Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Es wird die Fehlerquote bei der in-beam PET weiter gesenkt, in dem ihre statistische Sicherheit erhöht wird.

Mit der Erfindung soll die Effektivität der supraleitenden HF-Fotoelektrode und die Strahleigenschaft, insbesondere die transversale Emittanz, für mittlere und hohe Leistungen verbessert werden.

Mit der Erfindung wird erreicht, dass die sprunghafte Veränderung des übertragenen Drehmnoments nicht mehr oder in sehr abeschwächter Form geschieht und die Drehmomentveränderung über dem Drehzahlverhältnis zwischen Pumpen- und Turbinenrad weitgehend kontinuierlich erfolgt.

For several years Be-7 measurements have been conducted at high-altitude stations in Austria (Sonnblick, 3106 m), Switzerland (Jungfraujoch, 3580 m), Germany (Zugspitze, 2962 m), and Italy (Mt. Cimone 2165 m) with the aim to support a study on vertical ozone transport in the Alps (VOTALP project).
Aerosol samples, collected on filtering media with high volume samplers, are analysed for Be-7 by high-resolution gamma-spectrometry.
Prior to evalution of the Be-7 time series of the four stations, both sampling and measurement procedures were cheked for comparibility. The results of an intercomparison exercise performed within the mentioned project are reported.

The non-linear optical properties of solid state materials in the THz frequency region are to a large extent unexplored due to missing high-intensity coherent light sources in this frequency range. Although recent advances in table-top laser based THz systems have been enormous, free-electron lasers (FEL) are at present still the only tunable lasers which provide high peak intensities and a sufficient narrow spectral width to perform nonlinear spectroscopy at THz frequencies. Recently we investigated the dispersion of the second order nonlinear susceptibility (c(2)) in thin GaAs crystals below the optical phonon resonance via second harmonic generation (SHG) experiments with an FEL [1]. These experiments provide insight into the relative contributions of higher-order cohesive lattice forces to c(2). The nonlinear optical susceptibility in polar semiconductors in the THz frequency range is strongly influenced by the presence of optical phonons and should exhibit several peculiarities: A strong resonant enhancement of the SHG at half the frequency of the TO phonon (8.0 THz in GaAs) and at the TO phonon itself as well as a zero-crossing for frequencies between 4.0 THz and the TO phonon resonance due to the cancellation of higher order ionic and electronic contributions was predicted [2]. The experiments are performed with the THz FEL FELIX (Nieuwegein, Netherlands), which delivers picosecond pulses with µJ energy. We could observe both the resonance and the zero-crossing of c(2) below the Reststrahlen-band for the first time. From the value obtained for the zero-crossing of the nonlinear susceptibility we conclude that the contribution of the phonon interaction through the second-order lattice dipole moment has to be significantly smaller and the contribution from the third-order lattice potential anharmonicity has to be larger than determined previously [3]. Besides the relevance for the THz nonlinear susceptibility these terms are also important for two-phonon sidebands in the infrared absorption, phonon decay [3] and for a quantitative description of Raman spectra [4]. We propose that SHG below the optical phonon resonance is an elegant method to quantitatively determine the higher-order potential contributions to the nonlinear susceptibility.

[1] T. Dekorsy et al., Phys. Rev. Lett. 90, 055508 (2003).
[2] A. Mayer and F. Keilmann, Phys. Rev B 33, 6954 (1986).
[3] C. Flytzanis, Phys. Rev. B 6, 1264 (1972); Phys. Rev. Lett. 29, 772 (1972).
[4] S. Go, H. Bilz, and M. Cardona, Phys. Rev. Lett. 34, 580 (1975).

Summary: The palladium-mediated N-arylation of indoles with 4-[¹⁸F]fluoroiodobenzene as a novel radiolabelling method has been developed. Optimized reaction conditions were elaborated by variation of different catalyst systems (CuI/1,2-diamines and Pd₂(dba)₃/phosphine ligands), based and solvents in the reaction of indole with 4-[¹⁸F]fluoroiodobenzene. Optimized reaction conditions (Pd₂(dba)₃/(2-(dicyclohexyl-phosphino)-2´-(N,N-dimethylamino)-biphenyl, NaOBu^t, toluene, 100 °C for 20 min) were applied for the synthesis of ¹⁸F-labelled σ₂ receptor ligands [¹⁸F]-11 and [¹⁸F]-13 which were obtained in 91 and 84 % radiochemical yields, respectively.

The hypothetical scenario of a severe accident with core meltdown and formation of a melt pool in the lower plenum of a Light Water Reactor Pressure Vessel (RPV) can result in the failure of the RPV and the discharging of the melt to the containment. One accident management strategy could be to stabilize the in-vessel debris or melt pool configuration in the RPV as one major barrier against uncontrolled release of heat and radionuclides into the containment of the plant.
To obtain an improved understanding and knowledge of the melt pool convection, the vessel creep, possible failure processes and modes occurring during the late phase of a core melt down accident the FOREVER-experiments have been performed at the Division of Nuclear Power Safety of the Royal Institute of Technology, Stockholm. These experiments were simulating the behavior of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating.
An axisymmetric Finite Element (FE) model was developed to simulate these experiments. First the temperature field within the melt pool and within the vessel wall was calculated with a CFD-Model. But due to the lack of a turbulence model for very high internal Rayleigh numbers of up to 1017 in the prototypic case and due to the very time consuming CFD-solution, the Effective Conductivity Convectivity Model (ECCM) as proposed by Bui has been implemented. Once the temperature field in the vessel wall is evaluated, the transient structural mechanical calculations are then performed applying a creep model which takes into account the large temperature, stress and strain variations. The creep model includes the primary, secondary and tertiary creep stages.
In the prior work only a one-way coupling between the thermal and the mechanical model was applied: first the transient temperature field was calculated and then the transient mechanical calculation was performed applying the appropriate temperature field at each time step. To take into account the melt level drop by thermal expansion the initial level was lowered “by hand”. The feedback from the viscoplastic deformation to the temperature field was not correctly considered in the one-way coupling. On the other hand the earlier investigations showed that slight temperature shifts of only 10 K at an overall temperature level clearly above 1000 K had significant effects concerning the failure time of the vessel.
To overcome the disadvantages of the single coupling model a new recursively coupled model is developed. This paper deals with the new results and so far the results show that a recursively coupled thermal and mechanical solution is closer to reality than a single coupled model where the mechanical deformations have no impact to the thermal model. Due to the scaling effect it is expected, that the fully coupled model is necessary to be able to perform reliable best estimate calculations for prototypic light water reactor scenarios.

Photoconductive emitters are an attractive way for impulsive generation of THz radiation. There are two main categories, namely large-aperture emitters and interdigitated electrodes coupled to antennas. Large-aperture emitters have the advantage of a high active volume, while interdigitated structures provide high electric fields for efficient acceleration of photogenerated carriers. We present a large-aperture emitter consisting of a interdigitated metal-semiconductor-metal (MSM) structure, which combines both advantages. A second metallization layer, which is electrically insulated from the first one, blocks the optical excitation in every second period of the MSM structure, resulting in an unidirectional acceleration of carriers in the device. Focussing fs optical pulses with an average power of 100 mW from a Ti:sapphire oscillator on the emitter lead to THz field amplitudes of up to 85 V/cm (U_bias = 65 V). Excitation with unfocussed radiation from a 1 kHz repetition rate Ti:sapphire amplifier system (average power 10 mW) provided THz field amplitudes of 6 kV/cm (U_bias = 23 V). In case of the excitation with the Ti:sapphire amplifier system a pronounced nonlinear behavior of the THz field amplitude with respect to both the excitation density and the bias electric field was observed.

BACKGROUND: Alzheimer's disease (AD) is clinically characterized by cognitive impairment and behavioral disturbances. The aim of the study was to identify regional alterations in brain function associated with neuropsychiatric symptoms in early AD. METHODS: Patients underwent measures of cerebral glucose metabolism applying positron emission tomography (PET) and (18)F-fluorodeoxyglucose. Neuropsychiatric symptoms were assessed using the Neuropsychiatric Inventory (NPI). Positron emission tomography images of patients suffering a neuropsychiatric symptom of clinical significance (NPI subscore for a specific item >/=4 points) were compared with the images of patients without the specific symptom under study (NPI subscore for a specific item = 0 points). RESULTS: A total of 53 patients with AD (Mini-Mental State Examination [MMSE] 22.5 +/- 2.94 points) entered the study. Of all symptoms, apathy and depression were most frequently encountered. The patient group with apathy (n = 17) revealed significant decreases in left orbitofrontal regions when compared with patients free of apathy. Depression of clinical significance (n = 10) was associated with hypometabolism in dorsolateral prefrontal regions. CONCLUSIONS: These findings support the notion that different functional circuits underlie apathy and depression in early AD.

