Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The exchange coupling strength as a function of the buffer layer thickness is investigated for several carefully chosen seed materials. The crystal microstructure of the ferromagnetic(FM)-antiferromagnetic(AF) interface is directly related to the roughness and dimensionality of the buffer layer surface, which scales not only with such parameters as a texture and grain sizes but can be discussed as well in the frame of the wetting behavior of subsequent films. Particularly, it is shown that strong wetting between the substrate and the next layer can decrease the surface dimensionality and improve the growth conditions for the subsequent films. Thus, the smoothness of the FM-AF interface improves significantly which leads to a much stronger exchange coupling across the interface. In addition, it is demonstrated that the magnitude of the exchange bias is proportional to the grain sizes distribution, which is in good agreement with theoretical predictions.

no abstract available

Fragestellung: Die klassischen Teilchenbeschleuniger bieten einige 10 Pikosekunden (Elektronen) bzw. Nanosekunden (Protonen und Ionen) lange Pulse der Partikelstrahlung an. Mit der neuartigen Technologie der Laserbeschleunigung ist es möglich kürzere Teilchenpakete (einige 10 Femtosekunden) mit wesentlich geringerer Pulsfrequenz (einige Hertz gegenüber Megahertz) bei höherer Pulsintensität zu erhalten. Für eine Verwendung dieser Technologie in der Strahlentherapie muss eine möglicherweise andere biologische Wirksamkeit, sei es durch eine die andere Zeitstruktur oder durch die höhere Pulsdosisleistung, gegenüber den klassischen Teilchenstrahlen untersucht werden. Im Vortrag werden die weltweit ersten Zellbestrahlungen mit laserbeschleunigten Elektronen vorgestellt und diskutiert.
Methodik: Die Experimente wurden an dem 10-Terrawatt-Lasersystem JETI in Jena durchgeführt. Die Elektronenpakete haben eine Länge von ca. 150 fs und eine Wiederholrate von 2,5 Hz. Wichtige Vorraussetzungen für strahlenbiologische Experimente waren die Anpassung des Lasersystems, der Aufbau einer geeigneten Strahlführung und eines Dosimetriesystems. Bei einer ersten Serie von in-vitro Zellbestrahlungen mit Strahlendosen im Bereich von 0,3 bis 5 Gy wurde die Anzahl der Doppelstrangbrüche zu verschiedenen Zeitpunkten nach Bestrahlung in zwei Zelllinien bestimmt.
Ergebnisse: Das Lasersystem wurde erfolgreich für Zellbestrahlungen angepasst, d.h. die Zellproben werden homogen ausgeleuchtet und die Strahleigenschaften sind gut reproduzierbar. Die applizierte Dosis kann in Echtzeit monitoriert werden. Dadurch wird die Kontrolle und Steuerung der Zellbestrahlungen erleichtert. Eine genaue Dosisbestimmung ist nach der Bestrahlung mit Filmen, die am Zellkulturhalter befestigt waren, für jede Probe einzeln möglich. Das Gesamtsystem kann für systematische Untersuchungen eingesetzt werden, wie in einer ersten Zellbestrahlung demonstriert wurde. In diesem Experiment wurden Dosis-Effekt-Kurven bestimmt. Um eindeutige Aussagen zu erhalten, müssen die in Auswertung befindlichen Daten mit weiteren Experimenten ergänzt werden.
Schlussfolgerungen: In Zukunft werden systematische Messungen für verschiedene Tumor- und Normalgewebszellen sowie verschiedene biologische Endpunkte durchgeführt.

A brief overview of some mathematical aspects connected with the occurrence of spectral singularities will be presented. Based on simple matrix models we discuss stratified manifolds in parameter spaces on which the matrix eigenvalues degenerate. We comment on discriminant sets and similarity relations to canonical Jordan structures, demonstrate the mechanism underlying the formation of self-orthogonal (isotropic) eigenvectors, relate it to corresponding projectors. Special emphasis will be laid on the break-down of similarity transformations, the formation of corresponding transformation singularities and their resolution via projective extensions. Structural links to ultrarelativistic spinor models will be sketched. Finally, we comment on versal deformations and an unfolding rule for higher-order spectral singularities connected with the Hessenberg type of the perturbation.

The presence of actinides in radioactive wastes is of major concern because of their potential for migration from the waste repositories and long-term contamination of the environment. Studies have been and are being made on inorganic processes affecting the migration of radionuclides from these repositories to the environment but it is becoming increasingly evident that microbial processes are of importance as well. The relevance of microorganisms to actinide behavior arises from the overlap of the biosphere with the geosphere and the transformations that occur because of their interactions. The present study is intended to give a brief overview of the key processes implicated in the interaction of actinides e.g. uranium with bacterial strains isolated from different extreme environments relevant to radioactive repositories. A complex methodological approach involving a combination of wet chemistry, transmission electron microscopy, and advanced solid state speciation techniques is used. Fundamental understanding of the interaction of these bacteria with U will be useful for developing appropriate radioactive waste treatments, remediation and long-term management strategies as well as for predicting the microbial impacts on the performance of the radioactive waste repositories.

no abstract available

Management of long-lived nuclear wastes is, after safety, the main issue of nuclear industry, both in terms of scientific challenge as well as public acceptance. Among the different options that have been envisioned and explored for minor actinides over the past thirty years, two alternatives currently remain: long term disposal in a safe repository or nuclear wastes “burning” in a so-called transmutation process. Materials selected for such applications have to meet the following criteria: high incorporation amount of actinides, good structural and chemical stability, low thermal dilatation and resistance to radiation.
Among the various ceramics envisaged, zirconia based pyrochlore oxides of composition An2Zr2O7 (An=actinide) appear to be a very good candidate. Results obtained with lanthanide pyrochlores submitted to ion-beam irradiation show that Zr based pyrochlores, unlike Ti based, remain crystalline with a transition from pyrochlore structure to a defect fluorite structure [1]. However, this strong radiation tolerance still has to be confirmed on alpha emitter materials (e.g. americium). In that prospect, 241Am2Zr2O7 sample was synthesized [2] and its evolution under the effect of alpha self-irradiation as a function of time was followed by XRD. Figure 1 shows the transition from the pyrochlore phase to a defect-fluorite phase after ~200 days as the superstructure peaks (marked ) slowly vanish and completely disappear after about 200 days [3].

We study a non-Hermitian PT-symmetric generalization of an N-particle, two-mode Bose-Hubbard system, modeling for example a Bose-Einstein condensate in a double well potential coupled to a continuum via a sink in one of the wells and a source in the other. The effect of the interplay between the particle interaction and the non-Hermiticity on characteristic features of the spectrum is analyzed drawing special attention to the occurrence and unfolding of exceptional points (EPs). We find that for vanishing particle interaction there are only two EPs of order N+1 which under perturbation unfold either into [(N+1)/2] eigenvalue pairs (and in case of N+1 odd, into an additional zero-eigenvalue) or into eigenvalue triplets (third-order eigenvalue rings) and (N+1)mod 3 single eigenvalues, depending on the direction of the perturbation in parameter space. This behavior is described analytically using perturbational techniques. More general EP unfoldings into eigenvalue rings up to (N+1)th order are indicated.

Hintergrund:

In vielen Tumoren unterschiedlicher Patienten wie auch innerhalb eines individuellen Tumors kann eine heterogene [¹⁸F]FDGAufnahme nachgewiesen werden. Derzeit ist nicht bekannt ob diese intratumorale Heterogenität mit dem Ansprechen von Tumorsubvolumina korreliert und als biologischer Marker für eine heterogene Dosis-Verschreibung z. B. Dosis-Eskalation partieller Volumina verwendet werden kann. Für diese Fragestellung haben wir in einer präklinischen Modellsituation die Heterogenität der [¹⁸F]FDG-Aufnahme und den Dosis-Effekt in einer einzelnen, in Nacktmäusen transplantierten humanen Tumorzelllinie untersucht.

Methoden:

Die hSCC Zelllinie FaDu wurde subkutan auf das Hinterbein von NMRI Nacktmäusen transplantiert. Ab einem Tumordurchmesser von 7 mm erfolgte die Aufnahme in das Experiment. Jedes Tier erhielt eine [¹⁸F]FDG-PET-Untersuchung (microPET® P4, CTI) direkt vor Bestrahlung zur Bestimmung des Maximum Standardized Uptake Value (SUVmax). Die Einzeldosisbestrahlungen mit 25 Gy oder 35 Gy erfolgten
unter ambientem Blutfluss mit 200 kV Röntgenstrahlen (0.5 mm Cu, ∼ 1 Gy min-1). 62 Tiere wurden in dieser Studie untersucht, davon befinden sich noch fünf Tiere im Follow-up. Experimenteller Endpunkt war die lokale Tumorkontrolle am Tag 120 nach Bestrahlung.

Ergebnisse:

Die Spanne der SUVmax-Werte reichte von 0.72 bis 3.47, der Median war 1.59. Die lokalen Tumorkontrollraten für alle 62 Tiere betrugen 28% nach Bestrahlung mit 25 Gy und 57% nach 35 Gy (Kaplan-Meier-Analyse, Logrank-Test p = 0.007). Im nächsten Schritt wurde eine univariate
Analyse der Dosis-Effekt-Beziehung für die entsprechend des Median SUVmax stratifizierten Tiere durchgeführt. Für Tumoren < Median SUVmax
betrug die lokale Kontrolle 37% nach 25 Gy vs. 47% nach 35 Gy (p = 0.37). Im Gegensatz dazu fand sich ein signifikanter Unterschied der lokalen
Tumorkontrollraten für Tumoren > Median SUVmax (15% nach 25 Gy vs. 68% nach 35 Gy, p = 0.002). In der multivariaten Cox-Analyse mit
Strahlendosis und SUVmax als kontinuierliche Variablen, konnte eine signifikante Verringerung des Rezidivrisikos mit ansteigender Strahlendosis
(p = 0.007) und ein grenzwertig, signifikanter Effekt des SUVmax-Wertes nachgewiesen werden (p = 0.06).

Zusammenfassung:

Diese Daten zeigen einen größeren Effekt der Bestrahlungsdosis auf die lokale Kontrolle in Tumoren mit initial hoher [¹⁸F]FDG-Aufnahme im Vergleich zu Tumoren derselben Tumorlinie mit niedriger [¹⁸F]FDG-Aufnahme. Diese Ergebnisse unterstützen die Hypothese, dass ein prätherapeutisches [¹⁸F]FDG-PET wichtige Informationen für die Verschreibung einer heterogenen Bestrahlungsdosis liefern kann. In dieser Studie wurde nur ein Tumormodell und Einzeldosisbestrahlung untersucht. Weitere Experimente mit anderen Tumormodellen und fraktionierter Bestrahlung sind notwendig.

Gefördert im Rahmen des EU-Projektes „BioCare“ Molecular Imaging for Biologically Optimized Cancer Therapy #505785.

