence spectroscopy (TRLFS). The experiments with curium are performed in 0.1 M and 3.0 M NaClO4. The glycolic acid concentration is varied between 0.01 mol/L and 0.5 mol/L at pH 3. Cm(III) and Eu(III) fluorescence emission spectra are obtained at a fixed glycolic acid concentration of 0.5 mol/L, the pH is varied between 3 and 11. In addition to the Cm3+ aquo ion, two Cm(III)-glycolic acid species are observed by peak deconvolution: Cm(gly)2+ and Cm(gly)2+. Above pH 5 a chelate Cm-glycolate complex is formed. This curium-glycolate complex is characterised by its emission spectrum (peak maximum at 611.2 nm) and its fluorescence emission lifetime (172 ± 8 µs). The corresponding chelate europium-glycolate complex with 300 ± 10 µs lifetime is obtained above pH 6.83. In the pH range 6 to 8 the decay behaviour of the excited state is different in the Cm(III)- and Eu(III)-glycolate system. While a bi-exponential decay behaviour was observed for the Cm-system, indicating slow exchange kinetics in comparison to the fluorescence decay of the exited state, the corresponding Eu-system shows mono-exponential decay behaviour. More over the reversibility of Eu-chelating is much faster than in the case of the Cm(III) complex. The results show that the strength and kinetics of the chelating is different for Cm(III) and Eu(III).

For the study of the effectiveness of passive safety systems a high pressure (up to 7 MPa) and high power (up to 4 MW) test facility – named NOKO – has been constructed and operated at the Forschungszentrum Jülich. From 1996-1998 this facility was used for a project within the 4th FP of the EU "European BWR R&D Cluster for Innovative Passive Safety Systems". An overview and selected results are given for the tests with two bundles of the emergency condenser, with the building and plate condenser, with 4 different passive initiators, with a passive flooding system and with decay heat removal tests during shutdown.
It has been decided to decrease substantially the safety research at the Forschungszentrum Jülich; to maintain the experimental competence for two-phase flow the NOKO facility will be transferred to the Forschungszentrum Rossendorf by the end of the year 2000 up to the beginning of the year 2001. The facility will be named TOPFLOW; the main objectives of future tests will be oriented towards more generic research: investigation of steady state and transient two phase flow phenomena especially transient two phase flow patterns, the development of two-phase flow instrumentation, the generation of a data basis for Computational Fluid Dynamic (CFD)-Code validation and testing of heat exchangers and safety systems. An overview will be given about the modifications and improvements related to the test facility and the planned test.

Results of estimations of covariance matrices of neutron spectra in VVER-1000 reactor pressure vessel and cavity positions are presented. Two-dimensional calculations with the discrete ordinates transport code DORT in r-theta and r-z-geometries are used to determine the neutron group spectrum covariances including cross-correlations between interesting positions. The new Russian ABBN-93 data set and the CONSYST code are used to supply the transport calculations with neutron group data. All possible sources of uncertainties, as neutron cross sections, fission sources, geometrical dimensions and material densities, were considered, whereas, the uncertainty of the calculation method was assumed to be negligible in view of the available precision of Monte Carlo simulation.

The Rossendorf Beamline at the European Synchrotron Radiation Facility is equipped with a unique radiochemistry experimental station. This dedicated station has been designed to perform environmentally relevant experiments on radionuclides, in particular actinides, using synchrotron based X-ray absorption fine structure spectroscopy. The technical concepts and the layout of this experimental station, where radioactive solids and liquids with activities of up to 185 MBq can be studied, are presented. The radiological safety of experimenters, equipment, and of the environment are ensured by the specially developed radiochemistry safety system. The multibarrier concept, the ventilation and air monitoring systems, the radiological protection system, and special software components for recording and visualisation of the safety status are described in detail.

The title compound, [C24H30N4Si]2+·2Cl-·6CHCl3, contains a hexacoordinated Si atom located on a crystallographic centre of inversion. The coordination of the Si atom can be described as a slightly distorted octahedron, with the 4-picoline ligands in the equatorial plane and the two H atoms occupying axial positions. The title compound is isomorphous with its analogue where the Cl ions are substituted by Br ions.

Acta Cryst. (2001) E (submitted)

In order to improve models used for the predictive modeling of the actinide migration in natu-ral aquifer systems it is necessary to get more precise information about the interaction process between humic acids and actinide ions. This includes for instance a more profound knowledge about humic acid binding sites interacting with actinide ions at different pH values. In addition, natural humic acids contain small amounts of inorganic components, e.g., iron, that cannot be removed by usual purification methods. It is not known whether or not these components may influence the interaction between humic acids and actinide ions.
Applying humic acid model substances and natural humic acids with different functionalities we continue our studies concerning the interaction between humic acids and actinides [e.g., 1,2]. In order to specify humic acid binding sites interacting with actinide ions in the neutral pH range, we study the influence of phenolic OH and other acidic OH groups on the interaction process. We investigate the neptunium(V) complexation in neutral solution by near infra-red absorption spectroscopy and X-ray absorption spectroscopy applying modified synthetic and natural humic acids with blocked phenolic and other blocked acidic OH groups. The influence of inorganic humic acid components on the actinide complexation by humic acids is studied using an "ultra-pure" synthetic humic acid model substance. The neptunium(V) com-plexation of this humic acid is compared to the complexation behavior of natural and synthetic humic acids having small amounts of non-removable inorganic components.

[1] Pompe, S. et al.: Determination and Comparison of Uranyl Complexation Constants with Natural and Model Humic Acids. Radiochim. Acta 82, 89 (1998).
[2] Pompe, S. et al.: Investigation of Humic Acid Complexation Behavior with Uranyl Ions Using Modified Synthetic and Natural Humic Acids. Radiochim. Acta 88, 553 (2000).

no abstract delivered from author

Abstract

An der Vermischungsanlage ROCOM, einem 1:5 skalierten Modell des Druckwasserreaktors Konvoi wurden umfangreiche Geschwindigkeitsmessungen im Downcomer des Reaktordruckbehälters für verschiedene Schleifendurchsätze und Teilschleifenbetrieb durchgeführt. Durch Verwendung eines leistungsfähigen Lasers konnten auch transiente Geschwindigkeitsprofile aufgenommen werden. Einige der gemessenen Profile wurden mit dem numerischen Strömungsberechnungsprogramm CFX-4 nachgerechnet.