Nuclear medicine techniques, such as single photon emission tomography (SPECT) and positron emission tomography (PET) have been applied in patients in a vegetative state to investigate brain function in a non invasive manner. Parameters investigated include glucose metabolism, perfusion at rest, variations of regional perfusion after stimulation, and benzodiazepine receptor reduction of glucose metabolism and perfusion. While patients post-anoxia exhibit a rather homogenous cortical reduction of glucose metabolism, patients after head trauma often show severe cortical and sub-cortical reductions at the site of primary trauma. To distinguish reduced glucose metabolism due to neuronal inactivation from neuronal loss, flumazenil-PET, and indicator of benzodiazepine receptor density, could add valuable information on the extent of brain damage. Activation studies focus on the evaluation of residual brain network, looking for processing in secondary projection fields. So far the predictive strength concerning possible recovery for the individual patient is limited, and PET und SPECT are not routine procedures in the assessment of patients in a vegetative state.

We study electro-vortex flows generated by electro-magnetic forces in a shallow square layer of liquid metal. The force driving the flow is produced by the interaction between the electric current flowing through the layer and its own magnetic field. Rotational parts of that force are particularly caused by ferromagnetic yokes placed around the layer. Depending of the position and type of those yokes flows of one-, two- or four-eddies are initiated. The basic flow structure and the related velocity oscillations have been investigated both by experimental techniques using the ultrasound Doppler velocimetry and by numerical calculations. Compared to the single vortex flow the double vortex flow shows a much higher level of large-scale velocity oscillations. The theoretical model turned out to be in good agreement with the experimental data.

Using a novel metal-semiconductor-metal (MSM) structure, we combine a large-active-emitter volume with strong electric fields for carrier acceleration. We obtain THz field amplitudes of 6 kV/cm using excitation pulse energies of 10 µJ.

This thesis has contributed to the achievement of in-beam PET as a promising clinical monitoring technique. In response to a pressing medical demand, this work has provided a tool for quantification of local dose deviations in case of observed discrepancies between the measured and expected PET images. The implemented interactive approach described in chapter 3 is in clinical use since 2001. It provides the radio-oncologist with a valuable feedback which may allow a prompt reaction in the strategy of the therapy prior to the delivery of the successive treatment fraction in case of significant deviations between planned and actually applied dose. ...

Many bacteria possess a crystalline protein or glycoprotein surface layer (S-layer) as the outermost component of their cell wall. The interest in bacterial S-layers increased in the last time. This protein might be applied as biomolecular template for making nanostructures, e.g. for the development of biosensors. The surface layer of a natural Bacillus sphaericus isolate JG A-12, recovered from a uranium waste pile, was analyzed and compared to the surface layer
of a reference strain (Bacillus sphaericus NCTC 9602). The molecular weights of the S-layer proteins of both, the reference strain NCTC 9602 and the strain JG A-12, were examined with a denaturating polyacrylamid gel electrophoresis and were estimated to be approximately 135 kDa. In addition to that, the first 20 amino acids at the N-termini of the 135 kDa proteins of the strains 9602 and JG A-12 were identical. However, no similarity to the S-layer proteins of
the Bacillus sphaericus strains 2362 and P-1 was found. Interestingly, in the case of the uranium waste isolate, in addition to the S-layer protein a second, smaller protein with a size of 30 kDa was copurified. The amino acid sequence of the N-terminus of the 30 kDa protein was significantly different from those of the S-layer proteins. This small protein possesses a similarity to many flagellins of different bacteria. The S-layer of the reference strain Bacillus
sphaericus NCTC 9602 and of the uranium waste isolate JG A-12 were also characterized using transmission electron microscopy after negative staining. Both S-layers have a p4 symmetry with lattice constants of 12,9 nm (S-layer of Bacillus sphaericus NCTC 9602) and 12,5 nm (S-layer of JG A-12). It seems, that the reference strain Bacillus sphaericus NCTC 9602 and the isolate JG A-12 possess the S-layer protein with same structure.

Different types of biocers were prepared by dispersing vegetative cells, spores and surface layer proteins (S-layers) of Bacillus sphaericus JG-A12 in aqueous silica nanosols, gelling or coating on glass, and drying. The enzymatic activity of embedded B. sphaericus cells depends noticeably on the water content of the biocer. The cells are destroyed by drying and shrinkage of the silica network whereas embedded spores retain their ability for germination. The biosorption
of uranium and copper of these biocomposites was investigated. Biocers with cells possess the highest metal binding capacity compared to matrices with spores or S-layers. An additional increasement of the metal binding capacity is achieved by using penetration reagents like sorbitol. For renewed use biosorpted uranium and copper can be completely removed from the biocers by using aqueous citric acid. The use of spores as biocomponent offers new interesting possibilities for the preparation of storage-stable bioactive biocers.

We studied the stability of the oxidation state of U(VI) in the presence of natural humic acid from Aldrich and synthetic acids Hyd-Glu and Cat-Gly representing humic acid model substances with pronounced redox functionalities. Using laser-induced photoacoustic spectroscopy we obtained the first spectroscopic proof for the reduction of U(VI) to U(IV) by the applied synthetic humic acids. In contrast to that, no spectroscopic indications for an Aldrich humic acid-mediated reduction of U(VI) were found. From that we concluded that both humic acid-like products show higher U(VI) redox capacities than Aldrich humic acid.

The local modification of magnetic properties by means of ion irradiation has been demonstrated for perpendicularly magnetized Co/Pt [1], for amorphous soft magnetic alloys [2] and for exchange-bias systems [3-5]. In all cases the magnetic features are not determined by the patterning itself, but by the micromagnetic feature sizes. Therefore, if the pattern sizes are close to the intrinsic length scales of the system under investigation a change in the overall magnetic behaviour is expected. For an exchange bias system this intrinsic length scale is in the range between 100 – 1000 nm [5].
The aim of the present study is to investigate the domain structure of a micro-patterned exchange bias system during magnetization reversal. Special attention is paid to the interaction between adjacent features changing the overall magnetic behaviour of the system. As a test system we chose a bottom pinned exchange bias bilayer consisting of 20 nm PtMn and 6 nm NiFe, capped with 5 nm of Ta, prepared by ion beam and physical vapour deposition. PtMn is chosen as the antiferromagnetic material due to its technological relevance and due to the chemically ordered L10-phase which is required in order to obtain a large exchange bias field. This phase can easily be disordered by means of ion irradiation leading to a very low ion fluence required to suppress the exchange bias effectively [6]. Thus sputtering effects are minimized. Using a 25 keV Ga+ focused ion beam (FIB) a stripe array consisting of 1 µm wide lines exposed to a fluence 21014 Ga/cm2 separated by 1 µm spacing is created. The long axes of the lines are oriented parallel to the exchange bias direction.
The global magnetic properties of the stripe array were analyzed by means of magneto-optic Kerr effect magnetometry (MOKE) and Kerr microscopy. It was found, that the overall loop shift in the patterned region is reduced to ~30 Oe compared to an exchange bias field of 180 Oe in the unpatterned area. After saturation in an applied field of +800 Oe there is no domain pattern observed in remanence by Kerr microscopy. With increasing negative field first the magnetization in the irradiated stripes reverse. This leads to an alignment of the soft magnetic (irradiated) stripes parallel to the applied field direction while the magnetization of the non-irradiated stripes remains antiparallel. After saturation at -500 Oe and increase of the applied field a hysteretic behaviour was observed that is consistent with the MOKE-measurements leading to a remaining domain contrast in remanence.
At an applied field between -12 Oe and -80 Oe a sharp contrast originating from Néel walls between irradiated and non-irradiated regions is observed by magnetic force microscopy. Moreover, a successive increase of the domain width in the irradiated areas at the expense of those in the non-irradiated areas is observed. At an applied magnetic field of about -100 Oe the magnetization in the non-irradiated area is nearly completely reversed due to the influence of the adjacent soft magnetic areas which are reversed at lower field values already. A magnetization ripple as a remainder of the non-irradiated stripes persists up to large negative field values consistent with the large exchange bias field in the completely unpatterned region.

