Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

A benchmark exercise for thorium-plutionium fuel, based on experimental data, has been carried out. A thoriumplutonium oxide fuel rodlet was irradiated in a PWR for four consecutive cycles, to a burnup of about 37MWd/kgHM.
During the irradiation, the rodlet was inserted into a guide tube of a standardMOX fuel assembly. After the irradiation, the rod was subjected to several PIE measurements, including radiochemical analysis. Element concentrations and radial distributions in the rodlet, multiplication factors and distributions within the carrier assembly of burnup and power were calculated. Four participants in the study simulated the irradiation of the MOX fuel assemblies including the thorium-plutonium rodlet using their respective code systems; MCBurn, HELIOS, CASMO-5 and ECCO/ERANOS combined with TRAIN. The results of the simulations and the measured results of the radiochemical analysis were compared and found to be in fairly good agreement when the calculated results were calibrated to give the same burnup of the thorium-plutonium rodlet as that experimentally measured. Average concentrations of several minor actinides and fission products were well reproduced by all codes, to the extent that can be expected based on known uncertainties in the experimental setup and the cross section libraries. Calculated results which could not be confirmed by experimental measurement were compared and only two significant anomalies were found, which can probably be addressed by limited modifications of the codes.

1. Introduction
The F-18-benzoyl group is a useful functionality for the development of PET-radiotracers in order to introduce F-18 in a simple one step radiosynthesis. Since nitro leaving groups are common for the nucleophilic F-18-substitution, we utilized a nitro precursor for F-18-labeling of a vesamicol analog to evaluate it as new radioligand for the vesicular acetylcholine transporter (VAChT), which is an interesting target for imaging of presynaptic cholinergic deficiencies using PET.
The separation of a F-18-labeled compound from its nitro precursor in the radiosynthesis is often challenging, accordingly we firstly used the approach of reduction of the remaining nitro precursor to its amine, because this amine is normally easier to isolate from the radiotracer by semi-preparative HPLC than the nitro precursor itself. However, in order to avoid this additional step during the radiosynthetic procedure, we were interested to develop a suitable HPLC method to separate directly the radiotracer from its nitro precursor. Several analytical HPLC columns and eluent systems were investigated.

2. Materials & Methods
Because of the basic character of the analytes (tertiary amines) several columns were selected which are specially designated for the separation of basic analytes due to their potential to reduce peak tailing (LiChrospher Select B, Nucleosil AB, Reprosil Gold, Reprosil-Pur Basic HD). To study the influence of possible pi-pi-interactions, especially of the nitro precursor, we also used different phenyl and cyano columns (Nucleodur Sphinx, Fortis Phenyl, Reprosil Phenyl, LiChrospher CN). For comparison also a bare silica phase and commonly used AQ phases were investigated.
Aqueous acetonitrile and methanol mixtures with ammonium acetate, triethylamine/acetic acid, and trifluoroacetic acid were used as typical eluent systems.

3. Results
The aims of this HPLC study were: (i) to find a suitable separation method in which the fluoro compound clearly elutes in front of the nitro precursor, and (ii) to get more information about the suitability of different column types regarding separation data such as retention, peak tailing and resolution.
In general, with almost all columns the two compounds could be separated, however, the quality of separations was different and surprisingly, changes in elution order were observed. For example, using aqueous acetonitrile/ammonium acetate as eluent system, the fluoro compound elutes in front of the nitro precursor at low content of organic modifier. In contrast, a reversed retention behavior was observed at high content of acetonitrile which was also found by using methanol as organic modifier. Additionally, we observed that not all columns, designated to be especially appropriate for basic analytes, showed satisfying separation properties. Finally, a phenyl column was selected for the semi-preparative separation of the 18-F-labeled radiotracer from its nitro precursor and a reduction of the total radiosynthesis time by one hour could be achieved .

4. Conclusion
Due to this intensive analytical HPLC study, we were able to select a suitable column for an improved purification of a radiotracer from its remaining nitro precursor, which resulted in a considerable shortening of the radiosynthetic procedure.

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Radioactive carbonaceous aerosol particles deposit within the primary circuit of a high temperature reactor (HTR). These particles can pose a considerable threat if resuspended by a shock wave in the case of an unlikely loss-of-coolant accident and partially released into the environment (Kissane, 2009).
Stempniewicz et al. (2010) carried out simulations of the spatial and temporal development of carbonaceous dust deposits in the primary circuit of a HTR. Maximum dust layer thickness after full operation time of 60 years was well above 10 mm. However, the underlying multilayer models require additional experimental verification.
Therefore, particle deposition and resuspension experiments of multilayer graphite deposits have been conducted in a small-scale test facility. The results for particle layer thickness have been correlated to corresponding flow data as measured by means of a 2C2D Particle Image Velocimetry (PIV) system.
The experimental facility consists of a ventilated square duct (d = 100 mm), which is operated with air at ambient conditions. The average air velocity can be regulated over the range u = 1..7 m/s, corresponding to Reynolds numbers between Red = 8.9k..42k. As flow obstacles, periodic steps have been chosen (Fig. 1) allowing the comparison of results with previous studies on monolayer deposition (e.g. Lai et al., 1999).
Graphite aerosol particles (Thielmann Graphite, 23061) have been injected into the duct 15 diameters upstream of the test section by means of a dust disperser TOPAS - SAG 410. Setting the mass flux to 80 g/h an average mass concentration of airborne particles of up to 2 g/m³ is established. The aerodynamic particle size distribution of the graphite particles was determined by means of a TSI – APS 3321confirming that the particles cover well the range of interest for HTR conditions (quantiles:
dP,10 = 1.83 µm, dP,50 = 4.40 µm and dP,90 = 10.64 µm).
The deposition experiments have been conducted under different flow conditions and the development of graphite particle deposits in the vicinity of the steps have been observed by hourly laser triangulation measurements. Subsequently, the generated multilayer has been resuspended at a higher flow velocity and the thickness of the remaining structure has been measured using the same techniques.
Results show that for a relatively low Reynolds number of Red = 8.9k (Fig.2), deposition is mainly governed by gravitational settling and the deposition rate is almost independent of position and time. On the other hand, subsequent resuspension at higher flow velocities (Red =27.2k) reveals a strong relation between flow field and remaining layer (Fig.3), which is further being investigated.

Isokinetic sampling from stacks and ducts is a widely used method for air pollution control in many industrial and environmental applications.
During the last 40 years, U.S. EPA developed reference methods for air pollutant emission sampling of stationary sources, which included a compendium of technical guidelines for the monitoring of aerosol particles. One of the main parts of the sampling system is the sampling probe nozzle for which it was suggested in the reference methods that the lower bound diameter should be greater than di = 6 mm (Cohen, 2001). The influences of sampling nozzle tube diameter, the velocity ratio between free stream and the sampling tube as well as the tube inclination have been considered widely (Vincent, 2007). On the other hand, the influence of tube diameter has not been quantified by means of aerosol particle size spectrometry yet.
McFarland et al. (1997) as well as Peters and Leith (2004) experimentally investigated the deposition losses of aerosol particles in pipe bends. Both found a strong increase of deposition losses in the sampling tube for particle Stokes number of Stk > 0.3.
In this work, the influence of the nozzle diameter of the sampling probe on the aerosol particle size distribution was investigated by means of TSI APS 3321 and TOPAS LAP 321 measurements.
The considered gas/aerosol test facility is a small scale wind tunnel, which consists of a HEPA at the inlet and a square duct section in diameter of dhyd = 10 cm and length of l = 20dhyd = 2 m. The test section, where sampling takes place, is followed by a diffuser stage, an electrical precipitator and a radial fan in order to generate the desired pressure head. The average air velocity can be regulated over the range u = 1..7 m/s, corresponding to Reynolds numbers between Red = 8.9k..42k. In order to achieve isokinetic sampling, the flow rate of the sampling device has been accurately adjusted using Particle Image Velocimetry data.
AC Fine Test Dust (ISO 12103-1, dnom = 0.1..80 µm, bimodal distribution) was injected 17 diameter lengths upstream of the sampling point by means of a dust disperser TOPAS SAG 410. Four probe nozzle diameters di = [3,5,7,9] mm were chosen.
Figure 1 displays the volume weighted aerodynamic particle size distribution of AC Fine under variation of nozzle tube diameter as measured by the APS 3321. The modal dP,aero = 5 µm is roughly independent of nozzle size, whereas the values of the distribution for particle diameters above dP,aero > 12 µm increase continuously with increasing nozzle diameter.
A similar upward tendency in size distribution with increasing nozzle diameter is observed in the LAP measurement results (not shown here). This leads to the conclusion that deposition losses due to inertia, which consequently affect the larger particles, can be considerably reduced by accordingly increasing tube nozzle diameter. In addition, a comparison of aerodynamic particle size (APS 3321) and scattering particle size (LAP 321) will be presented.

This paper presents numerical and experimental investigations with respect to the fluid flow in the continuous casting process under the influence of an external DC magnetic field. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. The numerical results were validated by flow measurements carried out in a small-scale mockup using the eutectic alloy GaInSn. The jet flow discharging from the submerged entry nozzle was exposed to a level magnetic field spanning across the entire wide side of the mold. The comparison between our numerical calculations and the experimental results displays a very well agreement, in particular, we were able to reconstruct the peculiar phenomenon of an excitation of non-steady, non-isotropic large-scale flow perturbations due to the application of the DC magnetic field. Another important result of our study is the feature that the electrical boundary conditions, namely the wall conductivity ratio, have a serious influence on the mold flow just as it is exposed to an external magnetic field.

Until 2014 ELBE will be upgraded to a Centre for High Power Radiation Sources. The concept contains additional broad and narrow band coherent THz sources and the development of a 500 TW Ti:Sa Laser and even a 2 PW diode pumped Laser system. Laser plasma electron acceleration and proton acceleration experiments for medical applications are planed. Additionally coupled electron laser beam experiments like Thomson scattering or injection of ELBE electron into the laser plasma will be done.

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A superconducting Electron Linac with high Brilliance and low Emittance (ELBE) which provides an average beam current of 1 mA with maximum beam energy of 36 MeV was constructed in the Forschungszentrum Dresden-Rossendorf, Germany. The electron beam is used to generate infrared light (Free Electron Lasers), MeV-Bremsstrahlung, X-rays (electron channelling), fast neutrons and positrons. The ELBE secondary beams are used for a wide range of basic research like semiconductor physics, nuclear astrophysics and radio biological investigations. Furthermore a 150 TW Ti:Sa Laser delivers high intense and very short laser pulses used for laser plasma acceleration of electrons and protons.
ELBE was built by an internal project group of the Rossendorf research center. The professional structure of this project group, the project management tools and the available budget and the schedules will be discussed, as well.

