Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

For the first time, a superconducting RF gun where a photo cathode is inside a superconducting cavity has been working stably over a periode of seven weeks. The gun with a half cell cavity has been operated in the cryostat at 4.2K. A maximal field strength of 22MV/m in the cavity and maximal beam energy of 900keV have been obtained. Measurements of beam current, transmission, energy spread and transverse emittance are presented.

Owing to their antiviral and antitumoral properties polyoxometalates (POMs) are gaining in importance in the development of therapeutic agents. Such cluster molecules possessing a multitude of metal atoms might be took advantage in view of cancer treatment by photon activation therapy (PAT). In this nexus it is necessary to meet some requirements. So, POMs must have sufficient stability under physiological conditions. Furthermore, highly efficient transportation into cells, and finally the interaction with DNA is essential. The encapsulation of POMs by aminosaccharides seems to be a promising way to achieve that. In our previous study we reported about the possibility conditions to form complexes between various metal-oxoanions and sorbents having different diol-ligands. Now, we want to report the binding and sorption behavior of selected aminosaccharides towards polyoxotungstates.

During the commissioning of the first accelerator stage of ELBE, beam loss was measured with photomultipliers and self-testing integrating electronics. While the electronics worked flawless, the correct positioning of the monitors and finding a good trade off between sensitivity and saturation of the photomultipliers were a problem. A new BLM system, consisting of ionization chambers, acquisition electronics and monitoring software is now under construction. Coaxial cable with air dielectricum, normally used in high power applications, makes the ionization chamber and will be installed along the beamline. The outer conducter of the cable is subsectioned, the inner conductor not. The current on the inner conductor represents the total beam loss. The current from each outer conductor segment to ground is measured separately, providing position resolution of the beam loss. On each section, a RISC microcontroller (Slave) with built in ADC is used for data acquisition and continuous average calculation. One microcontroller (Master) handles the communication with the slaves via RS-485 bus and acts as an interface to a PC running monitoring software. First test have been done successfully.

At ELBE, beamloss is measured in two different ways. Long ionization chambers (LIC) made from coaxial cable and having an air dielectric are used to detect beam loss at critical sites of the machine. In the second system, beam current is measured at three different locations. The sum signals from two stripline beam position monitors and the nuclear physics beam dump current are compared. A difference in current at these points indicates that portions of the electron beam are lost somewhere. Above a certain level the interlock is triggered and the beam is switched off. Both kinds of measurement are described in detail elsewhere in this annual report.

During the first stages of commissioning ELBE, the beam current could be measured directly at the gun, the macropulser aperture and at the beam dump. Later, a package consisting of a resonant beam current monitor (RBCM) and a resonant beam position monitor was added. The result of the RBCM test are described in this paper.

The objective of this paper is the evaluation of the normalization method performance compared to the conventional standard method for a broad spectrum of different materials and specimen geometries. The normalization method based critical J-integral values were summarized and compared with the results of the unloading compliance tests. The results point out the applicability of the normalization method for the J-R curve determination for the investigated materials. The normalization method provided results with up to 15 % deviation from the values obtained with the unloading compliance method.

The work in this report, financed by the European Union through the Marie Curie Fellowship Association, was carried out at the FZ-Rossendorf. The subject of the research was to develop a method to investigate the damage, the high defect gradients at the tip of a ductile crack by means of Small Angle X-ray Scattering. The work explains the objectives and entails a brief introduction and background; it portrays and discusses the results which can be summarized as follows. Different damage parameters were investigated: the integral intensity, the total intensity on the detector, the anisotropy parameter and the fractal dimension. Of these, the anisotropy parameter is the most robust and most clearly depicts a damage region and the fractal dimension provides an idea of the structure of the scattering defect. The integral and total intensity provide comparable results only in some cases and are therefore not reliable.
From supportive investigations: Scanning and Transmission Electron Microscopy (S-TEM), Finite Element Analysis and X-Ray Diffraction, it is suggested that the scatterer created after deformation is related to large oriented dislocation networks.

Die uneingeschränkte Nutzung eines RDB bis zum Ende der Betriebsdauer des KKWs auf einem unverändert hohen Sicherheitsniveau ist nur durch ein ganzheitliches und umfassendes Programm von Maßnahmen und Instrumentarien zu gewährleisten. Entscheidend werden dafür die Weichen bereits bei der Auslegung gestellt, indem hochzähe, strahlenversprödungsresistente Werkstoffe verwendet werden, die Neutronenbelastung durch einen ausreichend breiten Wasserspalt redu-ziert wird, die fortschreitende Materialalterung durch ein gut konzipiertes repräsentatives Überwachungsprogramm erfasst und Herstellung und Konstruktion gute Prüfbarkeit ebenso wie die Vermeidung von Spannungsdiskontinuitäten absichern. Betriebliche Maßnahmen können die Bean-spruchung bei Betrieb oder im Störfall reduzieren (Transientenregime, Einspeisung von vorge-wärmten Notkühlwasser), die Neutronenflussdichte durch ein geeignetes Beladeregime senken oder mit aktualisierten Überwachungsprogrammen die Charakterisierung des Materialzustandes verbessern. Als ultimo ratio steht die Ausheilglühung zur Verfügung, deren Praktikabilität inzwi-schen bereits erwiesen ist.
Schließlich erweist sich nicht zuletzt die Einführung neuer Konzepte zur Sprödbruchsicherheitsanalyse als wertvoll. Als ein hinsichtlich seiner Einführung bereits fortgeschrittenes Beispiel dieser Art wurde das Master-Curve-Konzept vorgestellt. Dieses Konzept wird gegenwärtig zur Bestimmung einer bruchmechanisch definierten Übergangstemperatur be-nutzt, mit der die KIc-Universalkurve der Regelwerke materialspezifisch auf der Temperaturachse positioniert werden kann. Die so ermittelten Referenztemperaturen liegen ca. 40 - 60 K niedriger als die bisher verwendeten Referenztemperaturen, die auf den NDT- oder den Charpy-V-Übergangstemperaturen beruhen. Auf diese Weise kann eine unnötige Konservativität der Bewertung abgebaut werden. Das wurde bereits in realen Anwendungsfällen zweifelsfrei nachgewiesen. Langfristig könnte die statistisch definierte MC selbst als Bruchzähigkeitskurve verwendet werden. Damit erfolgt die Bestimmung der Materialparameter nach einem durchgehend physikalisch defi-nierten Konzept, welches Aussagen zur Versagenswahrscheinlichkeit ermöglicht.

Washout of ¹⁰C and ¹¹C implanted by radioactive beams in brain and thigh muscle of rabbits was studied. The biological washout effect in a living body is important in the range verification system or three-dimensional volume imaging in heavy ion therapy. Positron emitter beams were implanted in the rabbit and the annihilation gamma-rays were measured by an in situ positron camera which consisted of a pair of scintillation cameras set on either side of the target. The ROI (region of interest) was set as a two-dimensional position distribution and the time-activity curve of the ROI was measured. Experiments were done under two conditions: live and dead. By comparing the two sets of measurement data, it was deduced that there are at least three components in the washout process. Time-activity curves of both brain and thigh muscle were clearly explained by the three-component model analysis. The three components ratios (and washout half-lives) were 35% (2.0 s), 30% (140 s) and 35% (10191 s) for brain and 30% (10 s), 19% (195 s) and 52% (3175 s) for thigh muscle. The washout effect must be taken into account for the verification of treatment plans by means of positron camera measurements.

Radiopharmaka werden in der nuklearmedizinischen Diagnostik und Therapie eingesetzt. Diagnostisches Ziel ist es, möglichst viele biochemische Prozesse ohne Eingriff in diese Abläufe bildgestützt zu analysieren. Der menschliche Körper soll somit biochemisch transparent werden. Trotz allen Fortschritts sind noch viele neue, spezifische, radioaktive Sondenmoleküle, sogenannte Radiotracer, nötig.

Bezüglich eines hypothetischen Kernschmelzeszenarios in einem Leichtwasserreaktor ist es notwendig, mögliche Versagensformen des Reaktordruckbehälters sowie Versagenszeiträume zu untersuchen, um die Belastung für das Containment bestimmen zu können. Es wurden weltweit bereits eine Reihe von Experimenten durchgeführt, welche Erkenntnisse hierüber liefern sollen. Begleitend wurden in Einzelversuchen Materialeigenschaften ermittelt, sowie theoretische und numerische Arbeiten durchgeführt.
Für die Simulation von Experimenten zum Versagen der Bodenkalotte, wie OLHF oder FOREVER, ist es notwendig, Kriechen und Plastizität zu berücksichtigen. Gleichzeitig müssen geeignete Modelle das Temperaturfeld in der Behälterwand für die mechanischen Rechnungen bereitstellen. Vom Institut für Sicherheitsforschung des FZR wird ein Finite-Elemente-Modell erstellt, das sowohl die Temperaturfeldberechnung für die Wand als auch die elasto-plastische Mechanik der Behälterwand modelliert.
Am FZR wurde ein Finite Elemente Model entwickelt, das die Verwendung von einfachen Kriechgesetzen, die mit ihren angepassten Konstanten nur für begrenzte Spannungs- und Temperaturbereiche gültig sind, umgeht. Stattdessen wird eine numerische Kriechdatenbasis angelegt, in der die Kriechdehnrate in Abhängigkeit von der Gesamtdehnung, der Temperatur und der Vergleichsspannung abgelegt ist. Eine wesentliche Aufgabe für diese Vorgehensweise besteht in der Generierung und Validierung der Kriechdatenbasis. Zusätzlich wurden alle relevanten temperaturabhängigen Materialeigenschaften mit entsprechenden Modellen in den Code eingegeben. Für die Bestimmung der Versagenszeit wurde ein Schädigungsmodel nach einem Vorschlag von Lemaitre implementiert.
Die Validierung des numerischen Models erfolgte durch die Simulation von und den Vergleich mit den skalierten Integralexperimenten der FOREVER-Reihe, in denen die Bodenkalotte eines Druckwasserreaktors mit ihrer halbkugelförmigen Geometrie wiedergegeben wird. In Zusammenarbeit mit den Experimentatoren an der KTH in Stockholm wurden Pre- und Posttest-Rechnungen für diese bisher einzigartigen Experimente durchgeführt, deren Ergebnisse qualitativ und quantitativ sehr zufriedenstellend sind.
Ausgehend von diesen Arbeiten wird die Simulation prototypischer Szenarien angestrebt, welche im Vergleich zu FOREVER um den Faktor 10 größere Abmessungen aufweisen. Hierzu sind noch Modellerweiterungen notwendig, die daraus resultieren, dass eine vollständige einheitliche Skalierung aller thermischen und mechanischen Einflussgrößen nicht möglich ist.

The paper gives an overview on the RF-system developed for the Superconducting Photo RF Gun at FZ-Rossendorf and a brief discussion an RF-measurements at the superconducting gun-cavity.

The power-point presentation gives an overview on RF-coupler development, operational experience at the ELBE-Linac and the coupler test-equipment used at FZ-Rossendorf.

The ELBE LINAC is equipped with superconducting TESLA 9-cell cavity resonators. Its RF-coax coupler antennas are designed to operate each cavity withe 8...10 kW beam power. The paper describes a procedure on optimising the antenna- length of the RF-coupler at room temprature.

The low concentration of toxic radioactive metals in environmental samples often limits the interpretation of results of infrared studies investigating the interaction processes between the metal ions and environmental compartments. For the first time, we could show that photothermal infrared spectroscopy performed with a pulsed free-electron laser can provide reliable infrared spectra throughout a distinct spectral range of interest. In this model investigation, we provide vibrational absorption spectra of a rare earth metal salt dissolved in a KBr matrix and a natural calcite sample obtained by thermal beam deflection technique and FT-IR spectroscopy, respectively. General agreement was found between all spectra of the different recording techniques. Spectral deviations were observed with samples containing low concentration of the rare earth metal salt indicating a lower detection limit of the photothermal method as compared to conventional FT-IR spectroscopy. Furthermore, the photothermal method provide spatial information of a sample surface. This may result in a microspectrometric technique for determining the distribution of metal species on mineral surfaces. First experiments exploring the spatial resolution of photothermal spectroscopy were carried out by scanning the surface of a germanium substrate showing a localised region where O+-ions were implanted. The border range of this region was investigated by recording time curves of the deflection signal at distinct positions of the substrate surface with a constant free-electron laser wavelength of 11.6 micrometer.

