Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

This paper describes the application of three-layer perceptron networks to the identification and diagnosis of dangerous states in strongly exothermic semibatch reactions. To assess the potential danger of different faults, separate perceptron networks were used for danger assessment and for fault isolation. Results are presented to illustrate the performance of the neural-network approach on real process data obtained from typical faults of a catalytic esterification process which were simulated in a laboratory reactor.

Abstract
For today 's applications of superconducting accelerators like Linear Colliders and Free Electron Lasers (FEL) there is an increasing demand for high brightness beams. So get a high luminosity or high average laser beam power, the accelerator has to operate in cw mode or with a high duty factor. Therefore, new injectors are needed, delivering a low emittance beam with high average currents compatible to the acccelerator's macropulse structure. During the last 14 years the development of rf guns gained more and more importance for normal conducting accelerators. In this field they became the most advanced injector for high brightness beams. Nevertheless, because of the high rf losses they are, like normal conducting accelerators, limited to operation with low duty factors. At Forschungszentrum Rossendorf two concepts were developed to transfer the merits of the rf gun design to injectors with high duty factors. The first project is a thermionic 1.3 GHz rf gun with two decoupled cavities. A combination of rf and dc acceleration allows to operate the copper cavities at low gradients in cw mode. The design parameters of the injector are a low bunch charge of 1 pC with an emittance less than 1 π mm mrad. Because of the high repetiton rate of 1.3 GHz an average current of 400 µA can be reached. A test stand for the injector with a beamline for emittance, energy and bunch length measurement was built up. At average beam currents up to 80µA a normalized transverse emittance of 0.23 π mm mrad was measured. The measured energy width of 8 keV and the bunch length of 8 ps (FWHM) is in a very good agreement with the simulation results. The second project was realized in collaboration with the Budker Institute in Novosibirsk. The goal is the development of a photocathode rf gun with a superconducting cavity operating at high gradients in cw mode. A new design was worked out to solve the related rf and thermal problems. The beam dynamics of a superconducting 3½-cell rf gun were studied in detail by simulation. The resulting ernittance of 5.3 π mm mrad at a bunch charge of 200 pC opens a wide range of applications for high average power FELs. The fabrication of a half cell test cavity was finished in October 1997. First tests are scheduled for the middle of 1998 to prove the feasibility of our design.

Deep traps in the boron extended tail region of ion implanted 6HSiC pn junctions formed during annealing have been studied
using deep level transient spectroscopy. Dramatically high concentrations of ~ 1016 cm3 of the D center have been observed
through the unusual appearance of minority peaks in the majority carrier spectra. No evidence is found for any shallow boron
acceptor in this region, but an induced hole trap Ih at EV + 0.46 eV is found under cold implantation conditions. These results
support the picture of the extended tail, rich in boron-vacancy complexes such as the D center, which forms as a result of vacancy
enhanced indiffusion. The dominance of the electrically active D center in the depletion layer of the technologically important SiC
pn junction diode suggests the need for further research in this area. © 1998 American Institute of Physics.

Deep-level defect centers on the n-side of p + n junction diodes formed by low and elevated temperature aluminum-ion implantation into n-type 6H–SiC have been studied using deep-level transient spectroscopy. Two shallow Al-acceptor levels have been observed in the n region just beyond the implantation depth through their minority-carrier emission signatures. The dominant level is situated at 0.26 eV above the valence band and is accompanied by a shallower level of small intensity. Comparison with photoluminescence results suggests the dominant level (labeled Ak) and the shallower level (labeled Ah), are associated with the cubic and hexagonal lattice sites, respectively. Unlike previously reported results, which show many different implantation-induced donors within the implantation region, only one deep donor level at EC–0.44 eV is found to occur in the postimplantation region, indicating that the various crystal damage sites occur with different spatial distributions.

MeV ion beam analysis (IBA) is presented as a powerful tool for in situ, real-time process diagnostics. With minor additional experimental equipment such as diferential pumping or the installation of special detectors, dynamic stoichiometric profiles can be measured during ion beam or plasma exposure. Spectrum acquisition times of the order of a few minutes or less enable the study of fast and transient diffusion effects and transient surface coverages. Examples are given addressing the diffusion and trapping of hydrogen in nickel around room temperature, the ion beam synthesis of carbon±nitrogen films, the ion beam nitriding of stainless steel, and the diagnostics of the layered structure of cubic boron nitride films. The latter example combines stoichiometric in situ analysis using dynamic ERD and structural in situ analysis using optical ellipsometry.