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Aim: Cyclooxygenase-2 (COX-2) is an enzyme induced during inflammation, but overexpression of COX-2 also has been observed in carcinogenic processes. Noninvasive monitoring and quantitative characterization of functional expression of
COX-2 by means of PET would substantially improve understanding of the role of this enzyme during manifestation and progression of inflammatory diseases and cancer. Herein we report first radiosynthesis and cellular uptake studies of two
highly affine COX-2 inhibitors having a 1,2-diaryl substituted indole scaffold.
Materials and methods: The highly affine COX-2 inhibitors 3-(4-fluorophenyl)-2-(4-methylsulfonylphenyl)-1H-indole 1 and 3-(4-methoxyphenyl)-2-(4-methylsulfonylphenyl)-1H-indole 2 (both IC50 COX-2 ~ 20 nM) [1] served as nonradioactive references. The 18F-radiolabeled tracer [18F]1 was synthesized by nucleophilic substitution of an appropriate trimethylammonium-substituted aromatic precursor with [18F]fluoride and subsequent McMurry cyclization. The 11C-radiolabeled probe [11C]2 was formed via a methylation reaction of the corresponding desmethyl precursor with [11C]CH3I. Different human tumor cell lines showing selectively high COX-2 (FaDu, HT-29, A2058) or COX-1 expression (A375) were used to study the overall uptake or cellular association of [18F]1 and [11C]2 in vitro. To further differentiate the specific contribution of COX-1 and COX-2 to overall tracer uptake, unstimulated human monocytic leukemia cells (THP-1) and phorbol ester stimulated THP-1 macrophages (THP-1M) were used as models. The cell tracer uptake experiments using compounds [18F]1 and [11C]2 (0.4 MBq/mL) were performed in quadruplicate at 37°C for 30, 60, and 120 min.Results:[18F]1 was synthesized from [18F]fluoride in 10% yield (d.c.) in 98% radiochemical purity with a specific activity of 74-91 GBq/μmol. The 11Cradiolabeled compound [11C]2 was obtained in 23% yield (d.c.) in 99% radiochemical purity with a specific activity of 79-89 GBq/μmol. The radiotracer cellular uptake in each model used correlated well with the observed COX protein synthesis. Cell models with prominent COX-2 overexpression showed a substantially higher uptake of both [18F]1 and [11C]2 in the order FaDu>HT29>THP-1M>A2058 when compared to COX-1 overexpressing A375 cells. The lowest cellular uptake was observed in THP-1 showing no or very low baseline expression of both COX-1 and COX-2.
Conclusion:The new radiolabeled COX-2 inhibitors were synthesized in good radiochemical yield and high purity. Cellular studies demonstrated well correlation of the overall radiotracer uptake with COX expression/protein synthesis rate. Further exploration of the new COX-2 inhibitors [18F]1 and [11C]2 regarding in vivo metabolic stability and biodistribution, including dynamic small animal PET investigations in tumor bearing mice, is currently under the way.[1] Hu W., Bioorg. Med. Chem. 11, (2003), 1153

Vorstellung von geplanten Arbeiten am HIF

The recently introduced whole-body PET/MRI systems combine the unique metabolic imaging capabilities of positron emission tomography (PET) and the excellent soft tissue contrast of magnetic resonance imaging (MRI). The aim of this pilot study was to evaluate the feasibility of PET/MRI for initial staging of head and neck cancer.
Materials and Methods:Ten male patients aged (age 52 to 78 years, median age 62.8 y) with histologically proven squamous cell carcinoma of the head and neck region were examined using both a stand-alone PET scanner and a wholebody
PET/MRI scanner. Scanning started 60 minutes after intravenous administration of 350 MBq [18-F]-2-fluoro-2-deoxy-D-glucose (FDG) for the body trunk to exclude distant metastases. PET/MRI of the head and neck region followed immediately the first scan. The study was approved by the local ethics committee. A four-point-scale was used for qualitative evaluation of PET image quality. Furthermore, the signal-to-noise ratio (SNR) of the tumor and of both cerebellar hemispheres were determined for both PET data sets and used for semiquantitative comparison of image quality. Results were compared using the Wilcoxon matched-pair test.Results:The primary tumor was detected by PET/MRI in all 10 patients, by PET in 9 out of 10 cases, and by MRI in 9 out of 10 cases. Seven patients had lymph nodes suspect for metastatic disease. In two patients, lymph nodes considered suspect using MRI showed no pathological FDG uptake. In contrast, a single patient had lymph nodes considered suspect by PET but not by MRI. Visual evaluation of PET images showed consistent results (including regional contrast) for both scanners. There were no statistically significant differences regarding SNR between conventional PET and PET/MRI for the tumor and for both cerebellar hemispheres (p > 0.05).
Conclusion: PET/MRI of head and neck cancer is feasible with a whole-body PET/MRI scanner with excellent image quality and - fusion. While previously available PET/MRI systems were largely restricted to brain examinations, whole-body PET/MRI scanners allow comprehensive tumor staging. Further patients will be examined to evaluate the clinical role of PET/MRI in head and neck cancer.

This work shows the application of ion beam techiques to the structural characterization of different ZnO compounds. Taking advantage of ion channelling phenomena in combination with some specific nuclear resonances, the individual evaluation of defects in the IIb-metal and O sublattices is achieved.

The relative influence of the Lorentz force and the magnetic gradient force on micro-structured copper deposition is studied with simple magnetic elements consisting of cylindrical permanent magnets are placed closely behind the surface of the cathode. Analytical findings and numerical simulations reveal that for magnets of small diameter the magnetic gradient force dominates. Experimental investigations find that the thickness of the deposited copper layer increases in the vicinity of the magnets. The combined analysis of simulations and experiments shows that this enhancement of mass transfer results from a local convection towards the electrode which is forced by the magnetic gradient force.

Vorstellung der aktuellen und geplanten Forschungsarbeiten zum Thema (Rück)Gewinnung seltener Industriemetalle mittels biotechnologischer Verfahren am Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) und am Institut für Ressourcenökologie.

The adsorption of formic acid on clean TiO(2) anatase (101) and rutile (110) surfaces is studied by density-functional-based methods and compared with the results for coupling related phosphonic acids to titania surfaces. The preferred adsorption mode of the formic acid on both surfaces is a dissociative bridging bidentate complex, which is similar to the adsorption geometry of phosphonic acid. Higher adsorption energies and shorter Ti-O bond lengths indicate that phosphonic acid binds more strongly to TiO(2) than formic acid. The preference for the bidentate adsorption mode is supported by a detailed analysis of the charge distribution in the adsorption complexes. The strong interfacial electronic coupling between the adsorbate orbitals and the electronic states of the anatase (101) surface slab leads to additional states in the band gap of the clean surface. For rutile (110) no or only weak coupling of the adsorbate orbitals and the surface states occurs at the band edges, which leads to an increase of the band gap.

Overview presentation on the dependence of dimensionality, structure, size, composition, electronic properties and preparation conditions of molybdenum sulfide nanostructures at the Seifert group seminar.

Overview presentation of FWIO activities.

DFTEM 2011 Tutorial on nanoscale electronic transport

Workshop DFTEM 2011 - Introductory Lecture to DFT

In the central nervous system (CNS) ATP and adenosine act as transmitters and neuromodulators on their own receptors but it is still unknown which part of extracellular adenosine derives per se from cells and which part is formed from the hydrolysis of released ATP. In this study extracellular concentrations of adenosine and ATP from the rat striatum were estimated by the microdialysis technique under in vivo physiological conditions and after focal ischemia induced by medial cerebral artery occlusion. Under physiological conditions, adenosine and ATP concentrations were in the range of 130 nmol/L and 40 nmol/L, respectively. In the presence of the novel ecto-ATPase inhibitor, PV4 (100 nmol/L), the extracellular concentration of ATP increased 12-fold to ~360 nmol/L but the adenosine concentration was not altered. This demonstrates that, under physiological conditions, adenosine is not a product of extracellular ATP. In the first 4 h after ischemia,
adenosine increased to ~690 nmol/L and ATP to ~50 nmol/L. In the presence of PV4 the extracellular concentration of ATP was in the range of 450 nmol/L and a significant decrease in extracellular adenosine (to ~270 nmol/L) was measured. The contribution of extracellular ATP to extracellular adenosine was maximal in the first 20 min after ischemia onset. Furthermore we demonstrated, by immunoelectron microscopy, the presence of the concentrative nucleoside transporter CNT2 on plasma and vesicle membranes isolated from the rat striatum. These results are in favor that adenosine is transported in vesicles and is released in an excitation–secretion manner under in vivo physiological conditions. Early after ischemia, extracellular ATP is hydrolyzed by ecto-nucleotidases which significantly contribute to the increase in extracellular adenosine. To establish the contribution of extracellular ATP to adenosine might constitute the basis for devising a correct putative purinergic strategy aimed at protection from ischemic damage.

Semaxanib (SU5416) and 3-[4'-fluorobenzylidene]indolin-2-one (SU5205) are structurally similar drugs that are able to inhibit vascular endothelial growth factor receptor-2 (VEGFR2), but the former is 87 times more effective than the latter. Previously, SU5205 was used as a radiolabelled inhibitor (as surrogate for SU5416) and a radiotracer for positron emission tomography (PET) imaging, but the compound exhibited poor stability and only a moderate IC50 toward VEGFR2. In the current work, the relationship between the structure and activity of these drugs as VEGFR2 inhibitors was studied using 3D-QSAR, docking and molecular dynamics (MD) simulations. First, comparative molecular field analysis (CoMFA) was performed using 48 2-indolinone derivatives and their VEGFR2 inhibitory activities. The best CoMFA model was carried out over a training set including 40 compounds, and it included steric and electrostatic fields. In addition, this model gave satisfactory cross-validation results and adequately predicted 8 compounds contained in the test set. The plots of the CoMFA fields could explain the structural differences between semaxanib and SU5205. Docking and molecular dynamics simulations showed that both molecules have the same orientation and dynamics inside the VEGFR2 active site. However, the hydrophobic pocket of VEGFR2 was more exposed to the solvent media when it was complexed with SU5205. An energetic analysis, including Embrace and MM-GBSA calculations, revealed that the potency of ligand binding is governed by van der Waals contacts

The vascular endothelial growth factor (VEGF) is a key regulator of neovascularization and an elevated level of VEGF is known to correlate with increased metastatic invasion. Anti-angiogenic therapies focus on targeted inhibition of overexpressed growth factors with the aim of suppressing tumor proliferation, one approach is the attempt to block the intracellular tyrosine kinase at the adenosine triphosphate (ATP) binding site with small molecule inhibitors. For most effective treatment these targeted tumor therapies are accompanied with a more sensitive need for dose optimization and monitoring the therapeutic response. Direct non-invasive molecular imaging of tumor vascularization and of the angiogenic process in vivo would facilitate the selection of patients and help to evaluate the efficacy of an anti-angiogenic therapy. Radionuclide-based imaging technologies like PET and SPECT are progressively affecting the clinical diagnosis and treatment of cancer. A non-invasive and a reliable quantitative method to determine in vivo the levels of VEGFR expression using radiolabeled small molecules would help to develop a customized VEGFR-targeted chemotherapy. This review will give an overview on radiolabeled derivatives of small molecule VEGFR inhibitors basing on lead structures that have been approved or have reached clinical trials. It is covering aspects of the radiosynthesis as well the results of radiopharmacological and biological evaluation.

In this work the production of ⁶⁴Cu via the ⁶⁴Ni(p,n)⁶⁴Cu reaction with optimized conditions for low current irradiation is presented. Different target setups and cleaning steps for lowering metal contaminations in the product were applied. ⁶⁴Cu with high specific activities up to 1685 GBq/µmol were produced despite low overall activity ( ~ 4.2 GBq per run). The module processing leads to a highly reproducible, reliable product quality (< 1 µg Cu and < 7 µg Ni). Beside its diagnostic value ⁶⁴Cu may be of interest even for therapeutic purposes due to its decay characteristics.

