Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

We devised and tested a computed tomography approach that utilises a scanned electron beam X-ray source to produce multiple projections of an object at scan rates of 1000 frames per second and at an in-plane resolution of 1 mm. The measurement setup consists of an electron beam unit, a cylindrical tungsten target, and a detector line array which are operated inside a vacuum enclosure. By means of fast periodic electron beam deflection we produce a linearly moving focal X-ray spot on the tungsten target. The X-ray detector is read out in synchronisation with the beam deflection signal such that a set of consecutive tomographic projections from an object that is placed between target and detector can be obtained. This approach has some attractive features: it gives the highest achievable axial resolution, which is necessary to image fast moving flow structures and it is comparatively moderate in effort and costs. However, these advantages are compromised by the fact, that the projection data is incomplete with regard to the projection angle. The arising limited-angle problem may be solved by iterative image reconstruction algorithms. We will show, that this approach is suitable for a certain class of flow problems which are characterised by less complex object distributions and a high degree of available a-priori information, such as two-phase flows and particle tracking problems. In the presentation we will give an overview on the method, present first experimental results and discuss the image reconstruction process in some more detail.

We discuss the application of gamma tomography to the fully three-dimensional measurement of gas and fluid distributions inside rotating hydrodynamic machines. For such investigations we use a gamma tomography setup that currently employs a Cs-137 source of 180 GBq activity and approximately 5 mm focal spot together with a detector arc made of 64 scintillation crystals (BGO) with photomultiplier read-out. The detector is operated in pulse counting mode with energy discrimination. In the presentation we will introduce the principle of phase-correlated projection acquisition. Thus, projection data of a rotating object is acquired by a fast detector read-out and subsequent integration of the data for a set of equal angular intervals which are recorded by an angle sensor at the rotating object. As a first example we demonstrate the measurement of gas fractions in an axial pump that is in two-phase flow operation. In this study we were able to visualise the gas profiles at 10% gas fraction within the impeller of the pump at different axial measurement planes. The results directly provided an understanding of the interrelation between the hydraulic conveyance characteristics of the pump in two-phase flow operation and the flow structure in the impeller. In a second example we introduce the measurement of fluid distributions in a hydrodynamic coupling. In this study we successfully applied gamma tomography to visualise flow patterns inside the coupling for varying filling levels and slips. These results now find application in the optimisation of coupling designs and in the validation of computational fluid dynamics simulations for such devices.

The samples of erbium-doped lithium niobate (Er:LiNbO3) were prepared by the standard Czochralski method and treated by the annealed proton exchange (APE) procedure to create a planar waveguide for further optical application. The positions of Er atoms in the crystal lattice of pristine and APE treated Er:LiNbO3 samples were studied by the Rutherford backscattering spectrometry (RBS)-channeling method. The Er3+ ion positions in the pristine and the APE treated Er:LiNbO3 samples are compared. X-ray diffraction (XRD) was used to determine the damage to the crystal structure caused by the APE treatment. It was found that the APE treatment leads to significant crystal structure damage and to shifts of the Er3+ ions from their positions in the pristine crystal.

Chromium oxynitride films CrOxNy were prepared by reactive magnetron sputtering from a chromium target in Ar/O-2(N2O)/N-2 gas mixtures. The argon-to-nitrogen partial pressure ratio and the DC discharge power were kept constant in the experiments. By changing the gas composition the film stoichiometry can be continuously varied from CrN to Cr2O3. The film composition has been determined by Rutherford backscattering (RBS) and by elastic recoil detection analysis (ERDA). From an XRD analysis it was concluded that the films consist of CrN nanocrystals in an amorphous oxide matrix. Depending on the oxygen content [O], the electronic behaviour of the films changes, accompanied by the evolution of an optical band gap, which was determined by spectral transmission and reflection measurements. The (negative) temperature coefficient at approximate to 300 K of the resistivity of the films is in the range of 0.5 (CrN) to 2% K-1 (CrO0.5N0.7). This film property can be used for temperature-dependent resistors, for instance in thermal radiation detectors.

In the present work, the energy spectra of protons channeled along the (0 0 0 1) axis of SiC polytype crystals (namely 4H and 6H) in the energy range E-P = 400-650 keV, in the backscattering geometry, were taken and analyzed. Computer simulations are in very good agreement with the measured spectra. The accurate reproduction of the experimental channeling spectra in the backscattering geometry is strongly based on the investigation of the correct dechanneling function and a, the ratio of the stopping powers in the aligned and random mode. In the present work, the applicability of a Gompertz type sigmoidal dechanneling function, with two parameters, k and x(c), which represent characteristic dechanneling rate and range, respectively, is examined, and the results are compared to the ones obtained in the past, concerning the same polytype structures, based on the assumption that the dechanneling of protons follows an exponential law, for the energy range E-P = 1.7-2.4 MeV.

Pigs of three different age groups (newborns, 1 week old, 6 weeks old) were used to study the transport of the large neutral amino acids 6-[F-18]fluoro-L-DOPA ([F-18]FDOPA) and 3-O-methyl-6-[F-18]fluoro-L-DOPA ([F-18]OMFD) across the blood-brain barrier (BBB) with positron emission tomography (PET). Compartmental modeling of PET data was used to calculate the blood-brain clearance (K-1) and the rate constant for the brain-blood transfer (k(2)) of [F-18]FDOPA and [F-18]OMFD after i.v. injection. A 40-70% decrease of K-1(OMFD), K-1(FDOPA) and k(2)(OMFD) from newborns to juvenile pigs was found whereas k(2)(FDOPA) did not change. Generally, K-1(OMFD) and k(2)(OMFD) are lower than K-1(FDOPA) and k(2)(FDOPA) in all regions and age groups. The changes cannot be explained by differences in brain perfusion because the measured regional cerebral blood flow did not show major changes during the first 6 weeks after birth. In addition, alterations in plasma amino acids cannot account for the described transport changes. In newborn and juvenile pigs, HPLC measurements were performed. Despite significant changes of single amino acids (decrease: Met, Val, Leu; increase: Tyr), the sum of large neutral amino acids transported by LAT1 remained unchanged. Furthermore, treatment with a selective inhibitor of the LAT1 transporter (BCH) reduced the blood-brain transport of [F-18]FDOPA and [F-18]OMFD by 35% and 32%, respectively. Additional in-vitro studies using human LAT1 reveal a much lower affinity of FDOPA compared to OMFD or L-DOPA. The data indicate that the transport system(s) for neutral amino acids underlie(s) developmental changes after birth causing a decrease of the blood-brain barrier permeability for those amino acids during brain development. It is suggested that there is no tight coupling between brain amino acid supply and the demands of protein synthesis in the brain tissue. (C) 2004 Elsevier B.V. All rights reserved.

Planetary, stellar, and galactic magnetic fields are caused by the hydromagnetic dynamo action in moving electrically conducting fluids. While theory and numerics of hydromagnetic dynamos have flourished during the last decades, an experimental validation of the effect was missing until recently. Therefore, it was a nice coincidence that, after years of preparations, the large-scale liquid sodium dynamo facilities in Riga and Karlsruhe became operative nearly simultaneously at the end of 1999. Since those pioneering times, a number of runs have been carried out in either place, yielding reproducible data on the kinematic as well as on the saturation regime. With the main focus on the Riga experiment, I give a summary of what has been achieved so far and what is left for future dynamo experiments.