In the frame of a European program (EU BWR R&D Cluster), six
test series with an emergency condenser test bundle were
performed in 1996. Within the Physics and Thermalhydraulics
Complementary Action to the BWR Cluster (BWR/CA) the German
Forschungszentrum Rossendorf (FZR) e.V. and the French Com
missariat a l'Energie Atomique (CEA/DRN) have calculated 9
tests and an additional blind test of NOKO bundle experiments
in 1997. These post test calculations were carried out using
the ATHLET computer code (FZR) and the CATHARE2 computer code
(CEA DRN).
The comparison of the experimental and computational results
(e.g. for mass flows, temperatures, capacities, pressure
drops) show an excellent agreement. Despite the good
prediction of global parameters, a variation of local
parameters (e.g. film velocity, void fraction, heat flux) can
be observed. This can be explained by the significant effect
of the tube wall conduction in controlling the heat transfer.

A novel method is applied to investigate the as-implanted defect structure formed during keV implantation into Si. It uses a combination of time-ordered computer simulations based on the binary collision approximation (BCA) and classical molecular dynamics (MD) simulations.The as-implanted damage created in 30 keV P+, 15 keV As+, and 15 keV B+ implants is analyzed and depth profiles of different defect species are given.

Analysis and calculation of an abnormal event which occurred in 1989 at the NPP Greifswald (VVER-440/213) are reported about. This event was a scram failure at about 50% nominal power with two of six working main coolant pumps (MCP). The analysis revealed remarkable differences between the active and passive loops due to non-homogeneous coolant mixing in the downcomer and lower plenum in the initial state before the accident. An existing input data deck for the coupled code DYN3D/ATHLET was modified to carry out calculations of this accident. On account of the absence of a mixing model considering loops with forward and loops with backward flow at the same time, the six reactor loops were modeled by a 3-fold (passive), a 2-fold (active) and a single (with the MCP to be switched-off at the beginning of the transient) loop. The comparison of the stationary calculation with the reported data shows a good agreement taking into account the mentioned deviations between the loops. Most of the calculated thermohydraulic parameters during the accident are very close to the measured data. Deviations in the loop temperatures can be explained by the differences in the measured stationary data and by the fact of non-homogeneous coolant mixing in the downcomer and the lower plenum. A small, but continuous power increase was observed during the whole time in the calculation while the measured power was remaining nearly constant. The power behaviour was brought into agreement with the measured data by a correction of the moderator temperature coefficient within the accuracy recommendations of the Atomic Energy Research (AER).
The calculation of this accident is an important contribution to the validation of the coupled code DYN3D/ATHLET. It demonstrated problems of the analysis of real abnormal events on NPP`s.

Treatment of [ReO(SN(R)S)(SMe)] (HSN(R)SH=HS-CH₂ CH₂-N(R)- CH₂ CH₂-SH, R=n-propyl 4a, benzyl 4b) with an excess of CH₃I at room temperature gave the-SCH₃ displaced products [ReO(SN(R)S)I] 5a,b in about 80% yield. [(3-(Benzyl)azapentane-1,5-dithiolato)iodo]oxorheniumV 5b was characterized by single-crystal structure analysis revealing a distorted trigonal bipyramidal geometry with the oxygen and the sulfur atoms forming the equatorial plane. Compounds 5 allow clean transformation to new SNS/thiolato mixed ligand complexes as shown herein by a sample reaction with 1-beta-D-thiogalactose to give 6a.

Several approaches have been undertaken in a number of European countries to study and demonstrate the feasibility of innovative passive safety systems. The European BWR R&D Cluster combines experimental and analytical efforts that are mainly directed to the introduction of passive safety systems into boiling water reactor technology. The main objectives are to use the large scale European test facilities NOKO (Jülich, Germany), PANDA, LINX (Villingen, Switzerland), PANTHERS (Piacenza, Italy) as well as the demonstration power plant Dodewaard (Netherlands) for a synergistic experimental R&D program. The project should additionally contribute to validating and improving thermalhydraulic computer codes. In 1997 a BWR Physics and Thermohydraulic Complementary Action (BWRCA) was established to further assist and broaden the objectives of the EU BWR R&D Cluster. The work presented in this report is performed in the Workpackage Theoretical support to the NOKO experiments and divided into three tasks: Implementation of two phase flow instrumentation, ATHLET calculations of NOKO experiments and approach for the optimization of passive components. FZR is developing two phase flow measurement instrumentation (e.g. conductivity probes), which is installed in parallel to the emergency condenser test bundle. The experimental data are used for the validation of the improved ATHLET condensation model. The evaluation of these experiments shows an undesired accumulation of noncondensable gases in front of the water level and give valuable insights to the phenomena caused by noncondensables. An improved twophase flow instrumentation is suggested based on the collected experience and taking into account the detected problems.

