Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

For the modelling of different chemical aspects of a nuclear waste repository in salt rock, the Pitzer formalism is necessary. Therefore, a comprehensive database with the relevant species reaction constants and associated ion-ion interaction parameters including temperature-dependencies is required. A number of different tailored Pitzer databases are available. To judge their capabilities and limitations we performed comparative calculations for well-defined chemical systems (binary or ternary solubility diagrams). To avoid possible deviations due to different speciation codes all databases where transformed into the format specific for Geochemist’s Workbench. Additionally, model results are compared to experimental values from the literature.
Most results for the Oceanic Salt Systems (Na+, K+, Ca2+, Mg2+ / Cl−, SO42− – H2O) at 25 °C show a good agreement between experiment and model. At higher temperatures, sparse temperature-dependent data causes strong differences in the results.
For the radionuclides (e.g. Nd, Np), the solubility of their amorphous hydroxides in high salinar solutions was calculated as a function of pH. Missing anionic hydroxo-complex species or less reliable data produce inadequate predictions of the increasing solubility of mineral phases (e.g. fresh amorphous Nd(OH)3 or NpO2OH) in the strongly alkaline medium. This demonstrates the importance of complete chemical speciation data.
Caesium was chosen as example for a fission product. Only minor differences can be found in the calculated solubility diagrams and the occasional absence of solubility data for Cs phases is not significant for real-world scenarios due to the high solubility of these phases in comparison to other salts.
The revealed discrepancies illustrate the need for further database work. Joint benchmark activities could help to identify missing or weak data, enhance the quality of all databases and consequently increase the confidence in modelling results.

We present measurements of the absorption and emission cross-sections for Yb:YAG, Yb:LuAG and Yb:CaF2 as a function of temperature between 80 K and 340 K. The cross-sections are determined by the combination of the McCumber relation and the Fuchtbauer - Ladenburg equation to achieve reliable results in spectral regions of high and low absorption. The experimental setup used for the fluorescence measurements minimizes re-absorption effects due to the measurement from small sample volume, providing nearly undisturbed raw data for the Fuchtbauer - Ladenburg approach. The retrieved cross-sections together with the spectral characteristics of the tested materials provide important information for the design of energy efficient, high-power laser amplifiers.

Objectives: Members of the Eph receptor tyrosine kinase family play an essential role in the pathogenesis of cancer and, therefore, they are promising candidates for noninvasive molecular imaging, e.g. by PET. Several potent Eph inhibitors are reported either based on high molecular weight compounds like peptides which block the extracellular domain or on small organic molecules which bind to the intramolecular ATP binding pocket of the appropriate receptor. To date, only peptide-based radiotracers containing Cu-64 or In-111 are known which are specific for Eph receptors [1]. Due to favourable chemical and biological properties, small organic inhibitors based on the benzodioxolylpyrimidine structural motif were developed in the past [2]. Unfortunately, these tracers showed only a moderate uptake in tumor cells (A375) and no uptake in vivo in the respective tumor (A375) bearing mice. To overcome these problems, a novel lead structure 1 (IC₅₀ = 1.3 nM) was chosen based on a indazolylpyrazole core [3]. In silico studies were done to determine the best position for the introduction of fluorine-18. Further, the development and preparation of novel ¹¹C/¹⁸F-radiotracers is described. First biological studies were accomplished regarding the stability of the new tracers to figure out the ex vivo and in vivo behavior.
Methods: The first tracer prepared by isotopically labeling with [¹¹C]methyl iodide. For this purpose and for the ¹⁸F-labeling, a protecting group strategy was developed for the regioselective labeling due to three secondary amino groups of this compound. In silico docking studies were performed using the X-ray structure of the EphB4 receptor including a similar inhibitor. Based on these results, two novel references and precursors were evaluated and
prepared for the labeling with fluorine-18.
Results: For both labeling purposes, a protecting group strategy based on the ethoxyethyl (EOE) group was applied. The EOE group was introduced to block the amino function of the indazole core and to avoid radiolabeling on this position.
In the first labeling case, the ¹¹C-labeling was accomplished in a remotely controlled synthesis module in three steps. The first step involved the preparation of [¹¹C]methyl idodide from [¹¹C]methane, the second step comprehended the radiolabeling of the EOE-protected precursor and the final step included the cleavage of the protecting group under acidic conditions leading to [¹¹C]1.
Attempts were made using docking experiments to evaluate the optimal position for the introduction of fluorine-18/-19. In the first case, the methyl group of the molecule was changed against the 3-fluoropropyl residue leading to 2. Secondly, one of the morpholine rings was replaced with the (3-fluoropropyl)piperazinyl moiety yielding 3. Based on these findings, a preparation route to precursors and references was successfully established.
Conclusions: A novel ¹¹C-radiotracer was prepared for the imaging of Eph receptors in cancer using a three step labeling procedure. For radiofluorination purposes, references (2 and 3) as well as precursors were prepared
successfully. Radiolabeling and first promising biological studies are ongoing.
Acknowledgements: Support by the Fonds der chemischen Industrie (FCI-Germany).
References: [1] Xiong C, et al. (2011) J Nucl Med, 52, 241-8.
[2] Mamat C, et al. (2012) ChemMedChem, 7, 1991-2003. Bardelle C, et al. (2010) Biorg Med Chem Lett, 20, 6242-5.

