Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

A unique parameterization of secondary dilepton yields in heavy-ion experiments at CERN-SPS is proposed.
This parameterization resembles a thermal q \bar q annihilation rate and is supported by the ''dual'' description of hot, strongly interacting matter within either a hadronic or partonic base. Adding the thermal yield and the background contributions (hadronic cocktail, Drell-Yan, correlated semileptonic decays of open charm) the spectral shapes of the CERES/NA45, NA38, NA50 and HELIOS/3 data in experiments with lead and sulfur beams can be well described.

The data of direct single-photon measurements of the WA98 collaboration in the reaction Pb(158 AGeV) + Pb are analyzed within a thermal model with a minimum number of parameters adjusted to the dilepton data obtained by the CERES and
NA50 collaborations in the reactions Pb(158 AGeV) + Au, Pb.
The agreement of our model with the WA98 data points to a unique large thermal source emitting electromagnetic radiation observable in both the real and virtual photon channels.

The unique mechanical properties of ta-C films such as high hardness and Young modulus are directly related to the atomic structure of amorphous carbon. Atomic-scale modeling is a valuable tool to study both growth mechanisms of amorphous carbon films and the properties sensitive to details of their structure, primarily to the content of sp ³-bonded atoms. As it has been recently demonstrated, the steady-state growth of ta-C thin films can be modeled using the molecular dynamics method with realistic empirical interatomic potentials. It was shown that the experimentally observed high contents of i>sp ³-bonded atoms ( up to 90%) can be achieved using a potential function of Brenner with a slightly increased interaction radius. This provides a possibility to investigate the mechanical properties of amorphous carbon networks generated by a realistic growth process simulation, rather than by quenching the liquid carbon at high pressures as was done in previous
studies.

In this contribution we present results of the investigation of average and atomic-level elastic moduli of amorphous carbon networks with different sp ³-contents, corresponding to C⁺ ion energies of E = 30-80 eV in the ion-beam deposition process.
For the sake of comparison, the calculation of the elastic moduli was performed using not only the potential functions of Brenner, but also the potential function of Tersoff. The relaxational part of elastic moduli was computed using 3D-supercells with about
1000 atoms and an accurate iterative method for the solution of large linear systems. The elastic moduli tensor was found to show only small deviations from the elastic isotropy. Taking into account that the Brenner potential functions underestimate the bulk modulus of crystalline diamond, the results are in an agreement with experimental measurements.

It is planned to build a 50 MJ pulsed field laboratory at the Forschungszentrum Rossendorf (near Dresden) to obtain magnetic fields up to 100 T with 10 ms pulse duration. This facility would provide the appealing possibility to have access to Zeeman energies in the energy range of the infrared free electron lasers (5m to 250m) now under construction at the radiation source ELBE in Rossendorf. For gaining experience in the construction and operation of pulsed magnets, a smaller pulsed field laboratory was established at the Institute for Solid State Physics and Materials Research Dresden (IFW Dresden) in 1999. The laboratory includes pulse magnets with peak fields up to 50 T in a 24 mm bore and a rise time of about 10 ms, and a 40 T long pulse magnet with a 24 mm bore and rise time of about 80 ms. The coils are energized by a 1 MJ, 10 kV capacitor bank with thyristor switches. The bank is subdivided into four identical and independent units. A particular advantage is the possibility to reverse the polarity of the magnetic field pulse by means of a novel circuit with industrial circuit breakers. The design of the power supply is explained in detail. High precision measurements of magnetization and magnetotransport in the temperature range of 1.5 to 300 K have been performed.

The incident energy at which the azimuthal distributions in semi-central heavy ion collisions change from in-plane to out-of-plane enhancement is studied as a function of mass of emitted particles, their transverse momentum and centrality for Au+au collisions. The analysis is performed in a reference frame rotated with the sideward flow angle relative to the beam axis.

The ratio of K^- and K⁺ meson yields has been measured in the systems ⁹⁶Ru+⁹⁶Ru at 1.69 AGeV, ⁹⁶Ru+⁹⁶Zr at 1.69 AGeV, and ⁵⁸Ni+⁵⁸Ni at 1.93 AGeV incident beam kinetic energy. The yield ratio is observed to vary across the measured phase space. Relativistic transport-model calculations indicate that the data are best understood if in-medium modifications of the kaons are taken into account.

Ausgehend von der Entdeckung der Elemente 114, 116 und 118 im Jahre 1999 in Dubna und Berkeley [1, 2] wird ein Überblick über die experimentellen Techniken und die Ergebnisse der letzten 20 Jahre gegeben, die die Entdeckung der Elemente 107 bis 112 in Darmstadt einschließen [3]. Anhand des jahrelangen Prioritätsstreites über die Entdeckung der Elemente 102 bis 105, der durch die verbindliche Namensgebung durch die IUPAC bis einschließlich Element 109 im Jahre 1997 beendet wurde [4], werden die Kriterien für die Entdeckung eines neuen Elementes erläutert.
Im Hauptteil des Vortrages werden anhand eigener experimenteller Arbeiten zur physikochemischen Charakterisierung des Seaborgiums die Grundprinzipien, Methoden und Probleme der Erforschung der chemischen Eigenschaften der schwersten Elemente erläutert [5-7].
In einem Ausblick werden Konzepte zur chemischen Identifizierung der superschweren Elemente 112 und 114 vorgestellt [8,9].

[1] Yu. Ts. Oganessian et al., Physical Review Letters 83 (1999) 3154
[2] V. Ninov et al., Physical Review Letters 83 (1999) 1104
[3] S. Hofmann, G. Münzenberg, GSI Preprint 2000 - 02, submitted to Rev. Mod. Phys.
[4] Pure & Appl. Chem., 69 (1997) 2471
[5] M. Schädel et al., Nature 388 (1997) 55
[6] A. Türler et al., Angew. Chem. 111 (1999) 2349
[7] S. Hübener et al., TAN 99, Seeheim 1999, Extended Abstracts
[8] H.W. Gäggeler et al., GSI UNILAC Proposal, 2000
[9] S. Hübener et al., unveröffentlichte Mitteilung

Eine wesentliche Sanierungsaufgabe in der sächsischen und thüringischen Uranbergbauregion ist die Flutung von ausgedehnten Untertagebergwerken, die in hohem Maße mit Holz ausgebaut sind. Im Flutungsprozess wird das Grubenholz zunehmend vom Luftzutritt abgeschnitten und der natürliche Holzabbau unter der Einwirkung des Grubenwassers findet statt. Bei diesem Vorgang wird Sauerstoff verbraucht und es entstehen reduzierende Bedingungen [1].
Um diesen Prozess zu untersuchen, wurden Redoxpotenzialmessungen und Redoxtitrationen mit Kaliumhexacyanoferrat(III) an hydrothermalen Holzauszügen, Fichtenlignin und Huminsäu-ren unter Verwendung einer Platinelektrode in Kombination mit einer Silber-Silberchloridelek-trode in einer Zelle mit Überführung ausgeführt. Die Redoxpotenziale des Lignins und der Huminsäure wurden in Abhängigkeit vom pH-Wert und der Konzentration untersucht. Nach Extrapolation auf pH 0 und unendliche Verdünnung wurde für beide ein Redoxpotenzial (Eh) von 570"5 mV mit einem negativen pH-Gradienten von 54,0"1 mV/pH erhalten. Dieses Potenzial zeigt, dass organische Zersetzungsprodukte des Holzes Uran(VI) zu Uran(IV) reduzieren können.
Das Reduktionsprodukt Uran(IV) wurde sowohl spektrophotometrisch als U(IV)-arsenazo(III)-Komplex als auch mit Hilfe der laserinduzierten photoakustischen Spektroskopie (LIPAS) nachgewiesen. Photoakustisch fanden wir die für U(IV) typischen Absorptionsbanden bei 630, 650 and 670 nm. Das Vermögen des Lignins Uran(VI) zu reduzieren stieg im pH-Bereich 5-8 von 0,13@10-4 auf 5@10-4 mval/g. Im Falle von Eisen(III) erhielten wir bei pH 4,5 eine Reduktions-kapazität von 0,15 mval/g.
Um die durch den natürlichen Holzabbau im wässrigen Milieu verursachten reduzierenden Eigenschaften zu charakterisieren, wurden Untersuchungen im Hochmoor AKleiner Kranischsee@ am Erzgebirgskamm bei Johanngeorgenstadt durchgeführt. Bei Feldmessungen fanden wir, dass das Redoxpotenzial von der Oberfläche bis zu einer Tiefe von einem Meter um mehr als 800 mV abfiel. Aus der Analyse des Sumpfgases (49,6% CH4, 3,28% CO2, 1,65@10-3% H2S) konnte für das Redoxpotenzial im Moorgrund (pH 5,3, 4°C) ein Eh-Wert von -120 mV hergeleitet werden. Schließt man hiervon auf das Flutungswasser mit seinem höheren pH und seiner höheren Temperatur, so müssten Redoxpotenziale unter -200 mV möglich sein. Würde als Folge des Holzabbaus die Sulfatreduktion in Gang kommen und Sulfid in mikro-molarer Konzen-tration auftreten, so entspräche das einem Redoxpotenzial von -220 mV. Das würde bedeuten, dass so stark anoxische Bedingungen auftreten, das zur Uran(VI)-Reduktion die reduktive Immobilisierung von Arsen(V) als As2S3 (Auripigment) hinzu kommen kann [2].
In tieferen Wasserschichten gefluteter Bergwerke wurden Potenzialerniedrigungen um etwa 700 mV gemessen. Dies wird aber ausschließlich der Oxidation sulfidischer und arsenidischer Erze und Mineralien, wie beispielsweise Pyrit, Markasit und Arsenopyrit zu geschrieben. Diese Potenzialverminderung bewirkt, dass Uran(VI), als Carbonatokomplex vorliegend, unter Gruben-wasserbedingungen zu Uran(IV) reduziert wird, das als Uran(IV)-hydroxid ausfällt und sedimen-tiert.
Die vorliegenden Ergebnisse zeigen, dass die Zersetzung großer Holzmengen in den gefluteten Gruben mithilft reduzierende Bedingungen zu erzeugen und aufrecht zu erhalten. Der natürli-chen Holzabbau im Grubenwasser der zur Uranimmobilisierung beiträgt und u.U. weitergehende reduktive Ausscheidungen verursacht, entspricht damit einem eminent wichtigen natürlichen Reinigungsprozess.
Literatur:

[1] SMWK-Projektbericht 4-7541.83-FZR/512, Juni 1998: AUntersuchung des Einflusses der in Gruben- wässern gelösten organischen Verbindungen auf den Valenzzustand von Radionukliden@

[2] Baraniak et al.: ARedox Reaction Sequence in Flooded Wood-Supported Mines@, Report FZR-272 (1999) p. 51

Uranium(VI) complex formation at vegetative cells and spores of Bacillus cereus and Bacillus sphaericus was studied using uranium LII-edge and LIII-edge extended x-ray absorption fine structure (EXAFS) spectroscopy. A comparison of the measured equatorial U-O distances and other EXAFS structural parameters of uranyl complexes formed at the Bacillus strains with those of the uranyl structure family indicates that the uranium is predominantly bound as uranyl phosphate.

Es werden die Grundlagen, Möglichkeiten und Grenzen von EXAFS-Untersuchungen erläutert. Die für derartige Messungen erforderlichen leistungsfähigen Röntgenquellen stehen u. a. an der European Synchrotron Radiation Facility (ESRF) in Grenoble zur Verfügung. Dort unterhält das FZR ein eigenes Strahlrohr, die Rossendorfer Beamline (ROBL). Deren Aufbau und Anwendungsgebiete werden kurz beschrieben. Am Beispiel mittels Chromgerbstoffen quervernetzten Kollagens wird die Nützlichkeit von EXAFS-Untersuchungen auch auf gerbereichemischen Gebiet nachgewiesen. So konnte erstmalig experimentell bestätigt werden, dass die Chromgerbung durch zweikernige Chromkomplexe erfolgt. Dies war bisher nur postuliert oder durch Computermodelling wahrscheinlich gemacht worden.

Für zahlreiche technische Prozesse ist die Kenntnis des Schlupfes bzw. des Drift-Fluxes in Zweiphasenströmungen notwendig. Beispiele sind die Bestimmung der Druckverluste sowie der Wärme- und Stoffübertragungsvorgänge in Verdampfern oder Kondensatoren, der Phasenverweilzeit in chemischen Reaktoren sowie der Moderatorwirkung des zweiphasigen Kühlmittels innerhalb des Kerns eines Siedewasserreaktors.

Time-resolved measurements of the transverse electric field associated with relativistic electron bunches are presented. Using an ultra-fast electro-optic sensor close to the electron beam, the longitudinal profile of the electric field could be measured with sub-picosecond time resolution and without time-reversal abiguity. Results are shown for two cases: inside the vacuum beam line in the presence of wake fields, and in air behind a Be window, effectively probing the near-field transition radiation. Especially in the later case, reconstruction of the longitudinal electron bunch shape is straightforward.

For a simple spherically symmetric mean-field dynamo model the radial dependence of $\alpha$ is determined from eigenvalues of some spherical harmonics by means of an evolutionary strategy code. The same code is used for "energetic" optimization as well as for constructing dynamo models with level-crossing. The connection with isospectrality problems in quantum mechanics is outlined. Consequences for a general inverse dynamo theory are discussed.