Within the BWRCA FZR had performed 10 post test calculations and an additional blind test calculation of NOKO experiments. The results of these calculations are presented and discussed in detail. These calculations show that ATHLET is able to perform proper calculations. At least goals for an optimization of the emergency condenser are discussed. This is desirable because it allows the decrease of the pressurized BWR surface and the possibility of leakages.

Das Vorhaben erbrachte einen Beitrag zur operatorunabhängigen Beurteilung des Prozeß- und Anlagenzustandes chemischer Reaktoren, insbesondere zur Identifizierung gefährlicher Betriebszustände bei der diskontinuierlichen Fahrweise exothermer Reaktionen.
Die Eignung von Mustererkennungsmethoden zur Prozeßdiagnose wurde am Beispiel eines chemischen Laborreaktors für einen stark exothermen Referenzprozeß - säurekatalysierte Veresterung von Essigsäureanhydrid mit Methanol - untersucht. Vor ihrer Anwendung als Zustandsklassifikator mußten die Mustererkennungssysteme zunächst mit den Prozeßdaten des normalen und gestörter Reaktionsverläufe unter Zuhilfenahme von Expertenwissen trainiert werden, um das komplexe nichtlineare Prozeßverhalten bis hin zum Entscheidungsresultat abzubilden. Danach konnte der trainierte Klassifikator zur Prozeßdiagnose genutzt werden.
Die besten Ergebnisse bei der Erkennung von Betriebszuständen in Semibatch-Prozessen wurden mit dreischichtigen Perceptron-Netzen erreicht. Sie konnten auch Mehrfachfehler und nichttrainierte Reaktionsverläufe klassifizieren. Um das Gefährdungspotential von fehlerhaften Betriebszuständen beurteilen zu können, wurden separate Perceptron-Netze für die Gefahren- und Fehlerklassifikation eingesetzt. Ihre Leistungsfähigkeit wurde sowohl für den Semibatch-Betrieb als auch für die kontinuierliche Fahrweise experimentell nachgewiesen.

In diesem Projekt wurden für die WWER-1000-Reaktoren Balakovo-3 und Rovno-3 die Parameter der Neutronenbelastung experimentell und theoretisch bestimmt.
Der vorliegende Bericht beschreibt das methodische Vorgehen, welches aus dem reinen Berechnungsteil, der gammaspektrometrischen Analyse der Aktivierungsdetektoren und dem Vergleich der gemessenen und berechneten Werte einschließliche der Spektrumsjustierung besteht. Dieses Instrumentarium, welches allgemein bei der Bestimmung der Neutronenfluenz anwendbar ist, wurde im Projektzeitraum weiter verbessert.

Time- and depth-resolved compositional analysis has been performed during the nitriding of stainless steel in order to improve the understanding of the nitriding kinetics. It is directly observed that the surface oxide layer acts as a transport barrier. The experimental data are discussed on the basis of a simple transport model that considers the removal of the surface oxide layer due to sputtering, its regeneration from the residual gas and the ballistic implantation depth of nitrogen.

A new high resolution (D M/M < 1 %) and high acceptance (45 %) di-electron spectrometer (HADES) has been designed to investigate in-medium properties of hadrons. For tracking of all charged particles (in particular with sufficient resolution for electrons) a system of 24 low-mass drift chambers (Helium based counting gas and Aluminum field and cathode wires), arranged in four tracking planes, is used.
Design aspects of the chambers are reported. Results of performance optimization using various prototype detectors are discussed, including results of an ageing test. Stable operation in the high-multiplicity environment of heavy ion collisions, and a spatial resolution of 70 mm (s) over 80 % of a cell have been demonstrated in two beam experiments.

Neutron irradiation of the VVER-440-type reactor pressure vessel steel 15Kh2MFA at lower temperature effects an increase of the content of point defects in the iron lattice. The ratio between the magnetic and nuclear scattering of these point defects shows that not only vacancies but also substitution atoms are formed. Additionally small precipitates grow. These precipitates are smaller and have a weaker thermal stability than the precipitates grown in this steel after neutron irradiation at service temperature. In some cases the number of precipitates which can be found in the unirradiated state decreases significantly by irradiation at 60 °C. Annealing at 475 °C/1 h provokes coarsening of the precipitates and re-dissolution of the precipitates formed by irradiation at lower temperature.