Das Verbundprojekt "onCOOPtics - Hochintensitätslaser für die Radioonkologie" hat sich zum Ziel gesetzt eine neuartige und auf Laser basierende Technologie zur Erzeugung von Teilchenstrahlung für die Krebstherapie zu implementieren. Im Unterschied zu den klassischen, in der Strahlentherapie eingesetzen, Partikelstrahlungen, bestehen diese neuartigen Teilchenstrahlen aus wesentlich kürzeren Teilchenpaketen (einige 10 Femtosekunden gegenüber Piko- bzw. Nanosekunden Länge), die mit geringerer Pulsfrequenz (einige Hz statt MHz) aber höherer Pulsdosisleistung erzeugt werden. Diese Unterschiede in den Strahleigenschaften und ihr Einfluss auf die biologische Wirksamkeit müssen hinsichtlich eines möglichen Therapieeinsatzes untersucht werden; erste in - vitro Zellbestrahlungsexperimente mit laserbeschleunigten Elektronen hierzu werden im Vortrag vorgestellt.
Die ersten Experimente wurden mit dem 10 TW - Lasersystem JETI der Universität Jena durchgeführt. Mit diesem Lasersystem werden Elektronen aus einem Gasjet - Target heraus beschleunigt, wobei Elektronenpakete mit einer Länge von ca. 150 fs und einer Wiederholfrequenz von 2,5 Hz erzeugt werden. Das Lasersystem wurde an strahlenbiologische Erfordernisse, d.h. ausreichend großer Strahlfleck und hohe Dosisleistung, sowie von Bestrahlung zu Bestrahlung gut reproduzierbare Strahleigenschaften, angepasst und Zellbestrahlungen mit zwei verschiedenen Zelllinien im Dosisbereich von 0,3 bis 5 Gy durchgeführt. Zur Kontrolle der Experimente wurden verschiedene Systeme zur Strahl- bzw. Dosismonitorierung und retrospektiven Dosisbestimmung eingesetzt. Während der Bestrahlungen wurde die Elektronenstrahlintensität mit einem Faraday - Cup überwacht und die Dosisleistung im Strahl mittels Ionisationskammern gemessen. Die am Zellort applizierte Dosis wurde nach der Bestrahlung mittels Filmdosimeter, welche direkt vor den Zellproben positioniert waren, bestimmt.
Eine erste strahlenbiologische Charakterisierung der laserbeschleunigten Elektronen erfolgte mit dem Nachweis von DNS Doppelstrangbrüchen über die Antikörper - Doppelmarkierung von g - H2AX und 53BP1, zwei Molekülen, die direkt nach Bestrahlung an den Doppelstrangbrüchen der DNS aktiviert werden. Für beide untersuchten Zelllinien konnten erste Dosis - Effekt - Kurven dieses biologischen Endpunkts für verschiedene Zeitpunkte nach Bestrahlung bestimmt werden. Eindeutige Aussagen, auch im Vergleich zu verschiedenen Referenzstrahlungen, werden aber erst nach Abschluss der Experimentreihe möglich sein.
Ein Ausblick auf zukünftige Arbeiten mit verschiedenen Zelllinien und weiteren biologischen Endpunkten wird ebenfalls im Vortrag gegeben.

Introduction.
The development of the escalated BEACOPP regimen let to an improved outcome in patients with advanced Hodgkin Lymphoma (HD9 study of the GHSG). However, the application of high dose etoposide (cumulative 4,8 g/m² per 8 cycles) seems to be associated with an
increased incidence of secondary MDS and AML, respectively. Therefore, the aim of our ongoing multicenter pilot study is to evaluate the efficacy
and toxicity of the etoposide free as well as dose intensified BACOPP-D protocol.

Methods.
Since May 2000 a total of 115 patients with Hodgkin Lymphoma (HL) stage IIB, III, and IV were treated with BACOPP-D which included cyclophosphamide 1250 mg/m² (d1), adriamycin 25 mg/m²(d1+2), dacarbazine 250 mg/m² (d1-3), procarbazine 100 mg/m² (d1-7), prednisolone 40 mg/m² (d1-14), bleomycin 10 mg/m²(d8) and vincristine 1,4 mg/m² (maximum 2 mg, d8) at three-weekly intervals with granulocyte colony-stimulating factor (G-CSF). A consolidating involved field radiation (30 Gy) was performed only in patients who achieved less than CR following chemotherapy. Initial staging and post-treatment control included PET monitoring.

Results.
Until now 97 patients (median age 35 years, range 17-65; 61 male, 36 female) are assessable for toxicity and treatment outcome. We analyzed the acute toxicity for 728 cycles of BACOPP-D. CTC/WHO grade III/IV haematological toxicities per patient were observed as follows:
leukopenia 93%, anemia 39%, and thrombocytopenia 33%. CTC grade III/IV non-haematological side effects included documented infection (4%) and lung toxicity (one patient with reversible bleomycininduced pneumonitis). A total of 85 patients (88%) achieved complete remission, 9 patients (9%) achieved partial remission, three patients (3%) had progressive disease. At a median observation time of 39 months (0,9-77 months), six patients have relapsed, and nine deaths were documented (4 HL-specific and 3 treatment related deaths, 1 death due to ruptured Meckel diverticulum with peritonitis, one 65 year-old woman died in CR following myocardial infarction caused by coronary heart disease). One patient developed a second neoplasia (hypopharyngeal carcinoma in an alcoholic). The overall survival and freedom from treatment failure rates at 39 months were 91% and 85%, respectively.

Discussion.
BACOPP-D regimen appears as a feasible and safe treatment protocol with moderate acute toxicity in patients with advanced HL. No secondary AML or MDS occured until now.

Three different many-body wave-function-based ab initio methods for the calculation of correlated (or quasi-particle) band structures of periodic systems are presented: the local Hamiltonian approach, the incremental self-energy method, and the crystal orbital variant of the algebraic diagrammatic construction. All three methods explicitly exploit the local nature of electron correlation, and by consequently switching to representations in localized Wannier orbitals O(N) scaling could be achieved in all three cases. These methods were applied to single (HF)2 zigzag chains as found in solid hydrogen fluoride using the same geometries and basis sets. Essentially identical quasi-particle band structures were obtained, corroborating the appropriateness of the different concepts pursued in each of the presented quantum chemical correlation methods for band structures of infinite systems.

Stratified two-phase flows were investigated at two test facilities with horizontal test-sections. For both, rectangular channel cross-sections were chosen to provide optimal observation possibilities for the application of optical measurement techniques. In order to show the local flow structure, high-speed video observation was applied, which delivers the high resolution in space and time needed for CFD code validation.

The Horizontal Air/Water Channel (HAWAC) is made of acrylic glass and allows the investigation of air/water co-current flows at atmospheric pressure and room temperature. At the channel inlet, a special device was designed for well-defined and adjustable inlet boundary conditions. For the quantitative analysis of the optical measurements performed at the HAWAC, an algorithm was developed to recognise the stratified interface in the camera frames. This allows to make statistical treatments for comparison with CFD calculation results. As an example, the instable wave growth leading to slug flow is shown from the test-section inlet. Moreover, the hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was investigated in this closed channel. The structure of the hydraulic jump over time is revealed by the calculation of the probability density of the water level. A series of experiments show that the hydraulic jump profile and its position from the inlet vary sensibly with the inlet boundary conditions due to the momentum exchange between the phases.

The second channel is built in the pressure vessel of the TOPFLOW facility, which is used to perform air/water and steam/water experiments at pressures of up to 5.0 MPa and temperatures of up to 264°C, but under pressure equilibrium with the vessel inside. In the present experiment, the test-section represents a flat model of the hot leg of the German Konvoi pressurised water reactor scaled at 1:3. The investigations focus on the flow regimes observed in the region of the elbow and of the steam generator inlet chamber, which are equipped with glass side walls. An overview of the experimental methodology and of the acquired data is given. These cover experiments without water circulation, which can be seen as test cases for CFD development, as well as counter-current flow limitation experiments, representing transient validation cases of a typical nuclear reactor safety issue.

Introduction to the proceedings volume of the Europhysics Conference "Nuclear Physics in Astrophysics III", March 2007, Dresden

Kosmische Magnetfelder werden durch Selbsterregung in strömenden elektrisch leitfähigen Flüssigkeiten erzeugt. Lang andauernde Phasen relativer Feldstabilität können dabei von kurzen Phasen mit hoher Dynamik und damit einhergehenden Feldumpolungsprozessen unterbrochen werden. Jüngste numerische Untersuchungen an einem einfachen Dynamo-Modell im Sättigungsregime, dem kugelsymmetrischen alpha2-Dynamo mit algebraischem alpha-Quenching, deuten darauf hin, dass dynamische Feldumpolungen für eine Vielzahl von Dynamo-Konfigurationen auftreten und sich unter geeigneten Bedingungen eventuell sogar experimentell erzeugen lassen. Als wesentliches Kriterium für das Auftreten einer Feldumpolung konnte bisher das Vorhandensein eines spektralen Entartungspunktes mit Phasenübergang von nichtoszillierendem zu oszillierendem Dynamo-Regime in der Nähe des spektralen Nullpunktes identifiziert werden. Im Rahmen des einjährigen DFG-Projektes wurden anhand einfacher Dynamo-Modelle theoretische Grundlagenuntersuchungen zur Dynamik von Feldumpolungen durchgeführt.

We consider multidimensional gravitational models with a nonlinear scalar curvature term and form fields in the action functional. In our scenario it is assumed that the higher dimensional spacetime undergoes a spontaneous compactification to a warped product manifold. Particular attention is paid to models with quadratic scalar curvature terms and a Freund-Rubin-like ansatz for solitonic form fields. It is shown that for certain parameter ranges the extra dimensions are stabilized. In particular, stabilization is possible for any sign of the internal space curvature, the bulk cosmological constant and of the effective four-dimensional cosmological constant. Moreover, the effective cosmological constant can satisfy the observable limit on the dark energy density. Finally, we discuss the restrictions on the parameters of the considered nonlinear models and how they follow from the connection between the D-dimensional and the four-dimensional fundamental mass scales.

A non-linear gravitational model with a multidimensional geometry and quadratic scalar curvature is considered. For certain parameter ranges, the extra dimensions are stabilized if the internal spaces have negative curvature. As a consequence, the 4-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. The homogeneous and isotropic external space is asymptotically AdS. The connection between the D-dimensional and the 4-dimensional fundamental mass scales sets an additional restriction on the parameters of the considered non-linear models.

We consider non-linear gravitational models with a multidimensional warped product geometry. Particular attention is payed to models with quadratic scalar curvature terms. It is shown that for certain parameter ranges, the extra dimensions are stabilized if the internal spaces have negative constant curvature. In this case, the 4-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. As a consequence, the homogeneous and isotropic external space is asymptotically AdS. The connection between the D-dimensional and the 4-dimensional fundamental mass scales sets a restriction on the parameters of the considered non-linear models.

We show that for warped product space-times the conformal (geometric moduli) excitations of the internal compactified factor spaces should be observable as massive scalar fields in the external space-time. These scalar fields (gravitational excitons) describe weakly interacting particles and can be considered as dark matter component. On the other hand, they provide possible values for the effective cosmological constant.

In earlier work it was pointed out that for warped product spacetimes the conformal (geometrical moduli) excitations of the internal compactified factor spaces should be observable as massive scalar fields in the external spacetime. Here we show that these scalar fields (gravitational excitons) describe weakly interacting particles and can be considered as dark matter component. Masses of the gravexcitons are defined by the form of the effective potential of the theory and the stabilization scales of the internal space. This implies that different stabilization scales result in different types of DM. An essential role is played by the effective potential. On the one hand, its minima fix possible stabilization scales of the internal spaces; on the other hand, they provide possible values for the effective cosmological constant.

The possibility of dynamical stabilization of an internal space is investigated for a multidimensional cosmological model with minimal coupled scalar field as inflaton. It is shown that a successful dynamical compactification crucially depends on the type of interaction between the geometrical modulus field and the inflaton and its decay products. In the considered model a stable compactification can be ensured via trapping of the modulus field by a minimum of the effective potential.

Effective 4-dimensional theories are investigated which were obtained under dimensional reduction of multidimensional cosmological models with a minimal coupled scalar field as matter source. Conditions for the internal space stabilization are considered and the possibility for inflation in the external space is discussed. The electroweak as well as the Planck fundamental scale approaches are investigated and compared with each other. It is shown that there exists a rescaling for the effective cosmological constant as well as for gravitational exciton masses in the different approaches.

Multidimensional cosmological models in the presence of a bare cosmological constant and a perfect fluid are investigated under dimensional reduction to 4-dimensional effective models. Stable compactification of the internal spaces is achieved for a special class of perfect fluids. The external space behaves in accordance with the standard Friedmann model. Necessary restrictions on the parameters of the models are found to ensure dynamical behavior of the external (our) universe in agreement with observations.

Multidimensional cosmological models with a higher dimensional space-time manifold are investigated under dimensional reduction. In the Einstein conformal frame, the effective potential for the internal scale factors is obtained. The stable compactification of the internal spaces is achieved due to the Casimir effect. In the case of more than one internal space a Casimir-like ansatz for the energy density of the massless scalar field fluctuations is proposed. Stable configurations with respect to the internal scale factor excitations are found in the cases of one and two internal spaces.