The heavy ion time-of-flight elastic recoil detection analysis (HI-ERDA) technique was used to investigate the possibility of measuring near-surface elemental depth profiles of light and mid-Z elements in thin films of plasma-assisted molecular beam epitaxy (PAMBE)-grown GaN and helium-implanted titanium. The great advantage of HI-ERDA is the ability to measure mass-separated elemental depth profiles simultaneously. However for some materials it is not certain whether HI-ERDA can be used successfully because significant sputtering or other beam-induced damage may occur. The damage to the surfaces by a 77 MeV iodine beam was assessed using RBS, AFM and profilometry. The results show that for thin PAMBE-grown polycrystalline GaN films and for titanium that has been heavely implanted with helium a significant modification of the near-surface region is caused by the probing heavy ion beam. For the PAMBE-grown GaN films the most significant loss trend is observed for nitrogen. Surprisingly this was not accompanied by a change in surface topology. In contrast, an almost complete removal of the heavily helium-implanted surface layer was measured for the titanium specimens. The investigation shows that reference measurements with additional techniques such as RBS, AFM and profilometry have to be performed to ascertain sample integrity before HI-ERDA data can be used.

The evolution of ion beam synthesized Co and Ge nanoclusters in a SiO2 matrix during annealing processes has been investigated by in-situ X-ray diffraction and ex-situ transmission electron microscopy. Remarkable differences has been found for Ge and Co clusters. For Ge implanted SiO2 films a clear influence of near-surface Ge oxidation and nanocluster melting has been established. Annealing at temperatures at around 1000°C leads to the formation of an ensemble of small (d~5 nm) nanocrystals. The cluster growth is mainly thermodynamically driven by classical diffusion limited Ostwald ripening. Contrary, for Co-implanted SiO2 films a drastic transition in nanoclusters evolution has been established. Within a relatively small temperature range at around 800°C an ensemble of small (d~4nm) amorphous Co clusters is transformed into a bimodal cluster distribution with large Co nanocrystals of 20-40 nm diameter near the surface. The influence of oxidation or nanocluster melting can be neglected.

Some recent developments in the field of nuclear safety research will be presented. The contribution starts from the general aim of safety research – to contribute to the sustainability of nuclear energy compared with other energy resources.
The first two examples refers to the safety of operating NPPs. Possible boron dilution transients can lead to reactivity accidents at certain conditions. Comprehensive experimental and numerical studies were carried out to identify the critical conditions of such transients. Another topic – which belongs to the severe accident research - is the investigation of the reactor pressure vessel behaviour during core melt and corium in the lower plenum. Pre- and post-test calculations of the Swedish FOREVER-experiments will be presented.
The third topic deals with the transmutation of long-lived radionuclides. Up to now the radioactive waste has safely to be isolated for millions of years. Implementing new concepts a drastic reduction of waste and isolation time can be expected. As example accelerator driven systems (ADS) are discussed.

Due to improved hardness and oxidation resistance, Ti_1-xAl_xN coatings are constantly displacing TiN in tooling and microelectronic industry. Since the coating’s performance can be further increased by tailoring preferred orientation, an understanding of how deposition parameters influence thin film texture is crucial. The approach used here is in situ x-ray diffraction both in-plane and off-plane during film growth. For this purpose a growth chamber has been installed into the goniometer of the Rossendorf synchrotron BeamLine (ROBL) at the ESRF. Ti_1-xAl_xN films were deposited by reactive co-sputtering from metallic Ti and Al targets, varying substrate temperature, bias voltage and aluminum concentration. In-situ experiments with x~0.1 revealed competitive growth between low surface free energy (002) grains and low strain energy (111) grains parallel to the surface with (002) orientation dominating at higher substrate temperature in accordance with models found in literature. Contrary to pure TiN, here no sub-surface recrystallisation as a driving factor for texture crossover has been observed. Halving the deposition rate led to almost pure (002) fiber texture independent of film thickness pointing towards kinetic restrictions during film growth. Data of current experiments on nano-composite structured Ti_1-xAl_xN with x~0.5 will also be presented at the conference.

The nature of the heteroatom X incorporated in the five-member PXP-diphosphine spacer was found to play a primary unit role both in the stereochemical arrangement and overall stability of nitrido containing [M(N)(PXP)]²⁺ metal fragments (M = Tc, Re). Thus, by mixing PXP ligands with labile [Re(N)Cl₄]^- and [Tc(N)Cl₂(PPh₃)₂] nitrido precursors in CH₂Cl₂/MeOH mixtures, a series of neutral [M(N)Cl₂(PXP)] complexes (M = Tc, 1-5; M = Re, 8-9) was collected. In the resulting distorted octahedrons PXP adopted facial or meridional coordination, and combination with halide co-ligands produced three different stereochemical arrangements, i.e. fac,cis mer,cis and mer,trans, depending primarily on the nature of the diphosphine heteroatom X. When X = NH, mer,cis-[Tc(N)Cl₂(PNP1)] 1 was the only isomer formed. Alternatively, when a tertiary amine nitrogen (X = NR; R = CH₃, CH₂CH₂OCH₃) was introduced in the spacer, fac,cis-[M(N)Cl₂(PN(R)P)] complexes (M = Tc, 2, 3; M = Re, 8f) were obtained. Isomerization into the the mer,cis-[Re(N)Cl₂(PN(R)P)], 8m, species was observed only in the case of rhenium when the tertiary amine group carried the less encumbering methyl substituent. Fac,cis-[Tc(N)Cl₂(PSP)], 4f, was isolated in the solid state when X = S, but mixture of fac,cis-[Tc(N)Cl₂(PSP)] and mer,trans-[Tc(N)Cl₂(PSP)], 4m, isomers was found in equilibrium in the solution state. A similar equilibrium between fac,cis-[M(N)Cl₂(POP)] (M = Tc, 5f; M = Re, 9f) and mer,trans-[M(N)Cl₂(POP)] (M = Tc, 5m; M = Re, 9m) species was detected in POP containing complexes. The molecular structure of all of these complexes were assessed by means of conventional physico-chemical techniques including multinuclear NMR spectroscopy and X-ray diffraction analysis of representative mer,cis-[Tc(N)Cl₂(PN(H)P)] 1, fac,cis-[Tc(N)Cl₂(PSP)] 4f, and mer,cis-[Re(N)Cl₂(PN(Me)P)] 8m compounds.

¹⁸F-Labeled amino acids represent a promising class of imaging agents in tumors, particularly brain tumors. However, the determination of their potential to image peripheral tumors, possibly depending on individual transport characteristics, still remains an area of investigation. The present study investigated the transport mechanism for 3-O-methyl-6¹⁸F-fluoro-L-dopa (OMFD), a novel ¹⁸F-labeled phenylalanine derivative, into tumor cells. Methods: OMFD has routinely and reliably been prepared for clinical use in 20 % - 25 % radiochemical yield (decay corrected, related to ¹⁸F-F₂) using 6-¹⁸F-fluoro-L-3,4-dihydroxyphenylalanine preparation devices with minor modifications. In vitro uptake assays with HT-29 (human colon adenocarcinoma) cells, FaDu (squamous cell carcinoma) cells, and RBE4 (immortalized rat brain endothelial) cells were performed with OMFD under physiologic amino acid concentrations without and with the competitive transport inhibitors 2-aminobicyclo[2,2,1]-heptane-2-carboxylic acid and α-(methylamino)isobutyric acid plus serine and without or with Na⁺. Results: Transport inhibition experiments using specific competitive inhibitors demonstrated that uptake of OMFD in all cell lines tested was mediated mainly by the sodium-independent high-capacity amino acid transport systems. The highest OMFD uptake was in FaDu cells. Conclusion: OMFD seems to be a promising PET tracer for imaging of amino acid transport in tumors.