We present the results of the Riga dynamo experiment where magnetic field self-excitation was detected in November 1999 (Gailitis et al., Phys. Rev. Lett. 84, 4365, 8 May 2000). The observed growth rates, frequencies and spatial structures of the magnetic field are compared in some detail with the numerical prognoses.

The Forschungszentrum Rossendorf (FZR) is constructing a superconducting Electron Linac [F. Gabriel, J. Voigtländer, et al.,
ELBE Design Report 1998, http://www.fz-rossendorf.de/FWQ/report_d.htm; Annual Report 1996, FZR-179 (1997) 3; Annual
Report 1997, FZR-215 (1998) 3] with high Brilliance and low Emittance (ELBE) which can deliver a 1 mA cw beam of 40
MeV. ELBE will be equipped with a free-electron laser (FEL) system for the production of infrared (IR) light in the range 5¯300
um and will thus cover the range from the infrared to the THz regime. The electron beam can also be used to generate X-rays,
bremsstrahlung, positrons or fast neutrons.

4-HO-Phenylacetyl-[Lys-Psi(CH₂=NH)-Arg-Phe¹¹-t-Leu¹²-]NT(10-13) is a Neurotensin (NT) derivative with a Ki of 25 nM and is a good candidate for labelling with radio iodine. A fast and efficient radio iodination procedure by electrophilic substitution is proposed. 0.1 µmol of peptide together with 200 MBq of Na¹²⁵I in 1 ml of PBS of pH 7.4 were added to an Iodogen coated vial. Labelling was performed at 20°C for 5 min. QC by HPLC and Sep Pak showed labelling yields >98%. The pure n.c.a. (75 GBq/mmol) compound was obtained after semipreparative HPLC purification followed by recovery from a RPC-18 Bonda Pak column. Overall synthesis yields were over 80%. Biodistribution of 150 kBq of the n.c.a. compound in HT29 bearing nude mice revealed tumour uptake to ±5% of the I.D./g 10 min p.i. which could be inhibited for 75% by competition with native NT. The in vitro half-life of the pure peptide in human blood is 67 h. Due to its excellent biological half-life and its acceptable biological properties, the proposed ¹²³I labelled peptide is a good candidate as a new peptidergic SPECT tracer for NT receptor expressing pathologies.

Messungen an der Versuchsanlage ROCOM mit der in Rossendorf entwickelten Gittersensortechnik lieferten auch zeitabhängige mittlere Vermischungen an verschiedenen Modellpositionen. Der Versuch, diese mit Hilfe eines aufgestellten geschlossen-analytischen 1D-Rechenmodells der turbulenten Diffusion in einer stationären und symmetrischen Modellströmung nachzurechnen, erwies sich auch für den Fall einfachster Annahmen und einer Anpassung an nur einen Fluidmassenstrom, der bis auf das 6-fache erhöht wurde, als erfolgreich.

Zum Vergleich mit den Messungen und den Ergebnissen aus den analytischen Rechnungen werden auch CFX-4 Simulationen herangezogen, welche eine gute Übereinstimmung aller angewandten Verfahren zur Bestimmung der mittleren Vermischungen an der Modellanlage ROCOM bestätigen.

Insbesondere konnten auch in Abhängigkeit von der dimensionslosen Pfropfenlänge der Tracerdosierungen nicht nur die Maxima der mittleren Vermischungsverteilungen berechnet, sondern auch die zu erwartenden Maximalwerte selbst abgeschätzt werden.

Eine Anwendung des beschriebenen analytischen Verfahrens und der CFX-4 Simulationen auf prinzipiell beliebige Modelle und Originalkomponenten bei vergleichbaren turbulenten stationären und symmetrischen Strömungen läßt ebenso gute Ergebnisse erwarten.

2-¹²³I-phenylacetyl-NT(8-13)-OH (1) and 4-HO-2-¹²³I-phenylacetyl-[Phe¹¹]-NT(8-13)-OH (2) were developed as potential SPECT tracers for NT-receptor expressing tumors. The precursor compounds showed high affinity for NT-receptors on bulbus olfactorius membranes of rodent (Ki in the Mn range). (1) Was obtained by Cu¹ assisted non-isotopic exchange on 1 mg of the 2-Br-phenylacetyl analogue, with a labeling yield of 70%. (2) Was obtained by direct electrophilic substitution during 5 min at Rt using Iodogen on 0.1 mg 4-HO-phenylacetyl-[Phe¹¹]-NT(8-13)-OH with a yield >98%. The second method allows a two component kit application. In vivo in the rat fast degradation (t1/2: 1.5 min) was observed coupled to high long-acting liver uptake. This is probably caused by radioiodo-phenylacetyl-Arg, a compound that mimics MIBG. 4-HO-phenylacetyl-[Lys⁸Y(CH₂NH)Arg⁹]-[tLeu¹²]-NT(8-13)-OH, a double stabilized NT(8-13) analogue of type (2), from which high in vivo stability is expected, was synthesised.

Heat treatment of steels by electron beams with an energy density ranging from 1 to 10 kW/cm2 results in a considerable hardness improvement and wear reduction. Hence, electron beam treatment is a typical line-of-sight process and demands a complicated target manipulation and beam rastering system.
A new method is presented, circumventing the limitations inherent in the scanning electron beam treatment. The workpiece to be treated is immersed into a plasma and surrounded by a negatively biased grid, preventing the penetration of plasma electrons. Further the workpiece is connected to a positive DC high voltage source of about 20 kV and a capacitor, acting as an energy storage. Changing the grid bias, electrons are extracted from the plasma and accelerated by the positive potential towards the workpiece. During the pulsed electron bombardment power densities of about 10 kW/cm2 can be achieved resulting in a rapid thermal heating and self quenching, occurring after the electron pulse. Detailed investigations are presented on the response of a plasma if electrons are extracted by a large electrode with special emphasis on the processes near the wall and near the control grid.

OBJECTIVES: Restenosis is a major problem occuring after angioplasty, atherectomy and implantation of stents. It has been shown, that external beam teletherapy (X-rays) and intravascular brachytherapy (e.g. ¹⁹²Iridium ribbon seeds, ¹⁸⁸Re filled catheters, P-32-coated stents) prevents restenosis by inhibition of the proliferation of medial smooth muscle cells. The aim of this study was to investigate the potential of ¹⁸⁶Rhenium labeled stents to prevent restenosis in an animal model.

METHODS: New Zealand White rabbits were fed a 0.5% cholesterol diet four weeks prior to intervention. ¹⁸⁶Re (T = 3.8 d) labeled Palmaz-stents with an activity of 25.6 ± 2.5 MBq (n = 11) were placed in the infrarenal aorta of rabbits after balloon denudation. Animals with implanted unlabeled stents served as controls (n = 11). Whole body scintigrams were obtained after 1, 4, 24 hours and after 7 and 14 days to determine the bleaching of ¹⁸⁶Re from the stents in vivo. Seven weeks later, the animals were sacrified and morphometry and immunohistology was performed.

RESULTS: More than 80% of the ¹⁸⁶Re remained on the stent 14 days after implantation as determined by ROI analysis of the scintigrams. The neointimal area inducted seven weeks after implantation of the unlabeled stents was 2.2 ± 0.2 mm². No neointima was detectable in the aorta of animals with implanted radiolabeled stents. No intraluminal accumulation of fibrin and fibroblasts directly at the stent struts implies that the delivered dose can even be reduced.

CONCLUSION: Arterial implantation of ¹⁸⁶Re labeled stents was feasible and stable in vivo. The activity of 25.6 ± 2.5 MBq totally inhibited neointimal formation. In further studies we will reduce the stent activity in order to determine the therapeutic window of ¹⁸⁶Re labeled stents

In our effort to develop small molecular ^99mTc diagnostic probes to image malignant melanoma, tetradentate N₂S₂(AADT) ^99mTc-complexes of the general formula AADT-X-NR₂ (X = -(CH ₂) _n-, R = Et, Bu) were synthesized. The N-substituted AADT-X-NR₂ ligands were radiolabeled with ^99mTc(V) via transmetallation with [^99mTc]technetium(V)-glucoheptonate resulting in ^99mTc complexes in high radiochemical yield (86%-98%). These complexes were further characterized via HPLC coelution with similarly synthesized rhenium analogues. In-vitro evaluation in B16 murine melanoma cells revealed a distinct pattern of cell accumulation. The more lipophilic complex 2 [n = 2, R = Bu] displayed only an 8% melanoma uptake, whereas complex 1 [n = 2, R = Et] displayed a 44% cell uptake in 60 min. Complexes 3 [n = 3, R = Et] and 4 [n = 3, R = Bu] showed a 62% and 68% cell uptake at 60 min, respectively. In-vivo biodistribution studies in the C57B16/B16 mouse melanoma tumor model revealed a tumor accumulation of 7.6% ID/g at 60 min post injection (p.i.) and high melanoma/blood (10.8), melanoma/spleen (10.1) and melanoma/lung (7.3) ratios for complex 1. Although the tumor uptake of compound 3 was significantly lower (3.7% ID/g) at 60 min p.i., the melanoma/blood (19.1), melanoma/spleen (19.1) and melanoma /lung (12.7) ratios were considerably high. These results demonstrate the feasibility of developing N-substituted [^99mTc-AADT] complexes as small molecular probes for potential diagnostic imaging of malignant melanoma via SPECT.

OBJECTIVES: Development (synthesis, biologic evaluation and first results in humans) of a [¹⁸F]-labeled synthetic amino acid for tumor detection with PET.

METHODS: Synthesis of [¹⁸F]OMFD based on a new precursor (N-formyl-3-O-methyl-4-O-Boc-6-trimethylstannyl-L-DOPA-ethyl-ester). The biologic evaluation was performed in cell culture (HT-29;RBE-4) and tumor bearing nude mice (SC-Ca). First application in humans were obtained in 4 patients with recurrent glioblastoma multiforme with inconclusive CT and MRI. [¹⁸F]OMFD was used to identify localization and extent of recurrent tumor for treatment planning with stereotactic radiotherapy, which was the last treatment option for the individual patient.

RESULTS: The radiochemical yield of [¹⁸F]OMFD was 20-25% (decay corrected, related to [¹⁸F]F₂) in 50 min synthesis time. Cell culture experiments showed a high tracer uptake in tumor cells via the L-amino acid transporter without evidence for any metabolism or protein incorporation. Biodistribution in mice 60 min p.i. showed a high tumor uptake (12.4 ± 1.8%ID/g) with a high tumor/blood ratio (9.2 ± 0.845 min p.i.). In all patients an increased tracer uptake in the area of the suspected recurrence (lesion to non-lesion 2.2 ± 0.5) was found. In the whole body scan only little tracer uptake was observed in the muscles, thorax and abdomen.

CONCLUSION: In vitro and in vivo experiments showed increased [¹⁸F]OMFD uptake in tumor tissue. The results of preliminary diagnostic studies with [¹⁸F]OMFD in patients with glioblastoma multiforme indicate its potential for tumor imaging.

The ROssendorf BeamLine (ROBL) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, was built and is operated since 1999 by the Forschungszentrum Rossendorf. Two different experimental stations, a radiochemistry hutch and a materials research hutch, are available alternatively.
An overview of the experimental equipment of the materials research hutch (MRH) is given. This end-station is dedicated to diffraction and reflectometry with synchrotron radiation. Its basic instrument is a high precision six-circle goniometer for heavy duty. Various detector systems and special sample environments are available.
The contribution presents results from the Institute of Ion Beam Physics and Materials Research of the FZR so far obtained at ROBL-MRH. They demonstrate the capability of synchrotron radiation for the analysis of surface near structures produced by ion implantation or of thin surface films.
 Depth distribution of phases produced by ion implantation.
 Formation of SiC crystals by ion implantation of C in Si and the orientation correlation to the host lattice.
 Modification of interface roughness in Co/Cu-multilayers by ion beam mixing.

Deep gettering layers have been formed in n-type Si wafers by high-energy ion implantation of Si+, P+, Ge+ and As+ and subsequent annealing. The samples have been then contaminated with Cu by implanting the impurity into the backface and an additional thermal treatment. The resulting copper depth profiles measured by secondary ion mass spectrometry show strong gettering of Cu well behind the projected ion range Rp and formation of a separate gettering band therein. We call this phenomenon the "trans-Rp effect". It has been observed for P and As implants, whereas for Si and Ge implants it was missing. This effect indicates the presence of a significant amount of defects much deeper than Rp. The size of these defects is below the resolution limit of our transmission electron microscopy analysis and we suggest that they are small interstitial clusters. Their gettering ability should be higher than that of the extended defects at Rp since the amount of Cu atoms gettered beyond Rp is much greater than that in the implanted gettering layer. A mechanism of the defect formation and clustering in the trans-Rp region is proposed, and an explanation is given of the differences in the results for the P and As implants.