Bei Vierschleifenbetrieb konnte eine Unabhängigkeit der Geschwindigkeitsprofile von der Reynoldszahloberhalb über 100 m³/h pro Schleife im Modell nachgewiesen werden. Im Vergleich zu anderen Reaktortypen bestehen im Ringraum des RDB des DWR Konvoi einige konstruktive Besonderheiten, die die Vermischung nachhaltig beeinflussen. Der Downcomer ist verhältnismäßig kurz und besitzt eine diffusorartige Erweiterung unterhalb der Stutzenebene. Unterhalb der Eintrittsstutzen und Austrittsstutzen existieren Rezirkulationsgebiete mit geringen Geschwindigkeitsgradienten. Zwischen den Eintritts- und Austrittsstutzen liegen Gebiete hoher Geschwindigkeitsgradienten. Transiente Messungen bei Anfahren einer Pumpe belegen, daß die Strömung im Downcomer in den ersten Sekunden wie eine Potentialströmung anläuft. Das Geschwindigkeitsmaximum befindet sich dabei noch annähernd unterhalb des entsprechenden Kühlmittelstutzens. Erst mit einer gewissen Zeitverzögerung entwickeln sich die großräumigen Wirbelgebiete, die letztlich zum Geschwindigkeitsmaximum auf der der in Betrieb gegangenen Schleife entgegengesetzten Seite des Ringspalts führen.

Strömungsuntersuchungen im Downcomer mit Hilfe der LDA-Technik bei naturumlaufnahen Schleifendurchsätzen mit Hinzugabe von Glucose zur Simulation von Dichteeffekten sind geplant.

The S-[¹⁸F]fluoromethyl analogue of (+)-McN5652 was evaluated by autoradiographic ex vivo studies with rats.

The S-[¹⁸F]fluoromethyl analogue of (+)-McN5652 was prepared by reaction of demethylated (+)-McN5652 with [¹⁸F]bromofluoromethane in decay-corrected radiochemical yields of about 18% (related to [¹⁸F]fluoride). Autoradiographic ex vivo studies with rats and PET studies with piglets indicate that the ¹⁸F-labelled analogue of (+)-McN5652 is a potential PET tracer for the imaging of the serotonin transporter.

In Germany, besides salt formations also granitic subsurface environments are taken into account as potential host formations for the geological disposal of radioactive waste [1]. For safety assessments of radioactive waste repositories, amongst others, the sorption behavior of radionuclides onto the host rock has to be known. It is determined by various factors including pH, Eh, the presence of inorganic and organic ligands as well as the speciation of radionuclides in the aqueous and solid phase.
In the present work, the sorption of neptunium(V) onto granite and its main mineral constituents quartz, orthoclase, biotite, albite, and muscovite is studied under anaerobic conditions as a function of pH, ionic strength and solid/solution ratio in a series of batch equilibrium experiments. Furthermore, the effect of humic acid on the neptunium sorption is studied for different ligand concentrations. A 14C-labelled synthetic humic acid (type M42, [2]) is used for the experiments. Its sorption behavior is comparable to that of natural humic acids. The oxidation state of neptunium in the presence of humic acid and minerals is followed at selected pH values over a period of three months by NIR absorption spectroscopy. The neptunium sorption is affected by both the pH and the presence of organic material.
Neptunium species on the mineral surface are identified using neptunium LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The structural parameters of the near-neighbor surrounding of sorbed neptunium are compared to those of neptunium hydrate, hydroxide and humate complexes.

[1] Papp, R.: Gegenüberstellung von Endlagerkonzepten in Salz und Hartgestein. FZKA-PTE Nr. 3, Forschungszentrum Karlsruhe GmbH, Karlsruhe 1997.
[2] Bubner, M., et al.: Isotopically Labelled Humic Acids for Heavy Metal Complexation. J. Labelled Compounds and Radiopharmaceuticals XLI, 1017 (1998).

The paper presents a brief description of the DYN3D/RELAP5 code package developed on the base of coupling the system code RELAP5 and the 3D neutron kinetics code DYN3D. Elaboration of the coupling interface has been performed in the framework of a joint research project.
The fifth dynamic AER problem for VVER-440 reactor plant has been solved using the code package. Calculation results are compared with the results obtained earlier in the FZR using DYN3D/ATHLET. Code-to-code comparison shows a close agreement between the key transient parameters.

Presently, increased requirements are imposed to study transient and emergency operation modes of nuclear facilities from point of view of quality and adequacy their simulation. In particular, concerning the Ukrainian NPP's this is connected with the analysis of VVER-1000 safety for a whole number of dsign basic accidents.
The first experience was obtained for the use of the coupled code DYN3D/ATHLET caculating a transient connected with the switching-off of one main coolant pump at the unit 6 of the Zaporizhya NPP.

Magnetic properties of a presurface zone of the bulk, single-crystal (110)Cr, implanted with 119Sn ions were studied by means of conversion electron Mössbauer spectroscopy. A strong enhancement of the magnetic hyperfine field, B, was found. The increase is by a factor of ~2.7 in the average value of B and by a factor of ~2.3 in the most probable value of B (the amplitude of the spin-density waves, SDW's). The observed effects are explained in terms of the interference of two spin-density waves having the same amplitude phase but various polarizations. The relative contributions of the interfering SDW's was estimated as equal to ~60% for those with mutual perpendicular and ~40% for those with mutual parallel polarization.

Neutral lipophilic silicon organic compound of oxorhenium complexes were obtained by the "3+1" mixed ligand approach with the simultaneous complexation of one SSS tridentate ligand and a monodentate S-R ligand with the formation of the oxorhenium(V) complexes. Four trialkyl(triaryl)siloxyalkane(benzene)thiolato-(3-thiapentane-1,5-dithiolato)oxorhenium complexes of the general formula (SCH₂CH₂SCH₂CH₂S) ReO (SQOSiR₃) were synthesized and studied where
IV, Q = CH₂CH₂, R = CH₂ CH₃
V, Q = CH₂CH₂ CH₂, R = CH₂ CH₃
VI, Q = C₆H₅, R = CH₂CH₃
VII, Q = CH₂CH₂, R = C₆H₅
Identification and determination of structure of the compounds (IV-VII) and hydrolized products (I-III) were carried out by TLC, HPLC, elemental analysis and IR, UV and NMR spectroscopic methods. Lipophilicity was determined by reverse phase HPLC method. As a role the more lipophilic compounds should have stronger binding with the C18 chain of the column material giving higher retention time. The retention time of the silicon rhenium complexes(IV-(VII) and the corresponding OH compounds (I-III) of the general formula (SCH₂CH₂SCH₂CH₂S)ReO(SQOH) where I, Q= CH₂ CH₂, II, Q= CH₂CH₂ CH₂, R = III, Q=C₆H₅, were determined as