Experiments and simulations were conducted in a vertically oriented Hele-Shaw cell. Buoyancy driven convection, in particular plumes and double diffusive fingering as well as surface tension driven convection in the form of roll cells have been found in the experiments and reproduced numerically. The calculations reveal the mechanism of the enhancement of mass transfer rates in the presence of the instabilities. The model can be used to predict the mass transfer for the simple geometry of a flat surface.

Improvements of tribological properties of CrNiMo and CrCoMo alloys by nitrogen plasma immersion ion implantation

Chromium enrichment of AISI 304 stainless steel surface after nitrogen ion recoil bombardment of chromium film

Comparison of nitrogen ion beam and plasma immersion implantation in Al5052 alloy

Plasma immersion ion implantation of nitrogen into H13 steel under moderate temperatures

Thin tin-doped indium oxide films have a low resistivity (10-3-10-4 W·cm) and a high luminous transmittance (>80%) [1]. Therefore they find an application as electrodes in flat panel displays, solar cells, etc.
The lowest resistivities (in the order of 1·10-4 W·cm) are reported for ITO films prepared by sputtering of ceramic targets which are expensive and mechanically fragile. The stable process with metallic targets can be much more favorable for industrial application, because of low cost and high deposition rates. The production of ITO films with low resistivity by reactive sputtering usually requires postdeposition annealing step or deposition on heated substrates [1].
A number of publications were devoted to investigate ITO powders with different Sn content [2] and ITO films subjected to oxidizing and reducing annealing [3]. These films were prepared from ceramic targets. Mössbauer spectroscopy in combination with X-ray diffraction and Hall measurements have been applied in these studies on ITO to investigate the chemical state of Sn atoms.
Similar investigations on the ITO films prepared by reactive magnetron sputtering at elevated substrate temperatures are missing up to now. Therefore indium-tin oxides (ITO) films were deposited by reactive middle frequency dual magnetron sputtering at heated substrates.
The doping of Sn in In2O3 was investigated using the surface sensitive 119mSn Conversion-Electron Mössbauer Spectroscopy (CEMS) to investigate the chemical state of tin.

Scanning capacitance microscopy (SCM) and -spectroscopy (SCS) were applied to study the charge trapping and the charge retention in silicondioxide layers with embedded Ge- or Si-nanoclusters. The nanoclusters were formed by ion beam synthesis. Applying a dc bias to the conductive nano-tip charge injection into the dielectric was achieved. While SCM images visualize the localized trapped charge in the oxide, the locally recorded dC/dV versus V curves allow to quantify the trap density. The evaluation of dCldV shifts was used to compare the electronic properties of different oxide layers in dependence on the implantation parameters. In addition it is demonstrated, that combined SCM/SCS measurements are a suitable tool for the examination of the charge decay as well as of the reliability and degradation of oxide layers on a nanoscale.

The main luminescent centers in SiO2 films are the red luminescence R (1.85 eV) of the nonbridging oxygen hole center (NBOHC) and the oxygen deficient center (ODC) with a blue B (2.7 eV) and a UV (4.4 eV). By means of a new "track-stop" technique we have investigated especially the initial luminescence behaviour at the beginning of irradiation. Thus the blue-emitting center is produced under irradiation , but from existing precursers. Contrary to that, the dose behaviour of the red (R) luminescence in wet and dry oxide is quite different, decreasing in wet oxide from a high initial level and increasing in dry oxide from almost zero. We propose a model of luminescence center transformation based on radiolytic dissociation and the reactions of mobile oxygen and hydrogen.

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The coolant mixing in the downcomer and the lower plenum of pressurized water reactors (PWR) is significant for safety assessment of boron dilution and cold water transients.

The research project FLOMIX-R within the 5th Framework Programme of EC had the objective to obtain experimental data on the relevant coolant mixing phenomena using improved measurement techniques with enhanced resolution in space and time for CFD validation.

Recent experiments at the Rossendorf test facility ROCOM were integrated into this research project. ROCOM is a 1:5 scaled Plexiglas model of a German PWR allowing conductivity measurements by wire mesh sensors for analyzing the mixing pattern at selected positions in the reactor pressure vessel and velocity measurements by LDA technique.

A few benchmark problems based on selected experiments were used to study the effect of different turbulent mixing models under various flow conditions, to investigate the influence of the geometry, the boundary conditions, the grid and the time step in the CFD analyses. In doing the calculations the Best Practice Guidelines for nuclear reactor safety calculations have been followed. Results of this numerical mixing studies will be discussed.

A new experimental approach is introduced to investigate the relaxation of the nuclear deformation degrees of freedom. Highly excited fissioning systems with compact shapes and low angular momenta are produced in peripheral relativistic heavy-ion collisions. Both fission fragments are identified in atomic number. Fission cross sections and fission-fragment element distributions are determined as a function of the fissioning element. From the comparison of these new observables with a nuclear-reaction code a value for the transient time is deduced.

The A(e,e'K⁺)X reaction has been investigated at Jefferson Laboratory. Data were taken for Q² approx 0.35\,\rm GeV² at a beam energy of 3.245 GeV for ¹H,³He and ⁴He targets.
Evidence for Lambda-hypernuclear bound states is seen for ^3,4He targets. This is the first time that the electroproduction of these hypernuclei has been observed.

Superjunction devices (SJDs) are a novel class of power devices which break the physical limit of silicon with respect to the area specific turn-on-resistance. SJDs consist of a modified vertical MOSFET structure which is characterized by additional deep pillar-like p-type regions formed inside the n(-) epi-layer below the transistor gate. In the present investigation ultra-high energy boron ion implantation of 2-25 MeV were applied for forming the deep p-type regions laterally structured using Si stencilmasks. For energies above 12 MeV the incident ions exceed the Coulomb barrier for Si which leads (i) to a significant gamma and neutron emission during implantation and, (ii) an activation of the wafer and the mask material. Fortunately, the most relevant reaction (11B+28Si >n,alpha>34mCl> 34S+beta) has a half-life time of only 32 min so that the radiation level of the wafers drops below the critical radiation protection limit within the processing time. Based on the described technology Infineon Technologies successfully prepared a set of prototype wafers with fully functional high-voltage transistors. Typical blocking capability was in the range of 560 V with an on-state resistance of about 185 mOhm.

An in-situ X-ray diffraction study was performed to characterize aspects of the kinetics of struc-tural phase formations in transition metals during oxygen implantation. A special designed high-temperature vacuum chamber for X-ray measurements was installed at the high-energy implantation beamline of the 3 MV-Tandetron accelerator. Titanium and molybdenum sheets were implanted with oxygen ions with an energy of 1.5 MeV up to a fluence of 1.6 × 10¹⁸ O⁺-ions/cm² without sample cooling. During implantation, the phase formation was continually investigated by in-situ and real-time X-ray diffraction (XRD) with a position sensitive proportional counter system. The phase formation was studied during annealing treatments by in-situ XRD. The obtained results were com-pared with ex-situ XRD measurements performed by different techniques at a standard diffractometer. The analysis of XRD patterns indicates the formation of a buried MoO₂ layer in molybdenum. In the Ti-samples no buried oxide is formed due to significant oxygen diffusion.