To meet the need for small and "robust" chelates we focussed our recent investigations on new types of technetium(III) chelates, their synthesis and evaluation of molecular properties. Here we report on five-coordinated compounds with "3+1+1", "3+2", and "4+1" donor arrangements.
Such species, all belonging to the family of "n+1"mixed-ligand technetium complexes, were developed and characterized towards versatility, lipophilicity and stability.
The "3+2" approach make use of the combination of a tridentate HS-E-SH ligands with a PR₂-SH chelator, common action of the tripodal nitrilotris(ethanethiol) with isocyanide co-ligands leads to
trigonal-bipyramidal "4+1" Tc(III) complexes.
Both types enables easy functionalization and thus a fine-tuning of physicochemical properties of the complexes or to link the chelate unit to biomolecules.
The sterically well shielded oxo-free species are non-polar, showing higher logP values as the "3+1" oxotechnetium(V) compounds. The "3+2" and "4+1" complexes are stable towards re-oxidation and transchelation in challenge experiments with glutathione. The "3+2" type is the most versatile one while the compact "4+1" seems to be the most stable arrangement.
The presented "3+2" and "4+1" complex types are useful tools in designing of ^99mTc or ^186/188Re radiopharmaceuticals.

We present the results of a systematic investigation of neutron-irradiated and thermally-annealed model alloys using positron annihilation spectroscopy (PAS), including both lifetime and Doppler broadening techniques. The objective of this work is to use PAS to provide information on the irradiation-induced microstructural features that are thought to cause embrittlement in pressure-vessel steels. Such information could complement the results obtained by other techniques, especially small-angle neutron scattering (SANS) and atomic probe field ion microscopy (APFIM). We examined a series of model Fe-based alloys, in which the Cu, P and Ni concentration were systematically varied. These alloys were examined in the as-fabricated state, after irradiation to 1 x 10 19 nxcm-2, and to 8 x 10 19 nxcm-2, and after successive post-irradiation 30-minute isochronal anneals at temperatures ranging from 200 to 600 °C. In each case, we measured the positron annihilation lifetime distribution, the Doppler broadening (S-parameter), and the 15 N Rockwell hardness for the samples.

Experimental data on K+ meson and proton sideward flow measured with the FOPI detector at SIS/GSI in the reactions Ru+Ru at 1.69 AGeV and Ni+Ni at 1.93 AGeV are presented. The K+ sideward flow is found to be anti-correlated (correlated) with the one of protons at low (high) transverse momenta. When compared to the predictions of a transport model, the data favour the existence of an in-medium repulsive K+ nucleon potential.

The strong influence of dose rate and implantation temperature on the dose dependence of the shape of Ge channeling implantation profiles is demonstrated for the first time. Applying a focused ion beam (FIB) system allows the use of a very high (10¹⁸ cm^-2s^-1) and a very low (10¹⁰-10¹¹ cm^-2s^-1) dose rate. Implantations are performed at R.T. and at 250°C. At the high dose rate and R.T. the dose rate dependence of the profile shape is found to be most pronounced. Atomistic computer simulations using a relatively simple damage buildup model can explain the effects observed. It is shown that at R.T. defect relaxation processes can last up to 1 s, which is longer than assumed so far. The lifetime of implantation defects at 250°C is estimated to be in the order of 10s.

The amplitude of subthreshold phi-meson production is calculated using dominant tree-level diagrams for three-body collisions. It is shown that the production can overwhelmingly be described by two-step processes. The effect of the genuine three-body contribution (i.e. the contribution which cannot be factorized) is discussed. The production rate of phi-mesons is presented for proton induced reactions on carbon.

Surface modification of titanium is of interest considering the necessary improvement of mechanical properties of this material for
applications as e.g. artificial joints. This work is devoted to the formation of a layer with a high content of the titanium aluminides Ti3Al
and TiAl below the surface by high-dose aluminium implantation. If the maximum aluminium concentration exceeds 20 at.%,
precipitation of Ti3Al is detected by XRD already in the as-implanted state. For maximum aluminium concentrations between 50 and 55
at.%, the phase TiAl is found beside Ti3Al after annealing at 700°C. For a double implantation resulting in an aluminium concentration of
about 60 at.% in the depth range between 100 and 200 nm, a disordered fcc TiAl phase is observed after implantation as precursor for
the ordered tetragonal TiAl formed by subsequent annealing at 600°C.

Aufgabe der vorliegenden Erfindung ist es, die Messsysteme für Leitfähigkeits- und Temperaturmessung so zu verkleinern und aufeinander abzustimmen, dass beide Messungen weitestgehend am gleiche geometrischen Ort erfolgen können und somit eine höchstmögliche Messgenauigkeit für die um den Temperatureinfluss korrigierte Leitfähigkeit erzielt wird.

Aufgabe der Erfindung ist es, einen photochemischen Nanopartikelgenerator anzugeben, der mit toxisch unbedenklichen, chemisch stabieln und einfach zu handhabenden Ausgangssubstanzen betrieben werden kann, wobei die Bildung toxisch bedenklicher Reaktionsprodukte weitestgehend vermieden werden soll.

Der Erfindung liegt die Aufgabe zugrunde, einen integrierten Optokoppler und ein Verfahren zu seiner Herstellung vorzuschlagen, bei denen eine direkte monolithische Integration des gesamten Optokopplers in Silizium-Technologie mit geringem Aufwand erfolgen kann, wobei Einschränkungen bei der Herstellung des Optokopplers weitgehend vermieden werden sollen.

Die Erfindung geht von einem Optokoppler aus, bei dem Empfangs- und Sendeelement benachbart angeordnet und durch ein optisch transparentes und elektrisch isolierendes Material galvanisch getrennt sind.

Der Erfindung liegt die Aufgabe zugrunde, Ohmsche Kontakte mit geringem Kontaktwiderstand auf p-leitenden SiC-Halbleiterbereichen zu erzeugen, wobei die Maximaltemperatur bei der Prozessführung 1000oC nicht überschreiten soll.

Der Erfindung liegt die Aufgabe zugrunde, diese Nachteile zu überwinden und ein schnelles, reproduzierbares Herstellungsverfahren für chemisch und radiochemisch reine 16a- [18F]Fluorestradiolsulfamate, die wahlweise in 3-oder 17-Stellung monosulfamoyliert bzw. in 3, 17-Stellung disulfamoyliert worden sind, vorzustellen. Die Synthese kann, ausgehend von den 16,17-O-Sulfuryl-16-epiestriolderivaten, ohne Zwischenisolierung der intermediär anfallenden 16a-[18F]Fluorestradiolderivate in eigens für die Markierung vorgesehenen käuflichen Modulen mittels computergestützter Programme durchgeführt werden. Dadurch wird die Kontaminierungsgefahr mit radioaktivem Material auf ein Mindestmaß reduziert.

Aufgabe der Erfindung ist es, eine Beruhigung des Schmelzbades und des sich an der Walzenschneide ausbildenden Meniskus zu erreichen, um auf diese Weise den Schmelzextraktionsprozeß zu stabilisieren und die reproduzierbare Herstellung speziell von dünnen Fasern mit Durchmessern unterhalb 100 mm zu ermöglichen. Die statistische Verteilung des Durchmessers der produzierten Fasern um den durch die Prozeßparameter vorgegebenen mittleren Faserdurchmesser soll möglichst schmal sein.

Ziel: Zahlreiche Studien in den letzten Jahren belegen den Stellenwert der intraarteriellen Radioembolisation maligner Tumoren. Bisher sind aber in Europa keine mit einem Betastrahler kurzer Halbwertszeit markierte Mikrosphären kommerziell verfügbar. Nach erfolgreicher Markierung verschiedener, metabolisierbarer und nicht metabolisierbarer Partikel mit ¹⁸⁸Re (T_1/2=17h) in hoher Ausbeute wurde die Biokinetik von Humanserumalbuminmikrosphären (HSAM) mit einem Durchmesser von 25 µm hinsichtlich Belastung der Normalgewebe untersucht.

Methodik: Für die Markierung wurden ca. 370 MBq ¹⁸⁸Re Generatoreluat (2 ml) mit 6 mg Gentisinsäure, 7,5 mg SnCl₂ 2H₂O und 0,5-5 mg der HSAM gemischt und für 1 h bei 100 °C in einer Glasampulle erwärmt. Nach Entfernung des Überstandes durch Zentrifugation und zweimaliges Waschen erfolgte die Resuspension in NaCl-Lösung und Röntgenkontrastmittel. Zur Untersuchung der Biokinetik wurden nachi.v. Injektion Wistarratten nach 20 min, 4 h, 24 h, 48 h und 96 h getötet. Proben verschiedener Organe sowie von Blut, Urin und Faeces entnommen und der Radioaktivitätsgehalt gemessen (vgl. Tab.). Die Lunge diente dabei als Modell eines gut perfundierten Tumors.

Ergebnisse: Obwohl es sich bei den ¹⁸⁸Re-HSAM um biologisch abbaubare Partikel handelt, belegen unsere Ergebnisse die gute in-vivo-Stabilität mit geringer Anreicherung in den Normalgeweben bis 96 h p.i. Die Dosisberechnung nach MIRD-Modell mit dem PC-Programm Mirdose 3.1 zeigen, ausgehend von den experimentellen Daten, die Niere als kritisches Organ mit einer Belastung von 0,26 mGy/MBq.

Schlussfolgerungen: Da mehr als 100 GBq der ¹⁸⁸Re-HSAM appliziert werden müssten, um die TD_5/5 der Niere zu erreichen, erscheinen die bereits für die Lungenperfusionsszintigraphie zugelassenen Mikrosphären hinsichtlich der Anwendung am Menschen als sicher.

Biokinetik von ¹⁸⁸Re-HSAM (%/inj. Aktivität/Organ)

Zeit [h]........Lunge........Leber........Milz..........Nieren........Magen........Darm
----------------------------------------------------------------------------------------------------------------
0.33............98.2...........0.42.........0.02...........0.28...........0.05............0.08
4.................97.9...........2.3...........0.30...........0.35...........0.37........... 0.23
24...............94.0...........1.15.........0.10...........0.85...........0.11............0.21
48...............92.7...........0.81.........0.07...........1.34...........0.12............0.17
96...............91.3...........0.89.........0.10...........1.20...........0.05............0.12

Ziel: Entwicklung einer synthetischen Aminosäure als Tracer zur Tumordiagnostik. Synthese, biologische Evaluierung und erste Anwendung am Menschen von ¹⁸F-markierten OMFD.

Methode: Für die Synthese des [¹⁸F]OMFD wurde ein neuer Precursor entwickelt (n-Formyl-3-O-Methyl-4-O-Boc-6-trimethylstannyl-L-DOPA-ethyl-ester), der eine hohe Ausbeute bei relativ kurzer Synthesedauer ermöglicht. Die biologische Evaluierung erfolgte an Zellkulturen (HT-29;RBE-4) und tumortragenden Nacktmäusen (PE-Ca). Erste klinische Ergebnisse wurden bei 3 Patienten mit Glioblastoma multiforme erhoben, die bereits z.T. mehrfach voroperiert und bestrahlt worden waren. Zur Planung einer stereotaktischen Hirnbestrahlung bei klinischem V.a. Rezidiv und inkonklusiven Ergebnissen in der übrigen bildgebenden Diagnostik wurde ein Aminosäure-PET zur weiteren Abklärung durchgeführt. Nach Injektion von 330 MBq [¹⁸F]OMFD wurde eine dynamische Sequenz über 90 min und eine Aufnahme des Körperstammes durchgeführt.

Ergebnisse: Synthese: Die Ausbeute mit dem neuen Precursor beträgt 20-25% in 50 min Synthesezeit.
Zellkultur: In vitro zeigte sich eine hohe Traceraufnahme in die Tumorzellen über den L-Transporter ohne Nachweis einer Metabolisierung oder Proteininkorporation.
Tiermodell: Biodistributionsdaten zeigten eine hohe Tumoraufnahme (12,4±1,8%ID/g) mit hohem Tumor/Blut-Verhältnis (45 min p.i.: 9,2±0,8).
Patienten: Bei allen Patienten ließ sich im Gebiet des vermuteten Tumorrezidivs mit [¹⁸F]OMFD eine fokal erhöhte Traceraufnahme darstellen. Das Verhältnis von Tumor zu Nicht-Tumor betrug 2,2±0,5. Die maximale Traceraufnahme wurde zw. 12 min und 25 min p.i. beobachtet. Im Körperstamm zeigte sich nur eine sehr geringe Traceraufnahme in der Muskulatur, im Thorax und dem Abdomen.

Schlussfolgerung: Die in vivo- und in vitro-Experimente haben gezeigt, dass [¹⁸F]OMFD als synthetische Aminosäure in Tumoren angereichert wird. Die ersten diagnostischen Anwendungen an Patienten zeigten ermutigende Ergebnisse in der Lokalisation von Rezidivtumoren beim Glioblastom.

The intensive uranium mining and milling activities in the southeast of Germany (Saxony and Thuringia) have caused severe environmental pollution in this region. The uranium intrusion into the biosphere occurs most likely through aqueous transport. The prediction of the uranium transport behavior is essential for safety assessment studies and for the development of efficient remediation methods.
The seepage water of the rock piles and the flooding water of the mines contain relatively high amounts of magnesium, calcium, hydrogen carbonate/carbonate and sulfate ions. In these waters the pH values range from 7.0 to 8.0 and the uranium content is about 0.02 mmol/L /1/. In a former study /2/ we have found that Ca2[UO2(CO3)3]aq. is the dominating uranium species in mining related waters. Under these conditions the precipitation of the secondary uranium mineral - liebigite, Ca2[UO2(CO3)3] x 10H2O - is possible. In oxidizing water which contains uranyl, magnesium and hydrogen carbonate/carbonate ions, the formation of magnesium uranyl carbonate as solid or dissolved species could be expected. In nature the mineral bayleyite - Mg2[UO2(CO3)3] x 18H2O - is a comparatively common secondary mineral in uranium ore deposits set within an alkaline environment and associated with gypsum, carnotite and metaautunite.