Objectives: The enzyme cyclooxygenase-2 (COX-2) regulates inflammation-associated processes also in various cancer entities. Hence, the visualization of COX-2 expression in vivo by radiolabeled COX-2 inhibitors provides a promising approach for functional characterization of certain solid tumors and their metastases by PET. With the aim to get towards highly affine ¹⁸F-radiolabeled fluoroethoxy substituted COX-2 inhibitors we developed a versatile automated procedure for ¹⁸F-fluoroethylation of hydroxyl compounds with mono- as well as bicyclic core structure.
Methods: Starting from two potent COX-2 inhibitors A* (IC₅₀ COX-2: 3 nM, O-ethoxy (1)) and B* (IC₅₀ COX-2: 5 nM, O-methoxy (2)) two new fluoroethoxy substituted derivatives A and B were developed. An indirect radiolabeling approach was used starting from the corresponding hydroxy precursor and 2-[¹⁸F]fluoroethyltosylate in a one-pot reaction using an automated nucleophilic synthesizer TracerLABFXN (GE) with subsequent purification to yield [¹⁸F]A and [¹⁸F]B (Figure 1).
Results: By an enzymatic assay we could confirm that the COX-2 inhibition potency was only slightly altered when the ethoxy group of A* or the methoxy group of B* was replaced by the fluoroethoxy moiety. Optimization of labeling conditions in terms of equivalents of ethylen-1,2-ditosylate and Cs₂CO₃ resulted in complete consumption of [¹⁸F]fluoroethyltosylate in the second step and decreased amount of non-radioactive by-products; a prerequisite for a one-pot process. In this manner [¹⁸F]A was obtained starting from [¹⁸F]fluoride within 70 min in 7.5% radiochemical yield (d.c.) with >95% radiochemical purity and 27-71 GBq/μmol specific activity inclusive HPLC purification (n=5). Analogously, [¹⁸F]B was obtained after 80 min in 7.8% radiochemical yield (d.c.) with a radiochemical purity of 98% and a specific activity of 19-43 GBq/μmol (n=7).
Conclusions: The novel radiolabeled COX-2 inhibitors [¹⁸F]A and [¹⁸F]B were successfully synthesized with the developed automated ¹⁸F-fluoroethylation method. This strategy offers an effective approach to radiolabel further COX-2 inhibitors with hydroxy functionalities. The radiopharmacological evaluation of [¹⁸F]A and ¹⁸F]B is currently under way.
Acknowledgements: This work was part of research initiatives within the Radiation-Induced Vascular-Dysfunction (RIVAD) Research Network and the Helmholtz-Portfoliothema "Technologie und Medizin -Multimodale Bildgebung zur Aufklaerung des In-vivo-Verhaltens von polymeren Biomaterialien".
References: [1] Beswick P, et al. (2004) Bioorg Med Chem Lett, 2004, 14, 5445-8.
[2] Wüst F, et al. (2008) Bioorg Med Chem, 16, 7662-70.