Poster of experimental results of time resolved carrier relaxation of nitrogen containing GaAs

We report on the comparative analysis of the ultrafast carrier dynamics of pure GaAs and ion-implanted GaNAs. Different nitrogen concentrations (up to 4%) are implanted and subsequently annealed by rapid thermal annealing (RTA). Damage analysis by channeling Rutherford backscattering (RBS) reveals that the annealing step improves the crystal quality but does not restore the original quality. From photoreflectance measurements we conclude that the highest achieved active nitrogen content in the implanted samples is 0.5% for an equivalent implantation dose of 1%. Carrier dynamics are investigated by one-colour pump-probe measurements covering an excitation wavelength range from 730nm to 860nm (1.7eV to 1.44eV) with femtosecond time resolution. Comparison with non-implanted GaAs indicates that the carrier relaxation in the implanted samples is dominated by traps associated with implantation damage.

III-V-Halbleitern mit geringen Stickstoffkonzentrationen gelten sowohl als Materialsystem als auch für Anwendungen seit einiger Zeit gr¨oßeres Interesse. Neben epitaktischen Methoden bietet die Ionen-Implantation einen effektiven Weg zur Einbringung des Stickstoffs in das Substrat. Nachteil dieses Verfahrens ist der dem Gitter durch die Ionen-Implantation zugefügte Schaden.
Wir untersuchen die Effektivität des Einbaus von aktivem Stickstoff nach Implantation und thermischer Ausheilung (RTA). Bei RTA-Bedingungen von 650°C/30s ist der Einbau des Stickstoffs in die Matrix optimal. Eine Verbesserung der Gitterqualität kann durch Implantation bei erhöhten Temperaturen (T > 200°C) erreicht werden. Die Ladungsträger-Dynamik im sub-Pikosekunden-Bereich für Implantationen bei Raumtemperatur und bei erhöhten Temperaturen wird mit der von nicht-implantiertem GaAs verglichen. Es werden signifikante Unterschiede beobachtet, die auf eine starke Modifizierung der Bandstruktur des stickstoffhaltigen GaAs zurückzuführen sind.

Poster of experimental results of time resolved carrier dynamics of nitrogen containing GaAs.

The reduction of the a-Fe volume fraction and the a-Fe grain size represents a known objective for the improvement of this magnet material. It is attained here by a controlled influence on the melt flow via tailored magnetic fields. The reduction of the internal melt motion results in a significant decrease of the a-Fe volume fraction in the solidified Nd-Fe-B material.

Low-energy pi(+) (E-pi less than or similar to 35 MeV) from C-12 + Au-197 collisions at incident energies from 300 to 1800 MeV per nucleon were detected with the Si-Si(Li)-CsI(Tl) calibration telescopes of the INDRA multidetector. The inclusive angular distributions are approximately isotropic, consistent with multiple rescattering in the target spectator. The multiplicity correlations of the low-energy pions and of energetic protons (E-p greater than or similar to 150 MeV) with intermediate-mass fragments were determined from the measured coincidence data. The deduced correlation functions 1 + R approximate to 1.3 for inclusive event samples reflect the strong correlations evident from the common impact parameter dependence of the considered multiplicities. For narrow impact parameter bins (based on charged-particle multiplicity), the correlation functions are close to unity and do not indicate strong additional correlations. Only for pions at high particle multiplicities (! central collisions) a weak anticorrelation is observed, probably due to a limited competition between these emissions. Overall, the results are consistent with the equilibrium assumption made in statistical multifragmentation scenarios. Predictions obtained with intranuclear-cascade models coupled to the Statistical Multifragmentation Model are in good agreement with the experimental data.

The melt flow in the vertical Gradient Freeze growth of GaAs can efficiently be controlled by an external travelling magnetic field. The latter directly provides for a poloidal flow in the molten part. Controlling this flow offers the possibility to influence the interface shape, to increase the growth rate or to improve the homogeneity of the crystal. We report on the design of the magnetic field system and preliminary flow measurements with it.

Improved Binding of Polyoxotungstates by Polysaccharides

The work was aimed at the experimental investigation and numerical simulation of coolant mixing in the downcomer and the lower plenum of pressurized water reactors (PWR). For the investigation of the relevant mixing phenomena, the Rossendorf test facility ROCOM has been designed. ROCOM is a 1:5 scaled Plexiglas model of a German PWR (Fig. 1) allowing conductivity measurements by wire mesh sensors and velocity measurements by LDA technique. Due to the fact, that the mixing is dominated by turbulent mechanisms, it is assumed that the concentration field of a tracer solution can model both boron concentration and temperature fields. The salt significantly changes the conductivity of the water what can be measured by conductance methods. In the facility, so called wire mesh sensors are applied. The measured conductivities were transferred to a mixing scalar Qx,y,z(t) representing the contribution of the coolant from the disturbed loop to the mixture at the given position x,y,z.

It is calculated from the local instantaneous conductivity sx,y,z(t) by relating it to the amplitude of the conductivity range in the inlet nozzle of the disturbed loop.

Recent experiments at ROCOM, together with data on mixing obtained at the Vattenfall test facility; the Russian VVER-1000 mock-up and measurements at the VVER-440 NPP in Paks (Hungary) are integrated into the research project FLOMIX-R within the 5th Framework Programme of EC. The objective of the project is to obtain complementary and confirmatory data on slug mixing using improved measurement techniques with enhanced resolution in space and time. The experimental data will be used to contribute to the validation of CFD codes for the analysis of turbulent mixing problems. A few benchmark problems based on selected experiments will be used justify the application of various turbulence and turbulent mixing models for various flow conditions, to suppress numerical diffusion and to decrease grid, time step and user effects in the CFD analyses.

The CFD calculations were carried out with the CFD-code CFX-5. The ERCOFTAC Best Practice Guidelines, which have been specified for nuclear reactor safety calculations within the ECORA project, have been used when making sensitivity tests for: computational mesh, numerical schemes, convergence criteria, time step, boundary positions, boundary conditions, internal geometry modelling and turbulence models.
Based on these tests the production mesh was created and the final CFD calculations were performed.

In the case of stationary mixing (4 loop operation), the maximum value of the averaged mixing scalar in the downcomer (Fig. 2) and at the core inlet was found in the sector below the inlet nozzle, where the tracer was injected. There is a good agreement between the measurement and the CFD calculation, esp. in the averaged global mixing scalar at the core inlet (Fig. 3). In the calculation the maximum mixing scalar gives the same value at the peak in the same region compared to the experiment (94%).

For turbulent flows the CFD-Code CFX-5 were validated and can be used in reactor safety analysis. Due to the good agreement between measured results and the corresponding CFD-calculations efficient modules for the coupling of thermal hydraulic computer codes with three-dimensional neutron-kinetic models using the results of this work can be developed. A better description of the mixing processes inside the RPV is the basis of a more realistic safety assessment.

Strangeness and charm degrees of freedom in strongly interacting matter are discussed within a quasi-particle model adjusted to lattice QCD data. While strangeness is found to appear as copious as the other light quark and gluon excitations, the charm quarks are thermally suppressed.
The model allows to extrapolate lattice QCD data to large baryo-chemical potential.
We outline the thermal evolution of matter in the early universe at and slightly after confinement and comment briefly on charm dynamics in relativistic heavy-ion collisions.