The safety concept of the innovative boiling water reactor SWR 1000 is characterised by passive safety systems (e.g. emergency condensers, building condensers, passive initiators). The operation mode and the effectiveness of these safety systems is investigated in the multipurpose thermalhydraulic test facility NOKO at the Forschungszentrum Jülich (FZJ).
The effectiveness of the emergency condenser was determined in more than 200 experiments. Post-test calculations of the emergency condenser experiments were performed with an improved version of the ATHLET code. The comparison of the calculations and the experiments shows a good agreement.
Parallel, the performance of three different designs of the passive initiator was investigated experimentally. The experimental results are used to optimise the design of an additional passive initiator which will be tested in NOKO this year.
Additionally, more than 80 experiments were carried out in NOKO to determine the effectiveness of two different designs of the building condenser. Post-test calculations were performed using the modified computer code RALOC. The comparison of the calculations and the experiments shows a good agreement.

Cobalt disilicide microstructures were formed by 70 keV Co2+ focused ion beam implantation into Si(111) at substrate temperatures of about 400°C and a subsequent two step annealing (600°C, 60 min and 1000°C, 30 min in N2). It was found that the CoSi2 layer quality strongly depends on the pixel dwell-time and the implantation temperature. Only for properly chosen parameters countinuous CoSi2 layers could be obtained. Scanning electron microscopy and Rutherford backscatting/channelling investigations were carried out combined with a special preparation technique damage was investigated as a function of dwell-time (1-250 µs) and target temperature (355-415°C). The results show that the irradiation damage increases with the dwell-time.The Si top layer was ammorphization for longer dwell-times although the substrate temperature was always above the critical temperature for amorphization of about 270°C according to the model of Morehead and Crowder. For the high current density of a focused ion beam (1-10 A/cm2) the damage creation reate is higher than the rate of dynamic annealing.

In der vorliegenden Arbeit wurde die räumliche Verteilung der Einstrahlung für Sachsen anhand von vorwiegend an Solaranlagen gemessenen Einstrahlungswerten untersucht und diskutiert.
Dazu wurde zunächst eine umfangreiche Datenanalyse durchgeführt. Verschiedene Ergebnisse deuten darauf hin, daß an der DWD-Station Chemnitz vermutlich eine Überbewertung der gemessenen Globalstrahlung vorliegt.
Des weiteren wurde gezeigt, daß die an Solaranlagen auf Dächern von Ein- und Zwei-Familienhäusern in den urbanen Gebieten gemessenen Einstrahlungswerte infolge der unvermeidlichen Horizontabschirmung deutlich geringer sind als die auf der Grundlage der DWD-Daten mittels verschiedener Modelle berechnete Einstrahlung auf beliebig orientierte Flächen.
Die räumliche Verteilung der Einstrahlung in urbanen Gebieten Sachsens wurde anhand der im Rahmen des 1000-Dächer-Photovoltaik-Programms an über 20 Standorten in Sachsen gemessenen Einstrahlungswerten bestimmt. Dabei wurde deutlich, daß innerhalb Sachsens an solchen Standorten mit einer mittleren Globalstrahlung (auf die Horizontale) von ca. 900 kWh/m² gerechnet werden kann. Somit können für Neigungen zwischen 25° und 50° sowie Ausrichtungen bis zu 35° mittlere Einstrahlungswerte bis zu 1040 kWh/m² erreicht werden. Nur in günstigen örtlichen Lagen kann auch eine bis zu 15% höhere Einstrahlung erreicht werden.

Im Vortrag werden ausgewählte Ergebnisse zum 1000-Dächer-Langzeitmeßprogramm dargestellt. Dies schließt Ergebnisse zur solaren Meteorologie, der Anlagentechnik und der erreichten Erträge und dem Verbraucherverhalten (Privathaushalte) ein.

Zwischen 1993 und 1997 wurden 50 kleine netzgekoppelte Photovoltaikanlagen in Sachsen im Rahmen des 1000-Dächer-Photovoltaik-Programms systematisch untersucht. Neben der kontinuierlichen Auswertung der monatlichen Einstrahlung und der Energieerzeugung wurden alle Anlagen mittels eines PV-Anlagen-Analysators vermessen. An 5 Anlagen wurde ein erweitertes Messprogramm durchgeführt.
Die mittlere jährliche Einstrahlung auf geneigte Dachflächen in urbanen Gebieten Sachsens wurde zu 1050 kWh/m² bestimmt. Davon fallen 75 % während der Tageslastspitzen im Sommerhalbjahr an. Die ermittelten Kennlinien der eingesetzten Hauptkomponenten (Module, Wechselrichter) wichen teilweise erheblich von den Datenblattangaben ab. Gut ausgelegte und installierte Anlagen können bei einem Performance Ratio von 80 % einen jährlichen Ertrag von 840 kWh/kWp bringen. Künftig sollten Anlagen im kleinen Leistungsbereich (bis 5 kWp) als Einstranganlagen errichtet werden. Der Energieverbrauch der einbezogenen Haushalte war überraschend hoch. Bei solaren Deckungsgraden von etwa 100 % konnten nur 25 % des erzeugten Stromes direkt in den Haushalten verbraucht werden. Bei Deckungsgraden von kleiner 20 % erreichte der Direktnutzungsgrad etwa 70 %.