Theoretical and experimental investigations have pointed out the formation of dilute polydisperse system of spherical particles with diffusion zones embedded in matrix in the nucleation and growth evolution stages due to quenching, irradiation and other special kinds of treatment of multicomponent materials. Small-angle neutron and X-ray scattering provide information about the chemical composition as well as about the size distribution of the nanoscale defects.
Unlike to the case of homogeneously structurized scattering objects the analytical solution for heterogeneous scattering objects has not yet well-established. The paper states that the present approaches do not account in full measure the interference between the scattering intensities from the core and shell. Therefore, a more accurate procedure to calculate the scattering factor from heterogeneous objects is worked out. It bases on the formalism of the pair distribution function and the Porod' formula.
The suggested approach is verified on homogeneous scattering objects and then is applied to the set of shell models with different parameters of structure. For the calculation a Visual-Fortran programme is worked out. It is found that the homogeneous model and shell models produce the same scattering factor.
Model of the polydisperse nanoscale defects in neutron irradiated reactor steel is considered as composites of iron core and vacancy enriched shell with different sizes. The fitting procedure to determine the parameters of the size distribution function of irradiation induced precipitates from the magnetic part of small-angle neutron scattering is worked out. The results well agree with results of investigation by other methods for VVER steels with small Cu-content.

Das Vorhaben bestand in der Validierung des gekoppelten neutronenkinetisch-thermohydraulischen Programmkomplexes ATHLET/DYN3D für Siedewasserreaktoren durch Teilnahme an dem OECD/NRC Benchmark zum Turbinenschnellschluss. Das von der OECD und der amerikanischen NRC definierte Benchmark basiert auf einem Experiment mit Schließens des Turbinenschnellschlussventils, das 1977 im Rahmen einer Serie von 3 Experimenten im Kernkraftwerk Peach Bottom 2 durchgeführt wurde. Im Experiment erzeugte das Schließen des Ventils eine Druckwelle, die sich unter Abschwächung bis in den Reaktorkern ausbreitete. Die durch den Druckanstieg bewirkte Kondensation von Dampf im Reaktorkern führte zu einem positiven Reaktivitätseintrag. Der folgende Anstieg der Reaktorleistung wurde durch die Rückkopplung und das Einfahren der Regelstäbe begrenzt. Im Rahmen des Benchmarks konnten die Rechenprogramme durch Vergleiche mit den Messergebnissen und den Ergebnissen der anderen Teilnehmer an dem Benchmark validiert werden.

Das Benchmark wurde in 3 Phasen oder Exercises eingeteilt. Die Phase I diente der Überprüfung des thermohydraulischen Modells für das System bei vorgegebener Leistungsfreisetzung im Kern. In der Phase II wurden 3-dimensionale Berechnungen des Reaktorkerns für vorgegebene thermohydraulische Randbedingungen durchgeführt. Die gekoppelten Rechnungen für das ausgewählte Experiment und für 4 extreme Szenarien erfolgten in der Phase III. Im Rahmen des Projekts nahm FZR an Phase II und Phase III des Benchmarks teil. Die Rechnungen für Phase II erfolgten mit dem Kernmodell DYN3D unter Berücksichtigung der Heterogenitätsfaktoren und mit 764 thermohydraulischen Kanälen (1 Kanal/Brennelement). Der ATHLET-Eingabedatensatz für die Reaktoranlage wurde von der Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) übernommen und für die Rechnungen zu Phase III, die mit der parallelen Kopplung von ATHLET mit DYN3D erfolgten, geringfügig modifiziert.

Für räumlich gemittelte Parameter wurde eine gute Übereinstimmung mit den Messergebnissen und den Resultaten anderer Codes erzielt. Der Einfluss der Modellunterschiede wurde mit Hilfe von Variantenrechnungen zu Phase II untersucht. So können Unterschiede in der Leistungs- und Voidverteilung in einzelnen Brennelementen auf die unterschiedliche neutronenkinetische und thermohydraulische Modellierung des Reaktorkerns zurückgeführt werden.

Vergleiche zwischen ATHLET/DYN3D (parallele Kopplung) und ATHLET/QUABOX-CUBBOX (interne Kopplung) zeigen für räumlich gemittelte Parameter nur geringe Unterschiede. Abweichungen in den lokalen Parametern können im wesentlichen mit der unterschiedlichen Modellierung des Reaktorkerns erklärt werden (geringere Anzahl von modellierten Kühlkanälen, keine Berücksichtigung der Heterogenitätsfaktoren und ein anderes Siedemodell in der Rechnung mit ATHLET/QUABOX-CUBBOX).

Die Rechnungen für die extremen Szenarien von Phase III zeigen die Anwendbarkeit des gekoppelten Programms ATHLET/DYN3D für die Bedingungen bei Störfällen, die weit über das Experiment hinausgehen.

Within the Borel QCD sum rule approach at finite baryon density we study the role of the four-quark condensates % such as langle(overline{q} gamma_{mu} lambda^a)^2rangle_n , for the modifications of the vector mesons rho, omega and phi in nuclear matter.
We find that in-medium modifications of the rho and omega mesons are essentially dominated by the dependence of the 4-quark condensate on the nucleon density. In particular, the numerical value of a parameter (kappa_N), which describes the strength of the density dependence of the 4-quark condensate beyond the mean-field approximation, governs the decrease of the rho mass as a function of the density. For the omega meson the sign of the in-medium mass shift is changed by variations of kappa_N. To study consistently the in-medium broadening of the light vector mesons we employ rho N and omega N scattering amplitudes derived recently from a covariant unitary coupled channel approach adjusted to pion- and photo-induced reactions. In contrast to the rho and omega mesons, the in-medium mass of the phi meson is directly related to the chiral (strange) quark condensate. Measurements of the vector meson spectral change in heavy-ion collisions with HADES can shed light on the yet unknown density dependence of the 4-quark condensate.

An der Lausitzer Neiße wird seit 100 Jahren die Wasserkraft zur Stromerzeugung genutzt. Im vorliegenden Beitrag werden - ausgehend von den hydrologischen Bedingungen und der historischen Entwicklung - der heutige Stand der Wasserkraftnutzung am Grenzfluss Lausitzer Neiße sowie mögliche Perspektiven dargestellt.

Efficient electroluminescence with power efficiency up to 0.12 % is observed from silicon pn diodes prepared by boron implantation with boron concentrations above the solubility limit at the post-implantation annealing temperature. The electroluminescence spectra exhibit a transition from two bound-exciton bands towards the free electron-hole pair recombination with an anomalous increase in the total intensity with increasing temperature. The implantation dose and temperature dependences of the relative peak intensities provide evidence for the relevance of excitonic traps as a supply for free electron-hole pairs and thus the origin of the enhanced electroluminescence at elevated temperatures.

B+ implantation into epitaxial 6H-SiC has been carried out in order to create a laterally structured p-doped layer. The defects caused by the ion implantation should be minimized by implantation at higher substrate temperatures and post implantation annealing. Using Slow Positron Implantation Spectroscopy (SPIS), the distribution of vacancy-type defects after ion implantation could be evaluated and the efficiency of the annealing could be demonstrated. Furthermore, first results about the boron distribution after annealing are shown.

The data analysis of current dynamo experiments and the design of new experiments led to an increasing interest in the spectral properties of MHD dynamos. In particular, the huge amount of multichannel data measured with high spectral resolution at large magnetic sensor arrays outside the liquid sodium facilities calls for the development of tomographic methods for these experiments. In general, such methods would allow for a rough reconstruction of velocity and alpha profiles inside a facility from the magnetic field data measured outside the facility. Due to the fact that viable tomographic methods are crucially based on a correct interpretation of the measured data, one has first to deeply understand the spectral properties of the experimental setup and to clarify the uniqueness of the corresponding inverse problem.

As step in this direction and in order to keep the calculations at the beginning as simple as possible, in [1] the uniqueness of spectral data was studied numerically for the toy model of a spherically symmetric alpha^2-dynamo. The results, which were obtained by combining a spectral forward solver with an inverse problem solver, indicated a possibly existing isospectrality of spherically symmetric alpha^2-dynamos with different alpha-profiles alpha_1(r) and alpha_2(r) and a corresponding non-uniqueness of the inverse problem.

The present contribution is based on Ref. [2] and reports analytical results on the isospectrality problem of spherically symmetric alpha^2-dynamo operators. First, it is shown that the 2 x 2 operator matrix of the alpha^2-dynamo possesses a fundamental (canonical) symmetry J, so that the operator itself can be naturally described as J-pseudo-Hermitian operator in a Krein space (a Hilbert space with an additional indefinite inner product structure). Then this symmetry is used to extend the operator intertwining techniques of supersymmetric quantum mechanics to the operator matrix of the alpha^2-dynamo. The intertwiners are assumed as first-order matrix differential operators with coefficients which are highly constrained by a system of nonlinear matrix differential equations. The (hidden) symmetries of this equation system are analyzed by transforming it into a set of constrained and interlinked matrix Riccati equations. As next step, the structure of the spherically symmetric alpha^2-dynamo operator is tested on its compatibility with the considered intertwining ansatz and a no-go theorem is derived which states that the structure is not compatible with an intertwining ansatz based on first-order differential operators as intertwiners. This implies, that other, more powerful techniques should be used for a clarification of the isospectrality and uniqueness problem of the dynamo operator. Finally, the linear eigenvalue problem for the 2 x 2 dynamo operator matrix is transformed to the equivalent eigenvalue problem for the associated quadratic operator pencil. From this quadratic pencil a general functional equation is derived, which will be useful in future research (extending [3]) for discriminating oscillating dynamo regimes from non-oscillating regimes and for localizing the degenerate spectral intersection points where transitions from one regime to the other occur.

[1] F. Stefani and G. Gerbeth, Astron. Nachr. 321, (2000), 235, astro-ph/0010090; Phys. Earth Planet. Inter. 128, (2001), 109.

[2] U. Günther and F. Stefani, J. Math. Phys. 44, (2003), 3097, math-ph/0208012.

[3] F. Stefani and G. Gerbeth, Phys. Rev. E 67, (2003), 027302, astro-ph/0210412.

It is widely believed that almost all magnetic fields in a natural environment are the result of the dynamo process - the field generation in a moving nearly homogeneous electroconducting fluid in the depth of celestial bodies such as Earth, most of the planets, Sun, other stars and even galaxies.
We are not going to model in the laboratory any particular celestial body. Our aim is to demonstrate the very idea that the intense motion in the large volume of a good electroconducting liquid creates a magnetic field. As the working fluid serve 2 m^3 of molten sodium, which is the best electroconducting liquid available. It is filled in a 3 m long and 0.8 m thick cylinder. By means of two thin stainless steel internal walls the cylinder is divided into three coaxial channels. The swirling sodium circulation within the two central channels is produced by a propeller at the top of the cylinder powered by two 100 kW motors. When the circulation is fast enough the magnetic field appears. The field pattern slowly rotates around the axis of the cylinder hence any field sensor produces an AC signal.
The first results were reported in the third and fifth MHD days. In the present meeting we will touch upon such details as the radial profiles of field pattern, the turbulent spectra of field, the field produced motions in sodium etc.

Several fragments of ancient gold objects coming from an Eneolithic hoard and from Pietroasa .Clo#ca cu Puii de Aur. (.The Golden Brood Hen with Its Chickens.) hoard, unearthed on Romanian territory, and two Romanian native gold nuggets samples were analyzed using micro-PIXE technique. The purpose of the study was to clarify the metal provenance. Trace and minor elements (Cu, Te, Sn, Pb, Ti, Cr, V, Mn, Ta) and platinum group elements (PGE) concentrations were estimated. The presence of inclusions (micrometer size areas of composition different from the surroundings) was investigated. We found Si and Ca inclusions on two Eneolithic samples, and Ta inclusions on two samples from Pietroasa hoard. The measurements suggested an alluvial origin of gold for the Eneolithic samples and give indications for the possible gold ore sources of Pietroasa hoard.