Aim: Regional blood flow represents an important physiological parameter in experimental animals of various disease models. The ‘gold standard’ in large animals is to inject microspheres into the left ventricle using heart catheters; the number of microspheres trapped in the tissue capillaries is directly proportional to blood flow. Injection of radioactive microspheres directly into the left ventricle allows easy assessment of relative blood flow using imaging technologies. Absolute blood flow quantification will be also possible after additional arterial catheterization (required for reference blood sampling). However, up to now this technique has been rarely used in small rodents. In this pilot study we evaluated the technique in small rodents (mouse, rats) using radioactive microspheres.

Methods: Human serum albumin microspheres (20 µm diameter) were modified with NOTA. NOTA-microspheres were radiolabeled with Ga-68, Cu-64 or with F-18-fluoro-benzyol-succinimide using non modified microspheres. The number of injected microspheres was varied between 50,000 and 500,000. The microspheres were directly injected into the left ventricle over a time period of 30 s in desflurane-anesthetized animals on a heating pad. The animals were sacrificed 60 s after the end of injection. Total body activity was measured using a dose calibrator followed by small animal PET scan. The PET images were coregistered with MRI or CT images for identification of the tissues of interest. Standard uptake values were calculated and used for determination of relative blood flow.

Results: Radiolabeling resulted in high radiochemical yields and purity. The microsphere distribution was derived from the radioactivity distribution in the organs. The microspheres were virtually completely trapped (>99%) in the capillary bed. The injection is the most critical step of the experimental procedure. The number of applied microspheres was the limiting factor for measurements in low flow areas, where the number of measured microspheres was below 400. The heart was not included because of potential injury of the coronary arteries. The highest perfusion was found in the kidneys and the cerebellum while the blood flow in the anesthetized animals was low in the cerebral cortex. In rats it was also possible to assess the high flow in the thyroid gland.

Conclusion: This pilot study shows that the microsphere technique allows imaging and assessment of relative organ blood flow. This work will be continued to enable absolute blood flow measurements as well.

First results obtained from electron beam annealed sequentially implanted Pb⁺ (29 keV) and Se ⁺ (25 keV) ions into a SiO₂ matrix are presented. Key results from Rutherford backscattering spectrometry and transmission electron microscopy investigations are: (1) Pb and Se atoms are found to bond in the SiO₂ matrix during implantation, forming into nanoclusters even prior to the annealing step, (2) Pb and Se atoms are both present in the sample after annealing at high temperature (T = 760 °C, t = 45 min) and form into PbSe nanoclusters of varying sizes within the implanted region, and (3) the broader concentration profile of implanted Se creates a number of secondary features throughout the SiO₂ film, including voids and hollow shell Se nanoclusters. A sequential ion implantation approach has several advantages: selected areas of nanocrystals can be formed for integrated circuits, the technique is compatible with present silicon processing technology, and the nanocrystals are embedded in an inert matrix - making them highly durable. In addition, a higher concentration of nanocrystals is possible than with conventional glass melt techniques.

RATIONALE: Acid-aspiration is recognized as a risk factor for subsequent development of acute lung injury or ARDS. Areas of aspiration induced injury matches regions of high pulmonary blood flow (PBF) in the early stage of acute lung injury, as we shown recently. The aim this project was to characterize the changes of spatial PBF distribution as a function of time after injury.
METHODS: The protocol was approved by the Animal Studies Committee of the Landesdirektion Dresden. Eleven anesthetized, spontaneous breathing male Wistar rats were scanned with a small animal CT scanner before and after injury. Positron emission tomography (PET) was carried out after aspiration-induced lung injury. Aspiration was achieved by installation of 0.1 HCl (0.4 ml/kg body weight) through a tracheostomy tube. Pulmonary blood flow (PBF) was calculated from the radioactivity distribution in the lungs of infused 68Ga-DOTA-human serum albumin microspheres ten minutes after injury in group 1 (n=6) and two hours after injury in group 2 (n=5). CT- and PET images were co-registered. Areas of injury, as identified from CT derived changes in density, were labeled with a spherical mask. Regions of interest were derived using a threshold (80% of maximum) within the masks. Identical masks were used for the contralateral lung as reference. PBF was calculated and compared as a fraction of injured and reference side with Wilcoxon matched-pairs signed rank test. The PBF-fraction after the different time points was compared between the groups by unpaired t test with Welch's correction. RESULTS: Data presented are median (interquartile range). CT images after injury showed areas of lung injury different in size and location within the groups. Fraction of PBF was higher in group 1 (1.34 (1.15-1.45)) compared to group 2 (0.9 (0.85-1.06); P=0.0014) shown in Figure 1. The difference between both groups was determined by a high PBF in injured lung regions compared to the contralateral reference side at 10 min after injury (P = 0.03), whereas at 120 min after aspiration, injured regions have shown similar PBF compared to the contralateral reference side (0.81).
CONCLUSION: Regional PBF is increased 10 minutes after acid aspiration in regions of lung injury. This effect disappears within two hours after injury in anesthetized rats. These PBF-changes may be important for early treatment strategies after acid aspiration.

Background: To evaluate the influence of different SUV-measurements and patient-specific corrections thereof on the positive predictive value (PPV) of FDG-PET in pediatric Hodgkin lymphoma (pHL) using SUV-based response assessment.
Methods: PET-datasets of 33 children [female, n = 13, male, n = 20; range of age, 8.0–17.8 (mean, 15.0) years; follow-up, 44.5–83.3 (mean 63.0) months] with HL were analyzed retrospectively. PET-scans were obtained baseline (PET1) and after two cycles of chemotherapy (PET2). Within the leading lesion maximal SUV (SUVmax) and mean SUVs were generated by using isocontur-thresholds for different volumes of interest: Absolute, SUV2.5; relative to SUVmax, SUVmean40% to SUVmean70%. Generated SUVs were adjusted to body weight (SUV) and corrected for body surface area (SUV_BSA), patient's blood glucose and a combination thereof. The decrease in SUV or respective derivates thereof between PET1 and PET2 (ΔSUV) was assessed for response prediction using receiver operating characteristics (ROC)-analysis.
Results: Three patients had recurrence of disease. ROC-analysis showed the most accurate differentiation of responders and non-responders for ΔSUVmax_BSA [AUC, 0.97; P = 0.0026; sensitivity, 100%; specificity, 93.3%; PPV, 60.0%; negative predictive value (NPV), 100%; accuracy, 93.3%]. However, comparable results were obtained for conventional ΔSUVmax-determination (AUC, 0.96; P = 0.0112; sensitivity, 100%; specificity, 90.0%; PPV, 50.0%; NPV, 100%; accuracy, 90.9%). Threshold-based approaches were less effective or technically not performable in all patients.
Conclusions: At early response assessment by FDG-PET, patient-specific correction of ΔSUVmax by BSA improves PPV without impairment of excellent NPV in pHL. However, it is not statistically superior to simple ΔSUVmax-analyses. Larger cohorts are needed to investigate this observation.

Background: To achieve an acceptable signal-to-noise ratio (SNR) in PET images, smoothing filters (SF) are usually employed during or after image reconstruction preventing utilisation of the full intrinsic resolution of the respective scanner. Quite generally Gaussian-shaped moving average filters (MAF) are used for this purpose. A potential alternative to MAF is the group of so-called bilateral filters (BF) which provide a combination of noise reduction and edge preservation thus minimising resolution deterioration of the images. We have investigated the performance of this filter type with respect to improvement of SNR, influence on spatial resolution and for derivation of SUV_max values in target structures of varying size.
Methods: Data of ten patients with head and neck cancer were evaluated. The patients had been investigated by routine whole body scans (ECAT EXACT HR⁺, Siemens, Erlangen). Tomographic images were reconstructed (OSEM 6i/16s) using a Gaussian filter (full width half maximum (FWHM): Γ₀ = 4 mm). Image data were then postprocessed with a Gaussian MAF (FWHM: Γ_M = 7 mm) and a Gaussian BF (spatial domain: Γ_S = 9 mm, intensity domain: Γ_I = 2.5 SUV), respectively. Images were assessed regarding SNR as well as spatial resolution. Thirty-four lesions (volumes of about 1-100 mL) were analysed with respect to their SUV_max values in the original as well as in the MAF and BF filtered images.
Results: With the chosen filter parameters both filters improved SNR approximately by a factor of two in comparison to the original data. Spatial resolution was significantly better in the BF-filtered images in comparison to MAF (MAF: 9.5 mm, BF: 6.8 mm). In MAF-filtered data, the SUV_max was lower by 24.1 ± 9.9% compared to the original data and showed a strong size dependency. In the BF-filtered data, the SUV_max was lower by 4.6 ± 3.7% and no size effects were observed.
Conclusion: Bilateral filtering allows to increase the SNR of PET image data while preserving spatial resolution and preventing smoothing-induced underestimation of SUV_max values in small lesions. Bilateral filtering seems a
promising and superior alternative to standard smoothing filters.

Aim: Evaluation of a dedicated software tool for automatic delineation of 3D regions of interest in oncological PET. Patients, methods: The applied procedure encompasses segmentation of user-specified subvolumes within the tomographic data set into separate 3D ROIs, automatic background determination, and local adaptive thresholding of the background corrected data. Background correction and adaptive thresholding are combined in an iterative algorithm. Nine experienced observers used this algorithm for automatic delineation of a total of 37 ROIs in 14 patients. Additionally, the observers delineated the same ROIs also manually (using a freely chosen threshold for each ROI) and the results of automatic and manual ROI delineation were compared.
Results: For the investigated 37 ROIs the manual delineation shows a strong interobserver variability of (26.8±6.3)% (range: 15% to 45%) while the corresponding value for automatic delineation is (1.1±1.0)% (range: <0.1% to 3.6%). The fractional deviation of the automatic volumes from the observer-averaged manual ones is (3.7±12.7)%. Conclusion: The evaluated software provides results in very good agreement with observer-averaged manual evaluations, facilitates and accelerates the volumetric evaluation, eliminates the problem of interobserver variability and appears to be a useful tool for volumetric evaluation of oncological PET in clinical routine.

Aim: Image fusion of anatomical and functional data is an established procedure in nuclear medicine. Whereas elastic image fusion is expected to alter the information of the transformed data, we assessed whether rigid transformations also change the information contained in the PET-data.
Methods: F-18-FDG-PET/CT (Biograph 16, Siemens Medical, Erlangen, Germany) data of 14 tumor patients with a total of 18 solid pulmonary lesions were included in this retrospective analysis. For coregistration, rigid fast (RF) and rigid slow (RS) transformation algorithms of the Fusion7d-software were employed (Fusion7d, Mirada Solutions Ltd./Siemens Medical, Erlangen, Germany). Original PET-images (voxel size: 0.417cm x 0.417cm x 0.5cm) were fused with the attenuation-corrected CT (LR, voxel size: 0.417cm x 0.417cm x 0.5cm) and diagnostic CT (HR, voxel size: 0.098cm x 0.098cm x 0.1cm).PET data were saved in the respective CT-geometry and CT-resolution. Segmentation of lesions was performed using a 3D ROI volume determination software with automatic background detection (Rover, ABX GmbH, Radeberg, Germany). SUVmax, SUVmean, volume and metabolic volumes (volume*SUVmax and volume*SUVmean) of the lesions were determined in the original and in the coregistered PET data and compared. SUVmax in original PET ranged from to 1.6-30.9 (mean±SD, 8.8±7.0). CT-segmented volumes ranged from 1-58 ml (mean±SD, 9.9±15 ml).
Results: The relative differences of volume between original data and rigid fast fused-data ranged from 2-45% (mean±SD, 19%±13%) for LR-coregistration and from 0-12% (mean±SD, 3%±3%) for HR-coregistration. Fusing data with the rigid slow algorithm resulted in relative volume differences ranging from 1-48% (mean±SD, 20%±18%) for LR-coregistration and from 0-14% (mean±SD, 4%±4%) for HR-coregistration. Analyzing relative differences of metabolic volume products (volume*SUVmax) between original data and rigid fast fused-data ranged from 0-33% (mean±SD, 12%±9%) for LR-coregistration and from 0-11% (mean±SD, 3%±3%) for HR-coregistration. After fusion with the rigid slow method differences of volume*SUVmax ranged from 0-41% (mean±SD, 13%±13%) for LR-coregistration and from 0-16% (mean±SD, 4%±5%).Conclusions:Transformation of PET data by rigid coregistration algorithms results in a redistribution of the respective voxel information in the new coordinate system. Volumetric analysis based on a source-to-background algorithm showed substantial differences between original and coregistered data, which may have a potential impact on e.g. PET-based planning of radiotherapy or the assessment of treatment response by measurement of metabolic burden in follow-up studies. This effect is dependent on the source data (CT) resolution. The extent of the observed effect on the data of modern high resolution PET-systems remains to be evaluated.