Kinetic formula describing oxidation of several innovative Cbased HTR and fusion reactor materials in oxygen, steam and CO2 are reported for use in computer codes for safety analyses (air/steam ingress accidents). Most data deal with oxidation regime II (in-pore diffusion control) but some information on regime I and III are added, too. The data situation on oxidation of pure graphites and CFCs in O2 and H2O seems to be sufficient but for mixed materials, particularly Si/C composites to be used in fusion reactors, additional experiments are necessary.

Loss of 5-HT transporter (SERT) sites has been implicated in various neurodegenerative diseases and users of some amphetamine derivatives such as MDMA. Therefore, the development of suitable radioligands for neuroimaging of the SERT in the human brain is important. A large number of drugs have been labeled with ¹¹C, ¹⁸F or ¹²³I over the last ten years in order to achieve such radioligands. Despite these attempts most of the compounds were found unsuitable because of low target-to-nontarget ratios. Some cocaine-derived radioligands allow SERT imaging of the human brain using positron emission tomography (PET) although they have a limited selectivity. Among the various specific 5-HT uptake inhibitors only ¹²³I]iodonitroquipazine for single photon emission computed tomography (SPECT) and [¹¹CMcN5652 for PET appear to meet the criteria of a useful radioligand. There is still a need for the development of new radioligands for SERT imaging. Advances in tracer synthetic methodologies may bring further progress in this field.

Fuer die Qualitaetssicherung der Praezisionsbestrahlung mit schweren Ionen wurde der Positronen-Emissions-Tomograph BASTEI in die Therapieanlage der GSI Darmstadt integriert.Die Messung der durch Fragmentierung waehrend einer Bestrahlung erzeugten b+-Aktivitaet erlaubt eine Kontrolle der raeumlichen Dosisverteilung nach jeder Therapiefraktion. Als besondere Probleme dieser PET-Anwendung sind die Erfassung von
Annihilationsereignissen in einem eingeschreankten Winkelbereich und eine durch die Dosis limitierte Aktivitaet zu benennen, woraus eine geringe Zaehlstatistik folgt. Unter Beruecksichtigung dieser Messbedingungen wurde der MLE-Rekonstruktionsalgorithmus implementiert. Die Leistungsfaehigkeit des Verfahrens wird anhand von Phantomexperimenten und ersten Patientendaten dargestellt.
SCHLUESSELWOERTER:Positronen-Emissions-Tomographie, Bildrekonstruktion, MLE-Algorithmus, dreidimensional

The influence of the dwell-time in focused ion beam synthesis has been investigated. Cobalt disilicide layers have been produced by 70 keV Co²⁺ implantation into silicon and have been investigated by Rutherford backscattering spectroscopy and scanning electron microscopy. At an implantation temperature of about 400 °C, it is only possible to form continuous CoSi₂ layers using sufficiently short pixel dwell-times. This result is explained by an enhanced damage accumulation for longer dwell-times.

Seit Dezember 1997 werden an der experimentellen Therapieeinrichtung der Gesellschaft für Schwerionenforschung Darmstadt Tumorpatienten mit hochenergetischen Kohlenstoffionen behandelt. Diese Strahlen werden beim Eindringen in Gewebe kaum abgelenkt und geben ihre Energie am Ende ihrer Reichweite konzentriert und mit erhöhter biologischer Wirksamkeit ab. Mit einer speziell für diese Anwendung gebauten Positronenkamera werden während der Bestrahlung die Beta+-Zerfälle von Kernen gemessen, die als Nebenprodukt bei Fragmentierungsreaktionen der Ionen des stabilen Therapiestrahles mit den Atomen des Körpergewebes entstehen. Durch Vergleich der gemessenen mit der durch Simulationsrechnungen aus den Daten der Bestrahlungsplanung zu erwartenden Positronenemitterverteilung wird die Genauigkeit der Dosisapplikation jeder einzelnen Therapiefraktion beurteilt.

A method for controlling the quality of heavy ion tumour therapy by means of positron emission tomography is introduced. It registers the dynamic spatial distribution of beta⁺-emitters produced by nuclear fragmentation during the fractionated irradiations. It is non-invasive, needs no radioactive isotopes, is performed in-situ at the treatment place and provides a feedback for the therapist. Results of phantom experiments with ¹²C ion beams will be presented.