The aim of this work was to synthesize and to characterize the bayleyite using several analytical methods. This well characterized substance was used for the determination of its solubility and for speciation experiments.

Synthesis and characterization of Mg2[UO2(CO3)3] x 18H2O:
Several methods for preparation of bayleyite are described in the literature /3,4/. By variation of the preparation conditions, we could increase the reproducibility and the yield (95±3%) of the product. Bayleyite was prepared by mixing stoichiometric amounts of dissolved uranyl nitrate (Merck p.a.), mag-nesium carbonate (-Merck p.a.) and sodium carbonate (-Merck p.a.) at ambient temperature. During this process, carbon dioxide was passed through the solution until dissolution of all reactants. Then bayleyite was p--recipitated by s-low evaporation of the solution at room temperature. The product was purified by recrystallization. The obtained transparent green-ish yellow p-risms were dried on air.
The results of the chemical analysis are represented in Tab. 1. The determined chemical composition was in good agree-ment with the calculated values.

Tab. 1: Chemical analysis of Mg2[UO2(CO3)3] x18H2O

Element U Mg C H
Found (%) 28.92 ± 0.60 5.90 ± 0.70 4.34 ± 0.01 3.98 ± 0.28
Calculated (%) 28.92 5.91 4.38 4.41
Method ICP-MS AAS EA. EA.

The thermoanalytical measurements showed that the water is released in a temperature range from 22 to 338oC. The CO2 release occurred from 338 to 800oC. As a result from these measurements, the content of water and CO2 was determined to be 17.36±0.52 and 3.17±0.10 moles, respectively.

The synthesized bayleyite was identified and characterized by X-ray Powder Diffraction (XRD), Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS), and Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS).
The indexing of the diffraction pattern peaks observed in the X-ray diffraction diagram showed that the synthesized substance has monoclinic structure as described in the literature /3,5/. The lattice parameters (Tab. 2), which were calculated from all clearly identifiable reflections, are in good agree-ment with those found by Mayer et al. /5/ and described in PDF /6/.

Tab. 2: Lattice constants of Mg2[UO2(CO3)3] x18H2O

This work H. Mayer /5/ PDF /6/
a (Å ) 26.593 ± 0.101 26.560 (3) 26.65 (5)
b (Å) 15.263 ± 0.052 15.256 (2) 15.31 (5)
c (Å) 6.503 ± 0.026 6.505 (1) 6.53 (2)

We performed EXAFS measurements of the solid bayleyite and its solution (pH 8.0, Uconc. 0.182 mol/L) in order to compare the obtained structural parameters with the XRD data and to detect agreements or dif...

The influence of the dose rate on the damage creation in silicon has been investigated by means of high current density focused ion beam (FIB) implantation. 70 keV Co and Ge ions with a current density of about 1 A/cm2 have been implanted into silicon at target temperatures in the range from room temperature to 420°C. The effective dose rate was varied between 1013 ions/cm2s and about 1019 ions/cm2s applying different pixel dwell times from 1 µs to 250 µs. The samples have been investigated using Rutherford backscattering / channeling combined with a special preparation technique, scanning electron microscopy, micro-Raman spectroscopy and reflectivity measurements. It have been found that at short dwell times at implantation temperatures of about 400°C the silicon remains crystalline after Co as well as Ge ion bombardment also in the limit of high doses while at long dwell times the crystal becomes amorphous. These studies of damage accumulation and dynamic annealing reveal that the characteristic time of defect annealing lies in the µs-range.

The variation with temperature of the ion mass spectra of a liquid metal alloy ion source (LMAIS) (Au77Ge14Si9) is reported. Analysis of our results suggests the co-existence of two diffrent ion creation mechanisms for the doubly charged atomic ions. Whereas some doubly charged ions are post-ionised from the singly charged state, others are directly field-evaporated. The temperature dependence of the abundance of the ionic clusters emitted by the source has also been investigated.

Adenosine triphosphate is an important enzymatic compound, which is able to transfer the phosphate and diphosphate group between molecules. Heavy metal ions bound to the adenosine phosphates can be transported into living cells and than deposited.
In addition to studies of the soil-to-plant transfer factors /1/ and the interaction of the uranyl ion with microorganisms /2/ we studied the complex formation of the uranyl ion with adenosine triphosphate (ATP).
We found that adenosine phosphates are very strong quenchers of the fluorescence of the uranyl ion and also of the formed complexes. In the uranyl - adenosine monophosphate (AMP) system UV-vis measurements were carried out in the wavelength range from 180 nm to about 300 nm using a CARY5G spectrometer (VARIAN, Canberra). The adenosine monophosphate shows a strong absorption in this range and no fluorescence could be observed at all.
In the uranyl - adenosine triphosphate system fluorescence emission was observed only in a small range of the adenosine concentration. The deconvoluted fluorescence spectra show different emission maxima compared both to the uranyl ion and to phosphate complexes. This leads to the conclusion that a complex between uranyl and adenosine triphosphate is formed.

Our investigation supporting the feasibility of the in-situ
PET monitoring in proton therapy is presented. We simulated by means of the FLUKA code the amount and the spatial distribution of the main ß+ emitters created in PMMA targets by protons at typical therapeutic energies. The quantitative comparison with the activation induced by 12C ions of energies corresponding to the same range shows that the available signal at the same physical dose level should be up to two times more intense for protons than that actually successfully used for the control of carbon ion therapy at GSI Darmstadt. The spatial correlation between the activity and the dose profile for protons is poorer than for 12C nuclei. However, an important check of the particle range, dose localization and stability of the treatment during all the fractions seems to be possible.

Bacterial diversity in two uranium waste piles in Germany was studied. For this study, total DNA was recovered by two alternative procedures for direct lysis from a large number of soil samples drawn from different sites and depths of the piles. Significant differences in the bacterial composition of the samples investigated were revealed by the use of rep-APD, RISA, and 16S ARDREA. The 16S rDNA retrieval allowed also to demonstrate that both uranium wastes were dominated by Thiobacillus ferrooxidans and by several Pseudomonas species of g-subdivision of the Proteobacteria. Three kinds of T. ferrooxidans 16S and IGS rDNA specific fragments corresponding to the recently described three phylogenetic groups of this species (Flemming at al., 1999) were amplified in different ratios from distinct soil samples which were polluted with heavy metals to different extent. This microdiversity probably reflects the genetic adaptation of the uranium waste strains to the different heavy metal concentrations in their natural surrounding.

Nuklidvektor in verbrauchtem Kernbrennstoff;
Globale Plutoniumbilanz;
Recycling oder Endlagerung von Plutonium;
Accelerator-Driven-Systems (ADS) zur Aktiniden- und Spaltprodukttransformation

There is evidence that intrauterine growth restriction (IUGR) is associated with altered dopaminergic function in the immature brain. However, the relevant enzyme activities have not been measured in the living neonatal brain together with brain oxidative metabolism. Therefore ¹⁸F-labelled 6-fluoro-L-3,4-dihydroxyphenylalanine (FDOPA) was used together with positron-emission-tomography to estimate the activity of the aromatic amino acid decarboxylase in the brain of 10 newborn IUGR piglets (2 to 5 days old; body weight 908±109g) and in 10 normal-weight (3 to 5 d old; body weight 2142±373g) newborn piglets. The regional transport of FDOPA to the brain and the clearance rate of labeled metabolites from brain tissue were broadly similar in the two groups. However, the regional rate constant for back flux from the brain was markedly increased in IUGR piglets for striatum (72%) and frontal cortex (83%) (p < 0.05). Furthermore, the rate constant for conversion of FDOPA to fluordopamine was markedly increased (between 48 % in cerebellum and 91 % in mesencephalon, p < 0.05) in all brain regions of IUGR piglets studied.
Thus, it is suggested that IUGR induces an up-regulation of amino acid decarboxylase activity that is not related to alterations in brain oxidative metabolism.

A novel surface layer (S-layer) protein was found on Bacillus sphaericus isolate recovered from a uranium mining waste pile. Formation of highly ordered platinum and palladium nanoclusters on this crystalline protein template was studied. The average diameter of the metal clusters is 1.9±0.6 nm. They are located in the nano-sized pores and gaps of the crystalline S-layer. The atomic structure of the S-layer-metal nano-clusters was analysed by the use of EXAFS spectroscopy.
In addition, it was demonstrated that the B. sphaericus isolate is able to accumulate selectively large amounts of U, Pb, Cd, and Al from drain waters of the uranium mining waste pile. For this reason, this strain was chosen for construction of so called bio-ceramic "Biocere" which may be used for bioremediation of heavy metal contaminated liquid wastes. Our first analyses of the properties of this nano-scalic bio-ceramic will be presented.

Tritium depth profiling measurements by accelerator mass spectrometry have been performed at the facility installed at the Rossendorf 3 MV Tandetron. In order to achieve an uniform erosion at the target surface inside of a commercial Cs ion sputtering source and to avoid edge effects, the samples were mechanically scanned inside of a commercial Cs sputter ion source. The sputtered negative ions were mass analysed by the injection magnet of the Tandetron. Interesting ions except tritium are measured with the Faraday cup between the injection magnet and the accelerator, while the tritium is counted after the accelerator with semiconductor detectors. Depth profiles have been measured for carbon samples which had been exposed to the plasma at the first wall of the Garching fusion experiment ASDEX-Upgrade and from the European fusion experiment JET, Culham/UK. Tritium contents in the JET samples were up to six orders higher than in samples from ASDEX-Upgrade. Tritium beam currents from samples with high tritium content can be measured partly in the Faraday cup before the accelerator. A dedicated tritium AMS facility with an air-insulated 100 kV tandem accelerator is under construction. First results of test operation are presented.

For focused ion beam applications of Erbium as well as of several metal ions which are of interest for optical and semiconductor investigations a liquid metal ion source operating with an Er-stainless steel alloy was developed and investigated. This alloy consists of a mixture of Er70Fe22Cr5Ni3 and has a melting point of about 860°C. The wetted needle type tungsten emitter showed a stable emission behaviour down to 1µA emission current. The I-V characteristics, the temperature dependence of the extraction voltage, the mass spectrum, and the energy spread of the main beam components depending on the emission current were investigated. While in the case of singly charged metal ions the beam is not defined due to isotope interference in the case of doubly charged ions the species well separated for focused ion beam applications are available.

After 16alpha-[¹⁸F]fluoroestradiol ([¹⁸F]FES) has been successfully prepared in an automated module, the synthesis of 16alpha-[¹⁸F]fluoroestradiol-3,17beta-disulphamate ([¹⁸F]FESDS) is described as a module-assisted one-pot procedure which can provide 10 GBq [¹⁸F]FESDS with a radiochemical purity better than 99 %. The procedure is reliable and reproducible and requires a time of about 90 min. Because of its high sulphatase-inhibitory effect [¹⁸F]FESDS is thought to be a new PET tracer to image sites of high sulphatase activity.

The synthesis of 16alpha-[¹⁸F]fluorestradiol-3,17beta-disulphamate ([¹⁸F]FESDS) is described. 16alpha-[¹⁸F]fluorestradiol ([¹⁸F]FES) is converted using excess sulphamoyl chloride in absolute acetonitrile in the presence of Kryptofix 2.2.2 and potassium carbonate using an automatically operating module. The required time for the synthesis related to end of bombardment is 3h, the maximum yield is 6%, and the maximum decay-corrected yield is 20%. The radiochemical purity of [¹⁸F]FESDS is > 99%. The specific radioactivity of [¹⁸F]FESDS is found to be between 150 and 200 GBq/µmol.

Starting from the lead structure of ketanserin, a prototypic serotonin (5-HT) antagonist, a series of oxotechnetium(V) complexes were synthesized which are able to compete with [³H]ketanserin in receptor binding assays.
In order to imitate organic 5-HT₂ receptor ligands, fragments of ketanserin were combined with chelate moieties. Lipophilic complexes, consisting of a small S₄ or S₃N thiolate/thioether chelate unit, protonable nitrogen containing spacer and benzyl moiety significantly inhibited the specific binding of [³H]ketanserin with IC₅₀ values between 10 and 50 nM.
Low brain uptake is a generally accepted problem in developing ^99mTc brain receptor imaging agents. For some representatives of 5-HT_2A receptor binding agents it was tried to improve the original low brain uptake of 0.4 % ID in rats 5 min p.i. by modifying the lipophilic properties of the molecules. Because of the presence of a protonable nitrogen, which according to the pK value leads to ionization of the molecule at blood pH, the pK value was considered to be the parameter most suitable for adjustment of lipophilicity. Insertion of ether-oxygen in the molecule of 5 candidates lowers the apparent pK value from 10.0 to 8.3 and dramatically increases the brain uptake up to 1.3 % ID at 5 min.
Finally, the synthesis and in vitro autoradiography of a novel Tc-99m ligand with subnanomolar affinity to the 5-HT_2A receptor is reported. The complex combines the 4-(4-fluoro)-benzoyl piperidine portion derived from ketanserin with a neutral oxotechnetium(V) chelate in form of a mixed ligand "3+1" unit containing the SNS/S donor set. The analogous ⁹⁹Tc compound has been synthesized as a surrogate for the Tc-99m complex for use in receptor binding assays and for complete structural characterization.
In competition experiments the Tc-99 complex as well as its Re analogue display subnanomolar affinity towards the 5-HT_2A receptor (K_i 0.44 nM for Tc, 0.25 nM for Re).
In vitro autoradiographic studies clearly indicate the accumulation of the Tc-99m compound in 5-HT_2A receptor rich areas of the brain. This enrichment can be blocked by 5-HT_2A receptor antagonists such as mianserin and ketanserin and is therefore specific.