Compound.....Retention time (min)..............Compound.......Retention time (min)
I.....................2.60.....................................IV....................4.16
II....................2.64......................................V....................4.26
III...................2.87......................................VI....................4.46
I.....................2.60......................................VII.................. 4.93

It observed that the retention time of the compounds increases with the increase of lipophilicity as expected on the reverse phase column and the introduction of alkyl or arylsilyl radical to the oxygen atom greatly increases the lipophilicity. Stability of the silicon rhenium complexes (IV-VII) was studied in acetonitrile-water solution at different temperature and pH by reverse phase HPLC method. Of the four compounds triethylsiloxyalkylthiolato (IV and V) complexes were found to be the most stable with respect to both temperature and pH changes. Trialkylphenylsiloxy compound (VI) was found to be most unstable one. All the compounds were labile in acidic pH. The most lipophilic compound (VII) was less soluble in acetonitrile-water (1:1) system.

The paper presents a method for the prediction of the radial gas fraction profile from a given total bubble size distribution. The method is based on the assumption of the equilibrium of the forces acting on a bubble perpendicularly to the flow direction. A large number of bubble classes is assumed. Based on the radial profile of the liquid velocity, radial distributions are calculated separately for all bubble classes. The resulting local bubble size distributions can be used by models for bubble coalescence and break-up. It is supposed, that the attempts for a one-dimensional modelling of bubble coalescence and break-up suffer in case of pipe flow from neglecting the radial profiles of the particle densities for the single bubble classes. The model is the basis of a fast running one-dimensional steady state computer code. The results of the model are compared with experimental data for a number of gas and liquid volume flow rates.

F-18 labelled amino acid 3-O-methyl-6[¹⁸F]Fluor-L-DOPA (OMFD), not used for diagnostics until now, was synthesized, tested in cell cultures as well as in animals and studied in patients (pts) with recurrences of low differentiated brain tumors. Synthesis is based on a new precursor (N-formyl-3-O-methyl-4-O-Boc-6-trimethylstannyl-L-DOPA-ethyl-ester). Biologic behavior was tested HAT 29 and RBE-4-cell cultures and tumor bearing nude mice. First clinical studies we carried out in recurrent glioblastoma multiforme (4 pts.) with inconclusive MRT and CT. The application of OMFD was based on an individual decision. The aim was to detect localization and extent of recurrent tumor for planning of stereotactic radiotherapy. After 50 min synthesis time a radiochemical yield of 20 - 25% was reached. A high tracer uptake in tumor cells via L-amino-transporter was seen. However there was no evidence for metabolism or incorporation into proteins. Biodistribution in mice showed 60 min p.i. high intratumoral uptake (12.4 ± 1.8% ID/g) and a tumor/blood ratio of 9.5 ± 0.8. Increased radioactivity uptake was found in all pts. 60 min p.i. in the region of the suspected recurrences (lesion/nonlesion 2.2 ± 0.5), only little tracer uptake was found in the whole body scans in muscle, thorax and abdomen. Suspected recurrences were clearly seen in on PET images. Preliminary diagnostic studies in pts. With low differentiated tumor suggest that the new F-18 labelled amino acid is a valuable PET-tracer for tumor imaging.

Various radiotracers based on uracil nucleosides (e.g 2'-fluoro-2'-deoxy-5-[¹²⁴I]iodo-1-beta-D-arabinofuranosyluracil, [¹²⁴I]FIAU) and acycloguanosine derivatives (e.g. 9-[(3-[¹⁸F]fluoro-1-hydroxy-2-propoxy)methyl]guanine, [¹⁸F]FHPG) have been proposed as suitable substrates for the noninvasive imaging of herpes simplex virus type 1 thymidine kinase (HSV1-tk) reporter gene expression. However, for evaluation of these tracers different in vitro and in vivo models were used which did not permit a direct comparison of selectivity and affinity. Therefore, we directly compared [¹⁸F]FHPG and radioiodinated FIAU to assess their potential for PET imaging of transgene expression.
The uptake of [¹²⁵I]FIAU, [¹⁸F]FHPG and [³H]acyclovir was determined in vitro using four different HSV1-tk expressing cell lines and their respective negative controls. The in vitro tracer uptake was generally low in nontransduced cell lines demonstrating low affinity to cellular thymidine kinases. In HSV1-tk expressing cells, [³H]acyclovir showed approximately a 2-fold higher tracer accumulation, the [¹⁸F]FHPG uptake increased to approximately 6-fold and the [¹²⁵I]FIAU accumulation to approximately 28-fold after 120 min incubation of T1115 human glioblastoma cells. Similar results were found in the other cell lines. In addition, biodistribution and PET studies with [¹⁸F]FHPG and [^124/125I]FIAU were carried out in tumour-bearing BALB/c mice. Significantly higher specific tracer accumulation was found for [¹²⁵I]FIAU compared to [¹⁸F]FHPG. The ratio of specific tracer accumulation between [¹²⁵I]FIAU and [¹⁸F]FHPG increased from 21 (30 min p.i.) to 119 (4 hours p.i.). PET imaging, using [¹²⁴I]FIAU, clearly visualised and delineated HSV1-tk expressing tumours, whereas only a negligible uptake of [¹⁸F]FHPG was observed.
This study demonstrated that in vitro and in vivo, the radioiodine labelled uracil nucleoside FIAU has a significantly higher specific accumulation than the acycloguanosine derivative [¹⁸F]FHPG. This suggests that [¹²⁴I]FIAU should be the preferred reporter probe for PET imaging of HSV1-tk gene expression. However, the use of [¹²⁴I]FIAU is hampered by the relatively long physical half-life, the low positron emission and the limited availability of the radionuclide. Thus, further attempts to develop suitable PET tracers for the assessment of HSV1-tk gene expression should also focus on ¹⁸F-labelled uracil derivatives.

Experiments were performed to investigate heating up processes of fluids in storage tanks under the influence of an external heat source. As a consequence of an external fire, the heat-up of the inventory may lead to the evaporation of the liquid and to release of significant quantities of dangerous gases into the environment. Heating the vessel from the side walls, a strong temperature stratification is observed leading to large temperature gradients. At the top of the tank evaporation can start much earlier than the average temperature reaches saturation.
Several tests were performed both with heating from the bottom and with heating from the side walls. The test tank was equipped with thermocouples and with needle probes for measuring of the local void fraction.
In the FZ-Rossendorf calculations were performed using the CFD-code CFX-4. The simulation comprises two phase flow, subcooled boiling at the heated wall and steam release at the tank surface. The paper presents comparisons of measured and calculated temperatures and void fractions. The comparison allows, to test the used models, to clarify weak points of the models and to identify directions of further development of modelling boiling and two phase flow.