Objectives : As is well known, limited spatial resolution leads to partial volume effects and consequently to limited signal recovery. Determination of the true activity concentration of a target structure is thus compromised even at target sizes much larger than the reconstructed spatial resolution. This leads to serioussize-dependent underestimates of true signal intensity in hot spotimaging. For quantitative PET in general and in the context of therapy assessment in particular it is therefore mandatory to perform an adequate recovery correction (RC). The goal of our work was to
developand to validate a model-free RC for hot spot imaging.
Methods : The algorithm proceeds in two steps. Step 1: automatic estimation of the true object volume V with an automatic thresholdbased method and the corresponding total activity A within V. Step 2:automatic determination of the background corrected activity fractionB, which is measured outside the object due to the partial volume effect. The recovery coefficient is then given by R = A/(A+B). For validation, we used a cylindrical phantom with six sphere inserts(volume: 2.5 - 27
ml) and performed measurements at three different target/background levels. RC was computed using the analytical convolution of the object function with the best fitting Gaussianpoint spread function and then compared to the results of the model-free approach.
Results : For the investigated target/background contrasts the model-free approach yields RC values which agree very well with the known (computable) RC values for the spheres (mean deviation +/-5%). The model-free nature of the approach allows, however, direct application to real patient data where the exact target shape is not known and model-based RC would fail.
Conclusions : The described method provides an easy and essentially automated way of doing quantitative RC in oncological hot spotimaging. It works well for sufficiently high contrast (>5) and a homogeneous background. The limits of the method have to be investigated further.

The crystal and molecular structure of tert-butyl 4-(2-tert-butoxy-2-oxoethyl)-piperazine-1-carboxylate is reported. The title compound crystallizes from a petroleum ether/ethyl acetate mixture in the monoclinic space group P 21/c with four molecules in the unit cell. The unit cell parameters are: a = 8.4007(2) Å, b = 16.4716(4) Å, c = 12.4876(3) Å; β = 90.948(1)° and V = 1727.71(7) Å3. Bond lengths and angles of this piperazine-carboxylate are typical.

Two novel indazole derivatives protected with p-methoxybenzyl group were synthesized and characterized. The crystal and molecular structure of 2-(4-methoxybenzyl)-4-nitro-2H-indazole as one out of the two regioisomers is reported. The compound was obtained from a saturated petroleum ether/ethyl acetate mixture and crystallizes in the triclinic space group P`1. The unit cell parameters are: a = 6.8994(1) Å, b = 9.8052(2) Å, c = 11.1525(2) Å; α = 71.729(1)°, β = 79.436(1)°, γ = 74.349(1)° and V = 685.83(2) Å3. There are two independent molecules found in the asymmetric unit.

Germanium nanocrystals in silicondioxide were studied by atomic force microscopy (AFM) in order to reveal their size, density and distribution. The generation of the nanocrystals was accomplished by Ge+ ion implantation into a 100 nm silicondioxide layer and subsequent annealing at high temperatures in an inert atmosphere. Rutherford backscattering spectroscopy was applied in order to reveal the Ge distribution after implantation and annealing, and the formation of the nanocrystals was proven by transmission electron microscopy. The oxide layer was gradually etched in order to uncover the nanocrystals located at different depth positions within the SiO2 layer. Subsequently, the unveiled surfaces were examined by AFM in order to determine the size and density of the exposed nanocrystals. A correlation between the nanocrystal properties and the Ge implantation dose was corroborated.

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SPIRIT (Support of Public and Industrial Research using Ion beam Technology) is an Integrating Activities project integrating 11 leading European ion beam facilities. Transnational access is provided by supplying ions in an energy range from ~10 keV to 100 MeV for modification and analysis of solid surfaces, interfaces, thin films and nanostructured systems. The techniques cover materials, biomedical and environmental research and technology. Related R&D activities aim at the improvement of the experimental procedures and the installation of novel equipment. Numerous networking activities address both the interaction between the project partners and information and dissemination towards new users. The present contribution gives a short overview of the project structure and its activities, as well as its performance during the first two years.

For geochemical modeling of scenarios for the disposal of radioactive and (chemo)toxic waste, comprehensive and internally consistent thermodynamic data are required as well as sorption data for the surrounding host rocks. The use of different databases renders it difficult to compare results of geochemical modeling, due to incompleteness, inconsistencies, resticted ranges of variation (temperature, density, pressure), limitations in solution composition (ionic strength) and last but not least missing sorption data.
THEREDA (THErmodynamic REference DAtabase, www.thereda.de) – a cooperative project of leading research institutes in Germany – adresses these issues, providing full documentation, transparency of all data and a detailed quality assurance scheme [1,2].
THEREDA contains data for the three ion-ion interaction models: extendend Debye-Hückel, Specific Ion Interaction Theory, and Pitzer model. At present, two datasets has been released: the oceanic salt system (Na+, K+, Mg2+, Ca2+, Cl−, SO42−, H+, and H2O(l) within a temperature range of 273.15–523.15 K) and Am/Nd/Cm (Am(III), Nd(III), Cm(III), Na+, Mg2+, Ca2+, Cl−, H+, H2O(l) at 273.15 K). Tailored parameter files for various geochemical modeling codes are provided (PhreeqC, ChemApp, EQ3/6, Geochemist‘s Workbench). Documented benchmark calculations allow comparisons with other databases as well as between the different geochemical codes. All data, documentation and references are freely accessible via the projects homepage. Additionally, a user forum allows direct contact with the THEREDA members.
A holistic view of geochemical processes in the context of a safety analysis requires the inclusion of sorption calculations. A thermodynamically consistent treatment of these processes is only possible with surface complexation modeling (SCM). Respective data are already compiled in the RES³T database [3] (www.hzdr.de/res3t), providing competing entries for many systems. An integration into THEREDA thus not only requires a synchronisation of data structures but also a rigorous review process, leading to uniform recommended data sets for each sorbent-sorptive system. This data review process is already in progress.

[1] Altmaier et al. (2011), Report GRS-265, 63 p.
[2] Altmaier et al. (2008) ATW 53, 249–253.
[3] Brendler et al. (2003) J. Contam. Hydrol. 61, 281–291.

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The pump-induced transmission of graphene grown epitaxially on hexagonal SiC was studied in degenerate pump-probe experiments with photon energies in the range from 10 to 250 meV. Different relaxation times ranging from 0.5 ps to 300 ps were found. A strong increase of the relaxation time was observed when the photon energy was below the optical phonon energy (~200 meV). The experiments were complemented by microscopic modelling based on the graphene Bloch equations. This allowed us to identify the physical processes which are responsible for the carrier relaxation channels. We discuss the role of Auger-type processes, optical and acoustic phonons. The modelling, which is in good agreement with the experimental results, reveals that optical phonon scattering becomes significantly less efficient when the energy of the excitation photons is below the optical phonon energy. Surprisingly, however, scattering via optical phonons is still the predominant relaxation channel, even at lower energies. This is attributed to the presence of hot carriers, which can still fulfil energy conservation requirements [1].
For photon energies about twice the value of the Fermi energy Ef, which is about 10 meV for the quasi-intrinsic layers of the epitaxial graphene, an interesting effect is observed. As the photon energy is reduced below 2Ef, a transition from pump-induced transmission to pump-induced absorption occurs. While the induced transmission is associated with Pauli blocking of carriers which underwent interband transition, the induced absorption is caused by a change of the electron temperature due to intraband absorption.

In contrast to usual semiconductors in graphene the Landau levels (LL) are not equidistant. This provides the unique feature to investigate a single LL transition selectively. By applying magnetic fields of up to 7 T we could investigate three different transitions at a fixed wavelength of 16.5 µm via pump-probe measurements. By varying the magnetic field the photon energies got resonant to the different transitions. For the transition LL0(-1)->LL1(0) we could not only observe an increase of the pump-probe signal by a factor of 2.5 but also a decrease of the relaxation time from 20 ps to 5 ps. Interestingly, the reduced relaxation time is observed in a wider range of magnetic fields then the increase of the signal amplitude. Additionally the minimum of the relaxation time is shifted in respect to the maximum signal. For the transitions LL-1(-2)->LL2(1) and LL-2(-3)->LL3(2) we could only observe an slight increase of the pump-probe signal.

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We report on pump-probe measurements on quasi-neutral sheets of multilayer epitaxial graphene in magnetic fields. Using THz radiation, generated by the free electron laser, we directly probe the relaxation of Dirac fermions among well-resolved Landau levels (LLs). In contrast to conventional semiconductors, the Landau level spacing in graphene is not equidistant. Hence it is possible to investigate a single LL transition selectively. To this end we performed pump-probe measurements at a wavelength of 16.5 µm and applied a magnetic field of up to 7T. We varied the magnetic field for resonant measurements at different LL transitions. For the transitions LL-1(-2) -> LL2(1) and LL-2(-3) -> LL3(2) we could observe a slight increase of the pump-probe signal but no change in the relaxation time. For the transition LL-1(0) -> LL0(1) the pump-probe signal increased by a factor of 2.5 while the relaxation time decreased from 20 ps to 5 ps. These measurements were done with linear polarized radiation. To understand the decrease in the relaxation time additional measurements were carried out with circularly polarized radiation. The circularly polarized radiation enables to distinguish between the transition LL-1->LL0 and LL0->LL1. We performed the experiment in all combinations of left and right polarized radiation for the pump and probe beam. This revealed complex dynamics involving positive and negative signals. We suggest this to result from different relaxation channels including Auger processes.

wird nachgereicht

Armenian Precambrian basement rocks metamorphism P and T conditions are defined applying amphibole thermobarometer by means of 104 amphibole microprobe chemical analyses. Measurements have been done on 2 samples of ophiolitic metabasalte amphibolites of the Precambian Kasakh suite. The general trend of metamorphism has been defined in the average amphibolite and green-schist facies in ranges T=420-640°C and P=1,6-5,7 kbar of low geothermal gradient of 12°C/km. Prograde megnesiohornblende-tschermakite and retrograde megnesiohornblende-actinolite zonation has been revealed, and also relics of kaersutite have been found. Relics of kaersutite are preserved from primary magmatic hornblende of the initial basalts

Radiation pulse from a Self-Amplified Spontaneous Emission Free Electron Laser (SASE FEL) consists out of spikes (wavepackets). Energy loss in the electron beam (averaged over radiation wavelength) also exhibit spiky behavior on a typical scale of coherence length, and follows the radiation pulse envelope. These modulations of the electron beam energy are converted into large density (current) modulations on the same temporal scale with the help of a dispersion section, installed behind the x-ray undulator.
Powerful optical radiation is then generated with the help of a dedicated radiator (afterburner). We have recently demonstrated this principle at the Free Electron Laser in Hamburg (FLASH), and this paper present the first experimental results.