For the calculation of experiments simulating the behavior of the lower head of a nuclear power station in case of a core meltdown scenario like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model with 3 different physics environments is developed based on the code ANSYS® Multiphysics.
A thermal environment was build up including planar and contact elements for conductive heat transfer, additional surface elements to simulate convection and radiation from outer surface areas and a radiation matrix to account for internal radiative heat exchange. Normally a CFD-simulation would have been required for the natural convective heat transfer in the melt pool, but at very high internal Rayleigh numbers no turbulence model is capable for a correct simulation. Therefore an Effective Conductivity Convectivity Model (ECCM) was developed to simulate the heat transfer from the melt pool to its environment.
The resulting temperature field of the vessel wall is applied to the mechanical model. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied.
The third physics environment is a kind of fictitious physics environment: it uses hyperelasticity and contact to move the melt pool along with the creeping vessel wall.
In this paper problems on the numerical side are explained and differences between the results of a simple coupled and a kinematically coupled FE-simulation are highlighted. The final comparison with the experiments shows that the kinematically coupled model is closer to reality than the single step model.

The nuclides ⁹⁸Mo and¹⁰⁰Mo have been studied in photon-scattering experiments by using bremsstrahlung produced from electron beams with energies from 3.2 to 3.8 MeV. Six dipole transitions in ⁹⁸Mo and 19 in ¹⁰⁰Mo were observed for the first time in the energy range from 2 to 4 MeV.
A specific feature in both nuclides is the deexcitation of one state with spin J = 1 to the 0⁺ ground state as well as to the first excited 0⁺ state, which cannot be explained in standard models. We present a model based on one-particle-one-hole excitations, which allows us to deduce the mixing amplitudes for the two 0⁺ shape-isomeric states from the experimental ratio of the transition strengths from the J = 1 state to the 0⁺ ground state and to the 0⁺ excited state.

A new type of a cavity BPM proposed for beam position determination along the TESLA linac was tested at the accelerator ELBE in Rossendorf / Dresden. Measurements using an improved BPM (large and stable cross-talk isolation, signicantly less energy dissipation, a novel LO signal generation) were performed in single- and multi-bunch regimes. Agreement with expectations was found. The low bunch charge available allowed for preliminary measurements on sensitivity and position resolution, which extrapolated to TESLA would full the demands for precise bunch-to-bunch position determination. Possible improvements, in particular on the signal processing scheme, are also discussed.

We study the cross section of phi-meson production in proton-nucleus collisions. The decay width of the phi-meson is affected by the change of the masses of the phi, K+, K- mesons in medium. A strong attractive K_ potential leads to a broadening of the phi-meson, which results in a measurable change of the behavior of the cross section as a function of the target mass.

Solving the induction equation has become a synonym for kinematic dynamo studies. We present an alternative integral equation method to solve steady and time-dependent kinematic dynamo problems. This method, which relies on Biot-Savart's law, can be efficiently used to handle dynamos in arbitrary domains, for example in rectangular geometry and finite cylinders. The approach serves also as the basis for various inverse problems in MHD at small and large magnetic Reynolds numbers. The solution of such inverse problems is illustrated by the "Contactless inductive flow tomography" and by the inference of flow features in the Riga dynamo experiment from externally measured magnetic field data.

The experimental campaigns at the Riga sodium facility, carried out from November 1999 until recently, have brought about a wealth of data on the kinematic and the saturation regime of this hydromagnetic dynamo. In the kinematic regime, the measured growth rates and frequencies of the eigenfield differ from the numerical predictions only by a few per cent. A qualitative understanding of the saturation regime can be well achieved within a simple one-dimensional model of downward braking of the azimuthal velocity component by the Lorentz forces. This model can be refined by taking into account the Lorentz force driven flow in the outermost cylinder. We summarize our present understanding of the Riga experiment, and comment on some open questions.

In May 2004, the sixth experimental campaign has been carried out at the Riga dynamo facility. Besides the refined magnetic field measurements, we present pressure data recorded in the innermost cylinder and the first successful measurement of velocities in the outermost cylinder by ultrasonic Doppler velocimetry (UDV). The pressure data exhibit clear signals of the double and quadruple of the magnetic eigenmode frequency. The velocity UDV measurements confirm the numerical prediction that the Lorentz forces produce a global rotation and a double poloidal vortex in the outermost cylinder. We comment also on the demands and the prospects for future experimental campaigns.

The magnetorotational instability (MRI) is one of the most promising candidates to explain why accretion disks, which exhibit a Keplerian flow profile and should therefore be hydrodynamically stable, allow for a rate of angular transport which cannot be attributed to the molecular viscosity of the disk. Like the dynamo effect, MRI occurs only at large magnetic Reynolds numbers, making its laboratory investigation rather expensive. Recently, there are strong activities to study MRI in a liquid metal Taylor-Couette flow, and it might be that MRI has already been found in a spherical Couette flow of liquid sodium. We propose an alternative experimental configuration which is based on the Taylor-Dean flow. This flow is a combination of the usual cylindrical Couette flow and an additional Dean flow which is driven by an azimuthal force. This force can be realized in the form of an externally applied pressure gradient or, more elegantly, by a Lorentz force due to a radial current and an axial magnetic field. Our main idea is that, for a well adjusted ratio of Dean flow to Taylor-Couette flow, one gets an angular velocity that is decreasing with the radius and an angular momentum that is increasing with the radius, hence a situation that is prone to the study of MRI. Our main focus is on a particular configuration in which the outer and inner cylinders rotate at the same angular velocity. Evidently, this would simplify the mechanical part of the experiment dramatically. We find that, for sufficiently small values of the ratio of inner to outer radius, such an experiment seems indeed feasible.

For dynamo theory, the spherically symmetric alpha^2-dynamo represents a similar paradigm as the harmonic oscillator does for quantum mechanics. For alpha(r)=const, the spectrum is rather boring due to the self-adjointness of the dynamo operator. However, the spectral properties become more interesting if we allow alpha to vary with the radius. We illustrate the spectral behaviour of those dynamos, including such features as exceptional points, level crossings and avoided level crossings. Then we focus on truly oscillatory dynamos which have been identified only recently. When including a simple alpha-quenching back-reaction and some random fluctuation of alpha, these dynamos exhibit a quite similar time behaviour as the geodynamo, including chaotic reversals and asymmetric polarity transitions.

500 keV nitrogen implantations at different tilt angles (0o, 0.5o, 1.2o, 1.6o, 4o) with respect to the c-axis of 6H-SiC were carried out. Radiation damage distributions have been investigated by Backscattering Spectrometry combined with channeling technique (BS/C) using 3550 keV 4He+ ion beam. A comparative simultaneous evaluation of the damage depth distributions in the Si and C sublattices of 6H-SiC led to a <0001>-channeling to random correction factor of 0.8 in the electronic stopping power of 4He+ ions. Full-cascade Crystal-TRIM simulations with the same set of damage accumulation model parameters could reconstruct the measured shapes and heights of damage distributions for all implantation tilt angles. Secondary defect generation effects in addition to the primary point defect accumulation were assumed in the analysis.