Schwerpunkte:

• Technische und wirtschaftliche Entwicklungen im letzten Jahrzehnt
• Derzeitige Beiträge der einzelnen erneuerbaren Energien
• Wirtschaftlichkeit unter den aktuellen Rahmenbedingungen
• Mittelfristige Perspektiven der Nutzung erneuerbarer Energien in der Stromerzeugung

Three-dimensional hexagonal reactor dynamic codes have been developed for VVER type reactors and coupled with different thermal
hydraulic system codes. In the EU Phare project SRR1/95 these codes have been validated against collected real plant transients by the participants from 7 countries. The two experiments chosen for calculation were such that both primary circuit behaviour and fission power behaviour were strongly affected including movements of control rods. Critical boron concentrations, 3-D core power distributions, time behaviour of fission power, coolant temperatures and pressures were the main parameters utilised in the validation. Good accuracy of the results was generally achieved comparable to the measurement accuracy. Confidence in the results of the different code systems has increased and the consequences of certain model changes could be evaluated.

The integration of advanced computer codes from different safety analysis areas into code systems of expanded modeling capabilities results in a more detailed and accurate representation of reactor plant structural components. Less conservative predictions of advanced codes are needed to analyse the transients of LWRs. As a result of the joint FZR-IPPE research project, the coupled code system DYN3D/RELAP5 has been developed. The incorporation of the DYN3D spatial kinetics model into the RELAP5 code overcomes the restrictions of the stand-alone codes. AER-5 benchmark calculations for the VVER-440 reactor plant have been performed to validate the code. Code-to-code comparison (DYN3D/RELAP5-DYN3D/ATHLET) of simulation results shows a good agreement and confirm a validity of the developed internally coupled code system.

We have generalized the principle of resonant x-ray beam coupling to waveguiedes containing multiple guiding layers and characterised their x-ray optical properties. By measuring the farfield pattern formed by the interference of the beams, we demonstrate the possibility of using these devices as new tools to tailor the field distribution in the near- and far-field region for specific applications.

Different SiC-surfaces were coated with thin layers of Si or Ge and subsequently annealed to 900 °C respective 600 °C. According to AFM results, Si- or Ge-clusters, respectively, are formed whose number, size distribution and shape depend on the process parameters. Such samples were investigated with synchrotron x-ray diffraction on the ROBL-beamline at the ESRF. The /2 - scans show for all samples (111)- and (220)-reflections of Si or Ge, respectively. This reveals unambiguously that the clusters grow preferentially in two different orientations (<111>, <110>). Interestingly, for the Ge-samples those reflections are shifted towards the angular position of the corresponding Si-reflection. Such a peak shift could be explained by a lattice distortion due to the lattice mismatch or by the change in the lattice constant due to the formation of a Si/Ge solid solution. The lateral orientation of the (111)- and (110)-clusters was investigated by comparison of the -scans of a cluster-reflection (220-reflection for (111)-clusters and 111-reflection for (110)-clusters) with an appropriate substrate-reflection. This comparison showed that the (111)-clusters as well as the (110)-clusters grow coherently with respect to the substrate.

The design of a sputter deposition chamber for the in situ study of film growth by synchrotron x-ray diffraction and reflectivity is reported. Four x-ray windows, sealed with low cost, non-hazardous Kapton, enable scattering both in the horizontal as well as in the vertical scattering planes. The chamber fits into a standard six-circle goniometer from Huber which is relatively widespread in synchrotron laboratories. Two miniature magnetrons and additional gas inlets allow for the deposition of compound films or multilayers. Substrate heating up to 650°C and different substrate bias voltage are possible. The performance of the chamber was tested with the deposition of high quality TiN films of different thicknesses.

Die realitätsnahe Beschreibung der Wechselwirkung von Actiniden mit Huminsäuren sowie des Migrationsverhaltens von Actiniden in Gegenwart von Huminsäuren ist unerläßlich für zuverlässige Prognosen zur Ausbreitung von Actiniden in natürlichen Aquifersystemen. Da natürliche Huminsäuren jedoch in Abhängigkeit von ihrer Herkunft unterschiedliche strukturelle und funktionelle Eigenschaften zeigen, ergeben sich Schwierigkeiten bei der Beschreibung ihres chemischen Verhaltens. Zur Erlangung detaillierterer Kenntnisse über die Wechselwirkung von Huminsäuren mit Actiniden wurden verschiedenartige Huminsäuremodellverbindungen mit definierten chemischen Eigenschaften entsprechend dem Melanoidinkonzept entwickelt und hinsichtlich ihrer Eignung als Funktionalitätsmodelle für Huminsäuren untersucht [1]. Darüber hinaus wurden Verfahren zur Synthese von 14C-markierten Huminsäuren mit stabiler Markierung des Molekülgerüsts entwickelt [2], die aufgrund ihrer sehr empfindlichen Nachweisbarkeit in niedrigen Konzentrationsbereichen in Migrationsexperimenten, z. B. zur Untersuchung kinetischer Prozesse [3], einsetzbar sind.
Die vorliegende Arbeit demonstriert am Beispiel der synthetischen Huminsäure vom Typ M42, die mit natürlichen Huminsäuren vergleichbare Carboxylgruppenzahlen hat, die Synthese, die 14C-Markierung und die Modifizierung der Huminsäurefunktionalität als auch deren Einsatz in Komplexierungs- und Sorptionsexperimenten. Die unter Verwendung dieser Huminsäure erzielten Ergebnisse zur Untersuchung der Wechselwirkung von Huminsäuren mit Neptunium(V) werden vorgestellt. Dazu gehören auch Untersuchungen zum Einfluß phenolischer und anderer acider Gruppen auf das Komplexbildungsverhalten von Huminsäuren gegenüber Neptunium(V) im neutralen pH-Bereich. Der Vorteil der Radiotracertechnik durch Einsatz der 14C-markierten Huminsäure vom Typ M42 in Sorptionsexperimenten wird am Beispiel der Neptunium-Sorption an Granit in Gegenwart von Huminsäuren gezeigt.
Erste Ergebnisse zur Synthese von Huminsäuren mit ausgeprägt reduzierenden Eigenschaften werden dargestellt. Diese sollen zur Untersuchung von Redoxvorgängen bei der Wechselwirkung von Huminsäuren mit Actinidionen Einsatz finden.