We study inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold under dimensional reduction. Stability due to different types of effective potentials is analyzed for specific configurations of internal spaces. Necessary restrictions on the parameters of the models are found and masses of gravitational excitons (small inhomogeneous excitations of the scale factors of the internal spaces near minima of effective potentials) are calculated.

We study inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold under dimensional reduction and show that small inhomogeneous excitations of the scale factors of the internal spaces near minima of effective potentials should be observable as massive scalar particles (gravitational excitons) in the external space-time.

nhomogeneous multidimensional cosmological models with a higher-dimensional space-time manifold M=M₀×∏_i=1 ⁿM_i (n>~1) are investigated under dimensional reduction to D₀-dimensional effective models. In the Einstein conformal frame, small excitations of the scale factors of the internal spaces near minima of an effective potential can be observed as massive scalar fields in the external space-time. Parameters of models that ensure minima of the effective potentials are obtained for particular cases and masses of gravitational excitons are estimated.

An experimental investigation on the air/water counter-current two-phase flow in a horizontal rectangular channel connected to an inclined riser has been conducted. This test-section representing a model of the hot leg of a pressurized water reactor is mounted between two separators in a pressurized experimental vessel. The cross-section and length of the horizontal part of the test-section are (0.25 m × 0.05 m) and 2.59 m, respectively, whereas the inclination angle of the riser is 50°. The flow was captured by a high-speed camera in the bended region of the hot leg, delivering a detailed view of the stratified interface as well as of dispersed structures like bubbles and droplets. Countercurrent flow limitation (CCFL), or the onset of flooding, was found by analyzing the water levels measured in the separators. The counter-current flow limitation is defined as the maximum air mass flow rate at which the discharged water mass flow rate is equal to the inlet water mass flow rate.
From the high-speed observations it was found that the initiation of flooding coincides with the formation of slug flow. Furthermore, a hysteresis was noticed between flooding and deflooding. The CCFL data was compared with similar experiments and empirical correlations available in the literature. Therefore, the Wallis-parameter was calculated for the rectangular cross-sections by using the channel height as length, instead of the diameter. The agreement of the CCFL curve is good, but the zero liquid penetration was found at lower values of the Wallis parameter than in most of the previous work. This deviation can be attributed to the special rectangular geometry of the hot leg model of FZD, since the other investigations were done for pipes.

The counter-current flow limitation was investigated experimentally in a flat model of the hot leg of a pressurised water reactor. Counter-current flow limitation, or the onset of flooding, was found by analysing the water levels measured in the separators. A confrontation with high-speed observation images indicates that the initiation of flooding coincides with the reversal of the flow in the horizontal part of the hot leg due to high air velocities.

Furthermore, the CCFL data was compared with empirical correlations for analogue geometries available in the literature. This comparison shows that the Wallis-parameter can be applied to rectangular cross-sections by using the channel height as length, instead of the diameter. The obtained flooding curve is similar to those reported by other investigators, but its slope and the gaseous Wallis parameter for zero penetration are lower. This is attributed to the geometry of the hot leg model.

This paper presents some results concerning a benchmark for stratified two-phase flows conducted in the frame of the European Platform for NUclear REactor SIMulations (NURESIM). This benchmark relies on the FZD slug flow experiment performed in the Horizontal Air/Water Channel (HAWAC). For this test bench, special experimental arrangements have been taken in order to be able to properly model the boundary and initial conditions with CFD. A picture sequence recorded with a high-speed camera was used as reference for comparison with the simulations. For this benchmark, three different codes have been tried out. CFX was used with a turbulent two-fluid model in which a special turbulence damping function was implemented in the specific dissipation rate of the turbulent kinetic energy. This allowed a good qualitative representation of the slug dynamics, even though quantitative comparison were less relevant because of difficulties in modelling the inlet instabilities. The VOF approach in its laminar and turbulent form was also tried out trough the FLUENT code and was found to be inappropriate for those conditions due to the high velocity slip between phases. Moreover, NEPTUNE_CFD was tested with a new implemented model allowing free surface location and the computation of momentum transfer across this interface. This Large Interface Model (LIM) enables to detect "stratified cells" from the other and hence to apply local closure law. With this model, the results agreed well with experimental data qualitatively and quantitatively. This benchmark experience also allowed to draw basis concerning a best practice guideline in numerical simulation related to those flows in nuclear thermal hydraulics.

In this work we have investigated the changes of the magnetic properties of highly oriented pyrolytic graphite samples after irradiation either with ~3×10¹⁴ protons or 3.5×10¹³ ... 3.5×10¹⁴ iron ions with energies in the MeV range. Our results show that iron and proton irradiations can produce similar paramagnetic contributions depending on the implantation temperature. However, only protons induce a ferromagnetic effect.

This report is a consolidation of document NEA/SEN/SIN/AMA(2005)3, which aimed to evaluate the existing CFD assessment basis, identify gaps that need to be filled in order to adequately validate CFD codes for application to NRS problems, and propose a methodology for establishing assessment matrices relevant to NRS needs. The document is a revision of the original, and has been compiled by members of an expert Writing Group, WG2, under the auspices of the OECD/NEA secretariat. The group met three times during the period January 2005 to August 2007, the dates chosen to coordinate with the activities of the sister groups WG1 (Best Practice Guidelines) and WG3 (Multiphase Extensions).
The group has concentrated on single-phase phenomena, considering that two-phase CFD is not yet of sufficient maturity for a useful assessment basis to be constructed and that identification of the development areas (the task of Writing Group 3) should be undertaken first. The organisation of the report reflects the tasks the Group set itself.
To review critically the NRS problems where the use of CFD is needed for the analysis or where its use is expected to result in major benefits.
To review critically the existing assessment basis for CFD application to NRS issues.
To identify the gaps in the technology base, and the need for further development effort.
To organise a web-based NRS assessment database, regulated by an NEA webmaster.
To continue to look for suitable experiments that could form the basis of benchmarking exercises that are specifically tailored to NRS needs.
To organise an International Workshop, with OECD/NEA sponsorship, to promote the availability and distribution of experimental data suitable for NRS benchmarking, and to monitor the current status of CFD validation exercises relevant to NRS issues.
Beyond 2007, an amalgamation of Writing Groups WG1, WG2 and WG3, together with the NEA web-master and secretariat, is proposed to drive the activities further. This would be a core group of no more than five persons, meeting once per year.
This document is now submitted to the Working Group on the Analysis and Management of Accidents (GAMA) for evaluation.

In this study, a combination of X-ray absorption spectroscopy (XAS) and Fourier transformed infrared (FT-IR) was used to investigate at molecular scale the coordination of Pt(II) to the S-layer sheets B. sphaericus JG-A12, and to characterize the formation of Pt nanoacluster using this protein layer as template.

In this work, a combination of wet chemistry, spectroscopic and microscopic techniques was used to investigate and compare the interactions of uranium(VI) with one representative each of the domains Bacteria and Archaea. The bacterial strain Paenibacillus sp. JG-TB8 was isolated from a microbial consortium cultured from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. This consortium consisted not only of bacteria of the division Firmicutes but also of mesophilic 1.1b-Crenarchaeota. Because isolation approaches of these archaeal strains failed until now, the thermophilic relative Sulfolobus acidocaldius, which has already been found in comparable soil samples, was used for this study.
The U(VI) sorption studies showed that the cells of both microbial strains accumulated significant amounts of uranium.X-ray absorption spectroscopy was used to characterize, at molecular scale, the local coordination of uranium associated with the cells of the studied microorganisms. XANES analysis showed that in both cases the oxidation state of the U(VI) added to the cells was unchanged indicating that U(VI) was not reduced. The EXAFS spectrum of the U(VI) complexes formed by the cells of Paenibacillus sp. JG-TB8 showed a high similarity to that of meta-autunite, indicating that this radionuclide is precipitated by the cells as a meta-autunite-like phase. These uranium precipitates were located at the cell surface and intracellularly as needle-like fibrils as was demonstrated by transmission electron microscope analyses. In the case of Sulfolobus acidocaldarius, EXAFS analysis showed that the structural parameters of the uranium complexes formed by this archaeon are similar to those arising from the complexation of uranium with organic phosphate compounds such as fructose 6-phosphate.

The strain Bacillus sphaericus JG-A12, isolated from the uranium mining waste pile called Haberland in Saxony, Germany, is capable of selective and reversible accumulation of radionuclides and toxic metals. It was demonstrated that the main role by metal binding is played by the surface of protein layer.
The S-layer possesses a highly ordered lattice structure and can serve as a template for production transportation of noble metals.
The aim of this study was the characterization of the secondary structure and the stability of the protein after complexation Pt and also after the formation of nanoclusters by reduction.
The measurements by Fourier transformed infrared spectroscopy (FT-IR), revealed that the structure of the S-layer protein is stabilized after both sorption or reduction of Pt(II) against acidification.
An aspect for this conclusion is pH induced infrared absorption changes of the Pt(II)-bound S-layer. An effect of different pH-values is the protonation of carboxylic acids caused the reduction of the COO- stretching modes. The denaturation occurs near by pH of 0.8. This is shown by the downshift of amid I absorption.
The aim of the EXAFS measurement was the identification of functional groups of the s-layer protein which are involved in binding Pt(II) or Pt(0). The analysis which has been carried out at synchrotron beam line at ESRF in Grenoble approves the results of IR measurements for identification of functional groups. The first shell contains at a distance of 2.01 ± 0.02 Å oxygen and nitrogen whereas the system can not distinguish between this elements. In the second were found Pt-Pt bindings and the third was dominated by Pt-C bindings.

In this work, a combination of wet chemistry, spectroscopic and microscopic techniques was used to investigate the interactions of U(VI) with the cells of Paenibacillus sp. JG-TB8, a bacterial strain enriched from a microbial consortium isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. This consortium consisted of mesophilic 1.1b-Crenarchaeota and bacteria of the division Firmicutes.
The U(VI) sorption studies showed that cells of the studied Paenibacillus strain accumulated up to 85 mg U/g dry biomass from a solution with an uranium concentration of 120 mg U/l.
X-ray absorption spectroscopy was used to characterize, at molecular scale, the local coordination of uranium associated with the cells of the studied bacterium. XANES analysis showed that the oxidation state of the U(VI) added to the cells was unchanged indicating that U(VI) was not reduced. The EXAFS spectrum of the U(VI) complexes formed by the cells of Paenibacillus sp. JG-TB8 showed a high similarity to that of meta-autunite, indicating that this radionuclide is precipitated by the cells as a meta-autunite-like phase. These uranium precipitates were located at the cell surface and intracellularly as needle-like fibrils as was demonstrated by transmission electron microscope analyses.
The results found in this study indicated that the cells of Paenibacillus sp. JG-TB8 are involved in the biomineralization of uranium at aerobic and acidic conditions.

Die Resultate von VoF-Simulationen zum freien Aufstieg von Öltropfen in Wasser werden mit experimentellen Beobachtungen verglichen. Kleine Öltropfen steigen geradlinig mit einem stationären Nachlauf auf. Große Tropfen steigen in den Simulationen zunächst geradlinig auf mit einem stabilem Nachlauf, dessen Länge mit der Zeit anwächst. Der Tropfen beschleunigt, bis der Nachlauf instabil wird. Mit dem Einsetzen periodischer Wirbelablösung sinkt die Aufstiegsgeschwindigkeit ab auf die Endgeschwindigkeit. Die periodische Wirbelablösung im Nachlauf großer Tropfen geht einher mit einer Formoszillation und einer zickzackförmigen Trajektorie. Es werden Aufstiegsgeschwindigkeit, Tropfenform und Bewegungsverhalten in Abhängigkeit von der Tropfengröße ermittelt und mit experimentellen Resultaten verglichen. Der Dragkoeffizient für zickzackförmig aufsteigende Tropfen ist deutlich höher als für geradlinig aufsteigende Tropfen.