The effect of copper, phosphorus and nickel on the radiation embrittlement was investigated by using an irradiation experiment at surveillance positions in two Russian VVER-type reactors with 8 iron-base testing alloys. Their chemical composition varied between 0.015 to 0.42 % Cu, 0.002 to 0.039 % P, 0.01 to 1.98 % Ni, 0.09 to 0.37 % Si, and 0.35 to 0.49 % Mn. Charpy-V impact tests and tensile tests were performed with specimens machined from these alloys. The specimen were tested in the as-received state, in the irradiated state (fluence: 1×10 19 and 8×10 19 cm -2 [En > 0.5 MeV]) and in the post-irradiation annealed state.
Irradiation produces strong hardening and embrittlement. The effect increases with the Cu and P content. Ni causes an additional embrittlement. It does not depend on the Ni content within the range of 1.1 to 2 % Ni. The irradiation effect can be eliminated by annealing at 475 °C / 100 h but not absolutely in the case of high Cu or P content.
Small angle neutron scattering experiment at these alloys show that not only the volume fraction but also the type of the radiation defects vary in dependence on the composition of the alloys.

Dendrimer chemistry is a rapidly espanding field for both fundamental studies and applications. Their unique structural features and properties make them ideally suited for use in diagnostic imaging and therapy, transfection, and drug delivery. A short overview about some fields of application in medicine was given. It was reported the binding and transport behaviour of dendrimers having urea, azobenzene, methyl orange and diamidopyridine moieties at the periphery towards pertechnetate, and the nucleotides AMP, ADP and ATP.

Sequence analysis of the 16S rRNA genes of several reference strains and uranium mining waste pile isolates of Thiobacillus ferrooxidans revealed specific signatures which distinguish three types within the species. This allowed to develop a technique for analysis of the distribution of the T. ferrooxidans eco-types in the soil samples of a uranium mining waste pile.
The technique is based on amplification of 16S rDNA fragments in total soil DNA by the use of two T. ferrooxidans species specific primers 16S458F and 16S1473R (De Wulf-Durand et al., 1997). The resulting amplicons were then digested with a frequently cutting enzyme RsaI which produced three different type-specific profiles (Selenska-Pobell et al., 2000). Using this direct approach we have demonstrated that one of the T. ferrooxidans types (type I) was predominant in the soil samples studied and was found in more polluted sites, whereas the type II was found in less contaminated samples. The type III was found mostly to coexist with the type II.
The complexation of uranium by the three eco-types of T. ferrooxidans was investigated. The uranium sorption studies showed that the strains from the three different types possess different capability to accumulate uranium. The process of uranium accumulation is affected by the initial uranium concentration and pH. Using sodium carbonate as a desorbing agent, 97% of the biosorbed uranium was recovered from the cells of T. ferrooxidans type III, and 88.33 and 88.50% from the cells of the type I and II, respectivley. Extended x-ray absorption fine structure (EXAFS) and infrared (IR) spectroscopy were performed to obtain information about the exact chemical structure of the uranium complexes formed on the surfaces of the three eco-types of T. ferrooxidans.

Gram-positive spore-forming bacterial isolates belonging to the species Bacillus cereus, B. sphaericus and B. megaterium and also Gram-negative chemolithoautotrophic isolates of the species Thiobacillus ferrooxidans and Leptospirillum ferrooxidans were cultured from soil and sediment samples of several uranium polluted waste piles in Saxony, Germany. The interactions of these natural bacterial isolates with uranium (in particular, sorption - desorption, accumulation, reduction, and tolerance) were studied.
We have demonstrated that the natural Bacillus isolates are able to accumulate selectively and reversible a variety of toxic metals from drain waters of a uranium mining waste pile (Selenska-Pobell et al., 1999). By the use of extended X-ray absorption fine structure (EXAFS) analysis and time resolved laser fluorescence spectroscopy (TRLFS) it was demonstrated that the main chemical group involved in the interaction of the mentioned Bacillus strains with U(VI) is the phosphate group (Hennig et al., 1999; Panak et al., 2000).
Our studies on the interactions of the recently described in our laboratory three ecological types (eco-types) of T. ferrooxidans (Selenska-Pobell et al., 1999) and two eco-types of L. ferrooxidans (Tzvetkova et al., 1999) with uranium (VI) by the use of EXAFS, TRLFS, and infrared spectroscopy (IRS) indicate that the nature and the strength of the uranium complexes built by these Gram-negative acidophilic chemolithoauthotrops differ significantly from those built on the cell surfaces of the Gram-positive Bacilli. The tolerance and the interactions of the natural T. ferrooxidans isolates with U were type-specific.

The complexation of uranium by the cells of the three recently described eco-types of T. ferrooxidans (Flemming et al., 1999; Selenska-Pobell et al., 1999) was studied. The uranium sorption studies showed that the strains from the three different types possess different capability to accumulate uranium. We have found that the representatives of type II accumulate significantly higher amounts of uranium in comparison to the other T. ferrooxidans strains studied. The amount of accumulated uranium gradually increased with increasing metal concentration at pH 1.5 and 4. The uranium tolerance investigations demonstrated 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. Sodium carbonate was the most efficient desorbing agent tested, removing 97% of the uranium sorbed from the cells of T. ferrooxidans type III, and 88.33 and 88.50% from the cells of the types I and II, respectivley. Sodium citrate was the second best metal desorbing agent, whereas EDTA could remove only between 10 and 30% of the accumulated uranium. By the use of extended x-ray absorption fine structure (EXAFS) and infrared (IR) information was obtained about the exact chemical structure of the uranium complexes formed on the surface by the three eco-types of T. ferrooxidans.

The tilted axis cranking model is used in combination with the random phase approximation and particle number projection to analyze the influence of dynamical pairing correlations in the high-K bands of 178-W and their effect on relative energy and angular momentum. The calculations show the importance of dynamical pairing correlations to describe the experiment as well as advantages and problems with the different models in the superfluid and normal state regions.

A description of the fuel rod behaviour and heat transfer model used in the code DYN3D for nuclear reactor core dynamic simulations is given. Besides the solution of heat conduction equations in fuel and cladding, the model comprises detailed description of heat transfer in the gas gap by conduction, radiation and fuel-cladding contact. The gas gap behaviour is modeled in a mechanistic way taking into account transient changes of the gas gap parameters based on given conditions for the initial state. Thermal, elastic and plastic deformations of fuel and cladding are taken into account within 1D approximation. A creeping law for time-dependent estimation of plastic deformations is implemented. Metal-water reaction of the cladding material in the high temperature region is considered. The cladding - coolant heat transfer regime map covers the region from one-phase liquid convection to dispersed flow with superheated steam. Special emphasis is put on taking into account the impact of thermodynamic non-equlibrium conditions on heat transfer.

For the validation of the model, experiments on fuel rod behaviour during RIAs carried out in Russian and Japanese pulsed research reactors with shortened probes of fresh fuel rods are calculated. Comparisons between calculated and measured results are shown and discussed. It is shown, that the fuel rod behaviour is significantly influenced by plastic deformation of the cladding, post crisis heat transfer with subcooled liquid conditions and heat release from metal water reaction.

Numerical studies concerning the fuel rod behaviour under RIA conditions in power reactors are reported about. It is demonstrated, that fuel rod behaviour at high pressures and flow rates in power reactors is different from the behaviour under atmospheric pressure and stagnant flow conditions in the experiments. The mechanisms of fuel rod failure for fresh and burned fuel reported from the literature can be qualitatively reproduced by the DYN3D model. However, the model must be extended and improved for proper description of burned fuel behaviour.

The realistic simulation of the fuel rod behaviour is important not only under RIA conditions, but also for the analysis of operational transients. This has been shown in a calculation of an operational transient with power decrease after switching-off one from the two working feed water pumps in the NPP Balakovo (VVER-1000).

The reactivity of labile 3+1 mixed-ligand ^99mTc complexes of the type [^99mTcO(SES)(RS)] with SES being a tridentate dithiol ligand and glutathione or dimethylcysteamine as monodentate ligands RSH towards proteins was investigated in vitro and in vivo. It was found that the complexes undergo reversible transchelation reactions with SH group-containing components of blood such as albumin or hemoglobin. High labelling yields were obtained when 3+1 complexes with the tridentate SSS ligand were used. The biodistribution of blood proteins labelled by ligand-exchange reaction with the [^99mTcO(SSS)] or [^99mTcO(SNMeS)] core was studied and compared with the in vivo distribution of the labile 3+1 complexes containing glutathione as monodentate ligand.

He⁺ ions were implanted at 40 keV into Si <100> random direction at room temperature to fluences between 5×10¹⁵ He⁺/cm² and 3.5×10¹⁶ He⁺/cm². The samples were than contaminated with Cu in order to study the gettering of Cu atoms at the defective layer. A subsequent annealing at 800ºC was performed in order to recover the implantation damage and redistribute the Cu into the wafer. The samples were analyzed by Rutherford backscattering/channeling (RBS/C) and transmission electron microscopy (TEM) techniques. The Cu distribution was measured by secondary ion mass spectrometry (SIMS). The SIMS results show that the 5×10¹⁵ He⁺/cm² implant induces gettering at the He⁺ projected range (Rp) region, while the 8×10¹⁵ He⁺/cm² and 3.5×10¹⁶ He⁺/cm² implants have resulted in gettering at both the Rp and Rp/2 depths. The TEM micrographs show no visible defects at Rp/2 region. This corresponds to the so called Rp/2 gettering effect. It is important to note that in this study the Rp/2 related effect is observed after an implantation of a light ion at low energy.

The TEM study of titanium contained ZSM-5 zeolite before and after hydrothermal treatment was performed. The use of different TEM techniques - such as conventional TEM, HRTEM and EDX line scans provides important information about the zeolite catalyst consisting from several phases. The hydrothermal treatment of zeolite powder leads to strong changes in the morphology of the constituting particles. They are characterised by a homogeneous structure before hydrothermal treatment while the occurrence of holes after thermal treatment was observed. These changes lead to the enrichment of zeolite with titanium that enhance its catalytic activity. Some of the titanium surplus precipitates as TiO2 anatase nanoparticles within the holes.

Strong gettering of Cu atoms beyond the projected ion range RP has been found in single-crystal Si implanted with P+ and As+ ions at MeV energies. We call this phenomenon the "trans-RP effect". The formation of a separate Cu gettering band below RP, as detected by secondary ion mass spectrometry, indicates the presence of a significant amount of defects therein. These defects are not detectable by transmission electron microscopy and we suggest that they are small interstitial clusters. The amount of Cu atoms gettered beyond RP is, particularly for the P implants, much greater than that in the implanted gettering layer, indicating that the gettering ability of the defects beyond RP is higher than that of the extended defects at RP. A mechanism responsible for their formation and clustering in the trans-RP region is proposed, and an explanation is given of the differences in the results for the P and As implants.

There are two major reasons to study the effects of high dose implantation in SiC. First, the production of low-resistivity, p-type layers requires high acceptor concentrations which are far above the equilibrium solubility. It is essential to know the critical acceptor concentration for thermally stable, homogeneously doped SiC. On the other hand, there is a lack of information about the precipitation of new phases in SiC, their properties and influence on the SiC matrix. Such information is needed for the assessment whether insulating or conductive layers with device quality can be formed in SiC by ion beam synthesis. Two examples of high dose implantation in 6H-SiC are presented.

In the first example high doses of 350 keV Al+ ions were implanted in 6H-SiC single crystals at temperatures between 400oC and 800oC in order to preserve the crystallinity of the SiC matrix. The phase formation was studied by TEM, SIMS and AES. A critical Al concentration of about 10 at% was found below that the 6H-SiC structure remains stable during implantation at 500°C. The Al atoms occupy preferentially Si sites in the SiC lattice. At higher Al concentrations the SiC matrix is decomposed and precipitates of Si and Al4C3 are formed. It was found that the Al4C3 precipitates have a perfect epitaxial orientation to the SiC matrix. The phase transformation is accompanied by atomic redistribution and strong volume swelling. The observed atomic depth profiles can be accounted for by a a simple chemical reaction model. Implantation at 800°C leads to the formation of Si and Al precipitates accompanied by a dramatic volume swelling which results in surface cracking and material outflow. Post-implantation annealing above 1500°C severely deteriorate the SiC matrix by local melting of Al and Si precipitates.