Cubic SiC is implanted with carbon ions at 600, 900, 1100 and 1200 °C. X-ray diffraction and transmission electron microscopy revealed the influence of implantation temperature and dose rate on the formation of graphite and diamond precipitates, respectively. The high dose carbon implantation at 600 °C yields graphite already in a textured form. Spherical diamond grains, which are always epitaxial to the SiC, are found in samples implanted at 900 °C or higher. Increasing the dose rate leads to formation of graphite instead of diamond at 900 oC as well. Hence, a critical temperature for diamond evolution exists, which depends on dose rate. Size and shape of the formed diamond precipitates is not influenced by dose rate within the investigated range. Increasing the fluence results in bigger diamond nanocrystals, which are bordered by facets.

The influence of microorganisms on migration processes of actinides has to be taken into account for the assessment of potential high level nuclear waste disposal sites. Therefore it is necessary to characterize the actinide-bacteria species formed and to elucidate the reaction mechanisms involved. This work is focused on the sulfate-reducing bacterial (SRB) strain Desulfovibrio äspöensis DSM 10631T which frequently occurs in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden. We chose Cm(III) due to its high fluorescence spectroscopic sensitivity as a model system for exploring the interactions of trivalent actinides with D. äspöensis in the trace concentration range of 3 x 10-7 mol/L. A time-resolved laser fluorescence spectroscopy (TRLFS) study has been carried out in the pH range from 3.00 to 7.55 in 0.154 mol/L NaCl. We interpret the pH dependence of the emission spectra with a biosorption forming an inner-sphere surface complex of Cm(III) onto the D. äspöensis cell wall. This Cm(III)-D. äspöensis-surface complex is characterized by its emission spectrum (peak maximum at 600.1 nm) and its fluorescence lifetime (162 ± 5 µs). No evidence was found for incorporation of Cm(III) into the cells.

The problems with the crack length determination by the unloading compliance method are well known for Charpy size specimens. The final crack lengths calculated for bent specimens do not fulfill ASTM 1820 accuracy requirements. Some investigations have been performed to resolve this problem by correcting the compliance value, but satisfying results were not obtained. In the presented work the measured specimen compliance was taken as a correct value and the calculation procedure was modified. On the basis of experimentally obtained compliances of bent specimens and optically measured crack lengths a calculation procedure enabling accurate crack length calculation up to 5 mm of plastic deflection was developed. Applying the new procedure to a sample of 238 measured crack lengths, more than 80% of the values fulfilled the ASTM 1820 accuracy requirement, while presently used procedure provided only about 30% of valid results. The newly proposed procedure can be also prospectively used in modified form for specimens of a size being different from Charpy size.

The contribution of quantum shape fluctuations to inertial properties of rotating nuclei has been analysed for QQ-nuclear interaction using the random phase approximation (RPA). The different recipes to treat the cranking mean field plus RPA problem are considered. The effects of the dN = 2 quadrupole matrix elements and the role of the volume conservation condition are discussed.

no abstract

The separation of uranium(VI) from aqueous solution by textile bound uranophile calix[6]arenes was studied as a function of pH value and uranium concentration in the absence and presence of competing ions by means of batch experiments. Furthermore, the kinetics of the uranium binding was studied as well as the possibility for remobilization of the bound uranium by solutions of various pH values.
The results showed that calixarene modified textiles are suitable for the separation of uranium from aqueous solution at pH values higher than 4. The applicability in the acidic pH range is limited. Maximal 7.6x10-7 mol uranium per 1 g of the calixarene modified textile is bound at pH 5. The influence of competing ions (sodium, potassium, calcium, magnesium, carbonate and sulfate) on the uranium separation at pH 5 is very small. However, at pH 7 in carbonate rich waters calcium ions have a competing effect due to the formation of the Ca2UO2(CO3)3 (aq) complex.
Under environmentally relevant pH conditions (near-neutral pH range) the uranium is strongly bound to the calixarene modified textile and cannot be mobilized. On the other hand, under acidic conditions an almost complete regeneration of the calixarene modified textile is feasible. The regenerated textile filter material can be utilized for further uranium separation cycles.

Dipole and electric quadrupole excitations in ^{204, 206, 207, 208}Pb have been measured up to 6.75 MeV in resonant photon scattering experiments at the superconducting Darmstadt electron linear accelerator S-DALINAC using two Euroball-Cluster detector modules. In ²⁰⁸Pb, 14 excited states have been populated; in ²⁰⁶Pb, the decays of 41 states have been detected. Information about 45 heretofore unknown excited states in ²⁰⁴Pb could be measured as well as eleven known levels in ²⁰⁷Pb. The extracted dipole strength distributions are discussed within phenomenological ("pygmy resonance") and microscopic models (quasiparticle-phonon model). A strong fragmentation and a small shift of the detected E1 strength towards higher energies is observed with the opening of the neutron shell closure.

The combination of PIXE, RBS and PIGE proves ideal for non-destructive overall analysis of reverse paintings on glass. Simultaneous PIXE-RBS studies assist to clarify the thin-layered pigment arrangements of details painted on the reverse of the glass pane. In a second measurement, the spectra of both PIGE-PIXE taken from the pure glass front side inform on the individual glass type. This complete perception of corresponding unique objects is important and valuable regarding the knowledge of special painting techniques and the necessity of preventive conservation.

The cross section for producing K^- mesons in nucleon-hyperon collisions is estimated using the experimentally known pion-hyperon cross sections. The results are implemented in a transport model which is applied to calculation of proton-nucleus collisions. Contrarily to earlier estimates in heavy-ion collisions the inclusion of the nucleon-hyperon cross section roughly doubles the K^- production in near-threshold proton-nucleus collisions.

Natural and laboratory homogeneous dynamos can be modeled by supposing that the electrically conducting fluid fills a finite volume D surrounded by an insulating infinite region D'. Our considerations are restricted to the kinematic dynamo regime in which the back-reaction of the self-excited magnetic field on the flow is negligible. We also assume the velocity field to be steady. Even for such kinematic dynamo problems an analytical treatment is usually impossible, hence numerical methods have to be utilized.
A notorious problem with the usual differential equation approach is the handling of the non-local boundary conditions for the magnetic field. The integral equation approach provides a solution to the problem of non-local boundary conditions. The integral equation approach has a number of interesting features. The most important one is that it avoids the discretization of the infinite region D'. The second one is its intimate connection to inverse problems relevant not only for dynamos but also for technical applications of magnetohydrodynamics. The third one is its proven numerical robustness and stability.
We examine the integral equation approach by a few numerical examples, including the alpha^2 dynamo model with radially varying alpha, and the Bullard-Gellman model, and demonstrate its equivalence with the differential equation approach.

Scanning capacitance microscopy and spectroscopy (SCM/SCS) were applied to study the charge storage, the retention behaviour and the response on dynamic voltage stress of thin SiO2 layers containing Si or Ge nanoclusters. The formation of the nanoclusters was accomplished by ion beam synthesis (IBS) and verified by transmission electron microscopy (TEM). Local charge injection into the implanted layers was performed by applying a dc bias to the metallic probe tip, which was in contact with the SiO2 layer. The dC/dV-curves reveal a shift along the voltage axis compared to an equivalent curve on an unstressed control position. The curve shifts allowed a quantitative analysis of the trapped charge. Monitoring the SCM contrast between an injection spot and its unstressed surroundings over several days allows to visualize the charge decay. The retention time of the stored charge could be estimated from the measured charge decay.

Embedded nanoclusters in SiO2 films have attracted increasing interest for applications in memory devices. Charge storage effects are easily observed in MOS structures with nanoclusters, but the nature of the trap states is still unclear. In particular the implantation damage when the clusters are formed by ion beam synthesis might play a role. Spectroscopic and spatial information is required in order to examine the trapping sites responsible for the charge storage. Scanning probe techniques which detect electrical properties seem to be suitable to study the local trapping properties of implanted layers.
Scanning capacitance microscopy (SCM) and scanning capacitance spectroscopy (SCS) were developed recently to study the charging phenoma and trapping states in insulating films. Inspite of the unambiguous impact of trapped oxide charges on local dC/dV(V) curves the utilization of SCS data for a quantitative determination of local electrical properties of insulating films has not been used hitherto, due to experimental issues such as reproducibility, tip-sample effects and accuracy. We will demonstrate the suitability of the SCM / SCS method for the estimation of oxide trap densities and decay times of localized charges as well as for the implementation of local electrical stress in SiO2 films.
Nanocluster formation was accomplished by the implantation of Ge or Si into 20 nm SiO2 on (100) oriented p-type silicon and a subsequent annealing in N2 ambient at temperatures between 950°C and 1150°C, respectively. Applying a dc bias of up to +/- 10 V to the conductive tip for a certain time, a local charge injection either from the tip or the substrate into the SiO2 was performed. SCM images visualize the localized charge trapped in the injection spot area (Fig. 1).
In addition, at each spot the dC/dV signal was acquired by sweeping the dc bias between +5 V and -5 V. The shift of the peak position along the voltage axis is a measure of the trapped oxide charge (Fig. 2). Trap concentrations are derived for a set of different samples from SCS measurements and compared to results from high frequency capacitance voltage measurements on gated structures. Hysteresis effects will be discussed. Dependencies of the trap density on implantation dose and energy were detected by SCS. The decay of localized charge clusters was monitored on a timescale from a few minutes up to 14 days. At last, via tip biasing sequences local electrical stress was applied to the films. Local degradation and charge trapping is obvious from a comparison of SCS curves before and after the implementation of several stress routines.

Energies ranging between 24 and 50 keV, inclusively, are used for boron ion implantation of as-grown and thermochemically polished CVD diamond films at a total dose of 1E16 cm-2 in order to achieve p-type conductivity. N-type conductivity is acquired by lithium ion implantation of the films by a single energy of 50 keV at a dose of 2E16 cm-2. Current–voltage (I–V) characteristics reveal that leakage currents of diodes fabricated on as-grown films are approximately 2 orders of magnitude higher that those on polished films. Moreover, currents at higher voltages as less in the diodes of as-grown films in comparison to identical diodes on the polished films. The I–V characteristics of diodes on the polished films contain the trap filling, Frenkelpole emission, thermionic emission and the space charge limited current regimes but those on the as-grown films manifest a quasi-linear behavior probably due to lateral penetration of implants in the i-regions. A reduction in current of approximately 2 orders of magnitude is observed on n–i–n structures after annealing the films at 300 °C. Onset voltages of -10 V are due to the low concentration (~1E14 cm-2 ) of nitrogen centers in the diamond films.

Data from KEK on subthreshold (p) over bar as well as on π^± and K^± production in proton-nucleus reactions are described at projectile energies between 3.5 and 12.0 GeV. We use a model which considers a hadron-nucleus reaction as an incoherent sum over collisions of the projectile with a varying number of target nucleons. It samples complete events and thus allows for the simultaneous consideration of ail particle species measured. The overall reproduction of the data is quite satisfactory. It is shown that the contributions from the interaction of the projectile with groups of several target nucleons are decisive for the description of subthreshold production. Since the collective features of subthreshold production become especially significant far below the threshold, the results are extrapolated down to COSY energies. It is concluded that an p measurement at ANKE-COSY should be feasible, if the high background of other particles can be efficiently suppressed.

The problems with the crack length determination by the unloading compliance method are well known for Charpy size specimens. The final crack lengths calculated for bent specimens do not fulfil ASTM 1820 accuracy requirements. Therefore some investigations have been performed to resolve this problem. In those studies it was considered that measured compliance should be corrected for various factors, but satisfying results were not attained. In the presented work the problem was attacked from the other side, the measured specimen compliance was taken as a correct value and what had to be adjusted was the calculation procedure. On the basis of experimentally obtained compliances of bent specimens and optically measured crack lengths the investigation was carried out. Finally, a calculation procedure enabling accurate crack length calculation up to 5mm of plastic deflection was developed. Applying the new procedure, out of investigated 238 measured crack lengths, more than 80% of the values fulfilled the ASTM 1820 accuracy requirements, while presently used procedure provided only about 30% of valid results. The newly proposed procedure can be also prospectively used in modified form for the specimens of different than Charpy size.