Objectives: The ability of solid tumours to invade surrounding tissues and, in consequence, to metastasise to distant organs is mediated by bidirectional molecular interactions between tumour cells and the extracellular matrix [1,2]. Recently, the copper-dependent amine oxidase lysyl oxidase (LOX, EC 1.4.3.13) could be identified as one of the key players in these processes [3]. Therefore, the development of molecular probes that enable the imaging
of this enzyme in vivo by positron emission tomography (PET) was in the focus of this study.
Methods: As the enzyme is catalysing the oxidative crosslinking of lysine side chains in collagen and other extracellular proteins, the design of radiotracers based on substrates seemed to be promising. Thus, the N-terminal telopeptide of the α1-chain of type I collagen containing the key sequence Asp-Glu-Lys-Ser [4] and peptides derived from this were chosen to be labelled with fluorine-18 at their N-termini (Figure 1). To achieve this, a method was developed that allows the site-selective ¹⁸F-fluorobenzoylation of peptides [5]. The metabolic stability and biodistribution of these potential radiotracers was investigated in male wistar rats. To estimate the potential of the different lysine-containing peptides for crosslinking with collagen in vivo, their interaction with bovine atelocollagen was investigated by surface plasmon resonance (SPR) experiments. A panel of tumour cell lines was screened for expression of the enzyme. The presence of LOX could be confirmed for the human breast cancer celllines MDA-MB-231, MCF-7 and the melanoma cell line A375 by RT-PCR as well as western blots. Based on the human A375 cell line, an animal model was established consisting of nude mice bearing tumours derived from these cells. Expression of LOX in the developed tumours was proven by immunohistochemical methods and western blots.
Results: The developed labelling method for site-selective radiolabelling of peptides allowed to obtain the ¹⁸Ffluorobenzoylated telopeptide in high radiochemical yields and purities. All peptides show good stability in vivo and even no metabolites could be detected for the cyclohexapeptide. The biodistribution studies indicate no organ enrichment and fast renal elimination. For the first time, the telopeptide-collagen interaction could be studied quantitatively, indicating dissociation constants in the high micromolar range.
Conclusions: Despite unfavourable pharmokinetics due to fast blood clearance, the compounds show the potential to reflect the LOX activity in vivo, as concluded from PET imaging experiments with nude mice bearing A375 tumours.
References: [1] Fidler IJ, et al. (2003) Nat Rev Cancer, 3, 453.
[2] Rowe RG, et al. (2009) Annu Rev Cell Dev Biol, 25, 567.
[3] Erler JT, et al. (2006) Nature, 440, 1222-6.
[4] Helseth DL, et al. (1979) Biopolymers, 18, 3005.
[5] Kuchar M, et al. (2012) Amino Acids, 43, 1431-43.

Nuclear resonance fluorescence experiments have been performed at the bremsstrahlung facility of the ELBE accelerator in Dresden-Rossendorf. The electromagnetic dipole strength below the neutron separation energy of several nuclei in the chain of Xenon isotopes has been investigated.
The measurements in chain of gaseous isotopes allowed a comparison of the summed strength not only as a function of the neutron-to-proton ratio but also of the nuclear quadrupole deformation.
Experiments and calculations using a quasiparticle random-phase approximation have been used in the chain of Xenon isotopes to estimate the importance nuclear deformation in the energy region on the pygmy strength.