FTIR spectroscopy was employed to analyse the chromophore structure in the parent states Pr and Pfr of plant phytochrome phyA and the respective photoproducts lumi-R and lumi-F. The spectra were obtained from phyA adducts assembled with either uniformly or selectively isotope-labeled phytochromobilin and phycocyanobilin. The interpretation of the experimental spectra is based on the spectra of chromophore models calculated by density functional theory. Global 13C-labelling of the tetrapyrrole allows for the discrimination between chromophore and protein bands in the FTIR difference spectra. All IR difference spectra display a prominent difference band attributable to a stretching mode with large contributions from the methine bridge between the inner pyrrole rings (B-C stretching). Due to mode coupling, frequencies and isotopic shifts of this mode suggest that the Pr chromophore may adopt a distorted ZZZssa geometry with a twisted A-B methine bridge. The transition to lumi-R is associated with only minor changes of the amide I bands indicating limited protein structural changes during the isomerization site of the C-D methine bridge. Major protein structural changes occur upon the transition to Pfr in which the chromophore adopts a ZZEssa-like state. In addition, specific interactions with the protein alter the structure of the B-C methine bridge as concluded from the substantial downshift of the respective stretching mode. These interactions are removed during the photoreaction to lumi-F which affords a ZZZssa-like structure of the chromophore and involves only small protein structural changes.

Bubbles in shear flows experience a lift force, causing them to migrate sideward while they are rising. This lateral migration is also observed in numerical simulations, which are carried out with an extended version of the highly parallelized code FS3D, employing an advanced Volume-of-Fluid method. The movement of single bubbles in linear shear flows is simulated to obtain the magnitude of the lift force – expressed by the lift force coefficient – for various bubble diameters and material data. Simulation results are in good agreement with experiments for medium liquid phase viscosities. The pressure and the velocity fields near the interface are investigated and the contribution of dynamic pressure and the circulation of the lift force are discussed.

There is a clear and increasing interest in short time thermal processing far below one second, i.e. the lower limit of RTP (Rapid Thermal Processing) called spike annealing. It is the world of processing in the millisecond or nanosecond range. This was recently driven by the need of suppressing the so-called Transient Enhanced Diffusion in advanced boron-implanted shallow pn-junctions in the front-end silicon chip technology. Meanwhile the interest in flash lamp annealing (FLA) in the millisecond range spread out into other fields related to silicon technology and beyond. This talk reports shortly about the restart in flash lamp annealing of the Rossendorf group in collaboration with other groups and further on recent experiments regarding shallow junction engineering in germanium, annealing of ITO layers on glass and plastic foil to form an conductive layer as well as investigations which we did during the last years in the field of wide band gap semiconductor materials (SiC, ZnO). Moreover recent achievements in the field of silicon-based light emission basing on Metal-Oxide-Semiconductor Light Emitting Devices will be reported. Finally it will be demonstrated that short time thermal processing features also advantages regarding the casting of lead sheets to produce organ pipes in the spirit of the 17th century - as a completely different world of materials processing!

This experimental study considers the transient liquid metal flow which is generated inside a cylindrical container by discontinuously applying a rotating magnetic field (RMF). The focus is on the fluid motion arising from the impulsive spin-up from the resting state, a single pulse or a sequence of RMF pulses. The ultrasonic Doppler velocimetry (UDV) has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both the primary, swirling flow and the secondary flow in the radial-meridional plane. The experimental results show an excellent agreement with recently published numerical results. The investigations reveal that the recirculating flow in the radial- meridional plane undergoes characteristic oscillations. Periodic reversals of the meridional flow direction can be observed for a specific length of the RMF pulses.
Our results demonstrate that the utilisation of a time-modulated rotating magnetic field (RMF) offers a considerable potential to provide optimal flow pattern for an efficient melt mixing. For instance, such tailored methods of electromagnetic stirring can be applied during the solidification of metal alloys, where a well-aimed modification of casting properties is achieved by controlling the melt flow in the bulk and adjacent to the solidification front.

The electrical stability of rare-earth implanted SiO2 light emitting devices was improved by using a SiON dielectric buffer layer in an indium-tin-oxide/SiON/SiO2:Tb /Si device structure. At the expense of a small increase of the electroluminescence threshold voltage, a large increase of the breakdown electric field from 7.5 to 10.5 MV/cm was obtained in the SiO2:Tb layer, and the maximum injection current density was increased by three orders of magnitude from 4 mA/cm2 to 4 A/cm2 . The operation time of the electroluminescence devices was increased by more than three orders of magnitude at an injection current density of ~4 mA/cm2. Our experimental results are consistent with a theoretical model proposed for designing a stable and efficient thin-film light emitting device containing double-stacked dielectric layers.

In this study, the hydrothermal carbonation of calcium hydroxide under high CO2-Ar pressure (90 bar) coupled with a complex selenocystine fragmentation under O2-poor and O2-rich conditions was carried out by using a semi-batch
system (sampling with time) in order to synthesize an elemental selenium (Se0)/calcite composite. Under O2-poor conditions (i.e. with purge stage), the composite was mainly characterized by spherical selenium nanoparticles
(<500nm) deposed on the calcite matrix. The carbonate matrix was constituted by nano- and micro rhombohedral crystals (<2µm) and micrometric agglomerates and/or aggregates (<5mµ). For this case, the spherical Se nanoparticles give
a stable red coloration to the composite. In contrast, under O2-rich conditions (i.e. without purge stage), the composite was characterized by hexagonal selenium microparticles (<25µm) dispersed in the calcite matrix. For this case, a gray coloration of composite was observed. In conclusion, the gas purge in the system and the selenocystine dose (mg/kgwater) play a crucial role on the selenocystine fragmentation mechanism during Ca(OH)2 suspension heating (at 90°C) and carbonation stages, this leading the precipitation/growth of elemental selenium with different morphologies and particles sizes. Consequently, it was noticed that the selenocystine fragmentation participates to the precipitation/growth of calcite with unusual morphologies. Finally, the results presented here demonstrate that Se0/calcite composite, with spherical or hexagonal morphologies for elemental selenium can be produced, this composite possibly with a high potential for medical (ex. dietary supplement) or industrial (ex. pigments) applications.

The long-lived radionuclide 79Se is one of the elements of concern for the safe storage of high-level nuclear waste, since clay minerals in engineered barriers and natural aquifer sediments strongly adsorb cationic species, but to lesser extent anions like selenate (SeVIO42−) and selenite (SeIVO32−). Previous investigations have demonstrated, however, that SeIV and SeVI are reduced by surface-associated FeII, thereby forming insoluble Se0 and Fe selenides. Here we show that the mixed FeII/III (hydr)oxides green rust and magnetite, and the FeII sulfide mackinawite reduce selenite rapidly (< 1 day) to FeSe, while the slightly slower reduction by the FeII carbonate siderite produces elemental Se. In the case of mackinawite, both S−II and FeII surface atoms are oxidized at a ratio of one to four by producing a defective mackinawite surface. Comparison of these spectroscopic results with thermodynamic equilibrium modeling provides evidence that the nature of reduction end product in these FeII systems is controlled by the concentration of HSe−; Se0 forms only at lower HSe− concentrations related to slower HSeO3− reduction kinetics. Even under thermodynamically unstable conditions, the initially formed Se solid phases may remain stable for longer periods since their low solubility prevents the dissolution required for a phase transformation into more stable solids. The reduction by Fe2+-montmorillonite is generally much slower and restricted to a pH range, where selenite is adsorbed (pH < 7), stressing the importance of a heterogeneous, surface-enhanced electron transfer reaction. Although the solids precipitated by the redox reaction are nanocrystalline, their solubility remains below 6.3 × 10− 8 M. No evidence for aqueous metal selenide colloids nor for Se sorption to colloidal phases was found. Since FeII phases like the ones investigated here should be ubiquitous in the near field of nuclear waste disposals as well as in the surrounding aquifers, mobility of the fission product 79Se may be much lower than previously assumed.

Because of the dynamic equilibrium between Kerr self-focussing and plasma induced defocusing
and the inexistence of collisional ionization the critical intensity during femtosecond laser
filamentation in air is independent of pressure. An analytical analysis is given which is justified
by a direct experimental verification.
PACS: 42.65.Jx, 52.38.Hb, 52.70.Kz

In 2000, the University of Strathclyde, collaborating with the Rutherford Appleton Laboratory, organized the first workshop dealing with the potential of highpower laser technology in medicine. Two areas of potential were identified: firstly the production of positron emission tomography (PET) isotopes; and secondly, the potential for laser-accelerated proton and heavy ion beams for therapy. The attendees, mainly clinicians and radiation physicists, emphasised that the laser community should concentrate on developing laser and target technology for therapy rather than isotope production because of the potential advantages over conventional accelerator technology for that purpose. On the 30 March 2007, the universities of Strathclyde and Paisley organized a follow-up meeting to identify the progress made in laser-driven proton and ion beam technology with applications leading to proton and ion beam therapy for deep-seated tumours. The meeting was supported by the Scottish Uni!
versities Physics Alliance (SUPA) - an organization set up in Scotland to bring together all of the physics departments collaborating with life scientists to work on ground-breaking new science which no single university could attempt. This is a summary of the meeting.

Introduction:

Radiolabelled particles are an attractive tool in the therapy of malignancies of the liver. We consider particles manufactured from denatured human serum albumin (HSA) as useful carriers of therapeutic radionuclides. Covalent attachment of suitable chelators onto the surface of the spheres promises an easy access to radiolabelled HSA microspheres.

Methods:

We synthesized 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (DOTA) bearing smooth, medium-rough and rough surfaced HSA microspheres (mean diameter: 25 μm). In vitro stability of ⁸⁶Y-labelled particles was determined after incubation in human plasma and in a DTPA challenge experiment. In vivo stability of ⁸⁶Y DOTA-HSA microspheres was determined after single intravenous application in rats. Subsequently, the particles were completely trapped in the lung microvasculature. Thus, the lung serves in our experiments as target organ.

Results:

DOTA-HSA microspheres were ⁸⁶Y labelled in reproducible high yields (N95%). No differences between smooth and rough surfaced spheres were found for both DOTA coupling and ⁸⁶Y labelling. Labelled microspheres showed high in vitro stability in human plasma and in DTPA solution with only 8±1% and 2±0% loss of radioactivity from the surface, respectively, 48 h postinjection (pi). The three batches (smooth, medium-rough and rough surfaced microspheres) differed considerably in their radioactivity recovery in the lungs of rats 48 h pi. Smooth particles showed the highest in vivo stability of the radiolabel on the surface of the spheres, presumably because of slower proteolytic degradation.

Conclusion:

We found that for the preparation of HSA-derived microspheres for radiotherapeutic application, smooth surfaced spheres are superior to rough spheres due to their higher in vivo stability of the radionuclide fixation.

kein Abstract verfügbar

Carbon and C:V, C:Co, C:Cu nanocomposite films grown by ion beam cosputtering in the temperature range from room temperature (RT) to 500 °C are investigated. Soft X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) have been used to determine electronic structure of the occupied and unoccupied electronic states of the coexisting carbon and transition metal (TM) constituents. The results from the spectroscopy are supplemented by the film composition data and TM inclusion phase structural information obtained by elastic recoil detection analysis and X-ray diffraction, respectively. The TM(2p) XAS shows that V (Cu) is in carbidic (metallic) state over the whole temperature range, while Co shows a transition from a carbidic toward a metallic state when the growth temperature increases from RT to 500 °C. The C(1s) XAS demonstrates that the increase in the growth temperature favors the formation of graphite-like structures in carbon films. On the other hand, the TM metal incorporation strongly promotes the sp3 admixture in the surrounding carbon phase which manifests itself through a significant increase in the intensity of a feature in the C(1s) XAS spectra positioned at ~291 eV resulting from 1s → σ* transitions. In addition, the codeposition of TM atoms with carbon enhances the formation of carbon structures with the prominent peak between π* and σ* regions in the C(1s) XAS spectra positioned at ~288.5 eV. The effect is independent of the TM tendency to form carbides or TM state (carbidic metallic) while its magnitude increases concomitantly with the TM content and decreases when the crystallinity degree of the inclusion phase increases. The results are discussed on the basis of the nanoparticle imposed curvature on the surrounding carbon network and interactions at the atomic level at the C−TM interfaces.