[1] Pompe, S., Bubner, M., Schmeide, K., Heise, K.H., Bernhard, G., Nitsche, H.: 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] Bubner, M., Pompe, S., Meyer, M., Heise, K.H., Nitsche, H.: Isotopically Labelled Humic Acids for Heavy Metal Complexation. J. Labelled Cpd. Radiopharm. XLI, 1057 (1998).
[3] Schmeide, K., Brendler, V., Pompe, S., Bubner, M., Heise, K.H., Bernhard, G.: Kinetic Studies of the Uranium(VI) and Humic Acid Sorption onto Phyllite, Ferrihydrite and Muscovite. In: Report FZKA 6524 (G. Buckau, ed.), Karlsruhe 2000, S. 149-169.

Alpha substituted carboxylic acids are present as degradation products of wood in nature and in repositories for low-level radioactive waste. Such substances find extensive application in separation processes of various types, i.e., group separations of 4f and 5f elements. Their interaction with radionuclides was investigated in the pH range 3 to 5 mainly by potentiometry and NMR techniques. Whereas information on their structural and spectroscopic properties are rare.

The complex formation in the binary uranium(VI)-glycolate, -alpha-hydoxyisobutyrate, -alpha-aminoisobutyrate systems in 1.0 M NaClO4 medium was investigated by means of UV-vis and TRLFS. From spectroscopic investigations by UV-vis, single component absorption spectra are suggested and extinction coefficients calculated. An increase in absorption and a red shift of the spectra, 5 nm compared to the free UO22+, are indicating the interaction of UO22+ and a-substituted carboxylic acids already at pH 2. 1:1 complexes are dominating the uranyl speciation in the glycolate, alpha-hydoxyisobutyrate, and alpha-aminoisobutyrate system at pH 2 and 3, respectively. The formation constant of the 1:2 complex of uranyl with alpha-aminoisobutyric acid is reported for the first time at pH 4. A variety of techniques, such as XRD, XAS, TRLFS, and IR, were applied to explore the structure of the main species in solution and in solid state.

This work was supported by the European Union under contract number: HPMF-CT-1999-00342.

Es wurde ein Zellcode (TransRay) entwickelt, der mit Hilfe der Ray-Tracing Technik die dreidimensionale Neutronenflußverteilung berechnet. Ziel war es dabei unter anderem, für dreidimensionale Probleme gemittelte makroskopische Wirkungsquerschnitte zu ermitteln. Als Anwendungsbeispiel werden in dieser Arbeit zwei Fälle betrachtet, der teilweise eingetauchte Regelstab und Void um einen Brennstab als Modell für eine Dampfblase im Moderatorgebiet. Hierfür mußte die Ray-Tracing Methode auf Gebiete mit Void erweitert werden. Das häufig verwendete kommerzielle Programm HELIOS berechnet die gemittelten Wirkungsquerschnitte nur zweidimensional. Für eine bestimmte Eintauchtiefe des Regelstabes muß daher zum Beispiel zwischen den berechneten Werten des vollständig eingetauchten und des gezogenen Regelstabes interpoliert werden. In diesem Artikel wird zunächst die Theorie erläutert und anschließend werden Ergebnisse für die beiden oben erwähnten Fälle am Beispiel der Kernkonfiguration eines Leichtwasserreaktors gezeigt und kurz diskutiert.

We report on a prelimery investigation on the maskless implantation of Ge ions into Si for the production of Si _1-x Ge_x microstructures. The technique employs a focused ion beam system using a liquid metal alloy ion source. Closely spaced simple structures down to about 1 µm in width, with well-defined boundaries, have been produced. On some of these structures, spreading resistance measruements were carried out.

This work involves an extensive study of the dependence on temperature (T) of the energy spread Delta E _1/2 and the potential energy deficit of the energy distribution of the Ge ⁺⁺ beam produced by a liquid metal alloy ion source. The liquid metal alloy is Au₇₇Ge₁₄Si₉. Differnces between consecutive sets of measurements were found but the energy spread versus temperature measurements agree remarkably well with a recent model that predicts Delta E _1/2 ~ T ^1/2 . However, some questions involving the results either remain unsolved or are tentatively answered.

Tianium and his alloys are widely used in medical applications, e.g. for artifical joints, dental prosthesis, teeth and so on. However, it these metals have to be coated with ceramic facing, some stability problems in the ceramic-titanium system arise due to the strong affinity of titanium to oxygen, which causes a reduction of the ceramic oxide. It is known that this reduction effect can be mitigated by alloying titanium or its alloys with a small amount of silicon using, e.g. an ion implantation technique. In the present work, we report the results of a new approach to alloying silicon to Ti6Al4V using high intensity pulsed plasma beams. The feasibility to from the silicide Ti5Si3 with grain size larger as 75 nm is demonstrated. This silicide has the highest melting point (2130 °C) among of all stable phases in the Si-Ti system.

Pd-Ti alloy surface layers in Ti formed by N- and Ar-plasma alloying of Pd films deposited by pulse erosion of Pd electrode tips were studied by RBS, XRD, SIMS, and gravimetric analysis. Layers of a thickness up to 2 µm and concentration up to 40% Pd at the surface were obtained. Pd is present as a solute in hcp alpha-Ti and as TiPd and TiPd3 phases. The Pd profiles follow gaussian distribution although no simple theoretical model can account for this behaviour.

A uniformly distributed multipolar microwave plasma reactor using electron cyclotron resonance at 2.45 GHz (600 W) was used to deposit a-C:H thin films at RT. C₂H₂ was used as precursor gas. Single crystal <100> Si and CR39 allelic resin substrates were RF biased to a negative voltage within the range between -10 and -200 V. The influence of the process parameters (gas flow and substrate bias) on the growth rate and hydrogen content have been investigated in detail. Optical parameters (optical gap E_T, index of refraction n and extinction coefficient k) were measured using spectroscopic ellipsometry. The resonant (6.385 MeV) nuclear reaction: ¹H(¹⁵N, alpha gamma)¹²C was used to determine the hydrogen content. For the C₂H₂ pressure range of 0.6 < P( C₂H₂) < 1.1 mTorr the optical parameters remain constant within the limits of experimental uncertainty. The sp³ content is seen to vary monotonically as a function of pressure and to be reaching a maximum of about 40% for 0.6 < P( C₂H₂) < 0.7 mTorr. The variation of the substrate bias within the range from -10 V to -190 V (at P( C₂H₂) = 0.6 mTorr) has no measurable impact neither on the deposition rate nor on the hydrogen content. The corresponding average values of E_T and n remain stable (E_T = 1.83 ± 0.11 eV, n = 2.12 ± 0.04). However, an increase in the bias is followed by a significant decrease of the extinction coefficient k and of the absorption tail width E₀ . The observed evolution of k and E₀ suggests that the sp² clustering mode may be related to the substrate bias.