References
[1]J. Lohau, A. Moser, C. T. Rettner, M. E. Best, B. D. Terris, Appl. Phys. Lett. 78, 990 (2001).
[2]J. McCord, J. Fassbender, M. Frommberger, M.O. Liedke, E. Quandt, L. Schultz, Appl. Phys. Lett., submitted.
[3]A. Mougin, S. Poppe, J. Fassbender, B. Hillebrands, G. Faini, U. Ebels, M. Jung, D. Engel, A. Ehresmann, H. Schmoranzer, J. Appl. Phys. 89, 6606 (2001).
[4]J. McCord, R. Schäfer, K. Theis-Bröhl, H. Zabel, J. Schmalhorst, V. Höink, H. Brückl, T. Weis, D. Engel, A. Ehresmann, J. Appl. Phys. accepted.
[5]S. Blomeier, D. McGrouther, S. McVitie, R. O’Neill, J. N. Chapman, M. C. Weber, B. Hillebrands, J. Fassbender, J. Magn. Magn. Mater. accepted.
...

Becquerelite, Ca[(UO₂)₆O₄(OH)₆]•8H₂O, and swartzite, CaMg[UO₂(CO₃)₃]•12H₂O, have been synthesized and identified by X-ray powder diffraction (XRD). Chemical compositions were verified by ICP–MS and AAS. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) and Fourier-transformed infrared spectroscopy (FTIR) were used for the first time to characterize these phases. In becquerelite, there are four fluorescence emission bands, at 518.9, 535.6, 553.4, and 578.9 nm, and a characteristic fluorescence lifetime of 3.1 ± 0.2 s. Swartzite shows six characteristic fluorescence emission bands, at 472.3, 488.9, 509.0, 531.1, 554.7, and 578.9 nm, and a fluorescence lifetime of 59.4 ± 0.1 s. The FTIR spectra of becquerelite are characterized by an intense asymmetric stretching vibration (v3 UO₂ ²⁺ mode) band at 946 cm^-1, with shoulders at approximately 925 and 902 cm^-1. Swartzite shows its characteristic v3 UO₂ ²⁺ mode of the uranyl cation at 898 cm^-1. As natural U⁶⁺-bearing samples commonly form thin coatings on rock or mineral surfaces or as a component mixed with other solids, it is generally difficult to identify small quantities of these secondary phases. Spectroscopic methods like TRLFS and FTIR spectroscopy are found to be promising methods to identify such secondary phases.

Data from KEK on subthreshold antiproton as well as on π^± and K^± production in proton-, deuteron- and alpha-particle-induced reactions at energies between 2.0 and 12.0 AGeV for C, Cu and Pb targets are described within a unified approach. We use a model which considers a nuclear reaction as an incoherent sum over collisions of varying numbers of projectile and target nucleons. It samples complete events and thus allows for the simultaneous consideration of all final particles including the decay products of the nuclear residues. The enormous enhancement of the antiproton cross section, as well as the moderate increase of meson production in deuteron and alpha induced compared to proton-induced reactions, is well reproduced. In our approach, the observed enhancement near the production threshold is mainly due to the contributions from the interactions of few-nucleon groups.

The understanding and the modification of the magnetic damping processes in thin ferromagnetic films has gained considerable interest in recent years. In addition to applied research on ultrafast magnetization reversal [1-3] also studies concerning the basic damping phenomena [4,5] and their modification by means of adjacent non-magnetic layers [6] or alloying [7] have been reported. Also the use of ion implantation to modify magnetic properties on a local scale has been addressed [8].

Here we report on investigations of the static and dynamic magnetic properties of 20 nm thick permalloy films as prepared and after 30 keV Cr implantation with different Cr fluences. Due to the doping the Curie temperature of the permalloy film decreases with the implantation fluence. At an averaged Cr concentration of about 7% (≈ 1.4·10^16 Cr/cm^2) the Curie temperature drops below room temperature. The uniaxial anisotropy, induced by a magnetic field during deposition, decreases but persists with increasing Cr fluence as indicated by the 2-fold symmetry of the magnetic remanence as a function of in-plane angle measured by magneto-optic Kerr effect magnetometry.

In order to investigate the magnetization damping pulsed inductive microwave magnetometry (PIMM) has been performed for various applied magnetic fields. In Fig. 3 the magnetization traces for the as-deposited permalloy film as well as the Cr-implanted samples are shown for an applied field of 10 Oe. Upon Cr implantation the PIMM amplitude is decreased consistent with a decrease in the uniaxial anisotropy AND a reduction in saturation magnetization. This results in a decrease of the precession frequency which is easily observed. However, the magnetic damping, i. e. the relaxation of the precession, is also altered by the Cr implantation. A detailed analysis of the damping parameter leads to 7-fold increase of the damping for only 4% of Cr doping. In order to clarify the basic mechanism for the enhancement the chemical and structural contributions to the magnetic damping parameter are separated.

References
[1] T. Gerrits, H. A. M. van den Berg, J. Hohlfeld, O. Gielkens, L. Bär, Th. Rasing, Nature 418, 509 (2002).
[2] S. Kaka, S. Russek, Appl. Phys. Lett. 80, 1958 (2002).
[3] H. W. Schumacher, C. Chappert, P. Crozat, R. C. Sousa, P. P. Freitas, J. Miltat, J. Fassbender, B. Hillebrands, Phys. Rev. Lett. 90, 017201 (2003).
[4] D. L. Mills, S. M. Rezende, Topics in Applied Physics 87, 27 (2003).
[5] B. Heinrich, in Ultrathin Magnetic Structures III, IV, edited by B. Heinrich and J. A. C. Bland (Springer-Verlag, Berlin, 2003).
[6] S. Mizukami, Y. Ando, T. Miyazaki, Jap. J. Appl. Phys. 40, 580 (2001).
[7] S. G. Reidy, L. Cheng, W. E. Bailey, Appl. Phys. Lett. 82, 1254 (2003).
[8] L. Folks, R. E. Fontana, B. A. Gurney, J. R. Childress, S. Maat, J. A. Katine, J. E. E. Baglin, A. J. Kellock, J. Phys. D: Appl. Phys. 36, 2601 (2003).

Owing to its large magneto-crystalline anisotropy energy, L10 ordered tetragonal FePt is among the most intensively discussed materials when it comes to pushing the superparamagnetic limit towards minimum particle sizes for future ultra-high density magnetic data storage media [1]. Depending on the preparation technique, however, the formation of the L10 thermodynamic equilibrium phase is often impeded by either a lack of thermodynamic driving forces or a lack of diffusivity.
Recently it has been shown [2,3] that gas phase prepared FePt nanoparticles can exhibit a very narrow size distribution with a mean diameter of roughly 6 nm. Together with a packing density of 2.8 × 10^12 particles /cm^2 a potential data storage density of 18 Tbit/inch^2 could be achieved. Unfortunately these particles are superparamagnetic at room temperature due to their multiply twinned icosahedral structure. Therefore it is of essential importance to transform these nanoparticles into the favourable L10 phase in a post-deposition treatment. Since annealing usually results in sintering of adjacent particles, a possible alternative is the use of ion irradiation techniques to create vacancies within the particles and thereby enhance the bulk diffusion of the constituents which has been successfully demonstrated to promote the L10 ordering in the case of FePd films [4].
In the present study, post-deposition 5 keV He irradiation has been performed on such gas phase prepared FePt nanoparticles. Structural characterization of the samples was carried out by means of High Resolution Transmission Electron Microscopy (HRTEM). Fig. 1 shows the HRTEM micrographs of two typical Fe42Pt58 particles with a mean diameterof dP = 6.2 nm. The power spectra as obtained by Fourier transform of the original images (see insets in Fig 1) clearly evidence that the particles are multiply twinned and of icosahedral structure. In Fig. 2, two typical HRTEM micrographs of particles are presented which had been subjected to irradiation with 5 keV He ions at a fluence of f = 3×10^17 ions/cm2. The particles are no longer multiply twinned but rather single crystal fcc, and their mean diameter is reduced to dP_irr = 5.2 nm. This size reduction is ascribed to irradiation induced sputtering of the particles. Although the defect concentration apparently increases the atomic diffusivity temporarily to an extent that allows for structural transformations in the FePt nanoparticles at RT, no L10 ordered particles have been observed. This observation is in contrast to the bulk phase diagram [5], theoretical calculations [6], and thermodynamic investigations in thin films [7], based on which the L10 phase is expected to be energetically favoured over the fcc phase by some 0.1 eV/atom.
There are two possible origins for the experimental findings. Either the particles investigated are already smaller than a critical particle size below which the L10 phase is no longer the thermodynamic equilibrium phase in FePt, or kinetic aspects may be of increasing importance at these length scales. Since the sputtering process that comes along with the ion irradiation is element specific and tends to remove more iron than platinum atoms, the He ion irradiation results in a shift of the elemental composition of the FePt nanoparticles towards a more Pt-rich concentration. As a consequence, the remaining alloy approaches the borderline of the L10
stability region in the phase diagram. Concurrently, the thermodynamic ordering temperature is reduced and the chemical driving force for the L10 ordering will be significantly reduced.