Suicide gene therapy with the herpes simplex virus type-1 thymidine kinase gene (HSV-1 tk) is considered to be a promising approach to the treatment of cancer. Making use of the lower specificity of the viral enzyme compared to human thymidine kinase, the therapy involves the administration of antiviral agents (e.g. ganciclovir) as prodrugs to induce enzymatic cell death in those cells that express the transferred gene. ¹⁸F labeled derivatives have been described for monitoring location, duration and magnitude of the viral kinase enzyme activity by positron emission tomography (PET). Since an optimal radiotracer has not been developed, novel substances were synthesized for monitoring gene expression. A group of 13 nucleoside analogues were synthesized, among them N¹-methyl-9-[(1,3-dihydroxy-2-propoxy)methyl]guanine 5 and N¹-methyl-9-[(4-hydroxy)-3-hydroxy-methylbutyl]guanine 7 as methyl analogues of ganciclovir and penciclovir and their related fluoro compounds (6, 8). Further novel derivatives include N⁶-methyl-9-[(1,3-dihydroxy-2-propoxy)methyl]-, N⁶-methyl-9-[(4-hydroxy)-3-hydroxymethylbutyl]adenine (9, 10) as well as the uracil derivatives 5-hydroxy-1-[(1,3-dihydroxy-2-propoxy)methyl]uracil 11, 6-methyl-1-[(1,3-dihydroxy-2-propoxy)-methyl]uracil 12 and its 3-fluoro-derivative 13.

Die Positronen-Emissions-Tomographie (PET) ist eine etablierte Methode zur Untersuchung von Stoffwechselvorgängen im Menschen. Sie wird als Werkzeug in der medizinischen Forschung ebenso wie klinisch als Diagnoseverfahren zur Erkennung von Metastasen eingesetzt.
Dieses Projekt beschäftigt sich mit einer nichtmedizinischen Anwendung dieses bildgebenden Verfahrens – dem Aufbau und der Anwendung eines PET-Tomographen zur Untersuchung des Verhaltens von Schaum in Blasensäulen, dem Versuchsstand SCHAUMPET. Insbesondere wird auf die technische Realisierung des Projektes und die angewendeten Verfahren zur Bildgewinnung eingegangen. Am Beispiel von Natriumcapronat wird gezeigt, dass sich die Anreicherung eines Tensids in einer Schaumschicht mit Hilfe der Positronen-Emissions-Tomographie nachweisen lässt.

kein Abstract

The present paper describes the concept of a fast scanning X-ray tomograph, the hardware development, and measurement results of gas-liquid two-phase flow in a vertical pipe. The device uses 18 pulsed X-ray sources activated in a successive order. In this way, a complete set of 18 independent projections of the object is obtained within 38 ms, i.e. the measuring rate is about 250 frames per second. Finally, to evaluate the measurement capability of the fast X-ray CT, a wire-mesh sensor was installed in the flow loop and both systems were operated for the same two-phase flow simultaneously. Comparison of the time series of the cross section averaged void fraction from both systems showed sufficient agreement for slug flow at large void fractions, while the fast CT underestimated the void fraction of bubbly flow especially in low void fraction range. For the wire-mesh sensor, coerced deformation of slug bubble interface was found. Further hardware improvement is in progress to achieve better resolution with the fast X-ray CT scanner.

The most frequently used technetium compounds suitable for coupling the metal to biologically active molecules are square-pyramidal complexes of the oxo ion [Tc=O]³⁺ based on tetradentate N₂S₂ ligands. Properties and thus the in vivo behaviour of such complexes are strongly influenced by the presence of the quite polar [Tc=O]³⁺ unit. Whether such a polarity is beneficial or not is not obvious and depends on the requirements for specific radiotracers, e.g. for receptor targeting agents or for metabolic tracers. Another crucial point in tracer design is the stability of the respective Tc chelate towards ligand exchange in vivo. So there is a considerable interest in alternative chelate systems that offer lower polarity and enhanced in vivo stability. Such systems are based on oxo-free lower oxidation states. Here we offer a new type of Tc(III) chelate 1, formed by the tripodal 2,2‘,2“-nitrilotris(ethanethiol) and a monodentate isocyanide or tertiary phosphine.
The new compounds fulfil the requirements for a non-polar building block stable against ligand exchange reaction in vivo. Belonging to the family of "n+1" mixed-ligand technetium (and rhenium) species, such a "4+1" chelate offers the advantage of high versatility in conjugating biomolecules.
Another type of neutral Tc(III) complexes, [Tc(SCH₂CH₂-E-CH₂CH₂S)(PR₂S)] 2, can be obtained by association of a tridentate HS-E-SH ligand (E = N(CH₃), S) with a bidentate PR₂-SH chelator. This combination enables easy functionalization in order to fine-tune physico-chemical properties of the complexes as well as linking of the chelate unit to biomolecules.
^99mTc analogues can be prepared at no-carrier-added level in high radiochemical yields. The complexes are stable towards ligand exchange in challenge experiments with glutathione. Furthermore, there are no indications for re-oxidation of Tc(III) to Tc(V) species or pertechnetate. There is no tendency of these complexes to bind on plasma components. The substituents at the bidentate P,S chelator significantly influence the biodistribution pattern in rats. Therefore, we propose this new type of Tc(III) complexes as a useful tool in designing of tunable ^99mTc radiopharmaceuticals.

The copper rich cluster evolution in the neutron irradiated VVER steels is investigated beginning at the nucleation stage. For this, typical VVER-type reactor conditions are considered. The cluster dynamics approach is used for calculation of the density distribution of copper precipitates related to the number of Cu- atoms or radius; mean radius, volume content, number density of precipitates and the concentration of free Cu- atoms in dependence on the irradiation time. The results for time of one year are compared with the results of small angle neutron scattering experiments which were carried out at specimens irradiated at surveillance position of VVER reactors. It is revealed the intermediated type of the evolution kinetics between diffusion and interfacial kinetics limited regimes. The duration of the nucleation and deterministic stages is estimated. The coarsening stage does not occur.

Die in diesem Bericht vorgestellten Experimente betreffen die Kondensation von Dampf in horizontalen bzw. leicht geneigten Rohren bei hohen auftretenden Temperaturdifferenzen bis zu über 200 K. Weitere Besonderheiten sind die detaillierte Untersuchung des transienten Verhaltens eines nichtkondensierbaren Gases mit einer neuartigen Messtechnik sowie die Ermittlung des Einflusses des Gases auf den Kondensationsvorgang. Beim Experiment wurden schnelle Übergangsvorgänge ausgelöst, indem ein in einer Kühlwanne liegendes, leicht geneigtes Wärmeübertragerrohr plötzlich mit dem Dampfraum eines unter Druck stehenden Kessels verbunden wurde. Dabei wurden im Rohr unterschiedliche Anfangsbedingungen hinsichtlich der Vorlage von nichtkondensierbaren Gasen (in diesem Falle Luft) eingestellt. Es wurden Versuche mit Atmosphärendruck, mit erhöhtem Druck, aber auch mit vorheriger Evakuierung des Versuchsrohrs durchgeführt. Durch eine Instrumentierung mit neuartigen Nadelsonden, die eine Phasendetektion kombiniert mit einer schnellen lokalen Temperaturmessung ermöglichen, konnte die Umverteilung von Dampf, Kondensat und nichtkondensierbarem Gas als Funktion der Zeit beobachtet werden. Damit bieten die erhaltenen Daten die Möglichkeit, insbesondere die in den Thermohydraulikprogrammen vorhandenen Optionen zur Berechnung der Ausbreitung von nichtkondensierbaren Gasen unter transienten Bedingungen zu validieren.

Experimente mit neuartigen Messverfahren lieferten Daten über die Struktur von transienten Flüssig-keits-Gas-Strömungen für die Entwicklung und Validierung von mikroskopischen, d.h. geometrieunabhängigen Konstitutivbeziehungen zur Beschreibung des Impulsaustauschs zwischen Flüssig-phase und Gasblasen sowie zur Quantifizierung der Häufigkeit von Blasenkoaleszenz und -zerfall. Hierzu wurde eine vertikale Testsektion der Zweiphasentestschleife MTLoop in Rossendorf genutzt, wobei erstmals Gittersensoren mit einer Auflösung von 2-3 mm bei einer Messfrequenz von bis zu 10 kHz angewandt wurden. Dabei wurde die Evolution von Gasgehalts-, Geschwindigkeits- und Bla-sengrößenverteilungen entlang des Strömungsweges und bei schnellen Übergangsprozessen aufge-nommen und so die für die Modellbildung erforderlichen Daten bereitgestellt. Für den Test der Mo-dellbeziehungen wurde ein vereinfachtes Verfahren zur Lösung der Strömungsgleichungen entlang des Strömungswegs erstellt. Es basiert auf der Betrachtung einer größeren Anzahl von Blasengrö-ßenklassen. Die erhaltenen numerische Lösungen haben erstmals gezeigt, dass der bei Erhöhung der Gasvolumenstromdichte stattfindende Übergang von einer Blasenströmung mit Randmaximum zu einem Profil mit Zentrumsmaximum und anschließend zu einer Pfropfenströmung ausgehend von einem einheitlichen Satz physikalisch begründeter und geometrieunabhängiger Konstitutivgleichun-gen modelliert werden kann. Die Modellbeziehungen haben sich in einem abgegrenzten Gebiet der Volumenstromdichten als generalisierungsfähig erwiesen und sind für den Einbau in CFD-Modelle geeignet. Weiterhin wurden Arbeiten zur Kondensation durchgeführt, die direkten Bezug zu den Kon-densationsmodellen haben, die in Thermohydraulik-Codes enthalten sind. Die Untersuchung liefert darüber hinaus experimentelle Daten für die Modellvalidierung hinsichtlich des Verhaltens und des Einflusses nichtkondensierbarer Gase. Hierfür wurden spezielle Sonden für die Bestimmung der Konzentration und für die Lokalisierung von Pfropfen nichtkondensierbarer Gase entwickelt und bei transienten Kondensationsversuchen in einem leicht geneigten Wärmeübertragerrohr eingesetzt.

In order to improve the optical and mechanical performance of plastic ophthalmic lenses the use of surface coatings is necessary. However, the application of such coatings can be limited by bad adhesion to the substrate. One way to overcome this drawback is the use of a layered structure consisting in an adherent layer, an abrasion resistant hard layer and an antireflective (AR) multilayer (ML) stack. In this work we study the preparation of SiOxCy:H layered coatings to increase the mechanical durability of polymeric substrates and to accommodate gradually an external dielectric SiO2/TiO2 AR-ML. The coatings were grown by plasma assisted chemical vapor deposition (PACVD) using a mixture of hexamethyldisiloxane (HMDSO) and O2. The possibility of producing the whole layered stack by adjusting the HMDSO:O2 ratio was checked by analyzing the resulting elemental profiles obtained from ERDA. Finally, the optical properties of the different layers have been studied by spectroscopic ellipsometry in order to corroborate the adequate optical performance of the complete coating.

Depth profiling measurements of light elements by Accelerator Mass Spectrometry (AMS) have been performed at the Forschungszentrum Rossendorf. Using the AMS facility at the 3 MV Tandetron accelerator, tritium depth profiles in carbon samples have been measured which had been exposed to the plasma at the first wall of the fusion experiments ASDEX-Upgrade in Garching/Germany, JET Culham/GB and TFTR Princeton/USA. Additionally, our AMS facility at the 3 MV Tandetron has been applied to depth profiling of humidity penetrated into as-implanted SiO2 layers. For this aim, Ge+ and Si+ ion implanted SiO2 layers (1014-1016 cm-2) were exposed to an artificial atmosphere with H218O humidity. AMS allows the discrimination of isobar atomic and molecular ions, thus depth profiles of O-, (OH)- and (H2O)- molecular ions could be investigated. By measuring the 18O or the H species of these molecular ions, the process of humidity penetration in as-implanted SiO2 has been studied. The high tritium inventory of the samples from the European fusion experiment JET required a dedicated AMS facility to prevent contamination of the versatile 3 MV Tandetron. Therefore, an SF6-insulated 100 kV tandem accelerator has been developed and applied to high dose tritium measurements. This facility has been also tested for depth profiling of light elements in radioactive samples.