We report on both the global and micromagnetic properties of interlayer exchange coupled spin systems. Irradiation with Ne ions is employed to achieve a phase transition from antiferromagnetic to ferromagnetic coupling. For extended trilayer films a full quantitative analysis of the bilinear and biquadratic coupling constants is performed. With increasing ion fluence we observe a steady increase of the bilinear coupling constant at an almost negligible decrease in saturation magnetization. The mixing of atoms at the layer interfaces is identified as the origin for this. The effects of ion modification on the magnetic microstructure are studied for the model system of layered vortex pairs. X-ray microscopy is used to directly image the individual magnetization circulations in trilayer disks. The circulation configuration is found to be determined by the film coupling for both coupling orientations with a homogenous coupling angle throughout the structure. For the vortex cores however, micromagnetic simulations indicate that due to the significant local demagnetization fields the parallel states are always energetically preferred. Nevertheless antiparallel configurations are metastable, having their signature in reduced core diameters. Our study provides new results on spin structures in interlayer exchange coupled trilayers and it demonstrates a promising way to control the local interlayer coupling post-deposition.

Ion beam are used largely in industry for surface treatment and deposition. In the last years low energy ion beam irradiation have shown potential for surface nanostructuring, either by direct writing with a focused ion beam, or by self-organized pattern formation during broad beam irradiations. I will present current activities of the HZDR of surface nanostructuring with oin beams and the application of such patterns in magnetism and plasmonics.

Erosion of surfaces by ion beam sputtering leads frequently to the formation of periodic patterns, which show up as a ripple pattern under off-normal incidence and as hexagonally ordered dot patterns under normal or close to normal ion incidence.1 A first successful attempt to describe the formation of these patterns theoretically has been given by Bradley and Harper.2 In their model they assumed that ion sputtering is introducing a surface instability which is proportional to the surface curvature and will increase surface roughness. In addition, thermally activated surface self-diffusion has been considered as a smoothing mechanism. Finally, the interplay between these two competing mechanisms leads to a selection of a narrow range of surface modes which grow fastest under ion irradiation. This model has been translated into a linear continuum equation, now well known as the Bradley-Harper equation. The simplified partial differential equation already predicts successfully main experimental observations, like the change in ripple orientation when going to grazing incidence and isotropic patterns under normal incidence. However, it fails to explain the long time behaviour and the detailed dynamics of the pattern evolution.
Based on the Bradley-Harper model many extensions have been proposed since then. Some of them like the damped or undamped Kuramoto-Sivashinsky (KS) equation3 show a good qualitative agreement, however they still fail to predict several important experimental observations. In addition main improvements have been achieved by including the mass rearrangement on the surface induced by the ion impact.4
Recently, new models have been proposed for the description of pattern formation, which go beyond the KS equation. They introduce coupled fields, e.g. for the mobile species or the concentrations of the elements in compound materials.5 However, there is still a gap to be closed between the continuum equations and the microscopic model describing the collision cascade, the energy deposition into the surface, or the crater function induced by the ion impact. Here, theoretical approaches combining binary collision approximation for the ion irradiation and kinetic Monte Carlo simulations for the subsequent relaxation promise a detailed description of the mechanisms involved in the pattern formation process.
In this presentation the strengths and limitations of the existing continuum equations and extended models will be discussed and will be compared to experiments and kMC simulations.

The electrical transport properties of DNA molecules are important for future molecular electronics applications. We characterized the electrical conductance of single DNA fragments in ambient condition and in buffer solution using a Mechanically Controllable Break Junction (MCBJ) setup which allows us binding molecules between two gold electrodes. We analyzed the electrical conductance of double stranded DNA and G-quadruplex molecules. G-quadruplex molecules consist of four guanine bases arranged in the shape of a square and a cation in the center. The electrical characterization is done by investigating the I-V curves characteristics of the molecules in different conditions.

eingeladener Beitrag ohne Abstract

Due to their low solubility, tetravalent actinides, An(IV), are usually assumed to be immobile in natural waters. However, it is also well known that insoluble precipitation products can be mobile if they occur as colloids. For An(IV) oxyhydroxides this phenomenon has thoroughly been studied [1]. Here we describe the formation of a new type of An(IV) colloids [2].
Evidence is provided that uranium(IV) and Th(IV) can form silicate-containing colloids in near-neutral solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). These particles remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne An(IV) was observed which is a concentration significantly higher than the concentrations of truly dissolved or colloidally suspended waterborne An(IV) species hitherto reported for the near-neutral pH range. The prevailing size of the particles is below 20 nm. The higher the silicate concentration and the pH, the smaller (and obviously the more stable) are the particles that are formed (however, silicate at the concentrations tested does not form particles in the absence of the actinides). Electrostatic repulsion due to a negative zeta potential caused by the silicate stabilizes the nanoparticles. The mechanism of colloidal stabilization can be regarded as “sequestration” by silicate, a phenomenon well known from trivalent heavy metal ions such as iron(III) [3] or curium(III) [4], but never reported for tetravalent actinides so far. U-O-Si bonds, which increasingly replace the U-O-U bonds of the amorphous uranium(IV) oxyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids. The next-neighbor coordination of U(IV) in the U(IV)-silica colloids is comparable with that of coffinite, USiO4.
The assessment of actinide behavior in the aquatic environment should take the possible existence of An(IV)-silica colloids into consideration. Their occurrence might influence actinide migration in anoxic waters.

[1] Altmaier et al. (2004) Radiochim. Acta 92, 537-543. [2] Dreissig et al. (2011) Geochim. Cosmochim. Acta 75, 352-367. [3] Robinson et al. (1992) J. Am. Water Works Assn. 84, 77-82. [4] Panak et al. (2005) Radiochim. Acta 93, 133-139.

Methodology. Sorption on mineral surfaces of sediments is one important retardation process for radionuclides to be considered in long-term safety assessments for radioactive waste repositories. Previously, the Kd-concept with temporally constant values was applied to describe the radionuclide retardation in the far field of a repository.
In this study, pre-calculated distribution coefficients (Kds) based on surface complexation models (SCM) are implemented in the existing 3D transport program r3t [1]. The so-called smart Kd-values are calculated as a function of important environmental parameters to reflect changing geochemical conditions. Respective multi-dimensional Kd-matrices are generated and stored a-priori to any r³t run. The calculations follow a bottom-up approach, i.e. the sorption of an element on each single mineral phase contributes to the distribution coefficient for a sediment.
Results. As an exemplary proof-of-concept, the Gorleben site (a potential repository site in Germany) was selected. Figure 1 shows the 3D plot for the logKd-matrix of UO22+ in the upper aquifer (UAF) at the Gorleben site as a function of pH, [Ca], and [DIC] (logarithmic scale). These pre-calculated logKd-values vary between -6.8 and 0.75. Comparing to the temporally constant conservative logKd of -2.7 from [2], which was previously used in r³t for the retention of UO22+ in fresh water in the upper aquifer at the Gorleben site, the resulting mean logKd of -2.74 shows a good general agreement, but account now for geochemical variations.

Growth of thin films by physical vapour deposition and erosion of solid surfaces by ion beam sputtering have high relevance in the fields of micro- and nanotechnology. Therefore the theoretical modelling of the surface morphology and its evolution during growth and erosion has received considerable attention. Compared to atomistic models, continuum equations are able to cover a much larger spatial and temporal scale accessing the macroscopic scales at which nontrivial features of the morphological dynamics occur. This is especially relevant for surface erosion which can induce a linear instability of the surface, resulting in the formation of periodic nanoscale patterns.
In this chapter, the software package “Ripples and Dots” is presented which is designed for the numerical integration of continuum equations modelling the surface evolution during ion beam erosion in (2+1) dimensions. These equations are based on the Bradley-Harper (BH) model and often feature in addition to the linear instability also nonlinear and noise terms, e.g. the prominent Kuramoto-Sivashinsky (KS) equation. However, due to the similarity with continuum equations for interface growth the software package can be used as well for studying continuum equations describing thin film growth, like the well known Kadar-Parisi-Zhang (KPZ) equation, the Edwards-Wilkinson (EW) equation, and the linear molecular beam epitaxy (MBE) equation.
Numerical data obtained by integrating various continuum equations for surface erosion is presented and compared to analytical predictions and experimental observations. It is demonstrated that the evolution of the surface morphology observed in the numerical integrations is in good qualitative agreement with experimental results both for normal and oblique ion incidence. In addition, also the special cases of erosion at oblique ion incidence with simultaneous sample rotation and erosion with multiple ion beams are presented.

The radioactive isotope Selenium-79 is a long-lived fission product found in nuclear waste. Due to its long half live of 3.27 ∙ 105 years [1] it is expected to be one of the most contributing isotopes concerning safety assessments of nuclear waste underground repositories. The control of the mobility and bioavailability of selenium is therefore of great importance for a safe disposal of radioactive waste.
One major process controlling selenium mobility and bioavailability is the adsorption onto mineral surfaces of both the geological and engineered barrier.
The present study focuses on the impact of temperature on the sorption of selenate (SeO42-) onto anatase (TiO2). The sorption of selenate onto anatase at different temperatures (25°C – 60°C) was investigated both with batch experiments and ATR-FT-IR spectroscopy. In order to explain possible differences in sorption at higher temperatures, the surface of the anatase was investigated.

Introduction
Humic substances are ubiquitous in near-surface natural waters, and they are known to act as carriers for organic and inorganic contaminants [1, 2]. In order to assess the impact of such humic-bound mobilization, transport models are developed (see [3] for a review). As a prerequisite, reaction rates for adsorption and desorption are commonly assumed to be high enough to ensure a steady local equilibrium under flow conditions. For humic matter as a polydisperse system of highly charged colloids, however, it is unclear whether a dynamic adsorption equilibrium (i.e., a permanent run of adsorption and desorption at equal rates) actually exists. Low recoveries in column experiments with geological materials suggest a limited reversibility.

Experimental
Using kaolinite as an adsorbent, the kinetics of adsorption and desorption were studied for a humic acid (Aldrich) and a fulvic acid (isolated from bog water). Their radiolabeling with 14C (accomplished by azo coupling with [14C]aniline) allowed sensitive detection and enabled tracer exchange experiments at surface saturation, providing direct insight into the dynamics of the adsorption equilibria for the first time. In these studies, a negligible amount of radiolabeled humic or fulvic acid was contacted with equilibrated systems of kaolinite and non-labeled humic material at different durations ranging from 6 hours to 4 weeks.

Results
The equilibrium state of adsorption was attained within few hours for the fulvic acid, whereas the process took considerably longer for the humic acid (~ 2 days), possibly as a consequence of competition effects within the polydisperse system [4]. In desorption experiments, initiated by diluting the supernatant, not any release was observed within a time frame of 4 weeks, neither for the humic acid nor for the fulvic acid. In view of transport modeling, this finding is rather disturbing since the basic assumptions do not hold if adsorption is irreversible. Our tracer exchange experiments, however, revealed that labeled humic material is adsorbed even though it is confronted with a saturated surface. Consequently, an exchange must take place, indicating a reversible process, albeit an exchange time of ~ 4 weeks was required for both materials until the adsorption equilibrium was quantitatively represented by the tracer. Apparently, the competitive situation in its presence is a stronger driving force for desorption than is a concentration gradient. Models for humic-bound transport are thus applicable under comparable conditions.