Objectives: The molecular processes leading to tumour invasion and metastasis are closely associated with a network of intra- and extracellular proteolysis. A prominent role in this network was assigned to the thioldependent cathepsins [1]. Among this class of cysteine proteases, the involvement in tumour pathology could be confirmed for the cathepsins L, S, B, and K.
Due to the vital role of these enzymes in tumour biology, molecular probes that enable their functional imaging in vivo by PET are highly desirable. To this end, an inhibitor of the azadipeptide nitrile chemotype [2] labelled with fluorine-18 was developed. Its radiopharmacological characterisation in normal and tumour-bearing animals to evaluate its potential for PET imaging was the objective of this study.
Methods: Compound 1 (Figure 1A) could be reliably prepared in its ¹⁸F-labelled version in a one-pot, two-step process from the corresponding compound bearing the free hydroxy group with intermediary 2-[¹⁸F]fluoroethyl nosylate. Its high affinity to the cathepsins L, S, B, and K is reflected by inhibition constants ranging from 0.17 nM (cathepsin K) to 2.4 nM (cathepsin B). The radiopharmacological behaviour of [¹⁸F]1 in normal rats was studied in vitro investigating its stability in rat blood, ex vivo by determining its biodistribution and metabolite analysis as well as in vivo by dynamic PET imaging. To evaluate the potential of [¹⁸F]1 for imaging of the tumour-associated cathepsin activity its fate in nude mice bearing the tumours derived from the human alveolar carcinoma cell line NCI-H292 was followed with dynamic PET. The expression of the target enzymes in these tumours was studied by immunohistochemistry.
Results: Biodistribution data for [¹⁸F]1 after 60 min indicated that renal filtration is the main elimination pathway. Another large part is remaining in the blood, which is obvious from dynamic PET imaging as well (Figure 1B).
This could be partly attributed to the reaction of [¹⁸F]1 with glutathione in the blood. The glutathione conjugate of [¹⁸F]1 can be also found in the urine and the gut besides the corresponding cysteine conjugate.
Evaluation of the kinetics of [¹⁸F]1 in NCI-H292 tumour bearing nude mice revealed its accumulation in the tumours with tumour to muscle ratios up to 10 after 2 h (not shown here) which indicates a specific tumour uptake.
This conclusion is further supported by the fact that all four cathepsins could be detected immunohistochemically in the tumour sections.
Conclusions: The in vivo behaviour of [¹⁸F]1 could be well characterised in normal rats as well as in NCI-H292 tumour mice. Despite suboptimal pharmacokinetics due to its inherent thiol reactivity, [¹⁸F]1 has the potential for imaging the tumour-associated cathepsin activity, which will be confirmed in further studies.
References: [1] Mason SD, et al. (2011) Trends Cell Biol, 21, 228-37.
[2] Löser R, et al. (2008) Angew Chem Int Ed, 47, 4331-4.