References
[1] D. Weller, A. Moser, L. Folks, M.E. Best, W. Lee, M.F. Toney, M. Schwickert, J.-U. Thiele, and M.F. Doerner, IEEE Trans. Mag. 36, 10 (2000).
[2] S. Stappert, B. Rellinghaus, M. Acet, and E.F. Wassermann, J. Cryst. Growth 252, 440 (2003).
[3] B. Rellinghaus, S. Stappert, M. Acet, and E.F. Wassermann, J. Magn. Magn. Mater. 266, 142 (2003).
[4] H. Bernas, J.-Ph. ...

Small and large angle excitations in exchange bias systems have been investigated in real time by means of all-optical pump-probe experiments. Time resolved magneto-optics has been employed as a probe of the transient magnetic phenomena upon laser excitation. Due to an increased spin temperature upon photoexcitation, an unpinning of the interfacial exchange coupling takes place resulting in a collapse of the unidirectional anisotropy. An effective internal anisotropy pulse field with a rise time of the order of the pump laser pulse duration (τ =8.3 ps) is launched which governs the time evolution of the effective field acting on the magnetization of the ferromagnetic layer of the bilayer system. The time evolution of the exchange bias shift field and the zero-field susceptibility reveal a fingerprint of the internal field pulse and can be understood taking ultrafast thermal activation into account [1]. The excess energy of the spin system - upon a sudden increase of the interfacial spin temperature – can lead to the excitation of a high frequency precessional response of the magnetization of the ferromagnetic layer for both the easy and the hard axis geometry [2,3]. Even, the initial deflection direction of the magnetization of the ferromagnet away from the initial equilibrium orientation can be controlled on the picosecond timescale in the hard axis geometry. The magnitude of the internal pulse field, and thus the torque acting on the magnetization of the ferromagnetic layer, can be controlled by the absorbed photons [3]. Hence, the precessional motion depending on the magnitude of the anisotropy pulse field, i.e., the precession angle can
be investigated. Moreover, by comparing the measured real time precessional motion with solutions of the Landau-Lifshitz and Gilbert equation the dependence of the effective Gilbert parameter α on the precession angle can be studied. The extracted Gilbert parameter depends not or only rather weakly on the magnitude of the internal pulse field. There are no non-linear effects present for this material system. Both small and large angle precession of the ferromagnetic layer upon photoexcitation can be modeled with reasonable values of the Gilbert parameter within the Landau-Lifshitz and Gilbert framework.
Employing the known antiferromagnetic thickness dependence of the exchange bias field Heb, the exchange bias field dependence of the Gilbert parameter α was investigated. For this purpose a wedge shaped exchange bias bilayer with a fixed thickness of the ferromagnetic layer and a varying thickness of the antiferromagnetic layer along the sample was prepared and measured.
The extracted Gilbert parameter from the time-resolved Kerr traces and thus, the dissipation rate increases linearly with the exchange bias field magnitude. Local fluctuations of the interfacial exchange coupling, due to interface roughness, can increase the two-magnon relaxation probability, which in terms of an additional dissipation channel finally leads to an increased Gilbert damping parameter [4,5].
The work is supported by the Graduiertenkolleg 792 of the Deutsche Forschungsgemeinschaft and the European Communities Human Potential programs HPRN-CT-2002-00318
ULTRASWITCH and HPRN-CT-2002-00296 NEXBIAS.

References
[1] M.C. Weber, H. Nembach, and J. Fassbender, J. Appl. Phys. 95, 6613 (2004).
[2] G. Ju, A. V. Nurmikko, R.F.C. Farrow, R.F. Marks, M.J. Carey, and B.A. Gurney, Phys. Rev. Lett. 82, 3705 (1999).
[3] M.C. Weber, H. Nembach, B. Hillebrands, and J. Fassbender, Phys. Rev. B, submitted for publication.
[4] S.M. Rezende, A. Azevedo, M.A. Lucena, and F.M. de Aguiar, Phys. Rev. B 63, 214418 (2001).
[5] M.C. Weber, H. Nembach, B. Hillebrands, and J. Fassbender, J. Appl. Phys, in press.

The magnetic anisotropy in amorphous soft magnetic CoFeSiB films is modified by He-ion irradiation. A rotation of uniaxial anisotropy depending on the applied field direction in the irradiated areas is observed by magnetometry and complementary domain observation by Kerr microscopy. No significant degradation in magnetic properties relative to the as-deposited state is found from the magnetization loops on non-patterned films. Using irradiation together with photolithography the films were treated locally, resulting in ‘anisotropy patterned’ structures. Complicated periodic domain patterns form due to the locally varying anisotropy distribution. Overall magnetic properties and domain patterns can be adjusted.

The understanding of the damping processes of the magnetization dynamics is an important issue. Several different damping channels are proposed. Here the importance of magnon-magnon processes for the damping is investigated with a magneto-optical method. This method allows to determine the length of the magnetization vector and therefore gives an indication for magnon-magnon processes. Higher order magneto-optic effects are also taken into account, which allows the determination of the quadratic magneto-optic constant.
This work was supported by the DFG-Graduiertenkolleg 792 and the EU-RTN ULTRASWITCH network (HPRN-CT-2002-00318).

At the carbon ion therapy facility of GSI Darmstadt in-beam positron emission tomography (PET) is used for imaging the ß+-activity distributions which are produced via nuclear fragmentation reactions between the carbon ions and the atomic nuclei of the irradiated tissue. On the basis of these PET images the quality of the irradiation, i.e. the position of the field, the particle range in vivo and even local deviations between the planned and the applied dose distribution, can be evaluated. However, for such an evaluation the measured ß+-activity distributions have to be compared with those predicted from the treatment plan. The predictions are calculated as follows: a Monte Carlo event generator produces list mode data files of the same format as the PET scanner in order to be processed like the measured ones for tomographic reconstruction. The event generator models the whole chain from the interaction of the projectiles with the target, i.e. their stopping and nuclear reactions, the production and the decay of positron emitters, the motion of the positrons as well as the propagation and the detection of the annihilation photons. The steps of the modelling, the experimental validation and clinical implementation are presented.

Nanowires and chains of nanoparticles are of emerging interest in nanoelectronics, nano-optics and plasmonics as well as for their monolithic integration into microelectronic devices. CoSi2 is a promising material due to its CMOS-compatibility microelectronics technology. Two fabrication methods of CoSi2 -nanowires by using ion beam synthesis (IBS) with Focused Ion Beams (FIB) technique are presented. In a first approach, an oxide layer, structured by sputtering with a focused Ga+ ion beam, have been used as an implantation mask for large area homogeneous Co+ implantation. Alternatively, a mass separated FIB of cobalt ions, emitted from a Co36Nd64 alloy liquid metal ion source, is applied for a direct writing IBS process. Implantation into Si with doubly charged Co+ ions emitted from the Co source allows ion energies up to 60 keV, which result in CoSi2 nanostructures buried in silicon. The processes of damaging and annealing of the substrate due to extremely high current density of the FIB were investigated. The fabrication of nanowires down to 30 nm diameter has been demonstrated.

Die magnetischen und strukturellen Eigenschaften von Permalloy-Schichten lassen sich gezielt durch Cr-Implantation modifizieren. Dazu
wurde ein 20 nm Permalloy/5 nm Tantal/SiOx/Si Schichtsystem mit 30 keV Cr-Ionen im Dosisbereich zwischen 2×10^15 und 2×10^16 Ionen/cm^2
implantiert. Daraus resultiert ein Implantationsprofil mit einer mittleren Konzentration an Cr innerhalb der Permalloy-Schicht von 1 bis 10
%. Die Änderungen in der Schichtstruktur wurden mit Röntgenbeugung, Auger-Tiefenprofilanalyse, Rutherford-Backscattering und Querschnitts-
Transmissions-Elektronenmikroskopie untersucht. Neben der eigentlichen Implantation wird schon bei relativ kleinen Ionendosen eine Durchmischung
der Grenzfläche zwischen Permalloy und Tantal beobachtet. Mit steigender Ionendosis diffundiert Tantal zunehmend an die Oberfläche des Schichtstapels. Diese experimentellen Ergebnisse werden gut durch TRIDYN-Simulationen beschrieben [1].
[1] Transport and Range of Ions (Dynamic): W. Möller, W. Eckstein, Nucl. Instr. and Meth. B 2, 814 (1984).