[1] MacKay & Gschwend (2001) ES&T 35, 1320-1328. [2] Dearlove et al. (1991) Radiochim. Acta 52/53, 83-89. [3] Lippold & Lippmann-Pipke (2009) J. Contam. Hydrol. 109, 40-48. [4] Van de Weerd et al. (1999) ES&T 33, 1675-1681.

The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald NPP representing the first generation of Russian type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs represent different material conditions viz. irradiated, irradiated & annealed and irradiated, annealed and re-irradiated. The paper presents test results measured on the trepan taken from the forged base metal ring 0.3.1. located in the reactor core region of the Unit 4 RPV. This unit was shut down after 11 years of operation and represents the irradiated condition. The key part of the testing is focused on the determination of the reference temperature T0 following the ASTM test standard E1921-10. The T0 of 11 thickness locations from the inner to the outer RPV wall varies between 112°C and 130°C with a mean value of 121°C. These are very low values for WWER RPV steel irradiated with fluences between 5.4 to 1.2•1019n/cm2 (E>0.5 MeV) from the inner to the outer RPV wall.
The fracture toughness values at cleavage failure, KJc, measured on LS oriented pre-cracked and side-grooved Charpy size SE(B) specimens from defined thickness locations of the forged ring strongly scatter. More than allowed 2% of the specimen size adjusted KJc-1T values lie below the fracture toughness curve for 2% fracture probability. The application of modified MC based evaluation methods indicates the material as non-homogeneous. Because of very low KJc values the SINTAP step 3 evaluation gave a maximum T0SINTAP of -40°C. The multimodal MC evaluation of KJc values from all thickness locations gives a T0MM of -118°C and a standard deviation of 25 K. The course of the fracture toughness curves evaluated by multi modal approach also do not represent the measured KJc values since more than 2% lie below the fracture toughness curve for 2% fracture probability. The reason for the occurrence of very low KJc values is seen in intergranular planes detected on the fractured surfaces of the specimens.

The increasing age of European Nuclear Power Plants and envisaged extensions of reactor pressure vessel (RPV) lifetimes up to 80 years require the accurate prediction and management of RPV neutron irradiation embrittlement. LONGLIFE (“Treatment of long term irradiation embrittlement effects in RPV safety assessment”) is a collaborative project of the 7th Framework Programme of EURATOM. This project has been initiated as the next step forward towards obtaining an improved understanding of irradiation effects in RPV steels under conditions representative of long term operation (LTO) of RPVs. Phenomena which might become important at high neutron fluences (such as late-blooming effects and flux effects) must be considered in detail as part of the process of upgrading safety assessments and embrittlement surveillance procedures to underwrite the safety of LTO of RPVs. The work starts with the collection and evaluation of plant-specific information and data such as target neutron fluences for LTO and the chemical compositions of the materials. This includes a survey of available results of RPV materials data from decommissioned plants of validating surveillance data and studying specific irradiation effects relevant for LTO. Microstructural data are obtained from different techniques with the aim of assessing the adequacy of current dose-damage models with respect to their relevance to the mechanisms of irradiation damage associated with LTO of RPVs. Complementary mechanical tests are performed in order to address gaps in existing experimental data. Microstructural data pertaining to the evolution of irradiation damage are correlated with changes in mechanical properties, and the most important influencing factors will be identified. Surveillance guidelines for LTO of RPV base materials and welds will be developed as one of the principal outputs of the project. The scope of work and the project structure are outlined in the paper. Two LTO relevant phenomena – late blooming effect and flux effect – are discussed more detailed.

Numerical and experimental modelling of a VGF-type (VGF - Vertical Gradient Freeze) buoyant flow under the influence of both travelling and rotating magnetic fields (TMF and RMF, respectively) is presented. Low-temperature flow experiments were carried out using a GaInSn alloy as model fluid. Radial heating and cooling of the melt leading to a meridional double vortex flow like in typical VGF growth, was introduced using a double-walled melt container. The flow was found to be significantly influenced by the mutual interaction of buoyant and electromagnetically driven forces. With increasing axial temperature difference, the buoyant flow becomes more concentrated in the upper and lower part of the melt leaving an extended melt zone with low flow velocity around the mid-height. Furthermore, VGF-type buoyancy is found to stabilize TMF- and RMF-induced melt flows. Besides, the time evolution of the flow just above the stability threshold is studied. In the case of combined VGF-type/RMF flow complex fluctuation patterns are observed, which depends sensitively on the applied thermal field.

Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr precipitates in neutron irradiated Fe-9at%Cr and Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 1.5 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. For both alloys a saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC for the doses above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. CD modeling of Cr precipitates has been done with taking into account of deviation of this system from the ideal cluster gas. A specific surface tension of about 0.17 J/m2 between the alpha matrix and the Cr-rich alpha' precipitate and the rate at which Cr monomers are absorbed about 7.94 m-1 were found as best fit values for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS. Taking into account the formation and migration of Fe-Cr interstitial as additional link between the CD master equations for the self-defects and the CD master equations for the Cr precipitates, may lead to improve CD results for irradiated Fe-9at%Cr alloy. The assumption on the constant composition of Fe-Cr precipitates under neutron irradiation has been checked by means of new master equation of CD respect of the distribution function of clusters not only on size but also on composition. The slight dependence of the composition on the size of Fe-Cr precipitates is found.

For the safety assessment of high-level nuclear waste repositories in deep geologic formations, the understanding of actinide migration behaviour is one of the most important issues. In recent decades, the solution chemistry, e.g. hydrolysis [1], complexation with inorganic ligands [1], but also the interactions of the actinides at interfaces with the geo- and biosphere have been intensely investigated [2]. However, because of the experimental difficulties, only few studies have been performed at temperatures outside the range 20 – 30°C which hampers the prediction of actinide reactive transport in the environment of heat generating high-level nuclear waste repositories.
The speciation of (radioactive) metal ions in solution will be affected by the thermal conditions, since the properties of water, e.g. density, dielectric constant, viscosity, ion product, are altered with temperature and pressure [3,4].
The formation and distribution of U(VI) hydrolysis species is predicted to depend strongly on the temperature. In particular the stability of U(VI) polynuclear hydroxo complexes, which are dominant species at 25°C may change. According to experimental studies of other metal ions, namely Al(III) and La(III), the nuclearity of polynuclear complexes decreases upon increasing temperature [5,6]. At 25°C several spectroscopic techniques, namely UV-vis, TRLFS, EXAFS and vibrational spectroscopy have been applied for identification and structural characterization of U(VI) hydroxo species [7-10]. At elevated temperatures, TRLFS was used for the determination of luminescent characteristics of single hydroxo species as a function of the temperature [11,12]. But, approaches to examine alterations in the thermodynamic data itself are rare.
In this study, we investigate the U(VI) hydrolysis reactions up to 60°C using a multi-methodical approach by application of TRLFS and ATR FT-IR spectroscopy. The spectral data is compared to computed speciation patterns based on state-of-the-art thermodynamic models.

1.Guillaumont, R. et al., Update on the chemical thermodynamics of uranium, neptunium, plutonium, americium and technetium. Chemical Thermodynamics Vol. 5, OECD Nuclear Energy Agency, Elsevier (2003).
2.Brendler, V. et al., RES3T-Rossendorf expert system for surface and sorption thermodynamics, Journal of Contaminant Hydrology 281-291 (2003).
3.Marshall, W.L. et al., Io product of water substance, 0 - 1000°C, 1-10,000 bars - New international formulation and its background, Journal of Physical and Chemical Reference Data 2, 295-304 (1981).
4.Fernandez, D.P. et al., A formulation for the static permittivity of water and steam at temperatures from 238 K to 873 K at pressures up to 1200 MPa, including derivatives and Debye-Huckel coefficients, Journal of Physical and Chemical Reference Data 4, 1125-1166 (1997).
5.Mesmer, R.E. et al., Acidity measurements at elevated temperatures. 5. Aluminum ion hydrolysis, Inorg. Chem. 10, 2290-2296 (1971).
6.Ciavatta, L. et al., The hydrolysis of the La(II) ion in aqueous perchlorate solution at 60°C, Polyhedron 6, 1283-1290 (1987).
7.Meinrath, G., Uranium(VI) speciation by spectroscopy, J. Radioanal. Nucl. Chem. 1-2, 119-126 (1997).
8.Moulin, C. et al., Time-resolved laser-induced fluorescence as a unique tool for low-level uranium speciation, Appl. Spectrosc. 4, 528-535 (1998).
9.Müller, K. et al., Aqueous uranium(VI) hydrolysis species characterized by attenuated total reflection Fourier-transform infrared spectroscopy, Inorg. Chem. 21, 10127-10134 (2008).
10.Tsushima, S. et al., Stoichiometry and structure of uranyl(VI) hydroxo dimer and trimer complexes in aqueous solution, Inorg. Chem. 25, 10819-10826 (2007).
11.Eliet, V. et al., Time-resolved laser-induced fluorescence of uranium(VI) hydroxo-complexes at different temperatures, Appl. Spectrosc. 1, 99-105 (2000).

Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr precipitates in neutron irradiated Fe-9at%Cr and Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 1.5 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. For both alloys a saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. CD modeling of Cr precipitates has been done with taking into account of deviation of this system from the ideal cluster gas. A specific surface tension of about 0.17 J/m2 between the alpha matrix and the Cr-rich alpha' precipitate and the rate at which Cr monomers are absorbed about 7.94 m-1 were found as best fit values for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS.

U1-yAmyO2-x blankets are promising fuels for the transmutation of Minor Actinides (MA) in Fast Neutron Reactors. The fabrication of dense U1-yAmyO2-x pellet is challenging due to the high oxygen potential of the AmO2-x. As a consequence, a thermodynamical modelling is currently developed to determine optimum sintering conditions for given O/M ratios and MA content. Due to the lack of experimental data in the U-Am-O system [1] to refine the modelling, an experimental determination of the O/M ratio is mandatory as also its eventual consequences on the homogeneity of the solid solution. The present work focuses on the XAS characterization of U1-yAmyO2-x obtained by a conventional powder metallurgy process [2] for different sintering conditions and Am contents (10, 15, 20%). Thanks to XANES measurements, relative content of different U and Am oxidation states (+III, +IV, +V) have been obtained giving access to an experimental determination of O/M ratio as a function oxygen potential fixed during sintering. It was shown that the Am oxidation state remains unchanged at +III while there is a U(IV)/U(V) mixed valence depending on the oxygen potential. As expected, the calculated O/M ratio increase with the oxygen potential is only supported by a partial oxidation of uranium cations to U(+V). EXAFS data collected at Am and U edges showed, as suggested by laboratory XRD measurements, that a solid solution at molecular scale is obtained for all the Am content. From the calculated molar fraction of U4+, U5+ and Am3+ this solid solution can be written as U4+(1-Ay)(1-y)U5+Ay(1-y)Am3+O2-x where A is a constant.

[1] W. Bartscher and C. Sari, J. of Nuc. Mat., 118, 220-223(1983).
[2] D. Prieur and al, Powd. Tech., (2010).