Objectives: The epidermal growth factor receptor (EGFR) is overexpressed in many types of human epithelial cancers. Because of its important role in the initiation and progression of tumors, it is an interesting molecular target for new radiotracers. [1] Recently, two short peptides for targeting the EGFR have been reported - the D4 peptide (sequence: LARLLT) and the GE11 peptide (sequence: YHWYGYTPQNVI).[2,3] These short oligopeptides should provide a high specific binding to EGFR-positive tumor cells as well as a rapid tumor uptake and fast blood clearance. We investigated the chemical modification and radiolabeling of the two peptides and examined the application of the D4 peptide as a possible agent for diagnosis and therapy of cancer.
Methods: The D4 and the GE11 peptide haven been conjugated with several chelators, e.g. NOTA, DOTA and HYNIC, to allow radiolabeling with suitable radionuclides for diagnostic (e.g. ^99mTc, ⁶⁴Cu) or for therapeutic applications (e.g. ⁹⁰Y). The properties of the conjugates were modified by the previous insertion of the newly developed hydrophilic, heterobifunctional linker 1. Toxicity tests have been made using a cell viability assay MTS on the EGFR-expressing cell lines A431 (epidermoid carcinoma cells) and FaDu (squamous carcinoma cells). Binding assays were performed on membranes of A431-, FaDu- and non-EGFR-expressing MDA-MB435S cells.
Kinetics and saturation assays were conducted using the ⁶⁴Cu-labeled conjugate 2. First biodistribution PET studies in nude mice have been performed.
Results: Conjugation of the two peptides with the new linker 1 followed by the reaction with different chelators gave overall yields of 40-65%. The GE11 peptide itself, as well as all of its conjugates which did not contain the hydrophilic linker 1, were not soluble in water and therefore inapplicable for further experiments. The remaining compounds were labeled with ⁶⁴Cu and ⁶⁸Ga (NOTA conjugates), ^99mTc (HYNIC conjugates) and ⁹⁰Y (DOTA conjugates) with specific activities of up to 980 GBq/μmol for ⁶⁴Cu-2. No change of cell viability was observed after treating A431 and FaDu cells with plain D4 and D4-1 for 4 days at concentrations of up to 125 μM. Binding association with ⁶⁴Cu-2 on A431 membranes reached equilibrium after one hour, on FaDu membranes equilibrium was not complete after two hours. T_Diss½ was less than 5 min. In saturation assays, the affinity determination of ⁶⁴Cu-2 on A431 and FaDu membranes gave K_d values of 28 ± 6 nM and 72 ± 18 nM, respectively. No specific binding of ⁶⁴Cu-2 to MDA-MB453S cell membranes was observed. First PET studies with healthy nude mice showed a favorable biodistribution.
Conclusions: We successfully prepared and radiolabeled several conjugates of the EGFR-affine peptides D4 and GE11 with satisfying yields and high specific activities. The insertion of the new hydrophilic heterobifunctional linker 1 was necessary to achieve high solubility in water. The preservation of cell viability after D4 and D4-1 treatment indicates no toxic effect of the conjugates. The affinity of ⁶⁴Cu-2 to the high EGFR-expressing A431 cells and the moderate EGFR-expressing FaDu cells was in the expected range. Binding assays with radiolabeled GE11-conjugates as well as PET studies of GE11-conjugates and ⁶⁴Cu-2 with tumor-bearing nude mice are currently under investigation.
References: [1] Cardo-Vila M, et al. (2010) Proc Natl Acad Sci USA, 107, 5118-23.
[2] Song S, et al. (2009) FASEB, 23, 1396-404.
[3] Li Z, et al. (2005) FASEB, 19, 1978-85.

Objectives: The use of the [¹⁸F]cyclobutyl group as a potentially metabolic stable surrogate group for [¹⁸F]fluoroalkyl groups has been notified [1-3]. The radiolabeling of a cis-1,3-cyclobutanediol bis-toluenesulfonate
precursor and its conjugation to L-Tyrosine were reported with an overall yield of 8%±5.5 (n = 14, decay corrected). The aim of this work was to improve upon the yield by synthesizing various precursors with different sulfonate leaving groups and evaluating them for their ability to incorporate [¹⁸F]fluoride to form the 3-[¹⁸F]fluorocyclobutan-1-ol sulfonate 2. Furthermore the effect of these leaving groups on the conjugation reaction of 2 with L-Tyrosine to give the 3-[¹⁸F]fluorocyclobutyl-L-tyrosine ([¹⁸F]FCBT) should be assessed.
Methods: Various symmetrical cis-1,3-cyclobutanediol bis-sulfonates 1 were synthesized with the different commonly-used sulfonate leaving groups, i.e. tosylate, mesylate, triflate, nosylate and 3,4-dibromobenzenesulfonate. These precursors were subjected to n.c.a. nucleophilic radiofluorination. The ¹⁸F-labeled intermediates 2 were purified and the alkylation reaction with L-Tyrosine under standard conditions was tested to assess their conversion to [¹⁸F]FBCT.
Results: The cis-1,3-cyclobutanediol bis-sulfonates 1 were synthesized from the cis-1,3-cyclobutanediol using standard methodologies [3]. The triflate derivative was found to be unstable on storage and was eliminated from further evaluation. The radiofluorination of the tosylate (65%) and 3,4-dibromobenzenesulfonate (58%) precursors resulted in better [¹⁸F]fluoride incorporation than mesylate (30%) and nosylate (5%). The subsequent alkylation of the purified intermediates 2 with L-Tyrosine showed the same trend with 82% yield for tosylate and 69% yield for 2,3-dibromobenzenesulfonate () whereas mesylate gave only 4% yield and nosylate failed to give product.
Conclusions: By a systematic evaluation of different sulfonate leaving groups of the symmetrical cis-1,3-cyclobutanediol bis-sulfonates 1 and the conjugation of the resulting intermediate 2 with L-Tyrosine it was clearly demonstrated that tosylate and 3,4-dibromobenzenesulfonate are more favorable than mesylate and nosylate.
Acknowledgements: We gratefully acknowledge Selahattin Ede and Mario Mandau for technical assistance.
References: [1] Franck D, et al. (2011) J Nucl Med, 52, Suppl. 1, 168P. [2] Franck D, et al. (2011) J Label Compd
Radiopharm, 54, Suppl. 1, S447. [3] Franck D, et al. (2013) Bioorg Med Chem, 21, 643-52.