A bottom pinned exchange bias bilayer system consisting of 20 nm PtMn and 6 nm NiFe (produced using ion beam deposition (IBD) and physical vapour deposition (PVD, magnetron sputtering)) was laterally magnetic patterned by means of focused ion beam irradiation (FIB) on a micrometer scale. 25 keV ion irradiation with a fluence of
2×1014Ga+·cm−2 leads to a disordering of the as prepared chemically ordered PtMn-phase with only minor changes in sample topography. Thus the exchange bias field as well as the coercive field was reduced to a large extent on a local scale. The magnetic properties of FIB written 1µm wide stripes and their interaction with the non-irradiated spacing were analyzed by means of magneto-optic Kerr effect, magnetic force microscopy, and Kerr microscopy. The application of a magnetic field between -12
Oe and -80 Oe with respect to the exchange bias field direction leads to an antiparallel alignment of irradiated and non-irradiated stripes forming pronounced domain walls. A parallel alignment was found below -100 Oe and in the positive field region.

Das magnetische Dämpfungsverhalten, die Curie-Temperatur und die uniaxiale magnetische Anisotropie von 20 nm dicken Permalloy-Schichten wurde mittels Cr-Implantation modifiziert. Die Implantation wurde bei 30 keV Beschleunigungsspannung im Dosisbereich zwischen 2×10^15 und 2 × 10^16 Ionen/cm2 durchgeführt. Daraus resultiert ein Implantationsprofil mit einer mittleren Konzentration an Cr innerhalb der Permalloy-Schicht von 1 bis 10 %. Bei einer mittleren Konzentration von ca. 7% wird die Curie- Temperatur der Permalloy-Schicht auf Raumtemperatur abgesenkt. Damit einher geht eine leichte Verringerung der uniaxialen magnetischen Anisotropie. PIMM-Messungen (”pulsed inductive microwave magnetometry”) zeigen jedoch eine starke Vergrösserung des magnetischen Dämpfungsverhaltens durch die Cr-Implantation. Die möglichen Ursachen dieser Erhöhung werden diskutiert.

The alteration of magnetic properties in magnetic thin films by ion radiation has gained increasing attention in recent years. Here, we present data on the local alteration of the magnetic anisotropy axis in amorphous soft magnetic FeCoBSi films by He-ion irradiation in an applied magnetic in-plane field. Sputtered CoFeSiB (thickness 30 nm) were irradiated with 5 keV He-ions. A magnetic field of 600 Oe was applied during irradiation aligned orthogonal to the initial easy axis of anisotropy. Above a critical fluence an alignment of anisotropy in the applied field direction is observed by MOKE magnetometry and complementary domain observation by Kerr microscopy. Using irradiation together with photolithography the films were irradiated locally, thus resulting in anisotropypatterned structures. Domain patterns in different elements with varying angles of anisotropy and edge orientation, separating regions of different anisotropy alignment, are shown. The influence of the patterning on the (still) full film reversal is discussed in detail.

Preliminary results are presented on the structural and magnetic properties of epitaxial antiferromganetic NiMn and their correlation to the Exchange Bias Effect. Included are x-ray diffraction, reflection and rocking curves of pertinent diffraction peaks. The rocking curves have a FWHM of less than 3 indicating good epitaxial growth of the film. Polarized neutron reflectivity and high angle scattering measurements have been made in order to assess the magnetic properties of the system.

Using magnetron sputtering deposition a number of high exchange bias field samples were prepared for magnetic pattering investigations. The system prepared is as follow: glass/Ta 70 °A/PtMn 200 °A/ tCoFe = 20 - 60 °A/Ta 40 °A. One of such bottom pinned samples with 40 °A of CoFe was used for optical lithography. Several patterns have been etched physically with decreasing lateral sizes of either the edges or the spacing between the elements. The largest square is 50 × 50 µm and the smallest only 1 µm2. The separating lines are ranging from 10 µm to 2 µm width. The magnetic characterization of the samples have been done by VSM and MOKE. All samples exhibit well defined exchange bias field. A series of MFM images were taken from the structures. All images show a monodomain magnetization state in zero magnetic field. The shape
of the structure itself dose not influence stray field direction. The shape anisotropy contribution is thus smaller than the unidirectional anisotropy
given by the exchange bias. MFM investigation in an applied magnetic field have been done to get a deeper understanding of the domain pattern.

Monodisperse, vielfach verzwillingte FePt Nanopartikel mit ikosaedrischer Struktur und Konzentrationen im Bereich der stÄochiometrischen Zusammensetzung wurden durch DC-Sputtern in der Gasphase hergestellt. Die ikosaedrische Struktur der Partikel hat sich dabei als Äau¼erst stabil erwiesen, und weder thermisches Anlassen im Fluge noch nach der Deposition fÄuhrt zur Einstellung der magnetisch hochanisotropen, chemisch geordneten tetragonalen L10-Gleichgewichtsstruktur [1]. Eine Bestrahlung dieser Teilchen durch 5 keV He-Ionen bei Fluenzen von f > 10^17 Ionen/cm2 hingegen fÄuhrt zur Umwandlung in die kfz Struktur. Obwohl die Ionenbestrahlung die Versinterung benachbart liegender Partikel initiiert und somit eine erhÄohte Di®usion aufgrund einer temporär erhöhten Defektkonzentration belegt, wird die Einstellung der L10-Phase nicht beobachtet. Die Ergebnisse werden durch kinetisch bedingte Modifikationen der thermodynamischen Gleichgewichtsphasen erklärt.
[1] S. Stappert, B. Rellinghaus, M. Acet, and E.F. Wassermann, Proc. Mat. Res. Soc. Vol. 704, 73 (2002); S. Stappert, B. Rellinghaus, M. Acet, and E.F. Wassermann, J. Cryst. Growth 252, 440 (2003).
Gefördert durch die DFG im Rahmen des SFB 445.

The picosecond optical control of the exchange bias anisotropy was investigated in real time for different exchange bias bilayers (NiFe/FeMn, CoFe/NiMn, CoFe/IrMn) using time-resolved magneto-optics. Upon photoexcitation the spin temperature is increased leading to a collapse of the interfacial exchange coupling. Both the shift fields and the easy axis coercivities are reduced within the first 10 ps. The unpinning is followed by a slower spin-lattice relaxation process. The deduced relaxation times turn out to be quite comparable (< 205 ps) for all bilayers. The thermal decoupling of the bilayers can lead to a high frequency precession of the magnetization of the ferromagnetic layers. The precessional response of the CoFe/IrMn system reveals a Kittel type field dependence of the precession frequency. Brillouin light scattering measurements of the field dependence of the FMR frequency are in good agreement with the real time measurements, further supporting the homogeneous mode character of the optically excited precession.

Small and large angle excitations in exchange bias systems have beeninvestigated in real time by means of all-optical pump-probe experiments. Due to an increased spin temperature upon photoexcitation, an unpinning of the interfacial exchange coupling takes place resulting in a collapse of the unidirectional anisotropy. In terms of an internal pulse field the excess energy of the spin system leads to the excitation of a high frequency precessional response. The magnitude of the internal pulse field can be controlled by the absorbed photons [1]. Hence, the precessional motion depending on the precession angle can be investigated. The extracted Gilbert parameter does not depend on the magnitude of the internal pulse field. Both small and large angle precession can be modeled within the Landau-Lifshitz-Gilbert framework. Employing the antiferromagnetic thickness dependence of the exchange bias field, the exchange bias field dependence of the Gilbert parameter was investigated. The dissipation
rate increases linearly with the exchange bias field magnitude which can be understood taking local fluctuations of the interfacial exchange coupling as an additional dissipation mechanism into account [2].
[1] M. C. Weber et al., Phys. Rev. B, submitted. [2] M.C. Weber et al., J. Appl. Phys., in press.

This paper presents a novel boundary-integral equation (BIE) method for the calculation of poloidal axisymmetric magnetic fields applicable in a wide range of AC frequencies. The method is based on the vector potential formulation and it uses the Green's functions of Laplace and Helmholtz equations for the exterior and interior of conductors, respectively. In such a way, a coupled system of two complex surface-boundary equations is obtained that reduces the problem of finding the field distribution in the whole space to the determination of the vector potential and its normal derivative on the surface only. This reduction comes at the price of an increased complexity of the Green's function for the axisymmetric Helmholtz equation whose calculation is discussed in detail. The method is verified by comparing with the analytical solution for a sphere in a uniform external AC field. Application of the method is demonstrated for a simple model inductor.