Cobalt disilicid layers were formed by cobalt focused ion beam implantation into silicon. It was found that the CoSi2 layer formation strongly depends on the pixel dwell time. In order to obtain continuous layers, short dwell times of a few µs are needed. Rutherford backscattering and channeling mesuarements were carried out to understand this effect. The results suggest that the accumulated irradiation damage is larger for longer dwell times. The sputtering yield of cobalt ions was measured and the formation of CoSi2 in noncrystalline silicon investigated.

The structure of the magnetic dipole bands is studied by means of shell-modell
calculations. The calculations correlate with the data, showing a transition
from irregular sequences in the light isotopes to regular bands in the
heavy ones. The analysis of the wave functions reveals a more complex mechanism
of angular momentum generation than in the Pb isotopes: the shears mechanism
of the intruder orbitals and the normal parity neutrons make comparable
contributions.

Six rotational bands up to energies E_x=24.7 MeV and spins J^pi=(79/2^-)
have been identified in ¹⁰⁹Sn using the GAMMASPHERE gamma-detector
array. Four of the bands show smoothly decreasing dynamic moments of inertia
at rotational frequencies hv > 0.6 MeV. The bands arise at medium spins
from coupling of a valence d_5/2, g_7/2 or h_11/2
neutron to the deformed 2p2h proton excitation of the Z=50 core ¹⁰⁸Sn.
At very high hv these bands show the typical behaviour of smoothly terminating
bands, i.e. a gradual alignment of the angular momenta of the valence particles
and holes corresponding to a transition from high collectivity to noncollective
states.

Zur physikochemischen Charakterisierung des Seaborgiums ist die Hochtemperatur-Gaschromatographie im O2-H2O(g)/SiO2(s)-System gut geeignet.
In Thermochromatographieexperimenten mit trägerfreien, langlebigen Nukliden der Sg-Homologen Cr, Mo und W wurde nachgewiesen, daß der Transport von Spurenmengen dieser Elemente im Unterschied zum Transport makroskopischer Mengen einheitlich erfolgt. In trockenem Sauerstoff werden monomere Trioxide gebildet, die über einfache reversible Adsorption durch die Chromatographiesäule transportiert werden. Wegen der geringen Flüchtigkeit dieser Verbindungsklasse kommt eine Charakterisierung des Sg als Trioxid jedoch nicht in Betracht.
In feuchtem Sauerstoff bilden alle drei Sg-Homologen Oxidhydroxide, die reaktionsgaschromatographisch transportiert werden, wobei im adsorbierten Zustand wiederum das Trioxid vorliegt:
MO2(OH)2(g) « MO3(ads) + H2O(g)
Für diese Reaktion wurden thermodynamische Zustandsfunktionen bestimmt, die es erlauben, das Verhalten der Sg-Homologen unter veränderten experimentellen Bedingungen vorauszusagen und Sg-Experimente zu interpretieren.
Modellexperimente im Hinblick auf die physikochemische Charakterisierung des Sg wurden unter Nutzung kurzlebiger, trägerfreier Mo- und W-Isotope mittels isothermer on-line Hochtemperatur-Gaschromatographie durchgeführt. Durch Optimierung der experimentellen Bedingungen und verschiedene methodische Neuentwicklungen gelang es, die Gesamtretentionszeit für W von » 90 s auf » 10 s zu senken. Für 166W mit einer Halbwertszeit von 18,8 s, die etwa der des 266Sg (t1/2 = 21 s) entspricht, wurde eine Maximalausbeute von 53 % erhalten.

Erste Sg-Experimente im O2-H2O(g)/SiO2(s)-System sind für Juni/Juli 1998 geplant. Ergebnisse dieser Experimente sollen vorgestellt und diskutiert werden.

The influence of dwell-time effects on the formation of CoSi2 layers was investigated. The layers were produced on Si(111) and Si(100) by ion beam synthesis using a focused ion beam system. The experiments show that the dwell-time has a strong influence on the formation process of the cobalt disilicide films. In order to obtain high quality films suitable for applications short dwell-time (about 1µs) are necessary.

Channeling profile analysis is simulated using the dynamic binary collision code Crystal-TRIM. A good agreement between theoretical and experimental data is found for silicon targets which were predamaged by Si+ ions of different energies and analyzed by 140 keV B+ ions. For each example the depth profile of the defects relevant for the dechanneling of the analyzing ions is given. An estimation on the annealing of such defects is obtained by comparison of results for as-implanted and annealed samples.