Ob im Packeis, in der staubtrockenen Wüste, in Salzseen oder in sauren Halden – Bakterien und andere Kleinstlebewesen besiedeln alle Lebensräume. So leben sie auch in Schwermetall-belasteten und radioaktiv-kontaminierten Milieus z. B. in ehemaligen Uran-Bergwerken. Ihr Überleben in solchen extremen Umgebungen kann bei der Reinigung von Abwässern oder der Gewinnung von Rohstoffen sogar für den Menschen nützlich sein.

Objectives: Since the epidermal growth factor receptor (EGFR) is often overexpressed in HNSCCs, there is strong interest to inhibit the growth of these tumor entities via the EGFR. Thus, in this study pharmacological parameters (K_i and B_max) of the chimeric monoclonal anti-EGFR antibody cetuximab (C225), conjugated with the bifunctional chelator (BFC) CHX-A’’-DTPA (C1), labeled with the therapeutic radionuclide yttrium-90 were determined in three different HNSCC cell lines, whose EGFR expression was also estimated. Furthermore, nude mice bearing xenografts generated from these three HNSCC cells were studied in order to investigate whether internal irradiation with the radiolabeled antibody conjugate could improve the results of external irradiation alone.
Methods: C1 was conjugated to C225 via thiourea bridging. MALDI-TOF-MS revealed a BFC to C225 ratio of 4 to 1. The affinity of the yttrium-90 labeled conjugate C1-C225 was determined using membranes of the HNSCC cell lines FaDu, UT-SCC-5 and UT-SCC-8. The EGFR expression was determined by Western blotting. The tumor models were created by s.c. transplantation of pieces from the investigated tumor lines into the hind leg of nude mice (NMRI nu/nu). Different experimental groups were treated by either [⁹⁰Y]C1-C225 alone, C225 alone, external irradiation alone, external irradiation plus unlabeled C225 or external irradiation plus [⁹⁰Y]C1-C225.
Results: [⁹⁰Y]C1-C225 was routinely prepared with high specific activity (about 8 GBq/mg) and showed high affinity with K_d values in the low nanomolar range and a maximal number of binding sites (B_max) of 4.0, 4.9 and 10.4 pmol/mg in membranes of FaDu, UT-SCC-5 and UT-SCC-8 cells, respectively. In vitro the EFGR expression in these cell lines correlated well with the corresponding B_max values. In vivo the HNSCC tumors showed a different response to [⁹⁰Y]C1-C225 alone compared to unlabeled C225 receiving a specific tumor growth delay of 4.2, 0.07 and 3.7 for FaDu, UT-SCC-5 and UT-SCC-8. In FaDu the tumor control dose (TCD₅₀) was significantly decreased after external irradiation in combination with internal irradiation. In contrast to the effect in FaDu no change of the TCD₅₀ was observed in UT-SCC-5.
Conclusions: For [⁹⁰Y]C1-C225 a high affinity was determined in membranes of three different HNSCC cell lines and the B_max values correlated with the EGFR expression in vitro. Furthermore, in different HNSCC different responses to treatment were observed. However, the intertumoral heterogeneity did not correlate with the Bmax values, thus it seems that additional factors influence the response to internal irradiation.
Acknowledgements: Supported by 02NUK006A+B (Kompetenzverbund Strahlenforschung, KVSF)