In the second example the evolution of the binary system C -> SiC was studied as function of implantation temperature. 1 1018 cm-2, 60 keV carbon ions were implanted into single crystalline 6H silicon carbide (SiC) at elevated temperatures. The formation of carbon phases in the crystalline SiC lattice was investigated by cross sectional transmission electron microscopy. An amorphous, carbon rich phase was produced at 300oC. Precipitates of graphite were obtained at 600oC, whereas at 900oC small diamond grains were produced. These grains are in perfect epitaxial relation with the surrounding SiC lattice. The mechanism of the diamond formation by IBS in SiC is not quite clear. It can be assumed that the tetrahedrally coordinated SiC lattice, which is preserved during the high temperature implantation, acts as a template for the growth of diamond. In addition, local nonequilibrium conditions in the ion cascades (thermal spikes, shock waves) or temporary stress on interstitially incorporated carbon atoms by the surrounding SiC lattice could contribute to the diamond nucleation.

Results of a joint German/Russian irradiation programme performed on the prototype pressurized water reactor VVER-2 of the Rheinsberg nuclear power plant Germany) are summarized. The experiment comprises Charpy V-notch (CVN), precracked Charpy size (SENB) and compact tension (CT) specimens made of different heats of Russian VVER type reactor pressure vessel (RPV) base and weld metals. Reference temperatures, T0, were evaluated according to the Master Curve (MC) concept using the
multi temperature method. Neutron irradiation induced ductile-to-brittle transition temper ature (DBTT) shifts determined on the basis of CVN and SENB tests are compared. On the base of the DBTT the neutron embrittlement sensitivity and the annealing behaviour of tested RPV steels are evaluated. Different heats of the same VVER-RPV steel exhibit different neutron induced embrittlement and annealing behaviour. The determined CVN transition temperatures correlates to the T0 temperatures evaluated by the MC concept.

The sequence of phase transitions during the hot history of the universe is followed within a phenomenological framework.
Particular emphasis is put on the QCD confinement transition, which is at reach under earth laboratory conditions.
A tepid inflationary scenario on the GUT scale with bubble grow at moderate supercooling is discussed.

The overall process of uptake of heavy elements (actinides) into plant tissues from contaminated soils has been quantified using the soil-to-plant transfer factor (TF). Considering the radionuclide transfer, it is quantified as TF(RN) = plant specific activity (Bq/kg-1) /soil specific activity (Bq/kg-1). In practice the predominant pathway of plant contamination is direct contamination by deposition and resuspension. The comparable uptake via soil-plant transfer is about 10%. But this ratio strongly depends on the real accident scenario (distribution of contaminants via aerosol in air, as soluble or colloidal species in aquifer or surface water).Up to now, the chemistry of the various actinides has not been considered along the pathway soil-plant-animal-humans. The transfer factor has to be unfolded into the basic parameters like changes in oxidation state and complexation, differences in bonding of the elements like adsorption and ion exchange processes, formation of colloids e.g.
It was our goal to obtain first results on the change of uranium speciation during the soil-to-plant transfer. X- ray absorption spectroscopy (XAS) with synchrotron radiation and the time-resolved laser-induced fluorescence spectroscopy (TRLFS) were used as tools for the determination of uranium speciation in soil, water, and different parts of the plants. The reported investigations about the distribution and speciation of uranium were focused on lupins.

Radionuklidkontaminationen können über den Belastungspfad Boden-Pflanze-Nahrungkette deutlich zur Strahlenbelastung des Menschen beitragen. Die Bestimmung des Transfers von Radionukliden aus kontaminierten Böden ist daher für Risikoabschätzungen unbedingt erforderlich. Bisher stand die Bestimmung von Transferfaktoren im Mittelpunkt der Untersuchungen. Um zuverlässigere Abschätzungen über eine Radionuklidmigration im System Boden-Pflanze machen zu können, ist die Charakterisierung des chemischen Zustands der einzelnen Radionuklide notwendig. Bislang ist eine direkte Bestimmung der chemischen Speziation von Uran und anderen Actiniden in Pflanzen aus der Literatur nicht bekannt. Für die Bestimmung der chemischen Speziation von Uran in Pflanzen wurden insbesondere die Lupine und der Löwenzahn auf natürlich und künstlich mit Uran kontaminierten Böden und als Hydrokulturen in uranhaltiger Lösung gezüchtet. Frische und trockene Pflanzenproben wurden vorrangig mit Hilfe der zeitaufgelösten Laserfluoreszenzspektroskopie und der Röntgenabsorptionsspektroskopie als äußerst leistungsstarke und empfindliche Speziationsmethoden untersucht. Über die bisherigen Ergebnisse soll hier berichtet werden

The paper presents a method for the prediction of the radial gas profile in vertical pipe flow for a given bubble size distribution. The method assumes equilibrium of the forces acting on a bubble perpendicular to the flow direction. On basis of the radial profile of the liquid velocity, radial distributions of the volume fraction are calculated separately for all bubble classes according to a given bubble size distribution. The sum of these distributions is the radial profile of the gas fraction. 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.

The hydrate is the simplest chemical form of plutonium in aqueous solution. The knowledge of the structural parameters of the hydration sphere is important for the interpretation of EXAFS results on complicated aqueous plutonium complexes where the water molecules are partly or fully replaced by other ligands. Plutonium(VI) hydrate was prepared by dissolution of PuO2 (Pu-242, AEA Technology, QSA GmbH) and electrochemical oxidation. Part of this solution was reduced to Pu(III) in an electrochemical cell. The Pu(III) and Pu(VI) hydrates were in perchloric and nitric media (1 M acidic solution), respectively. The final Pu concentration was 50 mol/L. The Pu oxidation states were confirmed by UV/Vis spectroscopy. For the measurements 4.7 mL of solution (7.5 MBq)
was filled and sealed in polyethylene cuvettes. The samples were measured at the Rossendorf Beamline ROBL at the European Synchrotron Radiation Facility (ESRF), Grenoble, France within 48 hours after their preparation.

Multiple scans of the Pu LIII-edge EXAFS were collected in transmission mode at room temperature using the Si(111) double-crystal monochromator in fixed-exit mode /1/. The energy scale was calibrated using the first inflection point of the absorption spectrum of a Zr foil (17998 eV). The scattering phases and amplitudes where calculated for hypothetical clusters of PuO8, and PuO2O5 using FEFF6.

Results
As one can see from the XANES spectra given in Fig. 1, the LIII absorption edge of Pu(VI) is shifted by 4 eV toward higher energy as compared to that of Pu(III). The energy shift and the distinct XANES features of these two Pu hydrates can be used for the determination of the Pu oxidation states /2/.

The different electronic and molecular structures of Pu(III) and Pu(VI) hydrates are also reflected in the EXAFS shown in Fig. 2. The coordination sphere of Pu(III) hydrate can be written as Pu(H2O)83+ with an average Pu-O bond distance of 2.48 Å. The Fourier transform corresponding to the EXAFS of Pu(VI) hydrate shows two coordination shells. The Pu(VI) forms a plutonyl ion PuO2(H2O)4-52+. The axial and equatorial Pu-O bond distances are 1.74 and 2.42 Å, respectively. The structural parameters of Pu(VI) hydrate are nearly identical to those of U(VI) and Np(VI) hydrates (see Tab. 1), which were measured recently at ROBL /3/.

Fig. 2: Raw Pu LIII-edge k3-weighted EXAFS spectra (left) and corresponding Fourier transforms (right) of 50 mMol/L Pu hydrates. Solid line - theoretical fit; dots - experiment.

Tab. 1: EXAFS structural parameters for 50 mMol/L Pu hydrates and comparison with 50 mMol/L Np(VI) and U(VI) hydrates.
Sample Shell R(Å) N s2 a)
Pu(III) Pu-O 2.48 7.6(2) 1.02
Pu(VI) Pu -Oax 1.74 1.9 0.12
Pu -Oeq 2.42 4.4(2) 0.50
Np(VI) Np-Oax 1.75 2.0 0.15
Np-Oeq 2.42 4.6(2) 0.56
U(VI) U-Oax 1.76 1.9 0.12
U-Oeq 2.41 4.9(2) 0.61
a) s2 in units of 10-2 Å2

Two principal methods of neutron spectrum adjustment have been compared. Their advantages and problems were discussed. Thereby, the possible use of spectrum adjustment at the LR-0 facility Rez was considered. Recent improvements of the Rossendorf adjustment procedure COSA3 were described. A wider use of spectrum adjustment has been justified by its close relation to uncertainty analysis always required in serious investigations.

The dependence of ion flux, ion energy distribution, and neutral density of a planar radio frequency (RF) driven inductively coupled plasma source on pressure and power is analyzed using an energy selective mass spectrometer and a retarding field analyzer. The ion flux is about 7 mA/cm^2 at 5 Pa and 300 W and increases as RF power and argon pressure increase. The ion energy distribution consists of a single peak with a full width at half maximum of 3 eV for a discharge power in the range from 50 to 300 W and for a pressure in the range from 0.5 to 5 Pa. This indicates that inductive coupling mainly drives the discharge while capacitive coupling between coil and plasma is weak. A significant decrease in Ar neutral density is observed when the plasma is ignited. The Ar depletion increases with increasing RF power and increasing Ar base pressure and reaches 30 % at 5 Pa and 300 W. The decrease in neutral density cannot be explained by the ionization of Ar atoms only but is also attributed to heating of Ar atoms by collisions with energetic particles. A simple model is proposed to understand and to estimate the effect of these collisions on the neutral temperature.

The dependence of the iron nitride formation and the phase transformations in the nitrogen implanted layer on the thickness of the implanted material is investigated by Conversion Electron Mössbauer Spectroscopy (CEMS). Phase transformations in nitrogen-implanted iron layers of various thickness ranging from 60 nm to 870 nm deposited on SiO2 substrate by rf sputtering technique have been studied. Such prepared samples were implanted at room temperature with nitrogen ions with the energy of 50 keV with ion doses ranging from 1x1017 at. N/cm2 to 5x1017 at. N/cm2. After each implantation step the samples were characterized by CEMS using the gas flow electron counter with He-6%CH4 gas. The implanted samples were also investigated by the Grazing Angle X-ray Diffraction (GXRD). The results revealed that the nitride formation is strongly enhanced in thin films as compared to thicker layers or bulk iron samples. In thin iron films a given nitride phases (‘/”, -Fe3N, -Fe2N) are formed at lower nitrogen doses and the transformation of the original iron layer into iron nitrides is more complete than in the bulk -Fe. In bulk iron samples about 20 % of Fe atoms remain in the -Fe phase even for the highest implantation doses (5x1017 at. N/cm2) whereas the complete transformation of thin 60 - 230 nm iron layer into Fe nitrides has been observed.
The observed effects are not fully understood yet. The GXRD experiments performed for the same samples revealed that the stress in the interfacial region of Fe layer and the substrate is significantly larger than in the top (free) surface of the layer. The higher stress may favor the formation of iron nitrides. On the other hand the presence of the interface between Fe film and the substrate may block the in-bulk diffusion of N atoms leading to the higher nitrogen concentration in thin films as compared to the bulk.
The strong dependence of the nitride formation due to N-implantation on the thickness of the implanted material is important for implantation metallurgy, especially for implantation of thin coatings often used for the extension of lifetime of precise tools and details. The phase transformations in thin films may occur in significantly different way as compared to the bulk materials leading to the formation of new phases characterized by extremely high impurity concentration.

Considering the hypothetical core melt down scenario for a Light Water Reactor the behaviour of the Reactor Pressure Vessel during the late phase of the accident has to be investigated. The FOREVER-experiments, currently underway, are simulating the lower head under the load of a melt pool with internal heat sources. Due to the multi-axial creep deformation of the vessel with a non-uniform temperature field these experiments are an excellent possibility to validate numerical creep models. Therefore a Finite Element model is developed on the basis of a commercial multi-purpose code. Using the CFD module the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are performed using a new numerical approach which avoids the use of a single creep law with constants evaluated for a limited stress and temperature range. Instead of this a three-dimensional array is developed where the creep strain rate is evaluated according to the actual total strain, temperature and equivalent stress. Performing post-test calculations it was found that the assessment of the experimental data and of the numerical results has to be done very carefully. Considering the experiment FOREVER-C2, for example, the recorded creep process appears to be tertiary, if a constant temperature field is assumed. But slight temperature changes during the creep deformation stage could explain the observed creep behaviour, too. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.

In dem Vortrag werden Ergebnisse von Bestrahlungsexperimenten vorgestellt, die im Druckwasserreaktor WWER-2 des KKW Rheinsberg durchgeführt worden sind. Im WWER-2 wurden ISO-V und Bruchmechanikproben aus unterschiedlichen Chargen
von WWER-Grundwerkstoff und Schweißgut bestrahlt. Der Schwerpunkt liegt auf Ergebnissen eines Bestrahlungsprogrammes (WTZBRh), das im Rahmen der wissenschaftlich-technischen Zusammenarbeit zwischen Deutschland und Russland mit den Zielstellungen:der Untersuchung des Einflusses von Begleit- (P, Cu) und Legierungselementen (Ni) auf die bestrahlungsinduzierte Versprödung, der Bewertung der Gültigkeit der Vorhersageformeln des russischen Regelwerkes und der Untersuchung des Ausheilverhaltens durchgeführt worden ist. Die Prüfung der Proben des WTZBRh erfolgte im Rahmen von Förderprojekten des BMBF/BMWi durch das Forschungszentrum Jülich GmbH, die Staatliche Materialprüfungsanstalt Universität Stuttgart und das Forschungszentrum Rossendorf e.V.
Das Bestrahlungs- und Ausheilverhalten der WWER-RDB-Stähle wird auf der Basis der im ISO-V- und Bruchmechaniktests ermittelten Parameter bewertet. Als bruchmechanische Parameter wurden im unteren Spröd-Duktil Übergangsbereich
Referenztemperaturen T0 nach dem Master-Curve Konzept und im duktilen Bereich Risswiderstandskurven und Risseinleitungszähigkeiten ermittelt.