An antisite pair consists of two neighboring atoms on “wrong” lattice sites, namely a Si atom on a C site and a C atom on a Si site. This defect can be formed by irradiation with energetic particles, e.g. during ion implantation doping. Investigations on the thermal stability of the antisite pair are important for electronic and nuclear applications of SiC.
In this work the recombination of an antisite pair is studied by classical molecular dynamics simulations using the interatomic potential developed by Gao and Weber [1]. The formation energy of the antisite pair is calculated and compared with literature data. Then, the lifetime of the defect is determined for the temperatures between 800 and 2500 K, and the effective recombination barrier is estimated. The lifetime for 2000 and 2500 K is compared with the results obtained using ab-initio molecular dynamics simulations. The analysis of atomic rearrangements during recombination shows that the mechanism of the antisite pair recombination is a concerted exchange. Due to the different atomic sizes of Si and C, the concerted exchange mechanism in SiC is not identical to that proposed for silicon [2]. During recombination a number of intermediate defect configurations are observed. Two of them are similar to the bond defect in silicon [3,4]. They can be considered as the result of an incomplete recombination of a carbon vacancy and a C+Si<100> dumbbell interstitial. Therefore, the present work yields not only details of the recombination of the antisite pair but also information about possible mechanisms for antisite pair formation.
[1] F. Gao, W. J. Weber, Nucl. Instr. Meth. B 191 (2002) 504
[2] K. C. Pandey, Phys. Rev. Lett. 57 (1986) 2287
[3] M. Tang, L. Colombo, J. Zhu, T. Diaz de la Rubia, Phys. Rev. B55 (1997) 14279
[4] L. A. Marques, L. Pelaz, J. Hernandez, J. Barbolla, G. H. Gilmer, Phys. Rev. B 64 (2001) 045214

Nano structures, like wires or pearl chains play an increasing role in areas as plasmonics, nano-optics or nano-electronics as well as in the implementation of optical components in microelectronic devices. CoSi2 is a promising materials candidate due to its metallic behaviour with low resistivity and the compatibility to the microelectronics technology. Two methods to fabricate CoSi2 -nano – wires using FIB technique in terms of ion beam synthesis (IBS) are investigated. An oxide layer, structured by use of a high resolution Ga beam, acting as an implantation mask for a broad beam Co doping and subsequent annealing was investigated and discussed. Secondly, a mass separated FIB of cobalt is applied for a direct writing IBS process. Therefore different alloys as source materials were tested and applied in the FIB column (Canion 31Mplus, Orsay Physics). The use of the doubly charged ions emitted from the Co source allows to increase the implantation energy up to 60 keV, important to obtain buried structures of high quality.

The long-term risk assessment of underground repositories for radioactive waste requires among others diffusion coefficients of actinides in bentonite to account for the steady state diffusion process after exhaustion of the limited sorption capacity of the bentonite sealing. The determination of effective diffusion parameters of strong sorbing tracers such as actinides in laboratory diffusion experiments is very time consuming. For that, the sample thickness has to be reduced to a minimum. However, falling below a critical distance may lead to a distur-bance of the clay texture and to inadequate boundary conditions and thus, to a misinterpreta-tion of the diffusion data. Our work focuses on the dependence of the diffusion parameters of tritiated water (HTO) in bentonite on the sample thickness.
We conclude, that the clay plugs are mechanically stable and fulfill the hydraulic sealing function. From the relationship between sample thickness and De we see that the filter plates exert a significant influence on the boundary condition as soon as sample and filter plate are of the same thickness. Filter plates should be of about 1 to 2 mm thickness to resist the swell-ing pressure. Thus, a sample thickness in this dimension is possible to work with strong sorb-ing tracers minimizing the duration of the diffusion experiment and providing representative results.
Based on literature values for MX-80 pore water chemistry and sorption data of Uranium on montmorillonite a distribution coefficient KD was estimated. This approach utilized the sur-face complexation model and a respective data base (RES³T). Computations were performed with the FITEQL 3.2 code. The calculated KD’s range from 30 to 300 ml g-1. This enables a blind prediction of the accumulated diffused activity for different sample thickness. A time frame of at least one year will be necessary to reach steady state. This will be checked by re-spective long lasting diffusion experiments.

Changes of surface layer composition produced by ion bombardment of polyethylene and polypropylene samples were studied. These materials are under consideration for load bearing surfaces in biological and technical applications. To improve their tribological properties surface layers are usually modified by ionizing radiation. To study mechanism of transformations induced by ion beam bombardment selected polymers were implanted with H, He and Ar ions to the fluences ranging from 3x1014 to 2x1016 1/cm². RBS and NRA techniques were applied for sample analysis. Important hydrogen release was observed with increasing ion dose and was correlated with the ion stopping power. Another important effect observed was the rapid oxidation of samples, which apparently occurs after exposure of implanted samples to the air. Up to 10 at.% of oxygen can be incorporated in the implanted layer.

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Abstract:

Abstract:

The complex formation of curium(III) with adenosine 5’-triphosphate (ATP) was determined by time-resolved laser-induced fluorescence spectroscopy (TRLFS). The interaction between soluble species of curium(III) with ATP was studied at trace Cm(III) concentrations (3x10-7 M). The concentrations of ATP are varied between 6x10-7 and 1.5x10-4 M in the pH range of 1.5 to 7.0 using 0.154 M NaCl as background electrolyte.
Three Cm-ATP species, MpHqLr, could be identified from the fluorescence emission spectra: (i) CmH2ATP+ with a peak maximum at 598.6 nm, (ii) CmHATP with a peak maximum at 600.3 nm, and (iii) CmATP- with a peak maximum at 601.0 nm. The formation constants of these complexes were calculated from TRLFS measurements to be log β121 = 16.86 ± 0.09, log β111 = 13.23 ± 0.10, and log β101 = 8.19 ± 0.16. The hydrated Cm-ATP species showed fluorescence lifetimes between 88 and 96 µs; whereas the CmATP- complex has a significantly longer fluorescence lifetime of 187 ± 7 µs.

The status of the Rossendorf superconducting RF gun is discussed. This gun allows continuous wave operation with an energy of 9.5 MeV and an average current of 1mA. The 3½ cell niobium cavity contains a normal conducting photocathode. A special choke flange filter at the cathode side prevent the RF leakage of the cavity. The design of the cavity, the tuner, the RF coupler the LHevessel together with the cryostat is finished and now in manufacturing. In the paper three features are discussed, which follows from the special demands of the 3½ cell superconducting RF gun. The first feature is the tuning system. For the cavity two different tuners are necessary, one for the half cell (gun cell) and one for the accelerating cells. The second feature is the tuning of the cathode. The beam properties depend very sensitive on the athode position. Therefore a special cathode tuner has been developed, which allows to move and to adjust the cathode position inside the cavity. The third no conventional feature is the excitation of a second RF mode inside the cavity. This is a magnetic mode (TE mode) which replaces the static magnetic field in normal conducting RF guns and decreases the transverse emittance of the beam by more than a factor of two.

A characteristic feature of the nuclear microprobe using 3 MeV proton beam is the long range of particles: ≈ 70 µm in light matrices. The PIXE method, with EDS analysis and using the multilayer approach for treating the X-Ray spectrum allows the chemistry of an intracrystalline inclusion to be measured, provided the inclusion roof and thickness at the impact point of the beam (R and F, respectively) are known (the depth of the inclusion floor is R+F). The parameter R of an inclusion in a mineral can be measured with a precision of ±1 µm using a motorized microscope. However, this value may significantly depart from R if the analysed FI has a complex shape. The parameter F can hardly be measured optically, unless a confocal microscope is used.
Measuring R and F by RBS spectrometry:
A negative crystal-shaped FI in quartz, containing ≈ 4 wt.% solutes, was analysed by PIXE using a 2.5 MeV proton beam, 3 x 3 µm² in size (charge on the target 0.3 µC). Simultaneously, a RBS spectrum was obtained with an annular charged-particle detector (alpha ≈ 170°). The depression at 1500 keV on the spectrum corresponds to the H₂O-filled cavity along the beam path. Modeling of the spectrum using the SIMNRA program allows R to be measured at 11.6 µm, in good agreement with the optically determined value (11 µm). Simulation also fixes the depth of the FI floor at 17 µm in quartz. This paper will present preliminary measurements on synthetic samples to investigate the advantages of the technique, and also on natural solid and fluid inclusions in quartz. The influence of the geometrical parameters will be discussed with regard to the concentration determination by PIXE. In particular, accuracy of monazite micro-inclusion dating by coupled PIXE-RBS will be presented.