Dünne Schichten des Protonenleiters BaZr_0.85 Y_0.15O_2.925/H₂O (BZY15) wurden durch mehrfache Tauchbeschichtung mit einer mittleren Dicke von 900 nm hergestellt. Weiterhin wurden mikrokristalline und Nano-Pulver, mit Teilchengrößen zwischen 8 nm und 20 nm, präpariert.
Film- und mikrokristalline Proben wurden mit Wasserstoff, durch dissoziative Wasserdampfabsorption unter definierten Bedingungen, beladen. Die absoluten Wasserstoffkonzentrationen wurden mit der kernphysikalischen ¹⁵N Ionenstrahltechnik bestimmt. Mit einem Zweizustandsmodell, basierend auf Fermi-Dirak-Statistik, wurden die thermodynamischen Daten der Wasserdampfabsorption bestimmt [1].
Durch impedanzspektroskopische Messungen an gepressten und gesinterten mikrokristallinen Pulvern konnte die Bulkleitfähigkeit ermittelt werden. Aus der Kombination der Leitfähigkeit, den absoluten Protonenkonzentrationen und den protonischen Transportzahlen, bestimmt in Konzentrationszellenexperimenten, konnte der Leitfähigkeits-Diffusionskoeffizient des Bulkmaterials berechnet werden.
Weitere impedanzspektroskopische Messungen wurden an größenkontrolliert hergestellten Nano-Pulvern durchgeführt, um den Einfluss der Kristallgröße auf die protonische Leitfähigkeit zu ermitteln [2].

Literatur:

[1] B. Groß, J. Engeldinger, D. Grambole, F. Herrmann und R. Hempelmann,
Phys. Chem. Chem. Phys. 2 (2000) 297-301
[2] Ch. Beck, W. Härtl und R. Hempelmann,
J. Mater. Res. 13 (1998) 3174

The direction of current research activities by international producers of ignition elements for airbag systems is developing cheap elements which are possible to be integrated into an ignition microsystem. These integrated ignition element is the most important actuator in the whole airbag system.
In conformity with the integration of ignitor structure and electronic parts Si became the basic material. Related materials were selected for functional coatings.
The investigations involved preparation, characterization, testing, simulation and reliability of the functional coatings for ignition structures.
Poly-Si was used as reference material to compare our results with the literature. Furthermore hydrides of titanium, zirconium and hafnium were investigated. Optimaly conversions of the metallic coatings (deposited by sputtering) after a heat treatment in a hydrogen atmosphere could be observed by X-Ray Diffraction and the nuclearphysical 15N-method (Figure 1).
After a heat treatment (110°C, on air) the evaluation of stability over the time was performed by analysing the sheet resistance for TiHx- and HfHx - probes. The divergence of the resistance values related to the start value (without heat treatment) amounts 5% for TiHx and 1% for HfHx. Accordingly to /1/ the thermal stability of the metal hydrides increases from Ti to Hf.
To obtain suitable design parameters for the ignition elements, a coupled electrical and thermal simulation was performed by the commercial ANSYS FEM program.
Figure 2 shows an example of the good agreement between the curves of the simulated thermal behavior and the measured current.

/1/ Streb, Wasserstoff in den Metallen Titan, Zircon und Hafnium, Thesis, Frankfurt am Main, 1984
/2/ Weiß U., Löbner B., Abschlußbericht SIFA-MST, "Schneller Anzünder", Januar 1999
/3/ Weiß U., Dünnschichtanzündelement für pyrotechnische Wirkmassen, Patent DE 19721929

The degree of postimplantation damage in various semiconductor crystals depends on the dose rate applied. In particular strong effects have been observed at dose rates up to 10¹⁹ cm^-2s^-1 which are typical for focused ion beam (FIB) devices with sub-µm beam diameters. For a systematic study of such damages a nuclear microprobe must be employed for RBS/channeling measurements. But the fluence of the analysing beam of light ions is here orders of degree higher than usually in RBS/C experiments. Therefore the damage generation by the analysing beam must be considered.
We have studied the near-surface damage accumulation at room temperature in 6H-SiC by H, He and Li ions of various energies both for channeling and random incidence.
The fluence dependence of the regular damage, observed with beams in the MeV region, is much smaller than that with low and medium energies. The damage level observed by RBS/C seems to saturate at a cmin value far below unity. The calculated ratios of Rutherford cross section to deposited nuclear energy [SRIM 2000] for H, He, and Li ions predict lowest damage per backscattering yield for H ions at the lower energy end. But in the case of µm beam dimensions the lattice damage by the proton beam due to swelling, bubble formation, precipitation etc. exceeds by far the regular ballistic disorder and is higher than in the case of He or Li ions of the same energy.

A uniformly Distributed Multipolar Microwave plasma reactor using Electron Cyclotron Resonance at 2.45 GHz was used to deposit ta-C:H (DLC) films on silicon substrates at RT. The influence of the acetylene initial pressure (0.3 - 1.1 mTorr) and of the substrate bias (from -10 V to -190 V) on the DLC growth and structure has been investigated using spectroscopic ellipsometry. It is shown that the maximum sp³ content of about 40% (atomic) may be reached for the acetylene pressure of 0.6 - 0.7 mTorr. It is also shown that although the bias voltage has no measurable impact on the optical gap it has a significant influence on the extinction coefficient and the behaviour of the absorption tails. The results suggest that the sp² clustering mode and the sp² cluster size distribution are bias controlled.

Si+ ions of 50 keV in energy were implanted into a-Fe (95% 57Fe) with a nominal dose of 5x10E17 cmE-2.

The properties of polymer-like amorphous hydrogenated carbon thin films with low defect density have been studied. These films were implanted with carbon ions with a dose range of 10¹² - 10¹⁶ cm^-2. The purpose of the study is to investigate the effects of ion beam damage on this type of film. Optical absorption measurements observe a narrowing of the optical band gap, suggesting the introduction of a large number of defect states subsequent to the implantation resulting in the broadening of the band tails, only after a threshold ion dose of 10¹⁵ cm^-2. Nuclear reaction analysis suggests also a reduction in the hydrogen content of the film which coincides with film thinning.