Pressure vessel integrity assessment after long-term service irradiation is commonly based on surveillance program results. Radiation loading, metallurgical and environmental histories, however, can differ between surveillance and RPV materials. Therefore, the investigation of RPV material from decommissioned NPPs offers the unique opportunity to evaluate the real toughness response. A chance is given now through the investigation of material from the decommissioned Greifswald NPP (VVER-440/230) to evaluate the state of a standard RPV design and to assess the quality of prediction rules and assessment tools.

Some years ago first fluence calculations were done for the four Greifswald units in the frame of a TACIS project [1]. Neutron fluence integrals E>0.5MeV, E>1MeV and dpa-values at the inner and outer pressure vessel walls were obtained with the help of a Green’s functions method. New improved results will be presented based on new calculations of pin-wise time dependent neutron sources and an updated nuclear data base. The Monte Carlo calculations of neutron and gamma fluence spectra for different time intervals were done at all positions throughout the RPV wall, where the material specimens will be taken. The statistical error was estimated to be smaller than 1%. A comparison between the calculated fluences and experimental values (12th cycle of unit 1) shows a good agreement, the differences were smaller than 5 %.

The fluence at the inner wall of the RPV for E > 0.5 MeV for the critical weld was 4.64* 10^18 n/cm2. The maximum fluence at the RPV is larger by a factor 1.5. In addition, it could be shown that the fluence at the designated reference positions can be neglected (3 orders of magnitude smaller).

Because of changes in the dismantling procedure a new technology was developed to extract trepans from the interesting RPV positions. A special drilling machine is under development, which will be positioned at the ring water tank near the main coolant loops. The RPV will be moved by crane in the wanted positions (height and azimuth). The remotely controlled trepanning will start in 2005 at unit 1.

The testing and investigation program is focussed on the characterization of the material state as received. It comprises chemical analysis, microstructure investigations (by means of metallography, electron microscopy and SANS), and mechanical testing (hardness measurements, tensile, Charpy-V and fracture mechanics testing). The key part of the testing will be focussed on the determination of the reference temperature T0 following the ASTM test standard E1921-03. Trepans from 4 height positions (welds 3 and 4, base material from the maximum load position and from reference position) will be investigated..

[1] TACIS-Project NUCRUS 96601, Final Report, Brussels 2000

Experiments with air-water flows have been carried out in a vertical pipe of ~194-mm diameter and 9-m length, and a wide range of superficial liquid and gas velocities has been covered. At a distance of 7.6 m from the air injection, two wire-mesh sensors are installed, located at a distance of 63.3 mm from each other. The wire-mesh sensors measure sequences of instantaneous two-dimensional gas-fraction distributions in the cross section in which they are mounted, with a spatial resolution of 3 mm and a frequency of 2500 Hz. The spatial cross-correlations of the gas-fraction signals have been evaluated, and on their basis turbulent diffusion coefficients have been estimated.
It is found that for a given liquid superficial velocity, a sudden increase of the diffusion coefficient takes place when the superficial gas velocity is increased above a certain value. The abrupt increase of the diffusion coefficient occurs in correspondence of the transition from mono- to bimodal bubble size distributions.
The experimental diffusion coefficients are compared with the prediction of the Sato model (experimental gas-fraction profiles and bubble size distributions are given as input). Even though this model has been developed for bubbly flow, the general trends are well captured also in the churn-turbulent regime.

An experimental three-dimensional reconstruction and visualization of stationary and transient flashing flow in a vertical pipe (47 mm diameter) is presented. The measurements have been performed by means of wire-mesh sensors. This type of sensor delivers two-dimensional void fraction distributions in the pipe cross-section where it is mounted with a maximum sampling rate of 10,000 frames per second. A sampling rate of 1200 frames per second has been used in this work. Steam bubbles have been identified from the wire-mesh data and their complete three-dimensional reconstruction has been performed by taking into account the steam bubble velocity. For the estimation of the bubble velocity, two wire-mesh sensors positioned at a small axial distance from each other have been used. The velocity has been determined by cross-correlation of the two wire-mesh signals, by direct identification of the traveling time of the steam bubbles between the two sensors and by means of a drift-flux model. A comparison between the three methods of bubbles velocity measurement is reported. Stationary and time-dependent bubble size distributions have been derived. The stationary radial void-fraction profiles have been decomposed according to bubble size classes and compared with the results obtained with an equilibrium model.

An experimental three-dimensional reconstruction and visualization of stationary and transient flashing flow in a vertical pipe (47 mm diameter) is presented. The measurements have been performed by means of wire-mesh sensors. This type of sensor delivers two-dimensional void fraction distributions in the pipe cross-section where it is mounted with a maximum sampling rate of 10,000 frames per second. A sampling rate of 1200 frames per second has been used in this work. Steam bubbles have been identified from the wire-mesh data and their complete three-dimensional reconstruction has been performed by taking into account the steam bubble velocity. For the estimation of the bubble velocity, two wire-mesh sensors positioned at a small axial distance from each other have been used. The velocity has been determined by cross-correlation of the two wire-mesh signals and by direct identification of the travelling time of the steam bubbles between the two sensors. A comparison between the two methods of bubbles velocity measurement is reported. Stationary and time-dependent bubble size distributions have been derived. The stationary radial void-fraction profiles have been decomposed according to bubble size classes and compared with the results obtained with an equilibrium model.

This paper reports on the modeling and simulation of flashing-induced instabilities in natural circulation systems, with special emphasis on natural circulation Boiling Water Reactors (BWRs). For the modeling the 4-equation two-phase model FLOCAL (Rohde, 1986), developed at the Forschungszentrum Rossendorf (FZR, Germany), has been used. The model allows for the liquid and vapor to be in thermal non-equilibrium and, via drift-flux models, to have different velocities.
The phenomenology of the instability has been studied and the dominating physical effects have been determined. The results of the simulations have been compared qualitatively and quantitatively with experiments (Manera and van der Hagen, 2002) that have been carried out within the framework of a European project (NACUSP) on the CIRCUS facility. The facility, built at the Delft University of Technology in The Netherlands, is a water/steam 1:1 height-scaled loop of a typical natural-circulation-cooled BWR.

We apply ultrafast spectroscopy to establish a time-domain hierarchy between structural and electronic effects in a strongly correlated electron system. We discuss the case of the model system VO2, a prototypical nonmagnetic compound that exhibits cell doubling, charge localization, and a metal-insulator transition below 340 K. We initiate the formation of the metallic phase by prompt hole photo-doping into the valence band of the low-T insulator. The insulator-to-metal transition is, however, delayed with respect to hole injection, exhibiting a bottleneck time scale, associated with the phonon connecting the two crystallographic phases. This structural bottleneck is observed despite faster depletion of the d bands and is indicative of important bandlike character for this controversial insulator.

The coupling between Bloch oscillations and longitudinal optical (LO) phonons is investigated in ternary In0.53Ga0.47As / In0.52Al0.48As superlattices of different well widths. In femtosecond time-resolved studies, a strong increase of the coherent LO phonon amplitudes is observed when the Bloch oscillations are subsequently tuned into resonance with the different optical phonon modes of the ternary semiconductor materials. In a narrow-well superlattice where electronic minibands are energetically shifted close to the confining barrier potential, the phonon amplitudes are asymmetrically enhanced on the high-frequen cy edge
of the resonance. Here, at high electric fields, field induced tunneling into above-barrier continuum states leads to a rapid dephasing of Bloch oscillations. The associated polarization change provides an additional excitation process for coherent LO phonons.

Strain analysis of a laterally patterned Si-wafer was carried out utilizing X-ray grazing-incidence diffraction performed at the ID10B at the ESRF. The lateral patterning was done by focused ion beam implantation using a AuGeSi alloy liquid metal ion source. Samples were prepared by either a 35 keV Au+ ion beam (dose: 0.3, 2 ·10E14cm−2) or by a 70 keV Ge++ ion beam (dose: 8 · 10E14cm−2). It was shown that a periodical defect structure consisting of both implanted and not implanted stripes is created due to ion beam implantation. The induced strain distribution induced, however, shows no periodicity. This can be only explained by an overlap of the strain fields created in each implanted stripe. We found a maximum strain for the Au implanted samples in a depth of about 20 nm (da/a = −1,−3 · 10E−4 for the Au samples); for the Ge sample in a depth of 100nm (da/a = −1.2 · 10E−4). At depths 500nm below the sample surface the strain of the Ge sample becomes smaller than the detection limit (da/a < 2 · 10E−5). Using this technique we were able to create a buried Ge layer with a thickness of about 200 nm and an averaged Ge content of about 1%.