Lifetimes of exited states in 134Pr were measured by means of the recoil distance Doppler-shift and Doppler-shift attenuation techniques. The branching ratios and the electric or magnetic character of the transitions were also investigated. The experiments were performed at IReS, Strasbourg, using the EUROBALL IV spectrometer, in conjunction with the inner bismuth germanate ball and the Cologne coincidence plunger apparatus. Exited states in 134Pr were populated in the fusion-evaporation reaction 119Sn(19F, 4n)134Pr. The possible chiral interpretation of twin bands was investigated in the two-quasiparticle triaxial rotor and interacting boson-fermion-fermion models. The analysis of the wave functions has shown that the possibility for the angular momenta of the proton, neutron, and core to find themselves in the favorable, almost orthogonal geometry, is present but is far from being dominant. The structure is characterized by large beta and gamma fluctuations. The existence of doublets of bands in 134Pr can be attributed to weak chirality dominated by shape fluctuations.

Abstract not available. For details, please contact the first author.

The time dependence of the reduction of Np(V) to Np(IV) by humic substances of varying functionality has been studied under anaerobic conditions between pH 3.5 and pH 9.0. Synthetic humic acids with pronounced redox functionality were studied in comparison to natural humic substances. For Np redox speciation in solution solvent extraction, NIR absorption spectroscopy and ultrafiltration were applied. Exemplary, the application of a synthetic HA is shown for the study of the Np(IV) sorption onto kaolinite in the presence of HA.

kein Abstract verfügbar

kein Abstract verfügbar

INTRODUCTION
Radiopharmaceuticals based on metallic radionuclides, such as ^64/67Cu, ^99mTc, ^186/188Re and ^86/90Y, are often used for diagnostic and therapeutic purposes (1, 2). These nuclides are usually enveloped in organic ligands, such as heteromacrocyclic systems. To be effective, the ligands have to show fast metal complexation kinetics, form complexes with high in vitro and in vivo stability and contain a group that can be linked to biomolecules. We have developed a new ligand scaffold - based on bis(2-pyridylmethyl)triazacyclononane (DMPTACN) – that satisfies these requirements. This structure allows for the introduction of linker groups, such as carboxylic acids, maleinimide or isothiocyanate, thereby facilitating coupling of targeting molecules.

RESULTS AND DISCUSSION
A new TACN derivative, containing two pyridyl pendant arms as well as a carboxylic group for coupling to biomolecules has been synthesized and its copper(II) binding properties investigated. Conjugation of a stabilized octapeptide (bombesin βAla-βAla-[Cha¹³, Nle¹⁴]) was successfully achieved via amide coupling (3). Both the free ligand and the bombesin bioconjugate can rapidly form very stable radiocopper complexes. In vitro ligand competition experiments and stability studies in rat plasma medium gave no evidence of transchelation or demetalation. Biodistribution studies of the bombesin conjugate revealed an accumulation of the compound in the pancreas, which is the organ with highest levels of gastrin-releasing peptide receptor (GRPR) targeted by bombesin.
Our radiopharmalogical data indicate that bifunctional chelating TACN agents are attractive candidates for developing new copper radiotherapeutics. In this perspective, particular BFCAs will be attached to carrier molecules, such as oligonucleotides, antibodies and synthetic polymers, to deliver radiocopper isotopes to target tissues.

REFERENCES
1. Anderson C.J., Welch M.J. (1999) Metal complexes as diagnostic tools. Coord. Chem. Rev. 184, 3-66.
2. Volkert W.A., Hoffman T.J. (1999) Therapeutic radiopharmaceuticals. Chem. Rev. 99, 2269-2292.
3. Gasser G., Tjioe L., Graham B., Belousoff M. J., Juran S., Walther M., Künstler J.U., Bergmann R., Stephan H., Spiccia L. (2008)
Synthesis, Copper(II) Complexation, ⁶⁴Cu-Labeling, and Bioconjugation of a New Bis(2-pyridylmethyl) Derivative of 1,4,7-
Triazacyclononane. Bioconjugate Chem. In press

Nitriding of austenitic stainless steel (ASS) at moderate temperatures (~400ºC) leads to the formation of the supersaturated nitrogen solid solution often called in the literature “expanded austenite” or γN phase [1,2]. This causes an enhancement of the microhardness and the wear resistance without loss of the corrosion resistance. Moreover, this phase shows ferromagnetic behavior, whose origin is linked to the expansion of the austenite (γ) lattice due to the incorporation of nitrogen atoms into interstitial positions [3,4]. Actually, since there is a nitrogen depth profile and the onset of ferromagnetism is connected with nitrogen concentrations of ~15 at.%, the nitrided layer consists of two magnetically different parts (paramagnetic and ferromagnetic) determined by the obtained nitrogen concentration.

In this study, we report the influence of the nitriding temperature and time on the ASS ferromagnetic properties. AISI 304L ASS polycrystalline samples (discs of 10 mm diameter and 2 mm thickness) have been ion beam nitrided in the temperature range of 300-400ºC. The ion energy and the ion current density were ~1 keV and 0.5 mA/cm2 (the corresponding ion flux of ~5•1015 ions•cm-2•s-1), respectively. The processing times were 5 and/or 30 minutes [2]. Periodic arrays of ferromagnetic structures in the micrometer range have been prepared at the surface of the samples using a 2000 mesh Cu transmission electron microscopy grid as a shadow mask (mesh size of 7.5 x 7.5 µm2, 12.5 µm pitch, 20 µm thickness and 3.05 mm diameter). The structure was characterized by X-ray diffraction (XRD) and nuclear reaction analysis (NRA). The magnetic properties were determined by magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM).
The XRD patterns of the nitrided ASS samples are presented in Figure 1. The XRD pattern consistent with the FCC lattice structure can be identified for the virgin ASS sample (not shown). For the nitrided samples, each austenite peak exhibits a satellite peak, located at lower diffraction angles which is related with the formation of the “expanded austenite”. The amount of this “expanded” phase increases with the processing temperature, as it is evidenced by the increase of intensity of the γN XRD peaks in detriment to the γ ones.
This is consistent with NRA observations. For instance, a nitrided layer of around 1 µm depth is obtained in the sample nitrided at 400ºC for 30 min, whereas ~15 at.% of nitrogen is obtained around 0.5 µm of depth.
MOKE measurement results of the virgin and the nitrided sample at 400°C for 5 min are compared in Figures 2(a) and 2(b) (patterned area).
It can be seen that the virgin sample does not show any hysteretic behavior, i.e. it is non-ferromagnetic. Conversely, the nitrided samples show clear hysteresis loops indicating the existence of ferromagnetic constituents in the nitrided layer. Figure 2(c) shows the AFM image of a patterned area of the nitrided sample which shows that a moderate sputtering process of the surface has taken place during nitriding resulting in the formation of the periodic array of squared pits. Figure 2 (d) is the corresponding MFM image in an applied magnetic field of 70 mT, where a magnetic dipolar contrast can be clearly seen in each entity, confirming the feasibility of the production of periodic arrays of isolated ferromagnetic structures. It is worth noting that the hysteresis behavior of the continuously nitrided areas and the patterned ones are quite similar due to the fact that the induced ferromagnetic structures are relatively large (micrometer range), leading to entities with magnetic multi-domain configurations.

[1] M.P. Fewell et al., Surf. Coat. Technol. 131, 300 (2000)
[2] G. Abrasonis, et al., J. Appl. Phys. 97, 083531 (2005)
[3] O. Öztürk and D.L. Williamson, J. Appl. Phys. 77, 3839 (1995)
[4] J. Baranowska, Vacuum 81, 1216 (2007)

Sc3AlN with perovskite structure has been synthesized as the first ternary phase in the Sc-Al-N system. Magnetron sputter epitaxy at 650 °C was used to grow single-crystal, stoichiometric Sc3AlN(111) thin films onto MgO(111) substrates with ScN(111) seed layers as shown by elastic recoil detection analysis, X-ray diffraction, and transmission electron microscopy. The Sc3AlN phase has a lattice parameter of 4.40 Å, which is in good agreement with the theoretically predicted 4.42 Å. Comparisons of total formation energies show that Sc3AlN is thermodynamically stable with respect to all known binary compounds. Sc3AlN(111) films of 1.75 µm thickness exhibit a nanoindentation hardness of 14.2 GPa, an elastic modulus of 249 GPa, and a room-temperature electrical resistivity of 41.2 µΩ cm.

Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing in 3D wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert.
Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (Vakuum oder Dampf) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: Lineare Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.

Diamond platelets were implanted with 8.8 MeV He²⁺ ions, the equivalent of alpha particles generated in the natural ²¹²Po ---> ²⁰⁸Pb decay (Th decay chain). Implantation densities were varied in the range 10¹² - 10¹⁷ ions per cm². Visible green colouration was produced at He²⁺ fluences _>10¹⁵ cm^-2. The radioinduced colour is mainly due to a broad absorption band at ca. 16000 cm^-1, which is assigned to the GR1 centre. Raman line scans showed that a narrow, stongly damaged area is formed ca. 29 µm below the sample surface. This corresponds very well with the distribution of Frenkel-type defects as predicted by Monte Carlo simulations using the SRIM program ¹. Raman data obtained from naturally radiocoloured diamonds are discussed in light of our new results.
¹ Ziegler JF, Biersack JP, Littmark U. The stopping and range of ions in solids. Pergamon Press, New York, 1985.

Separation-by-Implantated-Oxygen (SIMOX) is an established technique to manufacture a buried oxide layer in silicon (SOI) by ion implantation and annealing. The so called energy-dose window defines implantation parameters suitable for the formation of a continuous buried oxide layer with the lowest ion dose. The study concerns the reason why defined combinations of ion energy and ion dose result in a high quality oxide layer. Excess defects induced by the O implantation are shown to influence the oxide layer formation. The depth distribution of excess defects fits very well with the final depth position of the oxide layer for O implants in the energy-dose window.

Microorganisms are very important for the bioremediation of the environment because they are able to adsorb radionuclides and other heavy metals. They significantly influence mobilization and immobilization of metal ions in soils.
We investigated representative the complexation of the uranyl ion with main parts of bacterial cell walls. Lipopolysaccharide (LPS) is the principal component of the cell wall of gram-negative bacteria, whereas peptidoglycan (PGN) represents the basis of the cell wall of gram-positve bacteria. Both biomolecules contain a high density of metal-binding functionalities like carboxyl, amino, and hydroxyl groups. LPS offers additionally a high amount on phosphoryl groups, which are missing in PGN.
We investigated the interaction of the uranyl cation (UO22+) with the biopolymers LPS and PGN by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH range (2.4 – 9) and at environmentally relevant low uranium concentrations (10-4 – 10-5 M).
Using potentiometric titration, the dissociation constants of the respective functional groups were determined. Furthermore essential uranyl complexes and their stability constants were identified.
With the aid of time-resolved laser-induced fluorescence spectroscopy (TRLFS) the luminescence properties of uranyl complexes with the biopolymers and the associated stability constants were investigated. At low pH values both biomolecules effect an increase of the luminescence intensity and a red-shift of about 8-10 nm, compared to the free UO22+ ion. With LPS the luminescence intensity increases up to pH 8. In contrast to LPS, the PGN polymer causes a decrease of the luminescence intensity over pH 4.5, indicating, that a non-luminescent complex has built.
As a result from both methods, we found that the uranyl ion prefers with LPS phosphoryl coordination, whereas PGN, with a lack of phosphoryl groups, forms stable carboxylate complexes.

It has been demonstrated recently that quantum chemical calculations can accurately perdict redox potentials of An(VI)/An(V) couples (An = U, Np, Pu, Am) if multireference effect and spin-orbit effects are treated properly ^[1,2]. The An(VI)/An(V) redox potentials obtained at the multireference CASPT2 level calculations with spin-orbit corrections were found to have fairly good agreement with those obtained by experiments.
Here, I extend such calculations to the higher oxidation states of actinide, namely Pu(VII) and Pu(VIII). Pu(VII) is known to be meta-stable in aqueous solution. Recently, Nikonov et al. have suggested that Pu(VIII) may be obtained by the ozonation of Pu(VI), although they were not able to find a direct evidence for the presence of Pu(VIII) ^[3]. The present work aims to discuss from a theoretical point of view whether or not Pu(VIII) may exist in water. Geometry optimizations and energy calculations of the complexes were performed at the B3LYP level, and spin-orbit effects were calculated separately at the CASSCF level.
The redox potential of the Pu^VIIIO₄(OH)₂ ^2-/ Pu^VIIO₄(OH)₂ ^3- couple was found to be as high as ~1.7V. At very high pH, Pu(VII) may exist as a penta-oxo complex, Pu^VIIO₅(OH)^4-. The redox potential of Pu^VIIIO₅(OH)^3-/ Pu^VIIO₅(OH)^4- couple was found to be ~1.3V. Spin-orbit effect was found to play a very important role for the total redox potential because the ground state energy lowering of Pu(VII) due to the spin-orbit splitting depends highly on the number of coordinating oxo ligands. The effect of coordinating ligands (OH^-, CO₃ ^2- etc.) and coordination number on the total redox potential was also studied. The calculations suggest that Pu(VIII) is unlikely to exist in both acidic and alkaline aqueous solutions, while Pu(VIII) may be present in non-aqueous solvents with a large redox window.