Clay minerals which are components of potential host rock formations for nuclear waste repositories can contain small organic molecules like formate, citrate or lactate. Such small organic molecules can like the ubiquitous humic acids influence the migration behavior of radionuclides. Different substituted benzoic acids can mimic the main functionalities and are often used as model compounds for humic substances.
The understanding of the complex behavior of radionuclides with such natural organic matter and the thermodynamic quantification of the interaction especially at elevated temperatures is of great importance to simulate and predict their migration behavior in the environment, particularly in the near field of nuclear waste disposals where higher temperatures are prevailing.
We present the investigation of the complex behavior of Am(III) and Eu(III) with lactate and salicylate at ambient and elevated temperatures with time-resolved laser-induced fluorescence spectroscopy (TRLFS) and the resulting thermodynamic data (reaction enthalpy, reaction entropy). Whereas the complexation with lactate is for both cations nearly temperature independent, is the complexation with salicylate clearly an endothermic reaction.

Understanding the irradiation behaviour of binary Fe-Cr alloys is basic for the optimization of ferritic/martensitic chromium steels for future applications under conditions of high neutron exposures. In this work self-ion irradiation with the ion beam scanned over the sample was used in order to simulate neutron damage in Fe-12.5at%Cr. The material irradiated at 300°C up to a damage level of 1 dpa was exposed to isochronal annealing treatments in the range from 300 to 550°C and the indentation hardness was measured as a function of annealing temperature. We have found the presence of two recovery steps. The first one takes place at 300°C, i.e. at irradiation temperature, and gives rise to a 45% recovery of the irradiation-induced hardness increase. The second step occurs in the range from 400 to 550°C and gives rise to full recovery. The findings are discussed in terms of the dissolution of hardening features, such as dislocation loops and ’-phase particles. In addition, rate theoretical considerations were used to investigate possible flux effects caused by the pulsed irradiation experienced by the material due to the scanning ion beam. It was found, that no significant additional flux effects arise from the pulsing.

Self-organization of regular surface pattern under ion beam erosion was described in detail by Navez in 1962. Several years later in 1986 Bradley and Harper (BH) published the first self-consistent theory on this phenomenon based on the competition of surface roughening described by Sigmund’s sputter theory and surface smoothing by Mullins-Herring diffusion. Many papers that followed BH theory introduced other processes responsible for the surface patterning e.g. viscous flow, redeposition, phase separation, preferential sputtering, etc. The present understanding is still not sufficient to specify the dominant driving forces responsible for self-organization. 3D atomistic simulations can improve the understanding by reproducing the pattern formation with the detailed microscopic description of the driving forces. 2D simulations published so far can contribute to this understanding only partially.

A novel program package for 3D atomistic simulations called trider (TRansport of Ions in matter with DEfect Relaxation), which unifies full collision cascade simulation with atomistic relaxation processes, has been developed. The collision cascades are provided by simulations based on the Binary Collision Approximation, and the relaxation processes are simulated with the 3D lattice kinetic Monte-Carlo method. This allows, without any phenomenological model, a full 3D atomistic description on experimental spatiotemporal scales. Recently discussed new mechanisms of surface patterning like ballistic mass drift or the dependence of the local morphology on sputtering yield are inherently included in our atomistic approach.

The atomistic 3D simulations do not depend so much on experimental assumptions like reported 2D simulations or continuum theories. The 3D computer experiments can even be considered as ’cleanest’ possible experiments for checking continuum theories. This work aims mainly at the methodology of a novel atomistic approach, showing that: (i) In general, sputtering is not the dominant driving force responsible for the ripple formation. Processes like bulk and surface defect kinetics dominate the surface morphology evolution. Only at grazing incidence the sputtering has been found to be a direct cause of the ripple formation. Bradley and Harper theory fails in explaining the ripple dynamics because it is based on the second-order-effect ‘sputtering’. However, taking into account the new mechanisms, a ‘Bradley-Harper equation’ with redefined parameters can be derived, which describes pattern formation satisfactorily. (ii) Kinetics of (bulk) defects has been revealed as the dominating driving force of pattern formation. Constantly created defects within the collision cascade, are responsible for local surface topography fluctuation and cause surface mass currents. The mass currents smooth the surface at normal and close to normal ion incidence angles, while ripples appear first at θ ≥ 40°.

The evolution of bimetallic interfaces under ion irradiation is another application of trider described in this thesis. The collisional mixing is in competition with diffusion and phase separation. The irradiation with He+ ions is studied for two extreme cases of bimetals: (i) Irradiation of interfaces formed by immiscible elements, here Al and Pb. Ballistic interface mixing is accompanied by phase separation. Al and Pb nanoclusters show a self-ordering (banding) parallel to the interface. (ii) Irradiation of interfaces by intermetallics forming species, here Pt and Co. Well-ordered layers of phases of intermetallics appear in the sequence Pt/Pt3Co/PtCo/PtCo3/Co. The trider program package has been proven to be an appropriate technique providing a complete picture of mixing mechanisms.

In 1992, strainers on the suction side of the ECCS pumps in Barsebäck NPP Unit 2 became partially clogged with mineral wool after a safety valve opened because steam impinged on the thermally-insulated equipment and released mineral wool. This event pointed out that strainer clogging in the course of a loss-of-coolant accident is an issue and induced many investigations to understand and prevent strainer clogging effects.

Modifications of the insulation material, the strainer area and mesh size were carried out in most of the German NPPs. Moreover, back flushing procedures to remove the mineral wool from the strainers and differential pressure measurement were implemented to assure the performance of emergency core cooling during the containment sump recirculation mode.

Nevertheless, it cannot be completely ruled out, that a limited amount of the smaller fractions of insulation material could be transported into the RPV. During a postulated cold leg LOCA with hot leg ECC injection, the fibres enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might affect the ECC flow into the core and could result in degradation of core cooling.

It was the aim of the numerical simulations presented to study where and how many mineral wool fibers are deposited at the upper spacer grid. The 3D, time dependent, multi-phase flow problem was modelled by applying the CFD code ANSYS CFX.

The spacer grids were modeled as a strainer, which completely retains all the insulation material that reaches the uppermost spacer level. There, the accumulation of the insulation material gives rise to the formation of a compressible fibrous layer, the permeability of which to the coolant flow is calculated in terms of the local amount of deposited material and the local value of the superficial liquid velocity.

Before the switch over of the ECC injection from the flooding mode to the sump mode, the coolant circulates in an inner convection loop in the core extending from the lower plenum to the upper plenum. The CFD simulations have shown that after starting the sump mode, the ECC water injected through the hot legs flows down into the core via so-called "brake through channels" located in the outer core region where the downward leg of the convection role had established. The hotter, lighter coolant rises in the center of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the break through zones. This means that the fibres are not uniformly deposited over the core cross section.

When the inner recirculation stops later in the transient, insulation material can also be collected in other regions of the core cross section at the level of the upper spacer grids. Nevertheless, with a total of 2.7 kg fiber material deposited at the uppermost spacer level, the pressure drop over the fiber cake is not higher than 8 kPa and all the ECC water could still enter the core. The CFD calculation does not yet include steam production in the core and also does not include re-suspension of the insulation material during reverse flow. This will certainly further improve the coolability of the core.

We show that the emergence of different surface patterns (ripples, dots) can be well understood by a suitable mapping onto the simplest nonequilibrium lattice gases and cellular automata. Using this efficient approach difficult, unanswered questions of surface growth and its scaling can be studied. The mapping onto binary variables facilitates effective simulations and enables one to consider very large system sizes. We have confirmed that the fundamental Kardar–Parisi–Zhang (KPZ) universality class is stable against a competing roughening diffusion, while a strong smoothing diffusion leads to logarithmic growth, a mean-field type behavior in two dimensions. The model can also describe anisotropic surface diffusion processes effectively. By analyzing the time-dependent structure factor we give numerical estimates for the wavelength coarsening behavior.

Ferritic/martensitic high-chromium steels are leading candidates for fission and fusion reactor components. Oxide dispersion strengthening is an effective way to improve properties related to thermal and irradiation-induced creep and to extend their elevated temperature applications. An extensive experimental study focusing on the microstructural characterization of oxide-dispersion strengthened Fe-9wt%Cr model alloys is reported. Several material variants were produced by means of high-energy milling of elemental powders of Fe, Cr and commercial yttria powders. Consolidation was based on spark plasma sintering. Special emphasis is placed on the characterization of the nano-particles using transmission electron microscopy, small-angle neutron scattering and atom probe tomography. The microstructure of the investigated alloys and the role of the process parameters are discussed. Implications for the reliability of the applied characterization techniques are also highlighted.

Artificial biomaterials play an important role in bioengineering, e.g. in regenerative medicine, biosensing, and orthopedics. The success of orthopedic implants depends on early bone formation and strong binding between bone and implant. The ability of osteogenic cells to adhere, proliferate, and differentiate on the implant surface is thus crucial for the formation of new bone tissue and the subsequent osseointegration of the implant.
Bone is a hierarchically composed biomaterial exhibiting topographical features such as fiber networks, interconnecting pores, and mineral crystallites with dimensions ranging from the macro to the nanoscale [1]. Micro and nanoscale surface topography thus has a strong influence on the proliferation, morphology, and differentiation of various cell types [2]. Therefore, the topographical design of implant surfaces is a promising route toward novel and improved medical implants [1].
Recently, it was demonstrated that even topographical features with a height below 10 nm can affect the adhesion and proliferation of mesenchymal stem cells (MSCs) [3]. However, only few techniques provide reliable control of the nanoscale surface topography over macroscopic areas. Therefore, in this work, we investigate the response of MSCs to well-defined nanorippled surfaces fabricated by ion beam sputtering which enables a precise tuning of the pattern dimensions by adjusting the ion energy [4]. The periodicity and height of the patterns range from 45 to 630 nm and from 3 nm to 70 nm, respectively. A strong influence of the ripple dimensions on MSC proliferation and morphology is observed.
[1] Stevens and George, Science, 310, 1135 (2005).
[2] Lord, Foss, and Besenbacher, Nano Today, 5, 66 (2010).
[3] Dolatshahi-Pirouz et al., ACS Nano, 4, 2874 (2010).
[4] Fassbender et al., New J. Phy., 11, 125002 (2009).

The search for the dominating driving force for surface pattern formation under ion irradiation is performed by atomistic 3D computer simulations taking into account the full ion-induced collision cascades as well as the defect relaxation kinetics. For this aim a novel program package called TRIDER (TRansport of Ions in matter with DEfect Relaxation), which unifies full collision cascade simulation with the calculation of atomistic relaxation processes, has been developed. The collision cascades are provided by simulations based on the Binary Collision Approximation, and the relaxation processes are simulated with the 3D lattice kinetic Monte-Carlo method. This allows, without any phenomenological model, a full 3D atomistic description on experimental spatiotemporal scales. The dependence of the local morphology on sputtering yield and recently discussed new mechanism contributing to surface patterning like ballistic mass drift are inherently included in our atomistic approach.
Compared to 2D simulations based on the Solid-On-Solid (SOS) approach or continuum theories, the presented 3D simulations include the contribution of ion-induced subsurface processes to pattern formation, e.g. bulk interstitial and vacancy recombination at the surface. In order to reveal the dominating driving force for pattern formation, collision cascade simulations have been performed for two artificial cases: (i) simulations where sputtering has been suppresses artificially, (ii) simulations where only sputter-induced vacancy creation is taken into account (the original idea for the formulation of the Bradley-Harper equation). In this connection, for checking continuum theories, the 3D computer experiments can be considered as ‘cleanest’ possible experiments.
The computer simulations predict that sputtering is not the dominant driving force of pattern formation. Processes like bulk and surface defect kinetics dominate the surface morphology evolution. Only at grazing incidence the sputtering has been found to dominate the ripple formation. Surface mass currents originating from bulk defect recombination at the surface cause smoothing at ion impact angles <45°.