Pentadentate bispidine ligands (3,7-diazabicyclo[3.3.1]nonanes) are optimized for maximum complex stability and facile functionalization with respect to their coupling to biological vector molecules and/or fluorescence markers for PET (positron emission tomography) and multimodal imaging (i.e., PET and optical imaging). The pentadentate ligand with two tertiary amine donors, two p-methoxy substituted pyridines, and one unsubsituted pyridine group is shown to best fulfill important conditions for PET applications, i.e., fast complexation with Cu^II and high in vivo stability, and this was predicted from the solution chemistry, in particular the Cu^II/I redox potentials. Also, solvent partition experiments to model the lipophilicity of the Cu^II complexes indicate that the bis p-methoxy substituted ligand leads to cationic complexes with an appreciable lipophilicity. This is supported by the biodistribution experiments that show that the complex with the p-methoxy substituted ligand is excreted very quickly and primarily via the renal route and therefore is ideally suited for the development of PET tracers with ligands of this type coupled to biomolecules.

Many low-energy excitations in solids fall into the meV or THz range. Whereas linear spectroscopy is a valuable tool to obtain information on the linear response of these excitations, recent progress in THz sources also enables one to access their nonlinear and time-resolved behavior. To this end we use a free-electron laser to study intraexcitonic transitions in quantum wells and carrier dynamics in graphene.
Excitons possess a hydrogen-like internal excitation spectrum with a characteristic energy scale in the THz range. We pump the 1s-2p intraexcitonic transition in GaAs and InGaAs multiquantum wells with a THz free-electron laser and probe the induced changes in the absorption spectrum via interband absorption using a near-infrared femtosecond laser. We observe a splitting of the 1s exciton line, which can be explained by the Autler-Townes or AC Stark effect [1]. The behavior is, however, much more complex than for an ideal two-level system. Since for electric fields in the 10 kV/cm range the Rabi energy is of the same order of magnitude as the 1s-2p transition energy, we are in fact clearly beyond the validity of the rotating wave approximation. At the highest fields, when also the ponderomotive energy (e2F2/4mw2) approaches the exciton binding energy, signatures of exciton field ionization are observed.
In graphene with its vanishing bandgap, interband excitations extend down to very low frequencies, where they compete with the free-carrier (intraband) absorption in lightly doped graphene (EF=13 meV). We have performed THz pump-probe experiments on multilayer graphene over a wide range of photon energies (10-250 meV) to investigate the carrier dynamics. Interestingly we observe a crossover from induced transmission (bleaching) for hw > 2EF to induced absorption for hw < 2EF. At these photon energies interband transitions are initially blocked, but become possible after intraband free-carrier absorption and heating [2]. In a magnetic field the bands split up into non-equidistant Landau levels, which can be pumped and probed selectively. Using left- and right-circularly polarized light reveals some surprising behavior related to the importance of Auger scattering.

Clinopyroxene and apatite are found to trace metasomatic processes in nepheline-bearing clinopyroxenites (tilaites) from the igneous, mafic-ultramafic Uralian-Alaskan-type complexes of Kytlym and Nizhny Tagil, Ural Mountains, Russian Federation. The clinopyroxenites consist predominantly of coarse-grained, partially to totally altered clinopyroxene phenocrysts in a matrix of fine-grained olivine, clinopyroxene, plagioclase, K-feldspar, and nepheline. Apatite occurs as idiomorphic inclusions (< 25 µm) in the clinopyroxene and as xenomorphic grains in the matrix.
In the matrix, plagioclase is partially to totally replaced by a fine-grained symplectitic intergrowth of K-feldspar and nepheline most likely due to the influx of an K₂O-, Na₂O-, and Al₂O₃-bearing fluid. During conversion of the plagioclase, CaO and SiO₂ were partitioned into the fluid. Altered areas in the clinopyroxene phenocrysts are characterized by the redistribution of major and trace elements. This includes depletion in Mg, Rb, and Sr and enrichment in Al, Na, Ba, U, Th, REE except Eu, and HFSE compared to the original magmatic areas in the clinopyroxene. Apatite inclusions in the altered areas of the clinopyroxene and in the matrix are enriched in Cl relative to apatite inclusions in the unaltered areas of clinopyroxene.
It is proposed that these rocks experienced a two-stage metasomatic process. Stage 1 was the partial to total alteration of plagioclase to K-feldspar and nepheline due to interaction with an infiltrating (K,Na)Cl-rich brine (most likely late magmatic) with an Al component, which enriched the fluid in CaCl₂. Stage 2 consisted of the partial to total chemical alteration of the original magmatic clinopyroxene by this now CaCl₂-enriched fluid through the mechanism of coupled dissolution-reprecipitation. This process also chemically altered the apatite inclusions from fluor-chlorapatite to chlor-fluorapatite and redistributed as well as partially removed the titanomagnetite inclusions in the altered areas. This is supported experimentally by the fact that alteration of fluorapatite to Cl-rich apatite can only take place in the presence of CaCl₂-bearing fluids and by the fact that in general Fe and Ti, along with most metal cations, are relatively mobile in Cl-rich fluids.
If this scenario is correct, the implications from this study are that inclusions of one mineral in a host mineral can be chemically overprinted during metasomatic alteration of the host mineral. While at the same time the original crystal shape and orientation of both the host phase as well as that of the inclusions are preserved.