There is currently a great deal of research interest in the development of molten salt technology, both classical high temperature melts and low temperature ionic liquids, for the electrochemical separation of the actinides from spent nuclear fuel. We are interested in gaining a better understanding of actinide and key fission product speciation and electrochemical properties in a range of melts. Our studies in high temperature alkali metal melts (including LiCl and LiCl-KCl and CsCl-NaCl eutectics) have focussed on in-situ species of U, Th, Tc & Ru using X-ray absorption spectroscopy (XAS, both EXAFS and XANES) electronic absorption spectroscopy (EAS) and Raman spectroscopy. We report unusual actinide speciation in high temperature melts and an evaluation of the likelihood of Ru or Tc volatilisation during plant operation. Our studies in lower temperature melts (ionic liquids) have focussed on salts containing tertiary alkyl group 15 cations and the bis(trifluormethyl)sulfonyl)limide anion, melts which we have shown to have exceptionally wide electrochemical windows. We report Ln, Th, U, Np and Pu speciation (XAS, EAS and vibrational spectroscopy) and electrochemistry in these melts and relate the solution studies to crystallographic characterised benchmark species.

The coordination of the U(IV) and U(VI) ions as a function of the chloride concentration in aqueous solution has been studied by U L_III-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The oxidation state of uranium was changed in situ using a gas-tight spectro-electrochemical cell, specifically designed for the safe use with radioactive solutions. For U(IV) the complexes U(H₂O)₈Cl³⁺, U(H₂O)_6-7Cl₂ ²⁺ and U(H₂O)₅Cl⁺.

The coordination of the U(IV) and U(VI) ions as a function of the chloride concentration in aqueous solution has been studied by U LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The oxidation state of uranium was changed in situ using a gas-tight spectro-electrochemical cell, specifically designed for the safe use with radioactive solutions. For U(VI) we observed the complexes UO2(H2O)4Cl+, UO2(H2O)3Cl20 and UO2(H2O)2Cl3 with [Cl] increasing from 3 to 9 M, and for U(IV) the complexes U(H2O)8Cl3+, U(H2O)6-7Cl22+ and U(H2O)5Cl3+. In the uranium coordination sphere U-O distances are 2.41-0.02 Å and U-Cl distances are 2.71-0.02 Å, independent of oxidation state and chloride concentration.

Bezüglich eines hypothetischen Kernschmelzeszenarios in einem Leichtwasserreak-tor (LWR) ist es notwendig, mögliche Versagensformen des Reaktordruckbehälters sowie Versagenszeiträume zu untersuchen, um die Belastung für das Containment bestimmen zu können. Es wurden bereits eine Reihe von Experimenten durchge-führt, welche Erkenntnisse hierüber liefern sollen.
Vom Institut für Sicherheitsforschung des FZR wurde ein Finite-Elemente-Modell er-stellt, das sowohl die Temperaturfeldberechnung für die Wand als auch die elasto-plastische Mechanik der Behälterwand beschreibt. Dabei wurde ein fortgeschrittenes Modell für das Kriechen und für die Materialschädigung entwickelt und an Hand von experimentellen Daten validiert. Die thermischen und mechanischen Berechnungen sind rekursiv und sequentiell gekoppelt. Das Modell ist in der Lage, Versagenszeit und Versagensposition eines Behälters mit beheiztem Schmelzepool zu berechnen.
Das Modell wurde für Voraus- und Nachrechnungen der FOREVER-Experimente, die den RDB eines LWR im Maßstab 1:10 nachbilden, angewendet. Diese Experimente wurden an der KTH Stockholm durchgeführt. Die Ergebnisse der Berechnungen sind qualitativ und quantitativ sehr zufriedenstellend.
Erste Rechnungen für eine LWR-Geometrie wurden durchgeführt, um Unterschiede und Gemeinsamkeiten zwischen prototypischen Szenarien und skalierten Experi-menten herauszuarbeiten.

In-beam positron emission tomography (PET) is currently the only method for an in-situ monitoring of charged hadron therapy.
However, in-beam PET data, measured at beams with a sub-microsecond-microstructure due to the accelerator radiofrequency (RF), are highly corrupted by random coincidences arising from prompt gamma-rays following nuclear reactions as the projectiles penetrate the tissue. Since random-correction techniques from conventional PET cannot be applied, the clinical in-beam PET at the therapy facility at the Gesellschaft fuer Schwerionenforschung (GSI) Darmstadt merely reconstructs events registered in the
pauses (~ 2 - 4 s) between the beam macropulses (< 2 s). We have successfully tested at GSI two methods for suppressing
the micropulse-induced random coincidences during beam extraction. Image statistics increased by about 90 %. Both methods rely on the synchronization of the gamma-gamma-coincidences measured by the positron camera with the time microstructure of the beam, either by using the RF-signal from the accelerator or the signal of a thin diamond detector placed in the beam path in front of the target. Energy and triple-coincidence time correlated spectra first-measured during beam extraction, combined with the corresponding tomographic images of the beta+ activity induced by the beam in a plastic phantom, clearly confirm the feasibility of the proposed random suppression methods. These methods provide the solution for applying in-beam PET at synchrotron and cyclotron radiotherapy facilities with optimal utilization of the annihilation photon flux.

Next-generation light sources and accelerators are being proposed that set unique requirements for the electron source parameters. No single source is suitable for the diverse applications, which have operating characteristics ranging from high-average-current, quasi-CW, to high-peak-current, single-pulse electron beams. Advanced Energy Systems, in collaboration with our various partners, is developing a variety of electron gun concepts for these important applications.

The field disturbance in the RF coupler plane increases the transverse emittance of RF electron guns. This effect has been calculated for the Rossendorf superconducting RF gun. For 10 kW beam power the increasing is smaller than 5 %.

A telescope of three silicon detectors has been installed close to the internal target position of the ANKE spectrometer, which is situated inside the ultra-high vacuum of the COSYJulich light-ion storage ring. The detection and identification of slow protons and deuterons emerging from a deuterium cluster-jet target thus becomes feasible. A good measurement of the energy and angle of such a spectator proton (p(sp)) allows one to identify a reaction as having taken place on the neutron in the target and then to determine the kinematical variables of the ion-neutron system on an event-by-event basis over a range of c.m. energies.The system has been successfully tested under laboratory conditions. By measuring the spectator proton in the pd-->p(sp)dpi(0) reaction in coincidence with a fast deuteron in the ANKE Forward Detector, values of the pn-->dpi(0) total cross-section have been deduced. Further applications of the telescope include the determination of the luminosity and ! beam polarisation which are required for several experiments.

We investigate the splitting and mixing of ρ and ω mesons in nuclear matter. The calculations were performed on the basis of QCD sum rules and include all operators up to mass dimension-6 twist-4 and up to first order in the coupling constants. Special attention is devoted to the impact of the scalar four-quark condensates on both effects. In nuclear matter the Landau damping governs the ρ-ω mass splitting while the scalar four-quark condensates govern the strength of individual mass shifts. A strong in-medium mass splitting causes the disappearance of the ρ-ω mixing.

The g factors and quadrupole moments of the 21/2(-) and 33/2(+) isomers in Pb-193 have been measured by the time-differential perturbed gamma-ray angular distribution method as g(21/2(-))=-0.059(11), \Q(21/2(-))\=0.22(2) eb and g(33/2(+))=-0.171(9), parallel toQ(33/2(+))\=0.45(4) eb. The results support the three-neutron configurations (1i(13/2))(12)(+2)x3p(3/2) and (1i(13/2))(3) for the 21/2(-) and 33/2(+) states, respectively. The quadrupole moment of the 12(+) isomer in Pb-194 described by the two-neutron (1i(13/2))(2) configuration has been remeasured as \Q(12(+))\=0.48(3) eb in perfect agreement with the previous data. The experimental results are discussed within a microscopic Bardeen-Cooper-Schrieffer approach in a number-projected one- and three-quasiparticle neutron space, and in the frame of the pairing plus quadrupole tilted-axis cranking model.

Contribution to 54. Jahrestagung der Österreichischen Physikalischen Gesellschaft

The modelling of ion transport and interactions in matter is a subject of growing interest, driven by the multiplication of applicaton fields. These include hadron therapy, dosimetry, and space missions, but there are also several fundamental research, accelerator physics, and cosmic ray physics issues where a reliable description of heavy ion induced cascades is important. In the present work, the capabilities of the FLUKA code for ion beams will be briefly recalled and some recent developments presented. Applications of the code to the simulation of therapeutic carbon, nitrogen and oxygen ion beams, and of iron beams, which are of direct interest for space mission related experiments, will be also presented, together with interesting consideration about the evaluation of dosimetric quantities. Both applications involve ion beams in the AGeV range.