The synthesis of new nucleosides by alkenylation of 5-iodo-2'-halo-2'-deoxyuridines with E-(1-tributylstannyl)-propene-1-ol via STILLE-coupline is described. The new compounds are characterized by ¹H NMR and elemental analysis. All nucleosides are evaluated by an enzymatic assay to be substrates of herpes simplex virus type 1 thymidine kinase (HSV-1 TK) and compared with uridine, thymidine and (E)-5-(2-iodovinyl)-2'fluoro-2'-deoxyuridine (IVFRU).

An der Anlage ROCOM wurden Experimente durchgeführt, um den Einfluss von Dichtedifferenzen und die Bedingungen des Übergangs zwischen auftriebsdominierter und impulsbetriebener Vermischung generisch zu untersuchen. In den Experimenten mit Dichteunterschieden wurden keine konkreten Störfallszenarien nachgebildet. In diesem Bericht werden nun die experimentellen Ergebnisse mit den Resultaten des Strömungsberechnungsprogrammes CFX-4 verglichen. Die Nachrechnung der Dichteexperimente an der ROCOM-Versuchsanlage ergab für die Randfälle impulsdominierte bzw. dichtedominierte Strömung als auch für Zwischenstadien eine gute qualitative Übereinstimmung mit den beobachteten, sehr unterschiedlichen Vermischungsbildern.

Usually, homogeneous dynamos are simulated in the framework of the differential equation approach. For purely kinematic models, the induction equation for the magnetic field has to be solved. For spherically shaped dynamo domains, such as planets and stars, the problem of implementing the non-local boundary conditions for the magnetic field is trivially solved by introducing separate boundary conditions for every degree of the spherical harmonics. However, for the simulation of other than spherically shaped dynamos, in particular for galactic and some of the recent laboratory dynamos, the handling of the boundary conditions is a notorious problem. The integral equation approach provides a solution to this problem. Basically, this approach is an application of Biot-Savart's law for dynamos. The magnetic field is produced by currents driven by an electromotive force that, in its turn, depends on the magnetic field. For the case of finite domains, the simple Biot-Savart equation has to be supplemented by a boundary integral equation for the electric potential. If the dynamo becomes time-dependent, yet another equation for the vector potential at the boundary has to be added. First numerical tests of the method for some well-investigated dynamo models in spherical domains have shown convincing agreement with the results of the differential equation method. The prospective advantage of the method, however, is its suitability to handle dynamos in other than spherical geometries.

At the Forschungszentrum Rossendorf (FZR) the new facility ELBE for research with various kinds of radiation is presently under construction. ELBE is centered around a superconductiong Electron Linac which will produce quasi-continuous beams of high Brillance and low Emittance. Preliminary results of the first stage accelerator tests will be shown. The 40 MeV / 1 mA electron beam will be used to drive free-electron lasers for the production of infrared light in the 5-510µm wavelength range. X-ray beams in the 5-50 keV energy range will be generated using channeling radiation. Additionally, the ELBE facility will provide bremsstrahlung and photoneutron beams for investigations in nuclear physics and technology.

The new radiation source "Strahlungsquelle ELBE" at the Forschungszentrum Rossendorf (FZR) will us the high brilliance electron beam from a linac with superconducting rf-cavities to porduce various secondary beams for experiments in nuclear science, solid state physics, materials research, environmental chemisty and in the life sciences. During the year 2001 all components belonging to the first stage of ELBE (20 MeV) were successfully put into operation. The main beam properties were measured and it was shown that all major design parameters could be reached with the ELBE accelerator. In the low bunch charge mode of operation intended for radiation physics applications a transversal emittance of 3 mm mrad was measured. At the 77 pC maximum bunch charge the emittance is still better than 10 mm mrad, well sufficient for driving the ELBE free-electron lasers. The longitudinal phase space properties are mainly determined by the capture process of the electron bunches into the first accelerator cavity and could, thus, be characterized by measuring the energy spectrum of the beam while scanning the rf-phase of the second cavity. These measurements at 3 pC bunch charge vielded an emittance of 57 keV ps and a bunchlength of 2 ps, in good agreement with theoretical predictions and with bunch length measurements using an autocorrelation technique.

The homogeneous dynamo effect is at the root of cosmic magnetic field generation. With only a very few exceptions, the numerical treatment of homogeneous dynamos is carried out in the framework of the differential equation approach. The present paper tries to facilitate the use of integral equations in dynamo research. Apart from the pedagogical value to illustrate dynamo action within the well-known picture of Biot-Savart's law, the integral equation approach has a number of practical advantages. The first advantage is its proven numerical robustness and stability. The second and perhaps most important advantage is its applicability to dynamos in arbitrary geometries. The third advantage is its intimate connection to inverse problems relevant not only for dynamos but also for technical applications of magnetohydrodynamics. The paper provides the first general formulation and application of the integral equation approach to time-dependent kinematic dynamos in finite domains. For the spherically symmetric alpha^2 dynamo model it is shown how the general formulation is reduced to a coupled system of two radial integral equations for the defining scalars of the poloidal and the toroidal field components. The integral equation formulation for spherical dynamos with general velocity fields is also derived. Two numerical examples, the alpha^2 dynamo model with radially varying alpha, and the Bullard-Gellman model illustrate the equivalence of the approach with the usual differential equation method.

ohne Abstract

A detailed investigation of the emission instabilities and their frequency spectra for Ga, AuGeSi and AuGe Liquid Metal Alloy Ion Sources (LMAIS) was carried out. The ion sources with an extracting electrode (triode scheme) as well as without an extractor (diode scheme) were applied. The ion current coming from the collector electrode was amplified and converted into a voltage. The amplifier has a -3 dB edge at 40 MHz and converting factor of 200 mV/µA. The frequency spectra from 0 to 50 MHz were measured using a HP8591 spectrum analyzer with a resolution of 300 kHz. Simultaneously the corresponding oscillograms of the emission current were obtained using a digital oscilloscope. The measured spectra are correlated with these oscillograms. The current for which pulses appear superimposed on the d.c. level of current is well predicted by existing theory. The pulses are believed to be the result of droplet emission, and their terminal frequency appears to coincide with the frequency of vibrations of the sides of the liquid cone at high currents. The emitted droplets screen the source tip. This leads to decreasing of the effective electric field and fluctuation of the emission process. The following disintegration of the droplets into smaller ones aggravate the noise. The fluctuation depends nonlinearly on the emission current. This dependence shows an S shape, at low emission current the noise is negligible, at 40-60 µA the fluctuation goes up rapidly and higher than 70 µA it comes to a saturation. The onset of the pulses (at about 30 µA) is also predictable from a criterion developed by Mair for the critical current. At 100 µA emission current the typical fluctuation is about 5 µA(rms). The alloy sources were investigated also at temperatures from 400 to 1100 °C and the dependence of the fluctuations of the emission on the temperature were obtained. With increasing temperature a stronger fluctuation was registered. Better understanding of the instabilities that develop on the liquid anode can be useful for deposition purposes.

In Umweltproben sind verschiedene langlebige Actinide von Bedeutung. In Wässern oder Salzlösungen mobilisierte Actinide sind mittels LS auch in Multielementspektren ohne chemische Trennung zuverlässig und schnell nachzuweisen. Die Energien müssen allerdings mindestens eine Halbwertsbreite auseinander liegen, um eine Trennung der Einzelnuklide mittels Spektrenentfaltung [1] zu erreichen. Für die Nuklide ²²⁶Ra (4,78 MeV), ²³⁷Np (4,79 MeV) und ²³³U (4,82 MeV) liegen die Energielinien zur einfachen Bestimmung mittels Peakfitting zu dicht beieinander. Bei der Bestimmung dieser Nuklide werden die Gleichgewichte von ²²⁶Ra und ²³⁷Np mit ihren radioaktiven Zerfallsprodukten ausgenutzt. Das ²²⁶Ra ist Glied der Uran-Radium-Familie. Es entsteht aus ²³⁸U durch Zerfall über Th und Pa. ²²⁶Ra zerfällt in der Reihe: 1600 a ²²⁶Ra (alpha: 4,78 MeV) 3,82 d ²²²Rn (alpha: 5,49 MeV) 3,05 min²¹⁸Po (alpha: 6,00 MeV) 26,8 min ²¹⁴Pb (beta) 19,8 min ²¹⁴Bi (beta) 164 µs ²¹⁴Po (alpha: 7,69 MeV) 22,3 a ²¹⁰Pb (beta) 5,02 d ²¹⁰Bi (beta) 138 d ²¹⁰Po (alpha: 5,31 MeV) st. ²⁰⁶Pb. Im alpha-LS-Spektrum treten folglich mit aufsteigender Energie die Peaks des ²²⁶Ra, des ²²²Rn, des ²¹⁸Po und des ²¹⁴Po auf. Mit zunehmenden Alter des ²²⁶Ra-Präparates bildet sich eine Spur des beta-Stahlers ²¹⁰Pb, aus der dann etwas ²¹⁰Po (5,31 MeV) hervorgeht. Die beta-Strahler erscheinen im LS-Spektrum, werden aber durch beta-Diskriminierung eliminiert, so dass ein reines alpha-Spektrum resultiert. Da das Tochterprodukt ²²²Rn gasförmig ist, kann ein Teil bei der Probenahme entweichen, so dass das radioaktive Gleichgewicht innerhalb der Zerfallskette gestört ist. Nach 8-10 Halbwertszeiten des ²²²Rn, also 5-6 Wochen, ist das Gleichgewicht wieder hergestellt. Die Probe wird also nach etwa 6 Wochen Wartezeit gemessen, wobei die Gesamtimpulsrate der alpha-Aktivität des ²²⁶Ra im Gleichgewicht mit seinen Folgeprodukten entspricht. Der ²²⁶Ra-Anteil wird aus den Peaks der ²²⁶Ra-Folgeprodukte bestimmt, die im Spektrum auf den ²³⁷Np/²³⁴U/²²⁶Ra-Summenpeak, der bei 4,8 MeV liegt, folgen und mittels Peakfitting zugänglich sind. Diese machen im radioaktiven Gleichgewicht mit dem ²²⁶Ra genau 74,9% der alpha-Counts aus, so dass 25,1% auf das ²²⁶Ra entfallen [2,3]. Das ²³⁷Np (2,144·106 a) ist im Gleichgewicht mit seiner Tochter ²³³Pa (26,976 d), das durch alpha-beta-Trennung gut von den alpha-strahlenden Nukliden abgetrennt werden kann. Auf Grund von Einzelmessungen bzw. Berechnungen ist das Aktivitätsverhältnis von ²³⁷Np zu ²³³Pa bekannt. So kann aus dem beta-Peak des ²³³Pa die ²³⁷Np-alpha-Aktivität berechnet werden. Durch Subtraktion des ²²⁶Ra und ²³⁷Np-Anteils des Summenpeaks bei 4,8MeV erhält man den Anteil des ²³³U.