Despite of intense studies in recent years, atomistic understanding of surface evolution during ion irradiation is still under discussion. Continuum models, like the Bradley and Harper theory, cannot explain microscopic processes during ion irradiation. So far, atomistic simulations could not describe pattern dynamics on spatiotemporal scales of experiments.
We present a novel program package that unifies the simulation of collision cascades with kinetic Monte-Carlo simulations. The 3D atom relocations were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of energetically unstable atomic configurations as well as diffusive processes were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code. Our studies show that: (i) bulk defects continuously created within the collision cascade are responsible for local surface topography fluctuations and induce surface mass currents. These currents smooth the surface from normal incidence up to 𝜃 = 40°, whereas at 𝜃 > 40° ripple
patterns appear; (ii) sputtering is not the dominant driving force for the ripple formation at non-grazing incidence angles. Surface patterning is caused by processes like bulk and surface defect migration, recombination, bulk and surface diffusion and ion induced diffusion.

XAS-based studies of the interaction of selenite with FeS2 and FeS at circum-neutral pH have shown that selenite is reduced to solid state zero-valent Se and FeSex, respectively [1-4]. While these results were initially unexpected, the occurrence of dissolved, low oxidation state selenium species in presence of insoluble elemental Se, resulting from selenite reduction in pyrite containing clay systems, was astonishing. In addition, several authors encountered an identical Se phase solid phase in presence of pyrite, but none of them has been able to relate this phase to a specific mineral.
Correlating selenium redox chemistry with sulphide mineral oxidation pathways allowed to relate these observations to the different oxidation behaviour observed between acid-soluble and acid-insoluble metal sulphides [5].
Acid insoluble metal sulphides such as pyrite, molybdenite or tungstenite exhibit oxidative dissolution only. Upon six consequent one-electron oxidation steps, a thiosulphate anion is liberated (thiosulphate pathway). Acid soluble metal sulphides (troilite, mackinawite, sphalerite, etc.) can exhibit both non-oxidative dissolution, hence liberating sulphide species (H2S, HS-,S2-), and oxidative dissolution in presence of FeIII with the release of sulphide cations (e.g. H2S+), that spontaneously dimerize into disulphide species which can further react to form polysulphide (polysulphide pathway) and finally elemental sulphur.
While the end products resulting from Se(IV) reduction by acid-soluble iron sulphur minerals are fairly well known, both the solid and liquid phase products from the interaction of SeO32- with pyrite are poorly characterized. Although the solid phase reaction product in could not yet be assigned to a specific phase, it was clearly identified as a Se0 compound and trigonal (grey) selenium could be excluded as a canditate species.[4]
The presence of an unexpectedly high concentration of reduced, dissolved species in presence of pyrite, induced the formulation of a new pyrite-based reduction mechanism. Based on this mechanism, hypothesis was put forward about the identity of the unknown dissolved species. In addition, the new mechanism allows explaining all current experimental observations, more specifically the presence of this currently non-identified dissolved species and the unexpected relation between Se(IV) reduction and pH.[6]

[1] Breynaert, E., et al. (2008) ES&T. 42(10): 3595-3601.
[2] Scheinost, A.C. and Charlet, L. (2008) ES&T. 42(6): 1984-1989.
[3] Scheinost, A.C., et al. (2008) J. Contam. Hydrol. 102(3-4): 228-245.
[4] Breynaert, E., et al. (2010) ES&T. 44(17): 6649-6655.
[5] Rohwerder, T. and Sand, W.(2007) in Microbial Processing of Metal Sulfides 35-58.
[6] Kang, M., et al. (2011) ES&T. 45: 2704-2710.

The oxalic conversion of plutonium into oxide is one of the most important steps of the present fuel cycle dealing with the recycling of plutonium contained in the used fuel. This operation, which occurs at the end of the PUREX process, includes two steps, oxalic precipitation followed by calcination in air, and permits to elaborate one of the main starting materials for the MOX fuel fabrication. Coordination chemistry of plutonium with oxalic acid is rich and several plutonium oxalate hydrates, the quite well-known PuIV(C2O4)2.6H2O1 and PuIII2(C2O4)3.10H2O2 and the other novel structures described here, can lead to PuO2. Considering the morphology of the plutonium oxalate particles, it is interesting to notice that there is a strong correlation between the shape of these particles and the crystal structure of the plutonium oxalate.

Oxide minerals or oxides comprise the oxides, hydroxides, oxyhydroxides, and hydrated oxides of Fe, Mn, Al, Si, and Ti. They commonly occur in soils, particularly those in advanced stages of weathering where they can sometimes account for as much as 50% of the total soil mass. In the discussion to follow, a polyhedral approach will be used to introduce the mineral species and highlight their major differences and similarities (Figure 22.1). For additional structural details, the reader is referred to the literature cited. Thereafter, their occurrence and formation in soils and their influence on soil properties will be discussed, concluding with the major techniques for identifying these minerals in soils.

No abstract available.

Hexagonally ordered nanohole patterns were produced on Ge(100) surfaces by focused Ga+ ion beam and by broad Ga+ ion beam irradiations with 5 keV energy under normal incidence. Identical patterns were obtained by irradiations with a scanning focussed ion beam under dierent irradiation conditions and with a broad Ga+ beam without scanning and ve orders of magnitude smaller ion flux. Thus we could demonstrate that nanohole pattern formation is independent of ion flux over several orders of magnitude and scanning of a FIB under appropriate conditions is identical to broad ion beam irradiation.

es hat kein Abstract vorgelegen!

Therapeutic irradiation with ions and protons is superior to a treatment with gammas with respect to tumour conformity of dose and damage of normal tissue. On the other hand, mispositioning of the patient or density changes in the treated volume may easily compromise the success of treatment.
For this reason, non-invasive, in-situ dose verification is necessary. The only clinically proven method up to now is Positron Emission Tomography [Eng04]. This method does not allow direct dose quantification due to limited angle artefacts and washout in the patient. Another promising approach is in-beam SPECT: the detection of prompt gamma-rays following nuclear interaction between the ions and the atoms of the penetrated tissue. Detection systems based on Compton-scattering and pair-conversion are now under investigation. So far, Compton-cameras have been used for diagnostic imaging in nuclear medicine and astronomy. In telescopes also pair-creation cameras are established [Zog04]. In contrast to this, in-beam dose verification systems have to manage the specific energy range and low count rates due to the patient dose.

A prototype of a Compton-camera is under construction at OncoRay [Kor10, Fie11, Kor11]. It consists of a scatter layer made from CZT and an absorption layer (LSO).
From the energy deposited in the detector planes a cone surface of all possible directions of the incident photon can be reconstructed [Sch11]. The expected energy distribution of the prompt gammas is calculated by means of simulations based on treatment plan data [Fie11].
To optimize the setup simulations are required. Therefore, the Monte-Carlo framework GEANT4 is used for:

(1) Analysis of the efficiency in dependence of the geometry;
(2) Study of background caused by backscattered photons and other secondary particles;
(3) Development of filters for event selection;
(4) Study parameters influencing the spatial resolution of the reconstructed image (multiple Compton-scattering inside a detector layer, escape of energy, intrinsic radioactivity of the detector material, Doppler-broadening);
(5) Creation of test data sets as input for the reconstruction.

For photon energies above 7 MeV the pair production is the dominant electromagnetic process in CZT. To use these events the Compton-camera might be combined with a pair-conversion camera by adding thin silicon layers in between to track the path of the electron and the positron produced during pair conversion. Exploiting this information the direction of the incident photon can be deduced.
Unfortunately, the angular resolution is heavily degraded especially for photons with rather low incident energies by small-angle scattering of the secondary particles and by the recoil of the nuclei when a pair production takes place [Gol11]. Both effects were studied whereas the latter is not included in the GEANT4 code version 9.3. This simulation serves as basis for the development of an iterative reconstruction algorithm dedicated to in-beam SPECT with a pair production camera. Apart from the analysis of efficiency, angular resolution and noise, the combination of a pair production and a Compton-camera is a challenging task.

Results on simulations for optimizing the setup and the refinement of the reconstruction algorithm for a clinical dose verification system will be presented.

[Eng04] W. Enghardt et al., Nucl. Instr. and Meth. A 525 (2004)
[Fie11] F. Fiedler et al., Nucl. Sci. Symp. IEEE (2011), accepted
[Gol11] C. Golnik et al., Nucl. Sci. Symp. IEEE (2011), accepted
[Kor10] T. Kormoll et al., Nucl. Instr. and Meth. A (2010)
[Kor11] T. Kormoll et al., Nucl. Sci. Symp. IEEE (2011), accepted
[Ric10] M.-H. Richard et al., IEEE Transactions on Nuclear Science (2010)
[Sch11] S. Schöne et al., Proc. Fully 3D Meeting (2011)
[Zog04] A. Zoglauer et al., Nucl. Sci. Symp. Conf. Rec. IEEE (2004)

Ubiquitous Pseudomonads have great potential to influence the speciation and mobility of actinides in the environment. This study explores the unknown interaction between curium(III) and cell-suspensions of Pseudomonas fluorescens (CCUG 32456) isolated from the Äspö site, Sweden.
The interaction between curium(III) and P. fluorescens cells was studied at trace curium(III) concentrations (0.3 µM) using time-resolved laser-induced fluorescence spectroscopy. Extraction studies have shown that the biosorption of curium(III) is a reversible process. Two Cm3+-P. fluorescens (CCUG 32456) species could be identified, R-O-PO3H-Cm2+ and R-COO-Cm2+, having emission maxima at 599.6 and 601.9 nm, respectively. The corresponding surface complexation constants were determined to be log β111 = 12.7 ± 0.6 and log β110 = 6.1 ± 0.5, respectively.

Activities of nuclides produced by neutron irradiation of reactor-pressure-vessel (RPV) steel are used to validate respective fluence calculations. Niobium, nickel and technetium isotopes from RPV trepans of the decommissioned NPP Greifswald (VVER-440) have been analyzed. The activities were determined by TRAMO (Monte-Carlo) fluence calculations,,newly applying 640 neutron-energy groups and ENDF/B7 data. Compared to former results, up to 20% higher fluences have been computed, leading to somewhat better agreement of measurement and calculation, particularly in case of Tc-99.

Based on density functional theory band-structure calculations, quantum Monte Carlo simulations, and highfield magnetization measurements, we address the microscopic magnetic model of BaAg₂Cu[VO₄]₂ that was recently proposed as a spin- 1/2 anisotropic triangular lattice system. We show that the actual physics of this compound is determined by a peculiar superposition of ferromagnetic and antiferromagnetic uniform spin chains with nearest-neighbor exchange couplings of J ⁽¹⁾ _a ~ −19 K and J ⁽²⁾ _a ~ 9.5 K, respectively. The two chains featuring different types of the magnetic exchange perfectly mimic the specific heat of a triangular spin lattice, while leaving a clear imprint on the magnetization curve that is incompatible with the triangular-lattice model. Both ferromagnetic and antiferromagnetic spin chains run along the crystallographic a direction, and slightly differ in the mutual arrangement of the magnetic CuO₄ plaquettes and nonmagnetic VO₄ tetrahedra. These subtle structural details are, therefore, crucial for the ferromagnetic or antiferromagnetic nature of the exchange couplings, and put forward the importance of comprehensive microscopic modeling for a proper understanding of quantum spin systems in transition-metal compounds.