The fish otolith is a calcium carbonate (usually aragonite) crystal that crows continuously by accretion over the life of the fish and unlike bone is not continuously re-metabolised. Consequently, the otolith has long been regarded as a potential store of information about the life history of an individual fish, and this information is encoded in the deposition pattern of trace elements in the otolith. The code has been difficult to crack. However, recent developments have show that: (1) Sr is one of the few non-mobile trace elements in the otolith; and (2) the pattern of Sr deposition summarises the effects of environment changes that affect the growth rate of the otolith crystal. The remaining difficulties in cracking the chemical code in the otolith have hinged about making reliable micro-measurements of the stable Sr content at spatial resolutions of 10 µm or less; this interval represents about 4-6 days of otolith growth in most species of fish. This paper describes high beam resolution 2 µm linear measurements, and 6 µm square measurements over narrow windows of about 300µm square, and links these micro-measures to macro-measures of 2D maps of the entire surface of sections of otoliths up to 5 mm square at beam resolutions of 25 µm square. The otoliths used in this study are from the Jurel, or Peruvian Jack mackerel, Trachurus murphyi (Carangidae: Teleostei).

The investigation by means of triple crystal X-ray diffractometry and synchrotron reflectivity measurements were performed in two different kinds of laterally structured samples: (i) the simple surface grating created by photolithography methods (the surface grating were of the same material as the substrate) and (ii) stepped surface created by the intentionally off-oriented surface. The X-ray triple crystal arrangement allows us to measure reciprocal space maps of the scattered intensity, separating the intensity contributions of the scattered truncation rods on the first kind of samples. The synchrotron non-specular reflectivity measurements at ESRF were essential for proving the existence of stepped surfaces and examination of their structure.

The samples with different laterally structured surfaces were investigated by means of triple crystal X-ray diffractometry and synchrotron reflectivity measurements. Studies including surface grating created by photolithography methods (the surface grating were of the same material as the substrate) and stepped surface created by the intentionally off-oriented surface were performed. The X-ray triple crystal arrangement allows us to measure reciprocal space maps of the scattered intensity, separating the intensity contributions of the scattered truncation rods on the first kind of samples. The synchrotron non-specular reflectivity measurements at ESRF were essential for proving the existence of stepped surfaces and examination of their structure.

SiC formation by implantation of C ions into silicon is not a single-step process [1]. The implantation results in an elastic distortion of the Si host lattice and in a formation of crystalline SiC particles or their prestages depending on ion fluence and thermal conditions.
One part of the samples was prepared by implantation of C ions with an energy of 195 keV into Si (001) wafers at fluences varying from 5E15 ions/cm2 to 4E17 ions/cm² and temperatures between room temperature and 800°C. The other part was produced by implantation of 3.25E17 /cm² of C (45 keV) ions at 500 °C and a subsequent annealing at 1200°C for 2 h. The whole fluence was applied as well in one step as in three steps, respectively. The maximum of the carbon content lies in a depth of 130 nm for ions with an energy of 45 keV and at 570 nm for ions with an energy of 195 keV, respectively.
The growth of the SiC particles and the strain in the Si matrix and its relaxation were studied with different x-ray scattering techniques: high-resolution diffraction, wide-angle diffraction for the phase identification [2], grazing incidence diffraction for particle size determination, reciprocal space mapping (RSM) and texture studies for revealing the orientation alignment of the particles to the matrix. Mostly the use of Synchrotron radiation was necessary in order to have a clearly detectable signal in spite of the very small volume part of SiC. Furthermore, high resolution diffraction for strain studies requires radiation with a low divergence. The material research goniometer of the Rossendorf Beamline (ROBL) at the ESRF Grenoble [3] enables such studies which allow to follow the early stage of phase formation.
From the measurements it can be stated:
1. At the lowest ion fluence a significant Si lattice expansion on the order of 1E-3 is observed. However, no crystalline SiC precipitates were found.
2. Intermediate ion fluences and temperatures generate very small SiC particles (pre-stages) with enhanced lattice spacings in relation to the value of 3C-SiC. Due to the SiC particle formation the strain in the Si lattice is reduced.
3. Finally, for the highest fluences and temperatures crystalline 3C-SiC particles are found. The SiC lattice itself is only negligible strained if the phase formation occurs during a high-temperature implantation process.
4. As it was revealed by RSM and texture studies the SiC crystallites are aligned to the Si host lattice in such a way that the cubic crystallographic axes of matrix and particles coincide within an accuracy of 2.5° to 5°. A narrower distribution of the SiC crystallite orientation is formed by implantation at higher temperatures. Elevated temperature during implantation is supposed to be more effective in forming an aligned crystallite distribution than a subsequent annealing even at higher temperature.
[1] M. Deguchi et al., Jap. J. Appl. Phys. 31, 343 (1992)
[2] F. Eichhorn et al., J. Appl. Phys. 86, 4184 (1999)
[3] W. Matz et al., J. Synchrotron Rad. 6, 1076 (1999)

SiC ion beam synthesis by implantation of C ions into Si is a multiple-step process. In our experiments C ion implantation was performed at TII = RT ... 800 °C to a C concentration in the range of 0.3 to 33.5 at% into Si and SIMOX substrates. SiC phase formation and the related lattice strain were studied by different synchrotron X-ray scattering techniques using ROBL at ESRF Grenoble and by transmission electron microscopy:

1. Low ion fluences result in a Si lattice expansion in the order of 1E-3.
2. Intermediate ion fluences and temperatures generate small SiC pre-cursors with enhanced lattice spacings and reduced strain in the Si lattice.
3. High fluences and temperatures form 3C-SiC crystallites with three types of orientation:

• random-like orientation
• fibre texture with axis parallel to the surface normal with a mean orientation spread of 6°
• high alignment to the Si matrix: SiC<001> || Si<001> and SiC<110> || Si<110> due to a partial coherent growth of SiC in the Si matrix. The orientation spread is in the range from 2° to 5°.