[1] Nebelung, C., Nitsche, H.: Stillegung und Rückbau Direktmessung alpha-aktiver Nuklide in Bauschutt zur Freigabeentscheidung Schlussbericht, BMBF Förder-vorhaben 02S7655, 1999
[3] Baraniak, L., Nebelung, C., Thieme, M.: Report FZR-343 (2002) 48
[4] Nebelung, C.: Report FZR-373 (2003) 53

Ziel dieser Arbeit war die experimentelle und numerische Beschreibung der Kühlmittelvermischung in Druckwasserreaktoren (DWR). Die Kühlmittelvermischung ist für zwei Klassen von Störfällen relevant: Borverdünnungsstörfälle und Kaltwassertransienten. Ausgehend von den Vermischungsphänomenen, die für diese Szenarien bedeutsam sind, wurde die Versuchs-anlage ROCOM (Rossendorf Coolant Mixing Facility) konzipiert und aufgebaut. Die Untersuchung der Vermischung erfolgt anhand eines Tracers (verdünnte Salzlösung) und der Messung der Leitfähigkeit des Fluids. Die numerische Simulation der Kühlmittelvermischung wurde mit dem CFD-Code CFX-4 durchgeführt. Vergleichende CFD-Rechnungen für das Modell und die Geometrie des Originalreaktors vom Konvoi-Typ belegten, dass eine Skalierung im Maßstab 1:5 die Übertragbarkeit der Ergebnisse gewährleistet. An ROCOM wurden umfangreiche Geschwindigkeitsmessungen im Ringspalt des Reaktordruckbehälters (RDB) für verschiedene Schleifendurchsätze und bei Teilschleifenbetrieb durchgeführt und mit CFX-4 Rechnungen verglichen. Bei Vollschleifenbetrieb konnte im Modell eine Unabhängigkeit der Geschwindigkeitsprofile von der Reynoldszahl im Bereich des Nominaldurchsatzes nachgewiesen werden. Besonders aufschlussreich waren, in Übereinstimmung mit CFX-4 Rechnungen, die Messungen transienter Geschwindigkeitsfelder mittels Hochleistungs-LDA-Technik. Damit konnte die Phänomenologie der beschleunigten Strömung aufgeklärt werden, wobei zunächst das Fluid als Ganzes beschleunigt wird, sich später aber große Wirbel im Ringraum herausbilden. Die Experimente an der ROCOM-Anlage zur stationären Kühlmittel-zirkulation bei Betrieb aller Schleifen zeigen übereinstimmend mit CFX-4 Berechnungen eine Beschränkung der Verteilung des eingespeisten Tracers am Kerneintritt überwiegend auf den Quadranten der mit dem Tracer beaufschlagten Schleife. Bei der Simulation von transienten Strömungsvorgängen, wie z. B. dem Anlaufen der Kühlmittelzirkulation, ergibt sich dagegen im Experiment und der korrespondierenden Rechnung ein vollständig anderes Vermischungsbild. Die Strömung teilt sich in eine linke und rechte Komponente um den Kernbehälter auf, so dass die Störung zuerst den Sektor des Reaktorkerns erfasst, der der Schleife gegenüberliegt, über die der Tracer eingespeist wird. Ergänzend wurden Berechnungen zum WWER-440 bei stationärem Durchsatz durchgeführt, die die Anwendbarkeit eines analytischen Ver-mischungsmodells für WWER-440 Reaktoren bestätigen. Für turbulente Strömungen konnte CFX-4 somit anhand von Experimenten validiert werden und steht für weitere Untersuchungen in der Reaktorsicherheitsforschung zur Verfügung. Weiterhin konnte gezeigt werden, dass die Vermischungsmittelwerte im DWR mit Hilfe einer Lösung der eindimensionalen konvektiv-diffusiven Transportgleichung längs des Strömungsweges abbildbar sind. Die Ergebnisse der Experimente, CFD-Rechnungen und des analytischen Modells fließen in ein Modul ein, welches in Computercodes für Störfallanalysen integriert wird. Über eine verbesserte Beschreibung der Vermischung wird dadurch eine realistische Störfallsimulation erreicht.

Zur hochempfindlichen in situ Detektion aquatischer Kolloide mit Partikeldurchmessern < 50 nm wurde im Institut für Radiochemie ein modulares Gerätesystem zur Laser-induzierten Breakdown-Detektion (LIBD) aufgebaut, orientiert an den im Institut für Nukleare Entsorgung des FZK entwickelten LIBD-Systemen. [1-2]
Als gepulste 532 nm-Lichtquelle wird ein diodengepumpter Nd:YAG-Laser eingesetzt. Die Laserpulsenergie wird mit einer Kombination aus Fresnelrhomben und Calcitpolarisator variiert und einem pyroelektrischen Detektor gemessen. Zur Strahlcharakterisierung wird ein kommerzielles Laserstrahlanalysesystem verwendet, das eine 14 Bit-CCD-Kamera, Abschwächungsoptik, PCI-Einschubkarte und Software umfasst. Durchfluss-Küvetten aus Quarzglas werden als Probengefäße benutzt. Die Breakdown-Ereignisse werden akustisch mit einem piezoelektrischen Sensor detektiert und gleichzeitig mit einem Kamerasystem ortsaufgelöst registriert. Systemsteuerung, Datenerfassung und –verarbeitung erfolgen über ein digitales Oszilloskop sowie zwei PC.
Test- und Kalibriermessungen erfolgten an wässrigen Dispersionen von Polystyrolpartikeln. Erste Anwendungen befassten sich mit der Charakterisierung von realen Wässern.
Das Gerätesystem wird ausführlich vorgestellt, die Ergebnisse der Kalibriermessungen, der Messungen an realen Wässern sowie erster Untersuchungen zur Kolloidbildung von U(IV) werden mitgeteilt und diskutiert.

Literatur:

[1] T. Bundschuh, W. Hauser, J.I. Kim, R. Knopp, F.J. Scherbaum, Colloid. Surf. A 180, 285, (2001)
[2] C. Walther, C. Bitea, W. Hauser, J.I. Kim, F.J. Scherbaum, Nucl. Instr. and Meth. B 195, 374, (2002)

Die Parameter des Elektronenstrahls an der Strahlungsquelle ELBE des Forschungszentrums Rossendorf sind u. a. eine variable Elektronenenergie zwischen 12 und 40 MeV, 1 mA maximaler Strom, eine maximale Frequenz von 13 MHz, eine Pulslänge kleiner als 10 ps und eine geringe Emittanz. Dies führte zu der Idee, die kurzen und intensiven Elektronenpulse in kurze Neutronenpulse umzuwandeln, um an einem Flugzeitspektrometer energieabhängige Neutronenwirkungsquerschnitte zu messen bei einem kurzen Flugweg von nur einigen Metern. Hauptziel ist dabei die Messung solcher Querschnitte für Konstruktionsmaterialien von Fusions- und Spaltreaktoren und für Abfälle aus solchen Reaktoren. Aufgrund der sehr hohen Energiedeposition durch die Elektronen im Neutronenradiator wurde flüssiges Metall (Blei) als Neutronenradiator gewählt. Für das Wandmaterial ist Molybdän der Hauptkandidat, für den thermomechanische und neutronenphysikalische Rechnungen vollständig gemacht wurden. Mit den Monte Carlo Codes MCNP und FLUKA wurden die Teilchentransportrechnungen ausgeführt. U.a. wurden aus Berechnungen des Neutronenstrahls und des Untergrunds am geplanten Messplatz Schlussfolgerungen für die Konstruktion und Materialauswahl der Photoneutronenquelle gezogen. Die Berechnung des Neutronenpulses am Messplatz zeigt, dass die Neutronen von den Photonen separiert werden können, sich die Neutronenpulse jedoch stark überlappen. Wird z. B. nur jeder vierte Elektronenpuls verwendet, so beträgt der Neutronenfluss am Messplatz zirka 2.5×10⁶ n/cm²/s und der nutzbare Energiebereich 660 keV bis 6 MeV bei den Parametern 3.6 m Flugweg, 11.2×11.2 mm² Querschnitt des Radiators, 30 MeV Elektronenenergie und 1 mA Elektronenstrom. Das FZR arbeitet an einer Elektronenquelle mit kleinerer Pulsfrequenz bei gleichem mittleren Strom von 1 mA. Die Energieauflösung am Messplatz liegt unter 1%.

The irradiation induced microstructure for two reactor pressure vessel (RPV) steel types after irradiation at different neutron exposure levels and annealing treatments were investigated by means of small-angle neutron scattering (SANS).
The radiation susceptibility changes with the type of steel. Therefore the role of particular material parameters in defect evolution was worked out. The characteristics of the irradiation-induced defects such as number density, size distribution, and volume content were determined and potential defect compositions were estimated. The type of RPV steel influences the volume content but hardly the size distribution. The evolution of the defect content for a particular steel is not linear in response to the irradiation damage described in displacements per atom. The defect type is not uniform. The average composition of defects is partly changed with increasing dpa-doses. Additionally, the redissolving behaviour of irradiation induced defect clusters was studied after gradual thermal treatments.
The analysis bases on the hypothesis that the radiation defects are not-ferromagnetic. The consistency of the results supports the correctness of the hypothesis.

There is a hypothesis which postulates the microstructural radiation defects as effective traps for hydrogen and this deposited hydrogen as a stabilizer of these features. Thus, the higher the content of hydrogen the stronger is the embrittlement. The H-trap hypothesis should be examined by a SANS experiment.

The measurement has shown that we can detect H-deposition (> 1x10-4 wt.-%) by SANS.

New oxorhenium complexes with 2-(diphenylphosphanyl)-N-(2-thioethyl)benzamide (H₂PNS) and trimethyl-, triethyl- and triphenyl-hydroxyl silylated monodentate thiols are reported. These new complexes have been prepared by reacting [NⁿBu₄][R-e(O)Cl₄] with the tridentate H₂PNS and the corresponding silylated thiol at room temperature. The characterization of the complexes involved elemental analysis, ³¹P and ¹H NMR spectroscopies and X-ray crystallographic analysis for the triethyl-silylated Re complex.

Heavy metals like actinides in the aquatic environment are normally transported as a complexed species. Knowledge about the complex formation is therefore essential for prediction of the migration of these elements.
Spectroscopic methods have the advantage to be non-invasive and non-destructive. The high intensity of laser light sources allows the excitation of all species in the illuminated volume. Therefore laser-based methods reach low detection limits.
Mainly Laser-induced Photoacoustic Spectroscopy (LIPAS) and Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS) were used for such speciation studies. The introduction of lasers with pulse durations in the pico- and femtosecond range in combination with short gated CCD-cameras enables studies of fluorescing species with fluorescence lifetimes of some nanoseconds.
As uranium, americium and curium show fluorescence properties time-resolved laser-induced fluorescence spectroscopy enables the determination of species up to detection limits of 10-8 M and less. Besides the study of the complex formation of uranium (sulfate, phosphate, arsenate) we determined the formed species in several mining related waters as function of pH. The change in the speciation of uranium(VI) is shown to be in agreement with calculations.
Absorption spectroscopy can be used as tool for direct determination of actinide species. However the concentration of actinides in the natural environment is much lower than the detection limit of conventional UV-VIS spectroscopy. Using laser-induced photoacoustic spectroscopy the detection limit can be decreased by about three orders of magnitude. Studies of the complex formation of uranium(IV) with phosphate and arsenate will be presented, demonstrating the advantage of direct speciation methods.
Polyelectrolytic organic macromolecules, like humic substances, are important complexing agents towards actinide metal ions. The investigation of simple model ligands would give a more detailed description of the binding behavior of humic substances. Especially the different bonding of carboxylic and phenolic group and the discrimination between them is of interest to get more detailed information about the complex formation. The various hydroxy benzoic acids allow the investigation of these differences.
To study the complex formation of actinides with such organic ligands we used the new, recently developed femtosecond laser-induced time-resolved fluorescence spectroscopy. The method uses the fluorescence properties of organic ligands with p-electron systems and their change by interaction with actinide ions to study the complex formation of these systems.

Commisioning and operating the ELBE accelerator requires exact knowledge and easy, reproduceable control of various parameters. Important parameters like beam position and beam current are measured with a system consisting of a stripline BPM (beam position monitor), conversion electronics, data acquisition and monitoring software. The design of the electronics is described in this paper

The ELBE accelerator needs a non-destructive system for measurement of the electron beam position at about 30 location. To obtain the required resolution about 100mm a system of stripline beam position monitors (BPM) is under design. The stripline BPM can work in full power mode almost without influence on the beam. To study the basic operational principle of the stripline BPM and to get information about BPM signal behavior we did a set of measurements on the ELBE injector. The resolution of the BPM was measured as a function of the electron beam current; at an electron beam current of 1mA the resolution is about 30mm. One of the BPMs will be installed upstream the cryomodule. Since the power spectrum of the beam depends on the bunch length, measurements in the frequency domain give us information about the length of the bunch entering the cryomodule with RF cavities. The BPM will serve for setting correct phase and power of both bunchers of the injector and for measurements of the electron beam position at the entrance of the cryomodule. There are two alternative schemes of the BPM electronics under development. The first one is based on the logarithmic amplifier AD8313, another one on the an rms-responding true power detector AD8361. Both of them can process RF signals with frequencies up to 2.5GHz. The BPM electronics will operate at the fundamental frequency of the accelerator which is 1.3GHz.