[1] Tsushima,S; Wahlgren, U.; Grenthe, I. J. Phys. Chem. A 2006, 110, 9175.
[2] Shamov, G.A.; Schreckenbach, G. J. Phys. Chem. A 2005, 109, 10961.
[3] Nikonov, M.V.; Gogolev, A.V.; Tananaev, I.G.; Myasoedov, B.F. Radiochemsitry 2004, 46, 340.

For more than two decades aquatic chemistry is constantly gaining knowledge about nanoscale processes in the environment. While in early years the co-transport of contaminants in the saturated zone of aquifers has been in the focus of aquatic nanosciences and nanogeosciences, nowadays the research activities have broadened and span across several disciplines. In the course of R & D activities on nanomaterials the question of the behavior, fate and useful or adverse effects of nanoparticles in the environment arose and has boosted the activities quite substantially. The working group Aquatic Nanosciences and Nanotechnology has responded to the current development by inviting European scientists from different fields to contribute their expertise into the group’s discussions and activities while still keeping the core expertise on characterization techniques inherited from the former working group “Colloids”. In 2007 the working group organized an international workshop which was held in Vienna during the 10th and 11th December. The aim of the event was to offer a platform for bridging the different disciplines and exchange the current knowledge in the fields. Scientists from aquatic and environmental chemistry, nanogeosciences, nano-engineering, eco-toxicology and risk assessment presented their contributions to the current state of the art. The overall conclusions drawn from 29 presentations are given.

Dipole-strength functions studied in photon-scattering experiments at ELBE

Phosphorus implantation (30 keV, 3x1015 cm−2) into preamorphized Ge and subsequent rapid thermal or flash lamp annealing is investigated. During annealing a significant P diffusion in amorphous Ge is not observed. However, the fast solid phase epitaxial regrowth causes a rapid redistribution of P. After completion of the regrowth and at temperatures above 500 °C, a concentration-dependent diffusion of P in crystalline Ge takes place and leads to considerable loss of P toward the surface. An appreciable influence of implantation defects on the diffusion coefficient of P is not detected. For 60 s rapid thermal annealing at 600 °C and for 20 ms flash lamp annealing at 900 °C, the junction depth and the sheet resistance vary between 140 and 200 nm and between
50 and 100 Ohm, respectively, and the maximum electrical activation of P is about 3–7 x1019 cm−3

Abstract for the description of the hydrodynamic phase of strongly interacting matter in relativistic HIC the equation of state (EOS) is of utmost importance. Lattice QCD can provide useful information on the EOS, mainly for small net baryon densities. The QCD quasiparticle model (QPM) provides a means to map lattice results into regions relevant for a variety of experiments. Recent work has enabled us to include collectives modes and damping effects into the QPM. Among physical implications are predictions for forthcoming heavy-ion collisions at LHC/ALICE.

Invited talk on possible medical applications of laser accelerated particle beams

Focusing and transport of laser-accelerated protons with quadrupoles

Tutorial on laserparticle acceleration and applications of such beams.

The long-term safety assessment of nuclear waste disposals requires detailed knowledge of the transport and interaction behavior of actinides within the technical, geotechnical and geological barriers. The migration and interaction behavior of actinides can be effectively influenced by humic substances, biopolymers ubiquitous in natural environments, due to their ability for complex and colloid formation and their redox properties. It is known, that especially their carboxylic and phenolic OH groups are able to complex metal ions. In addition to these oxygen containing functional groups, humic substances also offer sulfur and nitrogen containing functionalities.

The aim of this work is to determine the influence of various sulfur and nitrogen containing functional groups on the uranium(VI) complexation and to evaluate their contribution in comparison to oxygen containing functional groups. For this, simple organic model ligands that can occur as building blocks for humic substances are used in the first instance with the objective to transfer the results to humic substances. In this study, results are presented for the uranium(VI) complexation by the organic ligands benzenesulfonic acid and 4-hydrxybenzenesulfonic acid as well as anthranilic and nicotinic acid. The complex formation constants for the uranium(VI) complexation were determined applying time-resolved laser-induced fluorescence spectroscopy (TRLFS) as a function of pH.

kein Abstract vorhanden, da Vortrag

kein Abstract vorhanden, da Vortrag.

Laser cooling at ESR and laserplasma particle acceleration.

This paper will discuss recent experimental and numerical results from the authors' labs on the effects of moderate magnetic fields in electrochemical reactions. It is well established that the influence of the Lorentz force due to external homogeneous magnetic fields, known as magnetohydrodynamic (MHD) effect, manifests itself in the majority of cases in increased mass transport. However, a careful analysis of the governing equations shows that often a three-dimensional modeling of this effect is necessary. We will present numerical simulations of copper electrolysis in cuboid cells under the influence of homogeneous magnetic fields of different directions in the limiting current regime. In most cases there is a complex interplay of natural and magnetically driven convection. A comparison with recent experimental results (flow and concentration gradient visualization) will be given.

Acknowledgments: This work was supported by the German Science Foundation in frame of the collaborative research center 609 "Electromagnetic flow control in metallurgy, crystal growth and electrochemistry"

References:

1) K. Kim & T.Z. Fahidy, "An analysis of free-convective magnetoelectrolysis in constant magnetic fields", J. Electrochem. Soc. 142 (1995) 4196-4204
2) A.Bund, S.Koehler, H.Kuehnlein, W.Plieth, "Magnetic field effects on electrochemical processes", Electrochimica Acta 49 (2003) 147—152.
3) A. Bund, A. Ispas, G. Mutschke, "Magnetic field effects on electrochemical metal depositions", submitted to: Science and Technology of Advanced Materials, 2007
4) T. Weier, K. Eckert, S. Muehlenhoff, C. Cierpka, A. Bund, M. Uhlemann, Electrochem. Commun., 9 (2007) 2479.

The evolution of self-organized nanoscale ripple patterns induced by low energy ion sputtering of silicon was investigated. The quality of the patterns was monitored by calculating a normalized density of topological defects from atomic force microscopy images. A strong dependence of the normalized defect density on the applied ion fluence is observed with a well pronounced minimum at intermediate fluences. Simulations using the damped Kuramoto-Sivashinsky equation yield good agreement with the experiments and are further used to study the dynamics of single pattern defects.

The disposal of radioactive waste including the assessment of long-term safety is an open question in Germany. In addition to the choice of the repository host rock (salt, granite, clay) the basic necessity of a consistent and bindingly used reference database exists. Only by means of such a database it is possible to assess potential failure scenarios accurately and to make well-founded predictions about the long-term safety. Specific needs for waste repository and remediation projects in Germany are comprehensive datasets also covering high temperatures and high salinities. Against this background, available databases (NEA-TDB, IUPAC, NAGRA-PSI) do not suffice all these requests and are limited in their use, partly because of high restrictions and resulting incompleteness of thermodynamic datasets. Other databases rely on heterogeneous and therefore inconsistent data yielding in inadequately reproducible and plausible model calculations. Due to these deficiencies THEREDA, a joint project of institutions leading in the field of safety research for nuclear waste disposal in Germany, was started. It will provide consistent thermodynamic datasets and enhance the transparency and reliability of safety analyses.
Within the project THEREDA we seek to compile data of high quality, accordance and traceability, mainly from existing databases, and to complement this basis particularly with datasets for high saline systems (Pitzer and SIT parameters) and systems at elevated temperatures. Persistent data gaps are closed via estimated values. The identification of such gaps can also aid decisions about the scheduling of experimental programs. Each dataset included in THEREDA is documented in detail and gets a grade of quality attached. Higher grades of quality are allocated to thermodynamic parameters derived from experimental data, namely from non-thermochemical experiments, whereas estimated values determined from systematic trends in thermodynamical behavior or from studies of chemical analogs get lower ratings. Furthermore, numerical data uncertainties and the quality of data sources (primary or secondary literature, peer-reviewed or non-certified) are categorized.
THEREDA will represent a source of information on thermodynamic data that will be publicly accessible and free of charge via Internet (www.thereda.de) and set up on a SQL-database. A broad use of the database is ensured by export functions tailored to important geochemical codes such as EQ3/6, PHREEQC, GWB and ChemApp.

The migration behaviour of uranium in the geosphere is generally influenced by sorption processes in aqueous media. The solubility, mobility and bioavailability is determined by the molecular interactions between the dissolved actinide species and mineral surfaces in groundwater aquifers. In its hexavalent form, uranium usually exists in the environment as the dioxouranyl cation (UO22+) which can form highly soluble complexes with a variety of anionic species commonly increasing the solubility of uranium. However, since there is a high affinity of the UO22+ ion to hydrous iron oxides the mobility of U(VI) can be considerably reduced in the environment. The affinity of U(VI) to hydrous ferric oxides is strongest in the pH range from 5 to 8. But it is also dependent on the composition of the liquid phase. Strong complexing ligands such as carbonate potentially inhibit adsorption of U(VI) onto the mineral phase (1). Therefore, the structures of the uranyl surface complexes at iron hydroxide mineral phases such as hematite and ferrihydrite (Fh) in the presence of CO2 are still in the focus of recent spectroscopic investigations (2,3).
In this work we present results from sorption experiments of U(VI) on Fh using Attenuated Total Reflection Fourier-transform Infrared (ATR-FT-IR) spectroscopy which provide in situ spectral information of the sorption processes in aqueous solution. The sorption of the UO22+ ion was investigated at mildly acidic conditions in atmospheric equilibrium and under an inert gas atmosphere in order to study the influence of dissolved CO2 on the sorption process. The infrared spectra show a similar surface complex of the uranyl ion at the Fh-phase irrespective of the presence of atmospheric CO2. However, the binding of the carbonate ligand to the mineral phase changes considerably upon sorption of the actinide ion and a change from a monodentate to a bidentate binding upon sorption of UO22+ is concluded. Furthermore, we investigated the sorption and desorption behavior of carbonate ions on pristine Fh and after sorption of UO22+ onto the iron oxide phase.

References
(1) Hsi, C. D.; Langmuir, D. Geochim. Cosmochim. Acta 1985, 49, 1931-1941.
(2) Bargar, J. R.; Reitmeyer, R.; Davis, J. A. Environ. Sci. Technol. 1999, 33, 2481-2484.
(3) Ulrich, K. U.; Rossberg, A.; Foerstendorf, H.; Zänker, H.; Scheinost, A. C. Geochim. Cosmochim. Acta 2006, 70, 5469-5487.