Five fragments of ancient gold objects belonging to Pietroasa “Cloşca cu Puii de Aur” (“The Golden Brood Hen with Its Chickens”) Romanian hoard were analyzed using the micro-PIXE (Particle Induced X-ray Emission) technique. The purpose of the study was to gain some more knowledge regarding the metal provenance by determining the presence of PGE (Platinum Group Elements) and other high-temperature melting point trace elements (Ta, Nb, Cr) at a micrometric scale. Ta and Nb inclusions (micrometeric areas of composition different from the surroundings) on two samples and Pd inclusions on one sample were found. The measurements led to some conclusions for the possible gold ore sources of Pietroasa treasury: the South-Ural Mountains, Nubia (Sudan) and/or Anatolian deposits and Roman imperial coins.

One of the big challenges for wire sawing of semiconductor wafers is warp and waviness, which are mainly caused by wire deflection during cutting process. Therefore, lapping or grinding steps are often used to improve quality but accompanied by additional material losses. The mechanisms of a high quality wire sawing process for compound semiconductors will be presented here. The commonly accepted model for out-of-plane deviation of wires during wire sawing process was expanded by including intrinsic forces in addition to commonly considered technological ones, which are determined by material properties of the semiconductor used. For this the concept of a critical cutting depth for ductile-brittle-transition underlying cutting and grinding processes of brittle materials has been revised. Both Vickers hardness tests and single scratching tests were used to study the ductile-brittle-transition in greater detail. It was found that mainly two types of cracks (called A- and B-cracks) nucleate in GaAs, which are characterized by different threshold loads for their appearance. The effect is related to the existence of two types of dislocations with different PEIERLS-barriers, which dominate in III-V compounds, the 600 a- and b-dislocations. The micro crack nucleation is assisted by pile-ups of these dislocations, which leads to different crack initiation probabilities n for A- and B-cracks at a given load with nA > nB. This effect causes a significant dependence of the critical penetration depth for ductile-brittle-transition from the direction of a moving indenter in scratching tests. This critical penetration depth and the corresponding critical load determines measurable constraint forces, which act on the wire during the sawing process. Under certain well-defined conditions these constraint forces maintain the wire in a stable position perpendicular to the cutting direction, i. e. the out-of-plane-deviation of the wires is near to zero and, consequently, warp and bow will be minimal. This context has been proven by wire sawing experiments at a industrial multi-wire saw and by optical flatness measurements of GaAs-wafers. The result of this investigation was verified in a high efficient wire sawing technology for mass production of 150-mm-GaAs-wafers. Commonly used technological steps like lapping or surface grinding are no longer necessary and, in consequence, the material losses are reduced. Furthermore, the feed rates could be increased up to 400 percent compared to standard wire sawing of GaAs with improved geometrical parameters of the wafers.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was combined with batch experiments to study the sorption of uranium(VI) onto gibbsite (γ-Al(OH)₃). The experiments were performed under ambient conditions in 0.1 M NaClO₄ solution in the pH range from 5.0 to 8.5 using a total uranium concentration of 1 x 10-5 M, and a solid concentration of 0.5 g/40 mL. Two uranyl surface species with fluorescence lifetimes of 330 ± 115 ns and 5600 ± 1640 ns, respectively, were identified. The first species was dominating the more acid pH region whereas the second one became gradually more prominent towards higher pH values. The fluorescence spectra of both adsorbed uranyl(VI) surface species were described with six characteristic fluorescence emission bands situated at 479.5 ± 1.1, 497.4 ± 0.8, 518.7 ± 1.0, 541.6 ± 0.7, 563.9 ± 1.2, and 585.8 ± 2.1 nm. The surface species with the short-lived fluorescence lifetime of 330 ns is attributed to a bidentate mononuclear inner-sphere surface complex in which the uranyl(VI) is bound to two reactive OH- groups at the broken edge linked to one Al. The second surface species with the significant longer fluorescence lifetime of 5600 ns was attributed to small sorbed clusters of polynuclear uranyl(VI) surface species. The longer fluorescence lifetime of the long-lived uranyl surface species at pH 8.5 is explained with the growing average size of the adsorbed polynuclear uranyl surface species.

Spectroscopic evidence for two adsorbed uranium(VI) surface species on edge surfaces of a muscovite platelet was obtained by Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS). In contrast, no fluorescence signal was obtained on the basal plane surfaces clearly indicating that U(VI) sorption on muscovite predominantly takes place at the edge surfaces. TRLFS spectra of adsorbed U(VI) surface species on gibbsite are very similar and show that U(VI) sorption on muscovite occurs on aluminol sites of the edge surfaces.

Abstract:

X-rays in the range ~10 – 50 keV are widely applied in the diagnostic radiology (particularly mammography) and radiotherapy (e. g. brachytherapy). However, the published data about their relative biological effectiveness (RBE) allow up to now no definitive conclusions about the action on different biological systems. Moreover, the biological effects depend on the spectral distribution of the photon source. In order to study this dependence, the RBE of 10 kV and 25 kV X-rays has been determined relative to 200 kV X-rays by X-ray tube irradiation.
The studies were carried out on the mouse fibroblasts NIH/3T3 and the human mammary epithelial cells MCF-12A. For the soft X-rays irradiation, a tungsten-anode X-ray tube operated at 10 kV (no filtration) or at 25 kV (0.3 mm Al filtration) was used. The reference irradiation was performed with a 200 kV X-ray tube with 0.5 mm Cu filter. The dose rate for all irradiations was in the range 0.3 – 1.9 Gy/min. The spectral dose distribution of all radiation qualities was also determined. Cell survival was studied after irradiation with 0.5 – 10 Gy by the clonogenic assay. Chromosomal damage was assessed by the cytokinesis-block micronucleus (MN) test in the dose range 0.2 – 5 Gy. In addition, first results for the RBE determination by chromosomal aberrations induction in MCF-12A, will be presented.
The cell survival data were fitted to the linear-quadratic model, resulting in an RBE value of 1.1 – 1.3 at the 10% survival level, depending on the used radiation quality and cell line. For both cell lines, an increase of RBE was found with decreasing dose after 10 kV X-rays, whereas a decrease of RBE of 25 kV rays was observed. The MN test results for the fraction of binucleated cells (BNC) with MN and the number of MN per BNC were fitted to a quadratic dependence, resulting in an RBE of 1.1 – 1.4.
The data obtained in the present work are in good agreement with observations of other authors as well as with theoretical predictions for this photon energy range. However, the detailed RBE dependence on photon energy can be determined only at a monochromatic X-ray source. Currently, the installation of an intensive, tunable, quasi-monochromatic source for cell irradiation in the energy range 10 – 100 keV is under progress at the ELBE accelerator at Forschungszentrum Rossendorf. The experimental verification of the theoretical calculation of the spectral distribution and intensity of this novel photon source will be presented.

For the long-term performance assessment of nuclear waste repositories, knowledge concerning the interactions of actinide ions with mineral surfaces is imperative. The mobility of released radionuclides is strongly dependent on the sorption/desorption processes at mineral surfaces and their incorporation into the mineral frame. Hydrous iron oxides (ferrihydrite) are globally of great importance in the environment. Upon heating pure ferrihydrite converts to crystalline goethite and hematite. In the presence of di- or trivalent metal ions the transformation is affected leading to the promotion of one crystal formation over the other and incorporation of these ions. This Study deals with the question if released Am(III) can be immobilized by sorption onto 6-line-ferrihydrite. Moreover it is studied what happens if ferrihydrite transforms to a more crystalline phase.