1 FZR, , Germany
2 TJNAF, Newport News, Virginia, USA

The radiation source ELBE is based on a superconducting LINAC. Initially it was designed to operate in CW mode with repetition rates either 13 MHz either 260 MHz. Later it was decided to operate the accelerator with reduced repetition rates for diagnostic reasons and for certain users. Now it is possible to operate with bunch frequency 13/n MHz, where n can be 2,4,8,16,32,64 and 128. It is required that the BPM system supports any of these operation modes. A core element of the BPM electronics is a logarithmic detector AD8313 made by Analog Devices Inc. The logarithmic detector is a direct RF to DC converter rated up to 2.5 GHz. Initial design of the BPM electronic was sophisticated only for CW operation with repetition rate more than 10 MHz, since bandwidth of the AD8313 is about of 10 MHz. Additionally a sample and hold amplifier is built in to provide enough time for an ADC to make measurements. The sample and hold amplifier is synchronized with a bunch frequency. In the paper we present results of the modified BPM electronics test.

The radiation source ELBE at Forschungszentrum Rossendorf is based on a superconducting linear accelerator that produces a CW electron beam up to 40 MeV and 1 mA. In 2001 the first stage of the ELBE LINAC was put into operation. The main electron beam parameters like energy, transverse emittance, bunch length and energy spread were determined. Moreover, optimal machine parameters were specified and several online diagnostics were tested, such as beam position monitors and beam-loss detectors.

n the research center Rossendorf, the radiation source ELBE based on a super conducting LINAC is under construction. In the year 2001 the first accelerating module was commissioned. The electron beam parameters like emittance, bunch length, energy spread weremeasured. Here we present results of the measurements as well as the methodics used to make the measurements. In the ELBE injector, where electron beam energy is 250 keV, the emittance was measured with the help of multislit device. Emittance of the accelerated beam was measured by means of quadrupole scan method and is 8 mm×mrad at 77 pC bunch charge. Electron bunch length was measured using coherent transition radiation technique. At the maximum design
bunch charge of 77 pC the RMS bunch length was measured to be 2 ps. A set of online diagnostic systems is also under development. One of them a system of stripline beam position monitors is also described here. A BPM resolution of about 10 µm was achieved using logarithmic amplifier as the core element of the BPM electronics. A system of beam loss monitors based on the RF Heliax cable working as an ionization chamber is intended to be another online diagnostic system.

At the Forschungszentrum Rossendorf (FZR), the superconducting electron linear accelerator ELBE is under construction. It will deliver an electron beam with an energy of up to 40 MeV at an average beam current of up to 1mA. The accelerator uses standing wave DESY type RF cavities operating at 1.3 GHz. A non-destructive system for the measurement of the beam position at about 30 locations is needed. To obtain the required resolution of 100 mm, a system of stripline beam position monitors (BPM) is under design.

A comparison between ultra-fast X-ray CT and a wire-mesh sensor is presented. The measurements were carried out in a vertical pipe of 42 mm inner diameter, which was supplied with an air-water mixture. Both gas and liquid superficial velocities were varied. The X-ray CT delivered 263 frames per second, while the wire-mesh sensor was operated at a frequency four times higher. Two different gas injectors were used: 4 orifices of 5 mm diameter for creating large bubbles and gas plugs and a sintered plate with a pore size of 100 µm for generating a bubbly flow. It was found that the wire-mesh sensor has a significantly higher resolution than the X-ray CT. Small bubbles, which are clearly shown by the wire-mesh sensor, cannot be found in the CT images, because they cross the measuring plane before a complete scan can be performed. This causes artifacts in the reconstructed images, instead. Furthermore, there are large deviations between the quantitative information contained in the reconstructed tomographic 2D distributions and the gas fractions measured by the sensor, while the agreement is very good, when the gas fraction is obtained by a direct evaluation of the X-ray attenuation along the available through-transmission chords of the tomography setup. This shows that there are still potentials for an improvement of the image reconstruction method. Concerning the wire-mesh sensor it was found, that the gas fraction inside large bubbles is slightly underestimated. Furthermore, a significant distortion of large Taylor bubbles by the sensor was found for small liquid velocities up to 0.24 m/s. This effect vanished with growing superficial water velocity.

Positron emission tomography (PET) is currently the only technically feasible method for the non-invasive and in situ control of the precision of the irradiation in highly conformal heavy ion tumour therapy. ...

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is a useful tool to study the speciation of uranyl in solution and at mineral surfaces. Sorption experiments of U(VI) adsorbed on ferrihydrite samples were carried out under ambient atmosphere for pH 5.8 and 7.8 in 0.1 N NaClO₄ solution. A ferrihydrite suspension with an iron concentration of 1 mM was used. The total U(VI) concentration used in these experiments were 5·10^-5, 1·10^-5, and 1·10^-6 M. The contact time of U(VI) with the mineral was two to three days.
TRLFS measurements in the ferrihydrite system were carried for the supernatant. Characteristic fluorescence spectra of the remaining U(VI) in solution were found for the samples with 5·10^-5 and 1·10^-5 M at pH 5.8. No uranium fluorescence signal could be obtained for all samples at pH 7.8 indicating that the sorption at this pH was stronger than at pH 5.8. The emission bands for the detected fluorescence signal of the two pH 5.8 samples were found at 486, 502, 522, and 546 nm. These emission bands and the determined respective lifetime of 28500 ± 1000 ns and 4600 ± 100 ns are indicative for UO₂OH^-5 and UO₂(OH)₂.
Batch sorption experiments of U(VI) adsorbed on gibbsite samples were carried out under ambient atmosphere for pH 3.5 to 9.5 in 0.1 N and 0.01 N NaClO₄ solution. The solid concentration for the gibbsite samples was 12.5 g/L. The total U(VI) concentration used in these experiments was 1·10^-6 M. The gibbsite was separated from solution by centrifugation at 3500 rpm for 15 minutes. The residue was then taken up with a solution of the same ionic strength and pH and subsequently measured the suspension by TRLFS. This procedure guarantees that the detected signal was exclusively attributed to adsorbed U(VI) on the gibbsite surface.
The detected emission bands for the adsorbed U(VI) surface species on gibbsite were observed at 495, 518, 543, and 568 nm. The fluorescence spectrum was best described with one lifetime of 2400 ± 660 ns indicating that one U(VI) surface species on gibbsite has formed.

We report a X-ray diffraction and Fourier transform infrared spectroscopy study of highly strain compensated InxGa1-xAs/AlAs/ InyAl1-yAs multiple quantum well structures grown pseudomorphically grown on InP substrate by gas-source molecular beam epitaxy. X-ray diffraction patterns show compositional grading of the interfaces that markedly influence the absorption spectra. The intersubband transitions at wavelengths shorter than 2.0 mm for QW structures with different InGaAs well thickness are presented.

Porous silicon (PS) has a great potential in optical applications due to its tuneable refractive index. In particular, multilayer structures consisting on PS layers with different refractive indexes can be used as interference filters. Due to the characteristics of PS and its production process, many types of interence filters can be produced: Bragg reflectors, monochromatic filters for light emitting devices (which can also be based on PS), microcavities for biosensing applications, Fabry-Pérot resonators, photonic crystals, etc.

In the present work the optical properties of PS single layers and multilayer structures were studied. Since the refractive index of PS varies depending on the air content of the porous matrix, the PS structures were modelled as an homogeneous mixture of silicon and air (and, eventually, silicon dioxide), according to the effective medium theories (EMTs). By adjusting the refractive index and thickness of each individual layer, we can obtain a stack of PS layers with the desired optical properties, resulting in interference filters of predetermined band width.

The optical characterization has been carried out by spectrophotometric and spectroscopic ellipsommetry measurements. In addition, compositional analysis has been performed by means of Ion Beam Analysis (IBA) techniques, with special interest devoted to oxygen and hydrogen, in order to correlate the optical parameters and the chemical composition. Finally, multilayers structures have been produced and their operation has been checked.

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Cubic boron nitride (c-BN) films with low stress have been produced by simultaneous 35 keV N+ ion implantation during growth by Ion Assisted Sputtering (IAS). The stress release is achieved at the lost of a decrease in the c-BN content. Despite this fact, films with high c-BN content and relatively large thickness (~0.4 mm) have been successfully produced. The decrease on the c-BN content is discussed in terms of the damage induced by the medium energy ion implantation.

Ion beam assisted deposition (IBAD)techniques have been employed to produce thin films composed of boron, carbon, and nitrogen atoms, including amorphous carbon (a-C), carbon nitride (CNx) and ternary compounds (BCxNy). The films were deposited by evaporating either graphite or boron carbide (B4C) targets, with simultaneous ion bombardment from a precursor N2 +CH4+Ar gas mixture. The composition and bonding structure of the films have been carefully studied, including the analysis with time of flight elastic recoil detection analysis (TOF-ERDA) and X-ray absorption near-edge spectroscopy (XANES). Mechanical characterisation of the films has been also performed, including measurements of hardness, elastic modulus, and friction coefficients. The optimal values encountered are hardness of B35 GPa, and friction coeffivients of B0.05. Also, the thermal stability of the films has been examined by annealing under vacuum conditions. The applicability of the coatings is discussed in terms of all these parameters.

We report on the production of nanoscale patterning on Si substrates by low-energy ion-beam sputtering. The surface morphology and structure of the irradiated surface were studied by atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). Under ion irradiation at off-normal incidence angle (~50◦), AFM images show the formation of both nanoripple and sawtooth-like structures for sputtering times longer than 20 min. The latter feature coarsens appreciably after 60 min of sputtering, inducing a large increase in the surface roughness. This behaviour is attributed to the preferential direction determined on the substrate by the ion beam for this incidence angle, leading to shadowing effects among surface features in the sputtering process. Under irradiation at normal incidence, the formation of an hexagonal array of nanodots is induced for irradiation times longer than 2 min. The shape and crystallinity of the nanodots were determined by HRTEM. At this incidence angle, the surface roughness is very low and remains largely unchanged even after 16 h of sputtering. For the two angle conditions studied, the formation of the corresponding surface structures can be understood as the interplay between an instability due to the sputtering yield dependence on the local surface curvature and surface smoothing processes such as surface diffusion.

The isopeptide N^Epsilon-(Gamma-glutamyl)-L-lysine 4 was labelled with ¹⁸F via N-succinimidyl-4-[¹⁸F]fluorobenzoate ([¹⁸F]SFB). A modified approach for the convenient synthesis of [¹⁸F]SFB was used, and [¹⁸F]SFB could be obtained in decay-corrected radiochemical yields of 44-53% (n=20) and radiochemical purity >95% within 40 min after EOB. For labelling N^Epsilon-(Gamma-glutamyl)-L-lysine with [¹⁸F]SFB the effects of isopeptide concentration, temperature, and pH were studied to determine the optimum reaction conditions. The coupling reaction was shown to be temperature and pH independent while being strongly affected by the isopeptide concentration. Using the optimized labelling conditions, in a typical experiment 1.3 GBq of [¹⁸F]SFB could be converted into 447 MBq (46%, decay-corrected) of [¹⁸F]fluorobenzoylated isopeptide within 45 min, including HPLC purification.

Im kernnahen Bereich verändert der Reaktordruckbehälter unter dem Einfluss der Neutronenbestrahlung seine Eigenschaften. Das Phänomen ist als Neutronenversprödung bekannt und insbesondere für die Reaktoren vom Typ WWER von hoher sicherheitstechnischer Relevanz. Zur Vertiefung des Verständnisses und zur quantitativen Beschreibung der Zusammenhänge zwischen Gefüge, mechanischen Eigenschaften und der Strahlenbelastung wurden an WWER-Reaktordruckbehälterwerkstoffen Mikrostrukturuntersuchungen durchgeführt.