The distribution of aqueous species of actinide(VI) ions primarily defines their geochemical reactions, e.g. complexation in solution, sorption onto mineral and biological phases, and the formation of colloids, and thus, influences the migration behaviour in the environment. In aqueous solution under normal conditions both uranium and neptunium exist as dioxoactinyl ions AnO2n+ (An = U, Np). They form different complexed species depending on their concentration level, pH range and the presence of potential ligands, such as carbonate.
In recent years, the aqueous U(VI) system has been investigated intensively, in contrast to Np(VI). However, the stability constants used for thermodynamic calculations often arise from non-structural experiments, such as potentiometry and ion exchange, performed at defined sample parameters (1,2). Up to now, a spectroscopic verification of uranyl and neptunyl species is lacking in particular at low concentrations and at neutral pH conditions, reasonably in an environmental context. Thus, speciation modelling using extrapolated data, might be inadequate for the assessment of actinide migration.
In this study we used Attenuated Total Reflectance Fourier-transform Infrared (ATR-FTIR) spectroscopy to compare hydrolysis and carbonate complexation reactions of both U(VI) and Np(VI). Such comparative vibrational study is feasible since the ions NpO22+ and UO22+ are linear and symmetrical. The results are relevant for a comprehensive understanding of actinyl(VI) complexation in aqueous solution.
The experiments were performed at a micromolar concentration level (≤ 100 µM) and in the pH range 2 – 7 under both oxic and anoxic atmosphere. In the infrared spectra the asymmetric stretching vibrations ν3 of the free ions, UO22+ and NpO22+, found in solutions at very acidic pH, are observed at similar wavenumbers, 961 and 964 cm–1. Upon increasing the pH the IR spectra provide evidence for the formation of hydroxo complexes of both actinyl(VI) ions at pH ≥ 3, which is contradictive to current thermodynamic speciation modelling. Since the comparison of the spectral differences between the two actinides show red-shifted bands to a similar extent it can be assumed that analogous hydrolysis species are formed.

(1) Guillaumont, R.; Fanghänel, T.; Fuger, J.; Grenthe, I.; Neck, V.; Palmer, D. A.; Rand, M. H. Update on the Chemical Thermodynamics of U, Np, Pu, Am and Tc.; Elsevier: Amsterdam, 2003.
(2) Grenthe, I.; Fuger, J.; Lemire, R. J.; Muller, A. B.; Nguyen-Trung, C.; Wanner, H. Chemical Thermodynamics of Uranium. ; 1st ed.; Elsevier Science Publishers B. V.: Amsterdam, 1992.

Algae in soil and water can have a significant influence on the transport of actinides in the biological and geological environment in particular on the load pathway soil - plant - animal - human. The chemical characterization of the radionuclide species is essential for a reliable assessment of the migration. Due to the relative simple structure of mono-cellular green algal cells and their properties to bind high amounts of heavy metals and actinides they are used as model organisms for the investigations of different biosorption and bioaccumulation processes.
Sorption studies with Chlorella vulgaris cells have shown that up to 40 % of the initial uranium is bound by the algal cells at pH 3. The uranium removal is almost complete at pH 5 and 6 in our experiments. The use of the time-resolved laser-induced fluorescence spectroscopy (TRLFS) and X-ray absorption spectroscopy (XAS) is an effort to obtain information about the possible structure and the spectroscopic properties of the sorbed U(VI) species on the algal cells in comparison to those of the initial uranyl species in the contact solution.
The luminescence spectroscopic investigations of formed algal uranyl complexes indicate that the binding of U(VI) to carboxyl groups plays a dominating role at pH 3, whereas a minor impact of organic phosphate compounds on the U(VI) sorption can not be excluded. In contrast, at pH 5 and 6 the phosphate groups are mainly responsible for the removal and binding of U(VI) by formation of organic and/or inorganic uranyl phosphates. The results of the uranium LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopic measurements support these evidence.

Kohlenstoffnanotubes (CNTs) weisen einzigartige mechanische, elektronische und chemische Eigenschaften auf. Mit dem zunehmendem Einsatz dieser Materialien in Industrie- und Konsumgütern kann, realistisch betrachtet, ein unbeabsichtigter Eintrag in die Umwelt nicht ausgeschlossen werden. Bislang veröffentlichte Studien zum Verhalten und zum Lebenszyklus von CNTs in der Umwelt sind unzureichend.
Im Rahmen der Arbeit wird der Zusammenhang zwischen Oberflächeneigenschaften, Suspensionsstabilität und Sorptionseigenschaften von CNTs diskutiert, um Vorhersagen über das Verhalten dieser Materialien nach einer unbeabsichtigten Freisetzung in die Umwelt zu treffen.

The green alga Chlorella vulgaris has the ability to bind high amounts of uranium(VI) in the pH range from 3 to 6 and to a lesser extend at higher pH values. The uranium removal is almost complete at pH 4.4 and 6 by metabolic active and inactive cells under the given experimental conditions. Laser-induced fluorescence spectroscopy was used for the characterization of uranyl species formed in solutions and biomass. Fluorescence spectroscopic investigations indicate differences of the formed algal uranyl complexes in dependence of the metabolic activity of cells and the uranyl speciation. Scanning electron microscopy demonstrates that the algal cell wall is involved in the binding of U(VI).

To understand the toxicity, transport, deposition and elimination of man-made radioactive elements in the human organism, it is crucial to elucidate their chemical behavior and properties on a molecular level. The present work is part of a project to determine the speciation of curium(III) and its lanthanide analog europium(III) in human urine in order to identify potential decontamination agents, to discover possible metabolism pathways in the organism and to detect differences and similarities in the chemistry of trivalent lanthanides and actinides. The aim of this work was to investigate the complexation of curium(III) and europium(III) with urea, the main component of mammal urine. Since both elements exhibit unique luminescence properties, the complexation was studied by time-resolved laser-induced fluorescence spectroscopy with an excitation wavelength of 395 nm. The europium(III) and curium(III) concentration was 3x10-5 M and 3x10-7¬ M, respectively, in all series. The urea concentration was varied between 0.001 and 5 M, the pH ranged from 1 to 8. All measurements were carried out in a glove box under nitrogen atmosphere.

In aqueous solution the luminescence spectrum of europium(III) shows two typical peaks at 585-595 and 610-620 nm, respectively. Each of these peaks is slightly split, the first one into two peaks with emission maxima at 588 and 591nm, respectively, the second one into two peaks with luminescence maxima at 612 and 616 nm, respectively. Upon complexation with urea the position of all peaks remains unaltered but the ratio of the split peaks in the 610-620 nm range changes. Furthermore luminescence in this wavelength range is significantly increased by complexation. The lifetime of the europium(III)-aqua-ion was determined to be 110 µs. In contrast the complex exhibits a considerably longer lifetime (> 120 µs). Analysis of the time-resolved spectra indicated the formation of a 1:1 complex. At an urea concentration of 1 M the complex is stable till pH 6 but starting at pH 7 the luminescence spectrum changes due to formation of europium(III) hydroxides. Using the factor analysis program SPECFIT the stability constant of the complex log ß110 was determined to be -0.08.

In contrast to europium(III), the luminescence spectrum of curium(III) in aqueous solution shows only one emission peak at 593 nm. Upon complexation with urea the peak is red-shifted to 598 nm and the luminescence intensity decreases. The lifetime of the curium(III)-aqua-ion was determined to be 68 µs but the lifetime of the complex is considerably longer (> 75 µs). Analysis of the time-resolved spectra indicated the formation of a 1:1 complex. At an urea concentration of 1.5 M the complex is already formed at pH 1 and till pH 5 the luminescence spectra are identical. Starting at pH 6 the luminescence intensity decreases significantly due to the formation of curium(III) hydroxides. Using the factor analysis program SPECFIT the single spectra of the different species were calculated and the stability constant of the complex log ß110 was determined to be between -0.8 and -0.9.

Comparing the complexation of urea with europium(III) and curium(III), it seems that the latter is complexed inferior to the first one although it is obvious that both form very weak complexes. This can be explained with the structure of urea in aqueous solution over the whole pH range investigated in this study. The results obtained indicate that urea unlikely plays a role in heavy metal binding in urine and that other substances will have greater complexing potential.

The magnetorotational instability (MRI) is one of the most promising candidates to explain turbulence and angular momentum transport in accretion disks which is essential to understand the mass accumulation of stars and black holes. Only recently, a possible connection of MRI with the dynamo process in the Earth's core was discussed. We study a special type of MRI in a Taylor-Couette experiment with the liquid metal alloy GaInSn under the influence of a helical magnetic field (Phys. Rev. Lett. 97, 184502; Astrophys. J. 649, L145-L147; New J. Phys. 9, 295). This helical MRI sets in at Reynolds numbers of the order 1000 and Hartmann numbers of the order 10, quite in contrast to the standard MRI with an purely axial magnetic field which would require much larger values. Particular focus is laid on recent results of a modified experiment with strongly reduced Ekman pumping at the endplates in which sharper transitions between stable and unstable regimes are observed.

One of the most interesting features of Earth's magnetic field reversals is their pronounced asymmetry, including a slow dipole decay and a fast recreation of the reversed dipole. This asymmetry indicates a possible connection with relaxation oscillations as they were early studied by van der Pol. A simple mean-field dynamo model (Phys. Rev. Lett. 94 (2005), 184506) is analysed with view on this similarity, and a comparison of the time series and the phase space trajectories with those of paleomagnetic measurements is carried out. For the case of highly supercritical dynamos a very good agreement with the paleomagnetic data is achieved (Earth Planet. Sci. Lett. 143 (2006), 828; Geophys. Astrophys. Fluid Dyn. 101 (2007), 227). Deviations of both numerical and paleomagnetic reversal sequences from Poisson statistics are touched upon (Phys. Earth Planet. Inter. 164 (2007), 197). The observed clustering property of reversals is interpreted as a feature of ''punctuated equilibrium'' which is, in turn, typical for metastable systems. We show that both metastability and the relaxation oscillation character have their common root in the typical spectral behaviour of the non-selfadjoint dynamo operator. In addition, we try to constrain the most essential parameters of the dynamo model by the typical time scale of individual reversals, the clustering characteristics, and the stochastic resonance phenomenon (arxiv.org/0709.3932). The latter was recently shown to appear with a time period typical for the Milankovitch cycle of the Earth's orbit eccentricity.

Topographic and optical contrasts formed by Ga+ ion irradiation of thin films of amorphous silicon carbide have been investigated with scanning near-field optical microscopy. The influence of ion-irradiation dose has been studied in a pattern of sub-micrometre stripes. While the film thickness decreases monotonically with ion dose, the optical contrast rapidly increases to a maximum value and then decreases gradually. The results are discussed in terms of the competition between the effects of ion implantation and surface milling by the ion beam. The observed effects are important for uses of amorphous silicon carbide thin films as permanent archives in optical data storage applications.

Aqueous uranyl carbonate complexes play an important role in the hydrogeology of uranium mining areas and nuclear waste disposals. Many publications are available for the stability of uranyl carbonate complexes, but thermodynamical data like the enthalpy or entropy are rare. We determined thermodynamical data from spectroscopic studies for the uranyl carbonate complex UO2(CO3)34- in the temperature range from 5°C to 70°C. We found for the reaction enthalpy the value 36.25 ± 4.31 kJ/mol and for the reaction entropy a value of 297.082 ± 13.839 J/(K∙mol).

Verfahren zum Bestimmen der Materialzusammensetzung einer Strahlung abstrahlenden Materialprobe (12) mit den folgenden Verfahrensschritten: Aufnehmen (P2) eines Spektrums der in einem Detektormaterial durch die Strahlung deponierten Energie; Bestimmen einer in einem ersten Energiebereich deponierten ersten Energie (F1), einer in einem zweiten Energiebereich deponierten zweiten Energie (F2) und einer in einem dritten Energiebereich deponierten dritten Energie (F3); Zuordnen (P4) eines ersten Farbparameters (F1) zu der ersten deponierten Energie, eines zweiten Farbparameters (F2) zu der zweiten deponierten Energie und eines dritten Farbparameters (F3) zu der dritten deponierten Energie und Vergleichen (P5) der zugeordneten Farbparameter (F1, F2, F3) mit vorgegebenen Werten für die Farbparameter (R1, R2, R3), wobei die vorgegebenen Werte (R1, R2, R3) typischen Farbparametern einer vorbestimmten Materialzusammensetzung entsprechen.

Detektoranordnung (1) zur winkelauflösenden Detektion von Strahlung mit mindestens einem Detektorelement (2), welches eine Vorderseite (3) und eine Rückseite (4), ein erstes Detektormaterial und ein zweites Detektormaterial zwischen der Vorderseite (3) und der Rückseite (4) aufweist, wobei ein Raum zwischen der Vorderseite (3) und der Rückseite (4) des Detektorelementes (2) von mehreren Bereichen (6) aus dem ersten Detektormaterial und mindestens einem Bereich (5) aus dem zweiten Detektormaterial ausgefüllt ist und jeder Bereich die Vorderseite (3) mit der Rückseite (4) des Detektorelementes (2) verbindet und wobei eine Kollimation von durch die Vorderseite (3) in das Detektorelement (2) eintretender Strahlung (γ) durch die Detektormaterialien erfolgt.