The rapid growth of the microelectronics industry in the last decades made it possible to produce structures in the sub-micrometer scale on silicon chips and to reach an integration scale under 100 nm. Decreasing the size and increasing the complexity of these structures make a control of quality and defects investigation more difficult. During a long time ultrasound devices are being used for nondestructive investigation of materials, like ultrasound microscopes, scanning photo-acoustic microscopes or scanning electron-acoustic microscopes, where acoustic waves are generated by acoustic transducers, focused laser or electron beams, respectively.
The aim of this work is to investigate more precisely the acoustic wave generation by pulsed and periodically modulated ion beams in different solid materials depending on the beam parameters and to demonstrate the possibility to apply an intensity modulated focused ion beam (FIB) for acoustic emission and for nondestructive investigation of the internal structure of materials on a microscopic scale. The combination of a FIB and an ultrasound microscope in one device can provide the opportunity of nondestructive investigation, production and modification of micro- and nanostructures simultaneously. The FIB spot size in modern systems is comparable with that of a focused electron beam and the penetration depth of ions with energy of 20-60 keV is lower than 100 nm. This makes it possible to reach a sub-micrometer resolution of a scanning ion acoustic microscope. On the other hand side a FIB with energy of 20-60 keV is a good tool which can be used for the fabrication of nanostructures using ion milling, implantation or ion beam assisted deposition techniques.
The bulk ultrasound emission in a solid was investigated using a pulsed high energy ion beam focused on aluminum, copper, iron and silicon samples. Oxygen, silicon and gold ion beams were applied in charge states from 1+ to 4+ with the pulse duration of 0.5 - 4 µs and an energy of 1.5 - 10 MeV. Intensity of the detected acoustic waves shows a linear dependence on the energy of the incident ions, on the ion flux as well as on the pulse duration. No influence of the ion charge and ion mass to the emission of acoustic waves was observed.
The ion acoustic effect was applied for a nondestructive material inspection using intensity modulated FIB providing by the IMSA-100 FIB system with an accelerating potential of 30-35 kV. The achieved lateral resolution of this scanning ion acoustic microscope is in the micrometer range depending on the sample material and the beam modulation frequency. The resolution can be improved by increasing the frequency. The maximal modulation frequency which was obtained at IMSA-100 is about 2 MHz corresponding to lateral resolution of 4-5 µm on silicon. Using this microscope, some images of integrated microstructures on a silicon chip were obtained using the lock-in technique for filtering of the signal from the noise and increasing of the total imaging time. The possibility to visualize near sub-surface structure was demonstrated. Due to the strong sputtering effect and the long time of irradiation the imaged structures were significantly damaged. Si2+, Ge2+, Ga+ and Au+ ions were used. All these ions are quite heavy and have high sputtering coefficients. Long-time imaging improves the quality of acoustic images, i. e. the signal-to-noise ratio is reduced with the square root from the pixel time, but leads to significant erosion of the imaged structure.

Die Uranspeziation in ausgewählten Sicker- und Grubenwässern des ehemaligen Uranbergbaus wurde mittels spektroskopischer Methoden (TRLFS, LIPAS) untersucht. Deren Kenntnis in Abhängigkeit vom pH-Wert ermöglicht die Optimierung der Uranabtrennung mittels uranophiler Calixarene. Mittels Flüssig-Flüssig-Extraktion wurde gezeigt, dass COOH-derivatisierte Calix[6]arene als effektive Extraktionsmittel für die selektive Uranylabtrennung aus umweltrelevanten Wässern bei pH-Werten größer 4 geeignet sind und für Praxisanwendungen eingesetzt werden können. Extraktionskonstanten wurden bestimmt. Die durch Fixierung dieser Calixarenderivate auf Polyester dargestellten calixarenmodifizierten Vliese sind in der Lage Uranylionen aus synthetischen Grubenwässern in Anwesenheit von Konkurrenzionen abzutrennen. Die Untersuchungen zur Reversibilität der Uranbindung an calixarenausgerüsteten Polyestervliesen haben gezeigt, dass eine fast vollständige Regenerierung der calixarenmodifizierten Vliese mittels verdünnter Mineralsäuren möglich ist. Die regenerierten textilen Filtermaterialien können für weitere Uranabtrennungszyklen eingesetzt werden. Nach Auswahl geeigneter Calixarenderivate ist eine Übertragung des entwickelten Abtrennungsprinzipes auf weitere Actinide (z. B. Np, Pu) bzw. Schwermetall-Kontaminanten (z. B. As, Cd, Pb) möglich.

High-spin level structure of Mo-94 has been re-investigated using the modem multidetector array of GASP via the O-16(Se-82, 4ngamma)Mo-94 reaction at E(Se-82) = 459 MeV. The previously reported level scheme has been largely modified up to similar to 10 MeV in excitation energy due to identifications of some important linking transitions. The level structure of Mo-94 has been compared with the shell model calculations. It is suggested that the valence neutron excitation within d(5/2), g(7/2), and h(11/2) orbitals should be taken into account in order to adequately describe the high-spin level structure of Mo-94 above I-pi = 14(+).

Positron emission tomography is currently the only feasible method for in-situ and non-invasive 3D monitoring of the precision of the treatment in highly conformal ion therapy. Its positive clinical impact has been proven for fractionated carbon ion therapy of head and neck tumours at the experimental facility at the Gesellschaft f"ur Schwerionenforschung Darmstadt, Germany. Following previous promising experiments, the possible extension of the method to the monitoring of proton therapy has been investigated further in extensive in-beam measurements at GSI. Millimetre accuracy for verification of the lateral field position and for the most challenging issue of range monitoring has been demonstrated in mono-energetic and spread-out Bragg-peak proton irradiation of PMMA targets. The irradiation of an inhomogeneous phantom with tissue equivalent inserts in combination with further dynamic analysis has supported the extension of such millimetre precision to real clinical cases, at least in regions of interest for low perfused tissues. All the experimental investigations have been reproduced by the developed modeling rather well. This indicates the possible extraction of valuable clinical information as particle range in-vivo, irradiation field position and even local deviations from the dose prescription on the basis of the comparison between measured and predicted activity distributions. Hence, the clinical feasibility of in-beam PET for proton therapy monitoring is strongly supported.

We present a description of the equation of state of strongly interacting matter within a quasi-particle model.
The model is adjusted to lattice QCD data near T₀ at non-vanishing baryon density. We compare in detail the excess pressure and its expansion coefficients available from two-flavor lattice QCD calculations and outline prospects of the extrapolation to large baryon density.

Die Positronen-Emissions-Tomographie (PET) ist eine etablierte Untersuchungsmethode in der Medizin. Das vorgestellte Projekt beschäftigt sich mit einer nichtmedizinischen Anwendung dieses bildgebenden Verfahrens – dem Aufbau und der Anwendung eines PET-Tomographen zur Untersuchung des Verhaltens von Schaum in Blasensäulen. Am Beispiel von Natriumcapronat als schwaches Tensid, das einen feuchten, instabiler Schaum erzeugt, wird gezeigt, dass sich die Anreicherung eines Tensids in einer Schaumschicht mit der Positronen-Emissions-Tomographie nachweisen lässt.

In this paper we investigate the effect of implantation temperature on the structural properties of diamond implanted with high fluences of Si between 5.3 ´ 1017 Si cm-2 and 1 ´ 1018 Si cm-2. In order to reduce radiation-induced damage and to enhance SiC formation the implantations were performed at elevated temperatures in the range from 900 °C to 1200 °C. Subsequently, all samples were annealed for 10 minutes at 1500 °C in an rf-heated furnace. X-ray diffraction revealed the formation of cubic SiC nanocrystallites in a buried layer inside the implanted diamond. The implantation-induced damage was assessed by analyzing graphitization of the surface-near layer using Raman spectroscopy. With increasing Si fluence the implantation-induced damage rises and the nearly perfect alignment of the formed SiC crystallites within the host diamond lattice deteriorates. However, rising the implantation temperature from 900 °C to 1000 °C reduces the damage in the diamond and increases amount, size and epitaxial alignment of the crystalline SiC precipitates. Further increase of the implantation temperature gives no improvement in the quality of the SiC rich layer. Instead, the damaged diamond converts into graphite and the formation of SiC crystallites is obstructed.