The data about relative biological effectiveness (RBE) of low-energy X-rays as well as the RBE dependence on photon energy allow no definitive conclusions about their action on living cells. X-rays in the range ~10 – 50 keV are widely applied in the diagnostic radiology (particularly mammography) and radiotherapy (e. g. brachytherapy). The RBE of 10 kV and 25 kV X-rays relative to 200 kV X-rays by X-ray tube irradiation was determined for cell survival and micronuclei induction in mouse fibroblasts NIH/3T3 and human mammary epithelial cells MCF 12A. The RBE was found to be in the range from 1.0 to 1.4, depending on the used radiation quality, cell line and the biological endpoint. However, the detailed RBE dependence on photon energy can be determined only at a monochromatic X-ray source. A tunable, quasi-monochromatic X-ray source in the energy range 10 – 100 keV based on the channeling of a relativistic electron beam in a diamond crystal is under construction at the ELBE accelerator at Forschungszentrum Rossendorf. The status of the commissioning of the radiation source will be presented, such as the experimental verification of the theoretical calculation of the spatial energy and intensity distribution.

The precise determination of the relative biological effectiveness (RBE) of low-energy X-rays is important because of their wide application in diagnostic radiology (particularly mammography) and radiotherapy (e. g. brachytherapy). The RBE of both 10 kV and 25 kV X-rays relative to 200 kV X-rays by X-ray tube irradiation was found to be in the range from 1.0 to 1.4, depending on the used
radiation quality, cell line and the biological endpoint. In order to study in detail the RBE dependence on photon energy, the investigations will be continued at a monochromatic X-ray source. The installation of an intensive, tunable, quasi-monochromatic source in the energy range 10 - 100 keV is currently under progress at the ELBE accelerator at Forschungszentrum Rossendorf. X-rays are produced by channeling of a relativistic electron beam in a diamond crystal. The status of the commissioning of the radiation source will be presented, such as the experimental verification of the theoretical calculation of the spatial energy and intensity distribution. Furthermore, a monochromator, designed to minimize the contribution of the background radiation to the dose in the cell target, will be presented.

Electrical conductivity, thermopower and vsicosity of liquid Pb-Sn alloys are investigated in a wide temperature range. The revealed discrepancies between heating and cooling curves of temperature dependencies of some electrophysical and structural-sensitive properties as well as a hysteresis observed in the course of heating-cooling cycles suggest a metastable microheterogeneous structure of the Pb-Sn melts.

Tin is an important metal with new potential applications regarding the fabrication of novel devices. In this work the mass spectrum of a tin liquid metal ion source (LMIS) is studied in detail. Sn++ was found to dominate in the beam both over Sn+ and over cluster ions. By studying the behaviour of the relative intensities of Sn+ and Sn++, as a function of emission current, the conclusion is reached that both Sn+ and Sn++ are emitted as a result of direct field-evaporation from the liquid surface. Cluster ions form by ion impact-aided droplet disintegration.

A 200 mm amorphised Si wafer was implanted with 6-keV H+ ions at a nominal fluence of 5 x 10(16) atoms/cm(2). The uniformity of the implant was better than 2% over the wafer. Samples of the wafer were analysed for absolute H fluence by nuclear reaction analysis and elastic recoil detection (ERD) analysis, including both helium and heavy ion beams, using various types of detector (Si with range foil, time of flight ERD, and a position-sensitive gas ionisation DeltaE-E detector), various ion beams (He, Cl, Cu, I, Au) and independent analytical procedures. The results are compared and the inter-lab reproducibility is evaluated. The surface H, unstable under heavy ion beams, was resolved and accounted for throughout the analysis. Estimates of total combined uncertainties are about 6% for all participants, but the inter-lab reproducibility of the measurements was found to be 2.2%. Correct quantification of the H data from the gas ionisation detector is demonstrated. The uncertain! ty budget is discussed in detail.

The hadronic reaction pp --> Sigma(+)K(0)p was measured exclusively at a beam momentum of 2.95 GeV/c using the TOF detector at the COSY storage ring. A narrow peak was observed in the invariant mass spectrum of the K(0)p-subsystem at 1530 +/- 5 MeV/c(2) with a significance of 4-6 standard deviations, depending on background assumptions. The upper limit of 18 +/- 4 MeV/c(2) (FWHM) for its width is given by the experimental resolution. The corresponding total cross section is estimated to be about 0.4 +/- 0.1 (stat) 0.1 (syst) mub. Since a resonance in this subsystem must have strangeness S = + I we claim it to be the Theta(+) state for which very recently evidence was found in various experiments. (C) 2004 Elsevier B.V. All rights reserved.

First subject of the paper is a gamma-tomography setup for imaging a periodically changing density field. It is based on a time-resolved acquisition of the detector signals. The system consists in a 5 Ci source of Cs-137 and a detector arc with 64 BGO scintillation crystals coupled with photo-multipliers. It was used to visualize the gas fraction distribution within the impeller of an axial turbo-pump operating at about 1500 rpm, that delivered a gas-liquid mixture. The detectors operated in pulse mode. The pulses were counted by several banks of 64 counters activated in a successive order - each for a period of 100 µs. The counting procedure is restarted in the first bank after each full rotation of the impeller. After a measuring time of typically 3 -6 min, projections of the density distribution inside the object are acquired in a rotation-angle resolved manner. This allowed to afterwards reconstruct the void fraction distribution inside the rotating impeller structure by applying filtered back-projection algorithms. In a second application, the tomography system was applied to a hydraulic clutch (coupling). These measurements showed the distribution of the hydraulic liquid inside both semi-filled working wheel of the clutch at different slip ratios. An advanced detector system with a total number of 320 crystals is under construction. This will allow to increase the resolution from now about 7 mm to about 2-3 mm inside the measuring plane.
In the field of X-ray tomography, the status of the development of an ultra-fast system based on a scanning electron beam is presented. An electron beam is linearly deflected over a tungsten target with a frequency of 1 kHz. X-rays generated by the traveling focus penetrate the object and arrive at a detector line placed behind the object. The detectors are read-out with a sufficiently high speed in order to obtain projections of the density distribution in different projecting directions, which change thanks to the scanning. First results showing tomographic image sequences of a phantom consisting of small spheres kept in arbitrary motion in a cylindrical test box will be presented. Moving spheres of 3 mm diameter with cylindrical holes of 1 mm diameter were resolved at a framing rate of 1 kHz. For the experiments, an electron beam of a 150 kV gun with a current of 5 mA together with a line of 64 CdZnTe detectors working in current mode with a sampling frequency of 100 kHz for each detector (total data rate: 6.4 MHz) were used. It is planned to continue this development in direction towards an application in two-phase flow experiments.
A second application of X-rays concerns a cone-beam tomography of a stirred vessel reactor. In this case, time-averaged gas fraction distributions produced by a gassing stirrer were visualized using a standard X-ray tube and a 2D detector array. The rotation of the fluid inside the reactor was used to obtain the projections necessary for the 3D reconstruction.
The paper will furthermore present a summary of other kinds of two-phase instrumentation developed in the Research Center Rossendorf. Examples are: (1) local void probes based on impedance measurements, that are equipped with a micro-thermocouple substituting the traditional electrode applied to non-adiabatic gas-liquid flows, (2) the use of high-speed video imaging together with image processing techniques for bubble-column studies, (3) the developments of an optical tomograph and other optical sensors.