Der beschriebene Gittersensor wurde für eine schnelle Visualisierung von transienten Gasgehaltsverteilungen in einer Zweiphasenströmung entwickelt. Er basiert auf der Messung der momentanen örtlichen elektrischen Leitfähigkeit des Zweiphasengemischs. Der Sensor besteht aus zwei dicht hintereinander angeordneten Elektrodengittern mit jeweils 16 Elektroden. Die Messung erfolgt an den Kreuzungspunkten der Elektroden, d.h. an 16 x 16 Messpunkten, die gleichmäßig über die Querschnittsfläche des Strömungskanals verteilt sind. Die Zeitauflösung des Gerätes beträgt 1024 Messungen in der Sekunde.

Zur Bewertung des Energieertrages einer PV-Anlage ist das Performance Ratio der entscheidende Parameter. Die Einführung des Generatorfaktors als Verhältnis der Generator-Nennleistung und der nominalen Generatorleistung ermöglicht eine einfache Interpretation des Performance Ratio und zugleich die einfache Bestimmung der Generator-Nennleistung aus gemessenen PR-Werten.

Considering the hypothetical accident scenario of a core melt down for a Light Water Reactor the behaviour of the Reactor Pressure Vessel has to be investigated. Therefore the FOREVER-experiments (Failure Of Reactor VEssel Retention) are currently underway. These experiments are simulating the lower head of a reactor pressure vessel under the load of a melt pool with internal heat sources. The geometrical scale of the experiments is 1:10 compared to a common Light Water Reactor.
Due to the multiaxial creep deformation of the three-dimensional vessel with a non-uniform temperature field these experiments are an excellent possibility to validate numerical creep models which are developed on the basis of uniaxial creep tests.
Therefore a Finite Element model is developed on the basis of the comercial multi-purpose code ANSYS/Multiphysics®. Using the
Computational Fluid Dynamic module the temperature field within the vessel wall is evaluated. The transient structural mechanical
calculations are performed applying a creep model which is able to take into account great temperature, stress and strain variations within the model domain. The new numerical approach avoids the use of a single creep law with constants evaluated for a limited stress and temperature range. Instead of this a discrete creep data base is developed where pairs of strain and strain rate are stored for each temperature-stress combination. The creep strain increment is evaluated by linear or non-linear interpolation. Performing calculations for the FOREVER experiments gives a good opportunity to improve the simulation and understanding of real accident scenarios.

The effect of different alcohols on gas hold-up and bubble size in a semi-batch bub-ble column has been investigated. Even little amounts of alcohols added to the liquid preserve the homogeneous bubble flow up to higher gas velocities and gas hold-ups (up to 50 %). For a detailed description it is necessary to divide the flow into two flow regimes - bubble flow and foam. This work presents results from comparative meas-urements with three different methods: needle probes, gamma-densitometry and high speed video observation. The obtained information was used to check the qual-ity of existing foam models. It was found that the vertical gas hold-up profiles in wet unstable alcoholic foams deviate from the theoretical predictions closely above the bubble flow region and again at the top of the foam layer. The first is caused by the effect of inertia hindering the drainage additionally to the viscosity effects, the sec-ond is a consequence of the progressing coalescence. There is a need to improve the existing models for the application in wet unstable foams.

The synthesis is described of uniformly 14C-labelled PCB-congeners starting with [14C]benzene (1) via [14C]nitrobenzene (2), [14C]hydrazobenzene (3), [14C]benzidine dihydrochloride (4), N,N'-diacetyl-[14C]benzidine (5), 3,3'-dichloro-N,N'-diacetyl-[14C]benzidine (6), and 3,3'-dichloro-[14C]benzidine dihydrochloride (7). Elimination of the amino groups from 7 leads to [14C]PCB No. 11 (8), and their substitution by chlorine alternatively to [14C]PCB No.77 (9) /1/. Yields obtained for 8 and 9 are 20 % and 30 %, respectively. The specific activity of the products was 1.2 GBq/mmol. This approach, avoiding the isolation of free [14C]benzidine, may allow the synthesis of PCBs with higher specific activity. The described methods are also applicable to 13C-labelling. From the results of capillary GC-MS analysis /2/ of the unrefined PCBs, conclusions may be drawn about the course of chlorinating the 5: 87 % in 3,3'-position, 6 % in 3,3',5-position, 5 % in 3-position and only 2 % in 2,3'-position.
Because only negligible amounts of position isomers are produced by this method of preparation, the reaction products can be purified much easier with HPLC-techniques than the products obtained from other syntheses.

FZR-Report

The presented wire-mesh sensor produces sequences of instantaneous gas fraction distributions in a cross section with a time resolution of 1200 frames per second and a spatial resolution of about 2-3 mm. At moderate flow velocities (up to 1-2 m/s), bubble size distributions can be obtained, since each individual bubble is mapped in several successive distributions. The method was used to study the evolution of the bubble size distribution in a vertical two-phase flow. In order to assess the accuracy of the described method, a transparent flow channel with an integrated wire-mesh sensor was built. The interaction of gas bubbles with the electrode wires was visually observed. A high-speed video camera was used to record the contact of bubbles with the sensor. The video sequences are compared with the synchronously recorded sensor data. Conclusions are drawn concerning the distortion of the flow by the sensor and the accuracy of the measured gas fractions and bubble size distributions.

Crystal-GRID is a new and complementary method for studying interatomic solid state potentials in the energy range 1 eV to 1 keV. Due to a neutron capture induced photon emission an atom of the crystal starts moving with an energy of some hundreds of eV. Information on the movement of this nuclear probe can be read out by measuring the Doppler shift of a second in-flight emitted photon. The amount of information depends strongly on the nuclear level lifetime in between the two photon emissions and on the interatomic interaction. Systematic theoretical investigations will be presented showing under which requirements, e.g. for count rates or lifetimes, interatomic potentials can be investigated. Experimental results for ZnS and TiO2 will be presented. In these cases it was possible to simultaneously extract the nuclear level lifetime and the screening length of the screened Coulomb potential.

Durch das Forschungszentrum Rossendorf wurde in den Jahren 1996-1998 ein eigenes Strahlrohr fuer Experimente mit Synchrotronstrahlung an der ESRF (European Synchrotron Radioation Facility) in Grenoble/Frankreich aufgebaut. Das Strahlrohr verfuegt ueber zwei alternativ nutzbare Messplaetze fuer die Untersuchung von radioaktiven Proben mittels Roentgenabsorptionsspektroskopie und fuer Materialstrukturuntersuchungen mit Roentgendiffraktion.
Der Bericht konzentriert sich auf die Arbeiten, die fuer die Steuerung der Optik und die Nutzung der Messplaetze hinsichtlich der Elektronik, Rechentechnik und Software erforderlich waren. Nach einer Beschreibung der Randbedingungen und einer Kurzcharakteristik der geraetetechnischen Basis werden wichtige Hardwarekomponenten fuer die Instrumentierung der Systeme vorgestellt. Die rechentechnische Basis wird anschliessend beschrieben. Die angewendeten Software-Grundprinzipien werden erlaeutert und diskutiert sowie an einigen Applikationen beispielhaft verdeutlicht. Abschliessend werden spezifische Probleme bei der Programmierung von Applikationen mit grafischer Bedienoberflaeche in Verbindung mit Geraetezugriffen behandelt. Tabellen, in denen die benutzten Hardware-Module und die Softwarekomponenten zusammengestellt sind, ermoeglichen einen Ueberblick ueber das Gesamtsystem. Das Literaturverzeichnis dient als Leitfaden fuer die Detaildokumentationen.

Irradiation effects on iron disilicide layers were induced by 3.5 keV argon ion bombardment and studied by XPS, AES and the Mössbauer spectroscopy. The use of these electron spectroscopies enables the investigation of different regions of the altered layer.

The study of the interaction processes between humic acids (HAs) and actinide ions is important for a reliable long-term risk assessment with regard to the behavior of actinides in the environment. However, due to the heterogeneous nature of HAs the description of their complex formation with metal ions is difficult and not completely understood up to now.
To further improve the understanding of the HA-metal ion-interaction we studied the influence of phenolic OH groups on the complexation behavior of HAs with uranium(VI) using chemically modified HAs with blocked phenolic OH groups (synthetic HA type M1 and natural HAs Aldrich and Kranichsee). These modified HAs were synthesized by permethylation of the original HAs with diazomethane, and subsequent alkaline saponification of the permethylated HAs. The modified and unmodified HAs were characterized regarding their functional group content. Extensive comparative 13C-CP/MAS-NMR measurements were performed to verify the modification process and to detect whether or not significant structural changes of the HAs had occurred during their modification. The complexation behavior of the modified HAs with UO22+ at pH 4 was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and compared with the results of the UO22+ complexation of the original, unmodified HAs.
The NMR spectra of chemically modified 13C-labeled synthetic HAs type M1 as well as of the modified HAs with carbon-13 at natural abundance level have shown that the permethylation of the HAs with diazomethane and the subsequent alkaline saponification causes the intended structural changes on carboxyl and acidic OH groups. No significant structural changes of the HAs occur during modification.
For all HAs we determined comparable complexation constants by TRLFS. However, significant lower loading capacities with UO22+ were determined for the modified HAs type M1 and Aldrich (10.5 ± 0.9 % and 9.7 ± 1.6 %, respectively) than for the corresponding original, unmodified HAs (18.0 ± 2.0 % and 17.5 ± 1.6 %, respectively). That indicates a lower amount of maximal available complexing sites of the modified HAs compared to the unmodified HAs. Hence, it can be concluded that the modification of phenolic OH groups changes the complexation behavior of HAs with UO22+. Already at pH 4, phenolic OH groups contribute to the interaction between HA and UO22+ ions.

In spite of the fact that a great deal of research has been carried out on liquid metal ion sources, surprisingly few results exist on the temperature dependence of their electric characteristics. In this article we study two liquid metal alloy ion sources (LMAISs), namely Co36Nd64 and Au77Ge14 Si9. While the results of the former alloy were as expected, the latter displayed an entirely different dependence of its electric characteristics on temperature. The unusual results of the Au77Ge14Si9 LMAIS are explained in terms of the abnormal behaviour of its surface tension coefficient with temperature.

We studied the sorption of uranium and humic acid onto phyllite and ferrihydrite both by steady-state experiments in the pH range 3.5 to 9.5 and by kinetic experiments at pH 6.5. Furthermore, the sorption of uranium onto ferrihydrite in the presence of humic acid was studied by extended X-ray absorption fine structure (EXAFS).
Phyllite was used as site-specific rock material because it is closely associated with uranium deposits of the former uranium mining areas in East Germany. Ferrihydrite is known to be formed as secondary mineral phase due to weathering of phyllite. Its sorption behavior was therefore studied and compared to that of phyllite. As humic acid, we applied both a natural humic acid (Kranichsee HA) and a 14C-labeled synthetic humic acid (14C-M1).
The steady-state experiments have shown that humic acid is strongly taken up by both solids over the entire pH range. The uranium sorption is affected both by the pH and by the presence of organic material.
The kinetic experiments have shown that sorption of uranium and humic acid onto phyllite and ferrihydrite is rapid. The initial uranium sorption rates depend on the sequence of addition of uranium and humic acid. For ferrihydrite the initial uranium sorption rate decreases with increasing amounts of uranyl humate complexes in solution. For phyllite the dependence of the uranium sorption rate on the sequence of addition of uranium and humic acid does not exhibit a clear pattern which is attributed to the complex nature of the phyllite rock. The results have shown that the amount of uranium sorbed on solids in equilibrium is determined by the total number of surface sites and by their affinity and accessibility to solutes.
The results of the steady-state and the kinetic experiments show that the sorption behavior of phyllite for uranium and humic acid is dominated by small amounts of ferrihydrite. We conclude that the uranium mobility in an environment with phyllite as a major constituent is controlled by its sorption onto amorphous iron minerals.

A 4 PI silicon ball for detection and identification of light charged particles in large multidetector -arrays as
EUROBALL is presented. The design is based on a N=42 ball with 12 pentagons and 30 hexagons as used in the
GASP array. The absorptive material for -rays is minimized to the detector thickness of 300 or 500µm and a
0.63 mm ceramic backing. The geometrical coverage is designed for about 90% of 4. A pulse shape
discrimination method with totally depleted detectors working in the reverse mount allows identifying protons
and -particles above an energy threshold of about 2MeV. The performances of the ball were tested at the
tandem - booster accelerator combination of the MPI Heidelberg in two experiments using the high-recoil
reaction of 228MeV 58Ni+46Ti and the low-recoil reaction of 95MeV 16O+58Ni. The two-dimensional spectra of
zero-crossing (ZC) versus energy confirmed an excellent discrimination of protons and -particles in all the
detectors at different angles. The energy spectra of protons and -particles measured in the experiments are
presented, too. The -spectra measured in coincidence with various combinations of emitted particles showed a
high selectivity of the ball. The reduced total efficiency for protons of 59% and 55% and -particles of 44% and
32% measured in a nuclear spectroscopy application is analyzed in a Monte-Carlo simulation (GEANT). It is
due to a combined influence of a thick target needed to stop the recoiling residual nuclei and thick absorbers
needed to protect the Si-detectors from scattered beam. The results along with the GEANT extrapolation to
optimum experimental conditions confirm that RoSiB is a highly efficient and selective device for identification
of rare reaction channels with heavy ions.