Barium carbonate is a widely accepted stable chemical form for the safe disposal of carbon-14. This requires, however, oxidation of carbon-14-containing organic waste to carbon dioxide. We habe developed a method for the mineralization of organic compounds by anodic oxidation in silver-sulfate-containing sulfuric-chromic acid. This process can also be used for complete oxidation of "difficult" organic wastes, such as hydrophobic substances like hydrocarbons, plastics, activated carbon, etc. The generation of additional chromium-containing hazardous wastes are avoided in this process by electrolytically regenerating chromium(III) to chromium(VI). The degradation of C-14 labeled organic compounds during the process is monitored by on-line measurement the β-radiation of the produced ¹⁴CO₂

The investigation of the effects of humic substances (humic and fulvic acids) on the migration of radionuclides is important to assess their impact on the long-term safety of both radioactive waste repository sites (e.g. Gorleben, Germany) and abandoned uranium mines (Saxony and Thuringia, Germany).
We extracted humic substances from bog water of the 'Hochmoor Kleiner Kranichsee' which is in the vicinity of the uranium mining sites at Johanngeorgenstadt (Saxony). The humic material was separated into humic and fulvic acid fractions and characterized for its elemental composition, functional properties including proton exchange capacity, charge/size distribution ratios and spectroscopic characteristics. The size and size distribution of humic colloids were studied by photon correlation spectroscopy. Furthermore, the complexation of site specific humic substances with uranyl ions was studied. The results were compared with data of a commercial humic acid from Aldrich.

The influence of humic substances on the speciation of actinide ions and their migration behavior in natural aquifer
systems is of great interest within environmental research. Specified knowledge about this is required, for instance, to
develop strategies of risk assessment for long-time safety in the regions of the former uranium mining in Saxony and
Thuringia. Due to the complex and heterogeneous nature of humic substances a thermodynamic founded description of their
complexation behavior with metal ions is difficult. Numerous uncertainties exist in the description of the complexation
process, e.g., the kind and number of complexing functional groups is uncertain. Therefore, it is necessary to
investigate the complexation process with well defined model substances.
We synthesize and characterize humic acid functionality models from reducing sugars and  -amino acids, with functional
properties comparable to those of natural humic acids with respect to type and number of functional groups. Former
measurements have shown that this synthetic humic acids mimic the interaction humic acid - metal ion very well.
This work deals with the possibilities to synthesize modified humic acids, e.g., humic acids with blocked phenolic OH
groups. With this model substances we investigate the influence of phenolic OH groups on the complexation behavior
of humic acids with uranyl ions by time-resolved laser-induced fluorescence spectroscopy. We expect to get a better
understanding of the humic acid - metal ion interaction process and to gather information regarding geochemical
modeling in the presence of humic acids.

Natural humic acids are instable and chemically not well defined chemical systems. It is difficult to accurately describe their physical-chemical properties. Therefor, studies of the interaction between humic acids and heavy metals, including uranium and other actinide elements, are often limited by this fact. For systematic studies of the interaction processes, stable and wellcharacterized humic acid model compounds have been suggested.
We have separated humic-acid-like fractions with good chemical stability from synthetic melanoidins. It is possible to design the functionality of these melanoidins by varying their precursor substances and the conditions of the synthesis.
Furthermore, we have compared different melanoidins and their interaction with UO₂ ²⁺ with the behavior of a commercial natural humic acid (Aldrich) jby infrared spectroscopy (FTIR). The investigation reveals many functional similarities between the melanoidins and the natural humic acid. Comparable symmetric deformation vibrations of uranium in the far infrared range (FIR) indicate similar uranium coordination. In the middle infrared range (MIR), the antisymmetric stretching vibrations of the bound uranium are nearly identical.
In connection with other investigations we have shown, that the melanoidins are excellent humic acid model substances for fundamental radioexological research.

Capillary electrophoresis was applied to investigate pK_a values of ^99mTc radiotracers used in nuclear medicine. Therefore, the protonation equilibria of the carboxyl groups of ^99mTc- mercaptoacetylglycylglycylglycine (^99mTc-MAG₃) and ^99mTc-ethylenecysteine dimer (^99mTc-EC) were studied by pH-dependent determination of electrophoretical velocities. ^99methylenecysteine dimer diethyl ester (^99mTc-ECD) was used as a non-protonable standard. The capillary electrophoresis system was equipped with a radioactivity detector. Measurements were performed using a pressure-driven capillary zone electrophoresis which allowed runs even in the low pH range. For the determination of pK_a values, the electrophoretical velocities of the analytes were referred to the electrophoretical velocities of tetraphenyle arsonium chloride as a positively charged marker. Calculation of pK_a values was accomplished by non-linear curve fitting of both structure-based equilibria equations and sigmoidal decay functions to the experimental data. ^99mTc-MAG₃ was shown to have a carboxyl group pK_a value of 4.22. the value for the carboxyl groups of ^99mTc-EC is 2.90 (determined by structure-based equilibria equations), which represents a common value for both carboxyl groups. By the use of sigmoidal functions, similar values were elucidated. As expected, ^99mTc-ECD shows no protonation step.