Am Forschungszentrum Rossendorf wird zur Zeit ein Freie-Elektronen-Laser (FEL) gebaut, der Ende 2001 betriebsfertig sein soll. Mittelfristig soll ein Wellenlängenbereich von 5-200 um überstrichen werden können. Ich möchte einen Überblick über dieses Projekt geben, mit Darstellung der angeschlossenen experimentellen Infrastruktur. Desweiteren möchte ich über die möglichen spektroskopischen Anwendungen sprechen, die im Prinzip alle Systeme mit niederenergetischen Anregungen (10-100 meV) betreffen. Der Schwerpunkt dabei wird, gemäß meines Erfahrungshintergrundes, auf dem Gebiet der Halbleiter-Quantenstrukturen liegen.

please contact the author

The atomic positions of the silicon carbide polytypes 6H and 4H differ slightly from an ideal tetrahedron. These small deviations can be investigated by X-ray diffraction of so-called "quasiforbidden" reflectios, which are very sensitive to the extremly small variations in the structure.

formation of buried intermetallic Ti-Al-phases by high doose Al implantation

study of implantation treatment of Ti with Ca and P for improving hydroxylapatite formation

Übersicht über ROBL / ausgewählte Ergebnisse

Ultrafine-grained nickel samples were submitted to thermal treatment and cyclic plastic deformation in order to investigate the stability of the defect structure. Investigations by means of synchrotron radiation diffraction revealed that the mean volume expansion, long-range and short-range internal strains are diminished in consequence of the cyclic plastic deformation.

Ultra-fine grained nickel samples were cyclically deformed at room temperature and at 200°C. The mean grain size of about 200 nm, determined by SEM and from the broadening of synchrotron diffraction profiles remained nearly constant, whereas the spectrunm of internal strains changed in consequence of the cyclic deformation. The relation between the profile shape ans asymmetry and the {hkl} reflection type suggests the existence of long range granular stresses in the original ufg samples.

Carbon implantations into silicon were carried out in order to form thin surface layers of SiC. Single crystalline <100> silicon samples were implanted with 40 keV 13C ions with a fluence of 3.8x1017 ions/cm2 and subsequently thermally treated under high vacuum conditions at different temperatures using a 20 keV electron beam. The isotope 13C offers the advantage to measure the carbon redistribution caused by the thermal treatment process with the nuclear resonance reaction analysis. The crystallinity of the SiC surface layers is studied by X-ray diffraction and transmission electron microscopy measurements. A polycrystalline 3C-SiC surface layer with a low content of 6H-SiC grains is formed with a thickness of about 70 nm. The analysis of high resolution TEM micrographs from the interface region shows obviously that the 6H-SiC phase coexists with the 3C-SiC modification in SiC layer.

The possibilities and limitations of X-ray scattering techniques are discussed for the structure analysis of Ta-N barriers for Cu metallization.

Thin films of proton-conducting BaZr_0.85Y_0.15O_2.925 perovskite-type ceramics, prepared in a sol-gel process by multiple dip-coating on silicon single crystal wafers, and powder samples, prepared by the conventional carbonate route, were charged with hydrogen by dissociative water absorption at definite values of water vapour pressures and temperatures. The absolute content of the absorbed hydrogen was determined ex situ at room temperature using the ¹⁵N nuclear resonance reaction analysis. From the resulting water vapour pressure-hydrogen composition isotherms the absorption enthalpies and entropy were caculated, using our two site model, based on Fermi-Dirac statistics.

We consider the possibility to determine structural parameters from partial pair correlation functions (PCF's) for UO2(H2AsO4)2 x H2O assuming that its crystal structure is unknown. Since UO2(HAsO4) x 4H2O is chemically similar to UO2(H2AsO4)2 x H2O, we wanted to investigate whether the scattering characteristics calculated by FEFF-8 for the uranium hydrogen arsenate with a known crystal structure are transferable for the analysis of the uranium dihydrogen arsenate.
The Tikhonov regularization method was applied to solve the inverse ill-posed problem of finding up to three partial PCF's from one EXAFS spectrum of UO2(H2AsO4)2 x H2O. From the U L3-edge EXAFS spectrum, we determined the U-U, U-As, and U-O PCF's. The As-As, As-U, and As-O PCF's were received from the As K-edge EXAFS spectrum. The interatomic distances obtained for the first and in several cases also for the second coordination shell of all pairs are in agreement with recently published crystallographic values. This demonstrates that the Tikhonov regularization method is a powerful tool for the structural analysis of samples for which only chemical information (oxidation state, elemental composition, type of ligands) is known.

* Corresponding author: zayarnaya@imp.uran.ru

The regularization method is applied to determine three partial pair correlation functions (PCF) from one EXAFS spectrum. The mathematical procedure is discussed and applied to the EXAFS analysis of UO-2(HAsO4) x 4H2O.
The measurements were performed at the Rossendorf Beamline (ROBL) at the ESRF in Grenoble. The As K-edge and the U L3-edge absorption spectra were recorded in transmission mode at temperatures of 41 K and 15 K, respectively. From the U L3-edge EXAFS spectrum, we obtain the PCF's of the pairs U-U, U-As, and U-O and determine the structural parameters for the first and the second coordination shells of each pair. The PCF's of the pairs As-U, As-As, and As-O are obtained from the As K-edge EXAFS spectrum.

In the title compound, [Eu(NO3)3(H2O)4]·2H2O, the Eu atom is ten co-ordinated by three bidentate nitrates and four water molecules. Furthermore, two water molecules are included in the crystal structure forming a complicated network of hydrogen bonds. [Eu(NO3)3(H2O)4]·2H2O is isostructural with other lanthanide analogues.

Acta Cryst. (2001) E (submitted)

A new method for the prediction of the development of the bubble size distribution along the flow path is presented. It combines models for bubble coalescence and break-up with the calculation of radial gas fraction profiles. This model bases on the assumption of the equilibrium of the forces acting on a bubble perpendicularly to the flow direction. A large number of bubble classes is considered and the radial profile of the liquid velocity is taken into account.

The results of the model are compared with experimental data for a number of gas and liquid volume flow rates. The experiments were performed at a vertical test loop in Forschungszentrum Rossendorf (inner diameter 51.2 mm) using a wire mesh sensor. The sensor enables the determination of void distributions in the cross section of the loop. A special evaluation procedure supplies as well bubble size distributions as local distributions of bubbles within a predefined interval of bubble sizes.

In the aqueous environment of abandoned ore mines, iron sulphide ore crystals play a key role in the sulphide oxidation and water mineralization process occurring there. Highly miner-alised, red-coloured solutions are formed by weathering of ore particles which causes acid rock drainage (ARD). Major cationic components (>1 g/l) of the ARD solution under study were Zn, Fe, Mg, Al, and Mn. Important minor components were toxic heavy metals, e.g. As, Cu, Pb, and Cd. This XAS investigation deals with the in-situ characterisation of the near-order surrounding of As in ARD solutions containing colloidal particles as well as with the determination of the particle mineralogy. The atomic surrounding of Fe and As in ARD samples is compared to those found in model compounds. The presented study is an example for the broad applicability of X-ray absorption spectroscopy (XAS) techniques to environmental research.