Im Rahmen einer umfassenden Untersuchung zur inhärenten Borverdünnung nach kleinen Primärkühlmittelsystemlecks für die Anlage Mülheim-Kärlich wurde als konservatives Störfallszenario mit dem größten Kondensatanfall das 20 cm2-Leck in der kalten Hauptkühlmittelleitung hinter der Hauptkühlmittelpumpe ermittelt. Der Borverdünnungsprozeß und die Verlagerung des deborierten Kondensatvolumens zum Kern durch Naturumlauf wurde in thermohydraulischen Systemanalysen detailliert berechnet. Die Mischung des Kondensats nach dem Eindringen in den Reaktordruckbehälter mit der Hochdruckeinspeisung wurde durch Experimente an einer skalierten Versuchsanlage ermittelt. Die Ergebnisse dieser Versuche wurden für eine 3-dimensionale neutronenkinetische dynamische Kernanalyse benutzt. Diese Analyse zeigte, daß der Kern bei dem konservativen Störfallszenario wieder kritisch wird und kurzzeitig Leistung erzeugt, aber eine sehr große Marge zu einzuhaltenden Schutzziel besteht. Weder die Integrität der Brennstofftabletten noch die Integrität der Hüllrohre ist zu irgendeinem Zeitpunkt gefährdet, wie eine abschließende Heißkanalanalyse zeigt, die ein minimales DNB-Verhältnis von 1,53 ausweist.

An overview of the beamline design is given. The basic experimental equipment of the materials research hutch (MRH), i.e. the special six-circle diffractometer for heavy duty, a beam-deflector for investigations of liquids with free surfaces, special sample environments (high-temperature chambers) and the various detector systems (scintillator, photo-diode, 2-dim. CCD camera) will be described.

As represantative results so far obtained at ROBL-MRH the following scientific topics of the Institute of Ion Beam Physics and Materials Research of the Forschungszentrum Rossendorf are presented in more detail:

 Stress relaxation and precipitation of SiC in Si implanted with C;
 X-ray reflectivity and diffuse scattering on Co/Cu-multilayers near the absorption edges;
 Phase transformations studied in-situ during annealing of Ti4Al6V implanted with nitrogen.

Ziel:

Bei der Präzisionstherapie von Schädelbasis-Tumoren mit Strahlen beschleunigter Kohlenstoffionen wird bei jeder Therapiefraktion eine Kontrolle der Dosisdeposition unter Ausnutzung der bei der Bestrahlung erzeugten Positronenemitter vorgenommen.
Methodik:
Durch nukleare Fragmentierungsreaktionen zwischen einem Teil der stabilen ¹²C-Ionen des Therapiestrahles und Atomen des Körpergewebes wird eine charakteristische räumliche und zeitliche Positronenemitterverteilung im Körper des Patienten erzeugt. Eine aus zwei Detektorköpfen bestehende Positronenkamera, die direkt am Bestrahlungsplatz installiert wurde, detektiert während und wenige Minuten nach der etwa zehnnminütigen Bestrahlung eines Feldes mit einer Dosis von ungefähr 0,5 Gray einige zehntausend Koinzidenzereignsse. Da die Verteilungen von Dosis und vom stabilen Strahl erzeugter Aktivität voneinander abweichen, ist eine Berechnung der erwarteten Aktivitätsverteilung für den Vergleich mit der Messung erforderlich. Wegen der sehr geringen Zahl von Ereignissen und des im eingeschränkten Winkelbereich arbeitenden Tomographen erfolgt die Bildrekonstruktion iterativ nach der Maximum-Likelihood-Methode.
Ergebnisse:
Beim deutschen Schwerionentherapie-Pilotprojekt wurden bisher ca. 50 Patienten bei der Gesellschaft für Schwerionenforschung Darmstadt behandelt. Dabei erwies sich die in-situ Kontrolle mittels PET als ein wertvolles Werkzeug für die Verifikation der Bestrahlungspläne. Darüber hinaus wurden Beiträge zu einer Verbesserung der Kalibrierung zwischen CT-Hounsfield-Einheiten und dem Schwerionen-Bremsvermögen geliefert, die Grundlage für die Bestrahlungsplanung ist.
Schlussfolgerungen:
Um dem Anspruch nach höchstmöglicher Präzision bei der Schwerionentherapie gerecht zu werden, ist ein in-situ Monitoring jeder einzelnen Therapiefraktion mit PET unverzichtbar. Bei der gegenwärtigen Planung der klinischen Einrichtung zur Krebsbehandlung mit Ionenstrahlen wird der PET zur Therapiekontrolle ein wichtiger Stellenwert zugemessen.

The condensation in horizontal tubes plays an important role e.g. for the determination of the operation mode of horizontal steam generators of VVER reactors or passive safety systems for the next generation of nuclear power plants. Two different approaches (HOTKON and KONWAR) for modeling this process have been undertaken by Forschungszentrum Jülich (FZJ) and University for Applied Sciences Zittau/Görlitz (HTWS) and implemented into the 1D-thermohydraulic code ATHLET, which is developed by the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH for the analysis of anticipated and abnormal transients in light water reactors.
Although the improvements of the condensation models are developed for different applications (VVER steam generators - emergency condenser of the SWR1000) with strongly different operation conditions (e.g. the temperature difference over the tube wall in HORUS is up to 30 K and in NOKO up to 250 K, the heat flux density in HORUS is up to 40 kW/m² and in NOKO up to 1 GW/m²) both models are now compared and assessed by Forschungszentrum Rossendorf FZR e.V. Therefore post test calculations of four selected HORUS experiments were performed with ATHLET/KONWAR. It can be seen that the calculations with the extension KONWAR as well as HOTKON improve significantly the agreement between computational and experimental data.

Einleitung:
Bei Patienten mit onkologischer Fragestellung wurde die Abhängigkeit der Bildqualität von Rekonstruktionsparametern und Filtereinstellungen bei der iterativen Bildrekonstruktion (OSEM) und gefilterten Rückprojektion (FBP) an der PET-Kamera ECAT EXACT HR+ und der Software ECAT V7.1 (CTI/Siemens) untersucht. Für Patienten mit unterschiedlichem Körpergewicht bestimmten wir den Einfluß der Glättung durch verschiedene Gaußfilterbreiten auf die visuelle Bildqualität.

Durchführung:
Ausgehend von der Standardkonfiguration für die Einstellung der Rekonstruktions- und Filterparameter wurden bei einem Patienten mit 18F-FDG speichernden kleinen Metastasen die Anzahl der Iterationen und Subsets variiert. Bei der FBP wurde der Einfluß der Cut-Off-Frequenzen des HANNING-Filter untersucht. Die Wirkung der Gaußfilterbreite (Ganzkörper-Protokoll) auf die visuelle Bildqualität wurde bei einem Patienten mit abgegrenzter Metastase, bei Ganzkörperaufnahmen und bei Patienten mit unterschiedlichen Körpergewichten untersucht.

Ergebnisse:
Standardmäßig erfolgt die Rekonstruktion (OSEM) bei einer Iteration und 24 Subsets. Eine Erhöhung der Anzahl von Iterationen bei einer Verringerung der Subsetzahl brachte keine Verbesserung der Bildqualität (Untergrundrauschen, Detailerkennbarkeit), nur ein Verlängerung der Rechenzeit. Eine Variation der Subsetzahl bei einer Iteration zeigte ein Optimum bei 1:24. Die optimale Breite des Gaussfilters bei der abgegrenzten Metastase und bei Patienten mit 50 kg Körpergewicht lag etwa bei 5mm, bei 60-70 kg etwa 7mm, bei 130 kg 9 mm. Die mit veränderten Cut-Off-Frequenzen FBP rekonstruierten Bilder zeigten bei Frequenzen unter 0,3 eine verminderte Detailerkennbarkeit.

Schlussfolgerung:
Eine gute Darstellung wird bereits bei einer Iteration mit 24 Subsets erreicht. Die Gaußfilterbreite sollte in Abhängigkeit vom Patientengewicht und Umfang zwischen 4 und 9 mm eingestellt werden. Die Optimierung der Rekonstruktionsparameter reduziert den Arbeitsaufwand bei bestmöglichster Bildqualität.

Die Kerntechnische Gesellschaft hat die Notwendigkeit zu grundlegenden Reformen erkannt. In der Strategiediskussion "KTG nach 2000" sind hierzu wichtige Ziele sowie die zu Ihrer Umsetzung notwendigen Maßnahmen formuliert. In dem Strategiepapier fehlt jedoch eine klare Konzeption für die organisatorische Umsetzung. Der Vorstand der KTG unterschätzt bzw. verkennt hierbei die Möglichkeiten und Potentiale des Internets. Dies wiegt umso schwerer, da sich in den letzten Jahren der Umgang der Gesellschaft bei der Wahrnehmung und Verarbeitung von Informationen dramatisch verändert hat. Um auch zukünftig in der Gesellschaft präsent und anerkannt zu sein, nach innen sowie außen wirken zu können und speziell Interessenten und Nachwuchs für die KTG anzusprechen und zu gewinnen, ist eine angemessene Internetpräsenz überlebensnotwendig.
Das Internet könnte bereits jetzt Briefe, Rundschreiben, Aushänge, Ankündigungen in der atw und Telephonate gänzlich ersetzen. Auch heute würde ein Verzicht auf diese Kommunikationsmittel die Arbeit der FG bzw. OS nur minimal beeinträchtigen. Denn die Erfahrung zeigt, das engagierte KTG-Mitglieder von sich aus den Kontakt zur FG bzw. OS suchen und pflegen.
Erste Experimente mit Webseiten einzelner Fachgruppen - wie z. B. am Forschungszentrum Rossendorf - zeigen eine äußerst positive Resonanz. Die Seiten werden von den Mitgliedern angenommen und finden selbst bei Nicht-KTG-Mitgliedern eine Resonanz. Die KTG im Internet sollte wesentlich mehr sein als eine nette bunte Webseite, der man Hinweise zu Tagungen und Veranstaltungen entnehmen bzw. über die man mit der Geschäftsstelle, den Vorständen oder Ausschüssen kommunizieren kann. Durch den Aufbau eines effektiven Intranets ließen sich viele der in dem Strategiepapier angesprochenen Maßnahmen umsetzen und Ressourcen einsparen. Zahlreiche Anregungen und Beispiele hierzu finden sich in dem vorliegenden Beitrag. Auch für die KTG gilt derzeit leider noch der aus der Werbung bekannte Satz "Wir haben ja schon immer gewußt, daß wir das Internet brauchen, nur nicht wie dringend".

Due to their excellent mechanical and thermal properties C-based materials are used in High Temperature (HTR) and Fusion Reactor concepts for basic components: Fuel elements and reflectors of HTRs are made from graphite and in Fusion Reactors parts of the plasma facing components within the vacuum vessel consist of C-based materials. Because of their limited oxidation resistance at high temperatures accidents, leading to contact of oxidising gases (air or steam) with these carbon components, have to be considered in safety analyses. In addition, strength loss of carbon materials due to oxidation by impurities in cooling gas is an important aspect for HTR normal operation; accordingly, selection of carbon materials has to take into account their oxidation resistance.
This paper gives an overview on theoretical work and measurements in Jülich concerning oxidation kinetics of selected innovative C-based materials (graphite, CFC) with and without doping in oxygen (523 - 1223 K) and steam (1100 - 1523 K). Also data and theoretical models on depth of penetration of the oxidation process are presented. Data on oxidation induced release of hydrogen isotopes from redeposited a-C:H layers on first walls in fusion reactors are outlined, too.
Futheron, fields of insufficient knowledge are identified: These include data for an improved oxidation model considering both in-pore diffusion and chemical reaction and data/models on catalytic oxidation. Also, a lack of data on the Boudouard reaction, which has to be considered in course of air ingress accidents, was identified.

Studies of the turbulent dispersion of a radiotracer in an experimental setup with natural convection liquid­gaseous flow were carried out. In a series of experiments, a liquid­gaseous bubbly flow was generated in a narrow tank by injection of pressurized air into water, or by catalytic disintegration of H2O2. A small amount of a positron emitting radiotracer liquid was injected instantaneously at a certain point of the tank. The Positron Emission Tomogaphy (PET) technique was used to observe the spreading of this tracer liquid in the bubbly flow. For that case a double head gamma detector array was used for measuring the positron annihilation rate which is proportional to the tracer concentration. From the experimental data the dispersion coefficient D for the tracer liquid was calculated, assuming an isotropic spreading of the concentration profile after separation of the linear displacement of the maximum concentration point.
Calculations for this two­phase flow with spreading tracer were carried out for selected experiments with air injection into water using the computational fluid dynamics code CFX­4.3. Here, the Euler­Euler continuum approach using a homogeneous low Reynolds number K,epsilon­model was applied. The evolution of the bubble size distribution (coalescence and break-up of the bubbles) was taken into consideration. A reasonable agreement was achieved between calculated and measured values of the turbulent dispersion coefficient D. A nearly linear correlation between the gas superficial velocity vgas and D was found in agreement with other authors.