The long-term safety assessment of nuclear waste disposals requires detailed knowledge of the transport and interaction behavior of actinides within the technical, geotechnical and geological barriers. Humic substances, ubiquitous in natural environments, are able to influence the migration of actinides due to their ability for complex and colloid formation and their redox properties. It is known, that especially their carboxylic and phenolic OH groups are able to complex metal ions. In addition to these oxygen containing functional groups, humic substances also offer sulfur and nitrogen containing functionalities.
The aim of this work is to determine the influence of various sulfur and nitrogen containing functional groups on the uranium(VI) complexation and to evaluate their contribution in comparison to oxygen containing functional groups. For this, simple organic model ligands that can occur as building blocks for humic substances are used in the first instance with the objective to transfer the results to humic substances.
In this study, results are presented for the uranium(VI) complexation by the organic ligands benzenesulfonic and 4-hydroxybenzenesulfonic acid as well as for nicotinic and anthranilic acid. The complex formation constants for the uranium(VI) complexation were determined applying UV-vis absorption spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS) as a function of pH.
Interestingly, we did not see any interaction of the uranyl ion with benzenesulfonic acid (BSA). In contrast, for the uranium(VI) complexation by 4-hydroxybenzenesulfonic acid (HBSA) the formation of a 1:1 complex was detected. The stability constant for this complex of the type MpHqLr was determined with log ß101 = 3.9 ± 0.03.

Bacteria have a great influence on the migration behaviour of heavy metals in the environment. Peptidoglycan (PGN) forms the main part of the outer membrane of Gram-positive bacteria. We investigated the interaction of the uranyl cation (UO22+) with PGN from Bacillus subtilis by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH range (2.4 – 9) and at environmentally relevant low uranium concentrations (10-4 – 10-5 M). The PGN polymer contains a high density of functional groups for metal ion binding, like carboxyl, amino and hydroxyl groups.
With potentiometric titration the dissociation constants of the functional groups and the corresponding site densities could be detected. We found four functional groups, which can be dedicated to two different carboxyl functionalities, amino and hydroxyl groups. Using the same technique, two different uranyl PGN complexes could be identified, one complex with a carboxyl ligand (R-COO-UO2+) and a second complex with additional hydroxyl coordination (R-COO-UO2+-HO-R). The complex stability constants were determined to be log beta = 5.16 ± 0.13 for the first, and log beta = 13.00 ± 0.05 for the second complex, respectively.
TRLFS measurements show from pH 2.4 to 4.5 a red shift of the peak maxima of about 8 – 10 nm, in comparison to the free uranyl ion, connected with an increase of the luminescence intensity. Over pH 4.5 up to pH 9 the luminescence intensity decreases. The time resolved measurements show beneath the lifetimes of the free uranyl ion (1800 ± 200 ns) and the known uranyl hydroxides only one additional lifetime (224 ± 54 ns) which can be dedicated to a uranyl PGN complex species. From these we conclude that the two uranyl PGN complex species found by potentiometry can also be identified with TRLFS. The first complex (R-COO-UO2+) shows luminescence activity, but the second complex (R-COO-UO2+-HO-R) not. Complex stability constants for these two complexes were determined using the computer program SPECFIT. They are in good accordance to those calculated from potentiometric titrations.

The influence of external homogeneous magnetic fields during electrochemical metal deposition in cuboid cells is shortly reviewed. By analytical means, supported by numerical simulations, it is shown that a simplified two-dimensional approach is often misleading and has to be replaced by a more complex three-dimensional treatment as only the solenoidal part of the Lorentz force can cause convection.

Conformational substates of B-DNA have been reported to be involved in DNA recognition by proteins [1]. BI and BII substates, that co-exist in B-DNA, differ in the phosphate backbone conformation about the C3'-O3'-P segment related to the variability of the dihedral e and z angles (see figure left [2]). Typical IR marker bands have previously been identified which allow assessing the relative population of BI and BII conformers by FTIR spectroscopy for DNA from salmon testes, poly(dG-dC) and the d(CGCGAATTCGCG)2 dodecamer [3]. So far, BI/BII dynamics studies were restricted to static FTIR spectroscopy under isothermal relaxation at low temperatures . We have attempted to monitor the BI/BII transition under defined native-like conditions using rapid scan FTIR-difference-spectroscopy at a time resolution of 70 ms. An ATR-cell accessory was designed that allows both, the application of flashes to induce small temperature jumps and the adjustment of constant humidity of the sample. The latter is critical to address the role of backbone hydration in the dynamics of the BI/BII transition.

The Taylor coefficients of flavor diagonal and off-diagonal susceptibilities as well as baryon number, isovector and electric charge susceptibilities are considered within a phenomenological quasiparticle model of the quark-gluon plasma and successfully compared with lattice QCD data for two degenerate quark flavors. These susceptibility coefficients represent sensible probes of baryon density effects in the equation of state. The baryon charge is carried, in our model, by quark-quasiparticle excitations for hard momenta.

Activation of G protein-coupled receptors (GPCRs) orginates in ligand-induced structural changes that are transmitted across the plasma membrane to the cytosolic receptor surface. In rhodopsin-like class-1GPCRs, protonation of a carboxylic acid (Glu134 in rhodopsin) in the conserved cytosolic D(E)RY motif in transmembrane helix 3 (TM3) is coupled to receptor activation. Here, we have investigated the proton-sensitivity of the structure of synthetic peptides consisting of 30amino acids derived from TM3 of bovine rhodopsin (rho) and the chemokine receptor CCR3. ATR- Fourier-transform-infrared (FTIR) spectroscopy reveals a helical structure of the rho-TM3 peptide in PC vesicles and detergent micelles, where Glu134 exchanges protons with the solvent at a pKa of 5.5-6.0 as determined from the pH sensitivity of the COO- stretching mode. The amide I modes reveal a proton-induced helical turn formation in rho-TM3 and CCR3-TM3. The conformational change in the ERY motif is affects also the Tyr136 fluorescence which exhibits a strong pH sensitivity (pKa of 6) which is abolished upon replacement of Glu134 by Gln in rho-TM3. Förster-Resonance-Energy-transfer from a C-terminal Trp to DANSYL-labelled lipids in mixed micelles and lipid vesicles evidences that the D(E)RY motif constitutes an autonomous proton-driven conformational switch which couples protonation to helical turn formation and probably helix insertion depth. We propose that the protonation-controlled hydrophobicity profile at the cytosolic end of TM3 provides a pH-sensitive module that couples helix packing in the active receptor conformation of class I GPCRs to proton exchange reactions with the cytosol.

Actinides have been and will be introduced into shallow and deep groundwater environments via various human activities. The process of interaction between naturally occurring chelating substances and metals may influence the migration behavior of hazardous actinides in the environment once they have been released. Siderophores are chelating substances produced by microorganisms under iron-deficient conditions. For example, Powell et al. [1] demonstrated the occurrence of hydroxamate siderophores produced by microorganisms in concentrations ranging from 10-7 to 10-8 M in a variety of soils. In general catechol and hydroxamate groups in siderophores are the main functional groups involved in binding with actinides. As an example, Pseudomonas species are ubiquitous soil and groundwater bacteria that synthesize bacterial pyoverdin-type [2-5] and hydroxamate siderophores [6]. The observed mobilization effects of siderophore molecules on radionuclides probably due to the formation of strong soluble species motivated detailed investigation of their complexation characteristics, using a radionuclide suitable for spectroscopic methods.
To overcome the lack of information about actinide(III) siderophore interactions, we thus present findings regarding the complexation of curium(III) with pyoverdins (PYO) and desferrioxamine B (DFO), obtained using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The excellent luminescence properties of curium(III) were used to explore its complexation behavior with the two different bioligands at environmentally relevant curium(III) concentrations.
(A) PYO: Pseudomonas fluorescens (CCUG 32456) cells isolated from the granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden, secreted a pyoverdin mixture containing 4 main components [5].
(B) DFO: Desferrioxamine B (DFO) is a microbial produced trihydroxamate siderophore which is commercially available and could occur naturally in soils. Recently Essen et al. [6] could show the production of desferrioxamine siderophors by Pseudomonas stutzeri (CCUG 36651). This strain was also isolated at the Äspö Hard Rock Laboratory.

We explored the unknown luminescence properties, lifetimes and individual luminescence emission spectra of the formed Cm(III) species. The strength of the complex formation of the two bioligands will be discussed on the basis of the spectroscopic properties obtained in their individual systems. The results of this study increase our understanding of the mobilization of actinides by siderophores secreted by resident bacteria in a natural environment.

[1] Powell, P.E., et al., Nature 287 (1980) 833-834.
[2] Budzikiewicz H., Fortschr. Chem. Org. Naturst. 87 (2004) 83-237 .
[3] Kalinowski B.E., et al., Geomicrobiol. J. 23 (2006) 157-164.
[4] Moll, H., et al., BioMetals 21 (2008) 219-228.
[5] Moll, H., et al., Geomicrobiol. J. 25 (2008) 157-166.
[6] Essen, S.A., et al., Appl. Environ. Microbiol. 73 (2007) 5857-5864.

no abstract available

Natural and synthetic crystalline α-quartz, as well as synthetic SiO₂ glass, were irradiated with different doses of 8.8 MeV He²⁺ ions. The irradiation-induced alteration was characterised using Raman and cathodoluminescence (CL) spectroscopy, optical microscopy, transmission electron microscopy (TEM) and CL and electron microscope imaging. The initially dull bluishviolet CL colour of the two α-quartz samples was found to be transformed to bright yellow in the irradiated areas. The emission maximum was observed 45 μm below the surface, which corresponds well with correlated helium trajectory lengths and defect density distribution. Both, total intensity and radial intensity distribution of the CL emission change with the irradiation dose. Observations suggest a nonlinear, approximately logarithmic increase of the CL intensity depending on the alpha dose. Significant broadening of Raman bands is only observed near the far end of helium trajectories. This broadening is not only caused by the structural radiation damage but also by strain between strongly and lowly damaged areas.

Aureoles surrounding radioactive inclusions – so called radiohaloes – are a common feature often observed in several rock-forming minerals. These alterations are caused by the action of alpha-particles (i.e. He²⁺ ions) emitted into the host mineral.
While in some cases (e.g. biotite, cordierite) the most striking feature of radiohaloes is a strongly enhanced absorption of light, there are commonly no visible changes found in quartz. In this mineral, alpha irradiation leads to a marked change in the emission behaviour, which can be very well observed using cathodoluminescence (CL) imaging.
In the present study several micro- and nano-techniques [i.e., Raman spectroscopy, CL spectroscopy, and transmission electron microscopy (TEM)] were used to study the alteration in synthetic radiohaloes, produced by artificial alpha irradiation of various SiO₂ samples. Alpha-quartz of natural and synthetic origin as well as synthetic SiO₂ glass were implanted with different doses of 8.8 MeV He²⁺ ions (fluences in the range from 10¹³ to 10¹⁷ ions/cm²).
The initially dull bluish-violet CL colour of the crystalline quartz samples was found to be transformed to bright yellow in irradiated areas. Monte Carlo simulations predicted that the observed depth of alteration is in very good agreement with the calculated range of alpha particles in quartz. Both, total intensity and radial intensity distribution of the CL emission change with the irradiation dose. Observations suggest a non-linear, approximately logarithmic increase of the CL intensity depending on the alpha dose. In contrast, no significant change in CL emission was observed in the case of He-irradiated amorphous SiO₂.
The changed emission behaviour of He-irradiated areas in alpha-quartz is accompanied by structural damage, caused by the impact of the alpha particles. Significant broadening of Raman bands is only observed near the far end of helium trajectories. This broadening is not only caused by the structural radiation damage but also by strain, inter alia due to (locally heterogeneous) volume expansion of irradiated micro-areas.
Restricted to the end of the helium trajectories, there is a clearly defined, lense-shaped zone, characterised by changed optical and BSE behaviour. The structural state of this region, as investigated by TEM, will be discussed.