The paper presents an electrode-mesh tomograph for the high-speed visualisation of transient gas fraction distributions in two-phase flows in pipes. It is based on the measurement of the local instantaneous conductivity of the two-phase mixture. The time resolution of the device is 1024 frames per second. The sensor consists of two electrode grids with 16 electrodes each. This results in 16 x 16 sensitive points, which are equally distributed over the cross section. The sensor is available in two designs: (1) wire-mesh sensor for lab applications and (2) sensor with enforced electrode rods for high mechanical loads. The device was recently tested in a vertical and a horizontal air-water flow in a pipe of 51.2 mm diameter.

The impressive development of focused ion beam (FIB) systems from the laboratory level to high performance industrial machines during the last twenty years is briefly reported. The design and the functional principle of a liquid metal ion source as well as a FIB column are described. Main application fields of the FIB technology are stoichiometric writing implantation or ion milling which are dominated by the sputtering effect. The FIB is a very suitable tool for sputtering of well defined holes which can easily be analysed by surface profiling. By applying this volume loss method the sputtering yields and milling rates of crystalline, amorphous, and poly-silicon, as well as SiO2, CVD- and high pressure (HP) - diamond and 6H:SiC were investigated for 35 and 70 keV Co, Ga, Ge, Nd and Au ions. For crystalline silicon and 6H:SiC targets, the sputtering yield was determined as a function of the incident angle of the ions and the substrate temperature. In addition, the influence of the pixel dwell time on the erosion process in the case of high dose cobalt implantation was investigated. The experimental obtained yield data are compared with calculated values using different known models.

In the frame of the so-called BWR-CA concerted action of the European Union, one has to analyse some experiments performed on the NOKO facility using the CATHARE2 (CEA) and the ATHLET (FZR) thermalhydraulic codes. These calculations have shown that both CATHARE and ATHLET are able to predict the global performance of the NOKO emergency condenser. In reference calculations, the unrelevance of the Shah correlation used in CATHARE was not seen apart from the BLIND case. Taking into account the sensitivity calculations, it is thought that this problem is due to an overestimation of the liquid film velocity. This latter can be considered as a consequence of a wrong estimation of the film entrainment onset or as a limitation of the two-phase six-equation model (only one average liquid velocity). Further verification and qualification of computer codes require the analysis of tests with a better instrumentation. Measurements of local parameters like the inside tube temperature or the distribution of pressure losses, are really necessary to undertake this work. It is why it has been proposed, in the frame of a new concerted action, to use the NOKO single tube experiments already performed by FZJ and which are much better instrumented in comparison of the just considered bundle tests.

The SWR1000 is a new innovative boiling water reactor concept,
which is developed by Siemens AG. This concept is characterized
in particular by passive safety systems (e.g., four emergency
condensers, four building condensers, eight passive pressure
pulse transmitters, six gravitydriven core flooding lines).
Passive safety systems need no external energy sources. The
function is directly based on the physical phenomena:
gravity, natural convection and/or evaporation. Therefore the
effectiveness is independent of operator actions and smaller
failure rates are assigned to passive safety systems.
For the experimental investigation of the operation mode and
the effectiveness of these passive safety systems the multipurpose
thermohydraulic test facility NOKO (NOKO is an abbreviation for
the German translation of emergency condenser) was constructed
at the Forschungszentrum Jülich (FZJ). The facility has a maximum
power of 4 MW for steam production and a maximum operating pressure
of 10 MPa.

In the frame of an European Union programme (EU BWR R&D Cluster),
six test series with an emergency condenser test bundle were
performed in 1996. Within the Physics and Thermalhydraulics
Complementary Actions (BWR/CA) to the EU BWR R&D Cluster the
German Forschungszentrum Rossendorf (FZR) e.V. and the French
Commisariat a'l Energie Atomique (CEA/DRN) have calculated 9 tests
and an additional blind test of the NOKO bundle experiments. These
posttest calculations were carried out using ATHLET (FZR) and
CATHARE2 (CEA/DRN). The results of these calculations are presented
in this paper.

Detailed comparisons of ATHLET and CATHARE results show that despite
the good prediction of global parameters for both codes, the variations
of local parameters calculated (e.g., film velocity and temperature)
are not in such a good agreement. This can be explained by some
compensating errors in computer codes (e.g., an overestimation of
the condensing film velocity can hide an error in the condensation
correlation) and the significant effect of the tube wall conduction
in controlling the heat transfer. The emergency condenser test bundle
of the available and considered experiments were not instrumented.
Therefore a deeper analysis (including a detailed comparison of local
parameters) is not possible. New test series released in the frame of
a new European union action will be analyzed in 1998.