RF photo cathode electron guns are the source of choice for most high-performance accelerator systems. Their advantages are the ability to produce very bright beams of electrons with high bunch charges and small transverse and longitudinal emittance. At present, their drawback is the limited average current since the high RF fields in the cavities require a pulsed operation. On the other hand, advanced light sources uses linear accelerators with superconducting RF cavities which can operate in the cw mode and produce high average current electron beams. A preferred injector for these accelerators would be a photo electron gun with superconducting RF cavities.
In a research project [1], a superconducting RF photo electron gun (SRF gun) has been developed during the last years at the Forschungszentrum Rossendorf. The SRF gun was put successfully into operation and the efficiency of the concept could be demonstrated. A helium bath cryostat was used to cool down the cavity to 4.2 K. In a daily cycle the cryostat was filled up with liquid helium in the morning followed by a measuring time in the afternoon. The resonator is a niobium half cell with TESLA geometry operating at 1.3 GHz. The photo cathode had a Cs2Te layer deposited in a preparation chamber connected with the gun. In contrast to the cavity the cathode is not superconducting. It is thermally isolated from the cavity and its heat load goes in a special nitrogen cooling system. The cathode was illuminated by an UV laser of 263 nm with a micropulse frequency of 26 MHz and a maximum energy per pulse of 40 nJ. For evaluation of the produced electron beam a beam line is installed with two solenoids, insertable mask and view screens, spectrometer magnet, kicker cavity and Faraday-cup. Measurements of beam parameters and operation experience are reported.

1] E. Barthels et al., Nucl. Instr. and Meth. A 445 (2000) 408

The ELBE accelerator, an electron linac with superconducting cavities, is designed for a beam energy of 40 MeV, a cw current up to 1 mA and a maximum bunch charge of 77 pC. After acceleration, the electron beam will be used to generate a variety of electromagnetic radiation with different wavelength. Two FELs will deliver coherent infrared radiation, monochromatic x-rays will be produced by means of a channeling target and MeV photons with a bremsstrahlung target. Furthermore, converter targets for neutron and positron production will be installed. For the first commissioning tests, the injector with a thermionic gun, one cryomodule with two nine-cell cavities and a diagnostic beam-line were in operation. Energy and energy width were determined with a magnetic spectrometer. Transverse emittance measurements were carried out with a pepper-pot mask in the injector and with the quadrupole scan method for the accelerated beam. Bunch length was determined from the autocorrelation function of the coherent transition radiation with a Martin-Puplett interferometer. The results of these beam parameter measurements will be presented and evaluated

In the last year at the Forschungszentrum Rossendorf, in cooperation with the Budker Institute Novosibirsk, DESY, the Max-Born-Institut Berlin, and ACCEL, a superconducting rf photoelectron gun (SRF gun) has been developed [1]. On March 5, 2002 this gun is going into successful operation. A half-cell niobium cavity has been cooled down to 4 K. In this cavity a CsTe2 photocathode is installed, isolated electrically and thermally by a vacuum gap. The Q value and the accelerating field strength in the cavity have been measured. For 4 K, Q=2x108 and an accelerating field of 14 MV/m have been obtained. This value did not change during four weeks of operation time. The energy of the electron beam is 0.62 MeV and the bunch charge is 26 pC. The laser works with a duty factor of 25% and with a repetition rate of 26 MHz inside the macropulse. The average laser power in the macropulse is 1.5 W (l=260 nm), and the length of the micropulse is 5 ps FWHM. This corresponds to an average electron current of 170 µA and 680 µA in the macropulse. The isolated cathode allows the separate measurement of the cathode current and the current inside the beam dump as a function of the laser phase. The next measurements are planned for late May.

[1] E. Barthels et al., Nucl. Instr. and Meth. A 445 (2000) 408

Last year the first ELBE accelerating module was commissioned. During the commissioning the electron beam parameters such as transverse emittance, energy spread and bunch length were measured. Each of them was studied at different bunch charges as a function of RF field phase in the first accelerating cavity. Especially for an accelerator like ELBE, which is intended to be a driver for free electron laser (FEL), bunch length measurement in picosecond range becomes very important and impose some challenge. Coherent transition radiation (CTR) technique was used to measure bunch length. This technique uses the Martin-Puplett interferometer to measure the autocorrelation of the CTR pulse yielding a minimum 2 ps RMS bunch length at 77 pC bunch charge. Short description of the method, experimental setup, data evaluation procedure and results of the measurements will be presented.

By December 2001 we concluded the first operational period of the ELBE accelerator. The achieved results and measured parameters of the electron beam are presented here. Although the full beam energy of 20 MeV for the first accelerator stage has been reached, most measurements were performed at 12 MeV beam ernergy with varying beam currents and bunch charges. The nominal bunch charge of 77 pC was reched and the measured beam parameters (energy spread, bunchlength and transverse emittance) meet the previous predictions.

The ELBE project is intended to produce a wide spectrum of different radiation and neutrons, especially coherent light in the medium and far infrared by means of a free electron laser. The driver of the radiation source is a super-conducting electron linear accelerator designed for a wide range of beam parameters in order to satisfy the various requirements.
Recently, the forst cryostat containing two nine-cell niobium standing wave rf cavities for an acceleration up to 20 MeV has been put into operation and has been cooled down. For the first time, an accelerated electron beam has been produced successfully.
The helium cooling for the cryostat working at 1.8 K, the electron beam injector, the radio frequency system, beam control and beam diagnostics operate very reliably. In the paper the results of the beam parameter measurements and the experiences gained in the first operation period will be presented.

Als Bestandteil der Nebengesteine von Uranlagerstätten und potentiellen Endlagern für radioaktive Abfälle stellen Feldspäte eine mögliche Mineraloberfläche für die Sorption von mobilisierten Uran(VI) dar. Durch die Wechselwirkung zwischen Feldspat und der wässrigen Phase kann es neben der Adsorption von Uran(VI) zu Mineralauflösung und -neubildung kommen. Ziel der Arbeit ist es, mittels EXAFS-Spektroskopie (Extended X-ray Absorption Fine Structure) und TRLFS (Time-Resolved Laser-induced Fluorescence Spectroscopy) die Sorptionsmechanismen von Uran(VI) an Albit in Abhängigkeit von Mineralauflösungs-prozessen aufzuklären.

Die U(VI)-Adsorption an Albit, Na_0,86K_0,09Ca_0,05[Al_1,05Si_2,95O₈] /1/, der Korngröße 2-6,3 µm (BET: 2,2 m²/g) wurde in 0,01 M NaClO₄- Lösung im batch- und Durchflussversuch untersucht. Im Batchversuch erfolgte die U(VI)-Adsorption bei pH 6,4 und 1·10^-5 M U innerhalb einer Sorptionsdauer von 24 Stunden. Die Durchflussversuche erfolgten ohne vorherige Equilibrierung des pH-Wertes mit U(VI)-Konzentrationen von 5·10^-6 und 2·10^-5 M bei pH 5,8 über einen Zeitraum von 170 Tagen. Zusätzlich wurde Albit bei 40°C über mehrere Monate in 0,01 M HClO₄ sauer aktiviert. Die entstehende siliziumreiche Oberflächenschicht (leached layer) wurde duch Ultraschall abgetrennt und angereichert. An diesem sauer aktivierten Albit <2 µm (BET: 21,6 m²/g) wurde U(VI) bei pH 5,8 (2·10^-5 M U) und 5,0 (1·10^-4 M U) adsorbiert. Die Sorptionsproben wurden als feuchte Paste für die Messung der zeitaufgelösten Fluoreszenzspektren (TRLFS) und Röntgenabsorptionsspektren (EXAFS: ESRF, ROBL) präpariert.

Die Anpassung der EXAFS-Spektren ergeben für die U(VI)-Sorption an Albit im Batch und Durchflussversuch einen kurzen Abstand der äquatorialen Sauerstoffe O_eq von ca. 2,35 Å. Der kurze Abstand und der hohe Debye-Waller Faktor weisen auf eine inner-sphere Oberflächenkomplexierung hin. Bei Uran(VI) adsorbiert an sauer aktivierten Albit ist die äquatoriale Sauerstoffschale in zwei Schalen bei 2,23 Å und 2,44 Å gesplittet, was als die Präsenz einer inner-sphere Oberflächenspezies interpretiert werden kann. Bidentat koordiniertes Silizium wurde mit der EXAFS-Spektroskopie nicht beobachtet, die Detektion monodentater Uran(VI)-Silikat Koordinationen ist jedoch wegen destruktiv interferierender Mehrfachstreupfade stark eingeschränkt. Uran-Uran Rückstreuungen wurden nicht beobachtet, eine Präzipitation von Uran(VI)phasen ist demnach kein dominierender Sorptionsmechanismus. Die TRLFS zeigt für U(VI) sorbiert an Albit (Durchflussversuch) zwei Fluoreszenzspezies mit t₁ = 1 µs und t₂ = 10-20 µs, während bei U(VI) adsorbiert an sauer aktivierten Albit nur eine Fluoreszenzspezies beobachtet wurde, deren Spektrum und Lebensdauer t₂ entspricht. Das Spektrum von Fluoreszenzspezies t₂ ist dem von Uran(VI) adsorbiert an Silica ähnlich /2/. Sowohl die EXAFS- als auch die TRLFS-Ergebnisse zeigen, dass die Sorption von Uran(VI) an Albit bevorzugt als inner-sphere Oberflächenkomplexierung am Silikattetraeder stattfindet.

/1/ Zorn T. (2000) Dissertation TU Dresden.
/2/ Gabriel et al. (2001) J. Colloid Interface Sci. 239, 358-368.

Implantation-induced excess vacancies and the related Cu gettering was studied in Si and in the solid solution Si0.93Ge0.07. The excess vacancy and interstitial generation during normal and inclined ion implantation can be simulated by a simple binary collision process. The excess defects are shown to control the Cu gettering observed in Si after rapid thermal annealing at a temperature of 900oC. The vacancy concentration in the SiGe layer is higher than in Si. An additional vacancy concentration of about 3.15´1018cm-3 was determined in the SiGe layer beside the implantation-generated excess vacancies. These vacancies are presumably incorporated by the SiGe layer deposition on Si substrate. Vacancies agglomerate and form cavities during annealing. The cavities in SiGe were found to be significantly larger than in Si.

The neutron-deficient nucleus ⁶⁶Ge was populated at high spin in two experiments using the reaction ⁴⁰Ca(³²S, α2p) at beam energies of 105 and 95 MeV. In the first experiment, a self supporting ⁴⁰Ca target was used, while a gold-backed target of similar thickness was used in the second experiment. αγ rays were detected with the EUROBALL array, combined with the charged-particle detector array EUCLIDES and the Neutron Wall. The level scheme of ⁶⁶Ge was extended up to E=18MeV and I=(23^- ). Above angular momentum 10⁺, we found two sequences, connected by energetically staggered I=1 M1 transitions. The total Routhian surface calculations describe ⁶⁶Ge at lower spins as a αγ-soft nucleus a having moderate deformation of β₂=0.23, while a triaxial deformation is predicted for the band structures above I^π=10⁺. To our knowledge, this is the first observation of staggered M1 transitions in a deformed four-quasiparticle π(g² _9/2)νg² _9/2 ) structure.

precipitation formation in Al4Cu by ion irradiation

For a thermionic electron gun working at 250 kV and producing bunches up to 85 pC, the measurement of the transverse emittance shows an increase with bunch charge. In order to understand this effect numerical simulations have been performed. The influences of the electrode geometry, space charge and of the control mesh in front of the cathode are included in the simulation. The results show that the growth of the transverse emittance for higher bunch charges is mainly caused by the control mesh. The strong acceleration field penetrates through the mesh holes and for the electrons each hole acts as a small lens. The portion of electrons which are deflected increases with electron current. In the numerical simulation the field and electron trajector calculation was performed with the EGUN code [1]. For the electron transmission throught the potential barrier of the mesh the free electron gas approximation with a local penetration probability, a Maxwell energy distribution and an angular distribution according to Lambert´s law was applied.

1. W.B. Herrmannsfeldt, Report SLAC-331-UC-28, Stanford University, 1988