Samples of two deep-sea sediment cores from the Indian Ocean are analyzed with accelerator mass spectrometry (AMS) to search for traces of recent supernova activity ∼2 Myr ago. Here, long-lived radionuclides, which are synthesized in massive stars and ejected in supernova explosions, namely ²⁶Al, ⁵³Mn and ⁶⁰Fe, are extracted from the sediment samples. The cosmogenic isotope ¹⁰Be, which is mainly produced in the Earth’s atmosphere, is analyzed for dating purposes of the marine sediment cores. The first AMS measurement results for ¹⁰Be and ²⁶Al are presented, which represent for the first time a detailed study in the time period of 1.7-3.1 Myr with high time resolution. Our first results do not support a significant extraterrestrial signal of ²⁶Al above terrestrial background. However, there is evidence that, like ¹⁰Be, ²⁶Al might be a valuable isotope for dating of deep-sea sediment cores for the past few million years.

Motivated by the steadily increasing global demand for metalliferous resources – as expressed by increasing prices and protective measures by resource-rich countries - the Helmholtz Institute Freiberg for Resource Technology was established in 2011 with the objective to develop technologies for the energy- and resource efficient as well as environmentally benign production and recycling of metalliferous raw materials. The HIF belongs to Helmholtz-Zentrum Dresden-Rossendorf and is being established in close cooperation with the TU Bergakademie Freiberg. Metalliferous raw materials needed for the renewable energy sector, including the rare earth elements, indium, germanium and gallium, define the research focus of the Helmholtz-Institute as the rapidly increasing global demand for these metals needs to be urgently met by technological development. Research is carried out in close collaboration with partners from industry and academia in regional, national and international consortia. The Helmholtz-Institute also aims to make a relevant contribution to the education of a new generation of highly qualified academic and technical staff for German industry and academia.

Die Entwicklung von neuen Zweiphasen-CFD-Modellen zur Berechnung von komplexen Strömungsvorgängen stellen ein wichtiges Ziel für Industrie und Forschung dar. Um neue Modelle sorgfältig validieren zu können, werden experimentelle quantitative Daten entsprechender Strömungsformen mit hohen zeitlichen und räumlichen Auflösungen benötigt. An der TOPFLOW-Versuchsanlage des HZDR werden dazu umfangreiche Versuche an einer vertikalen DN50-Testsektion mit Luft-Wasser und Dampf-Wasser-Strömungen bis zu p = 65 bar und einer weiten Variation der Leerrohrgeschwindigkeiten für die Wasser- und die Gasphase durchgeführt. Unter Verwendung der am HZDR entwickelten ultraschnellen Zweiebenenröntgentomographie werden momentane Gasgehaltsverteilungen im Rohrquerschnitt mit Bildraten von bis zu 2500 frames/s, einer Messzeit von 10 s und einer räumlichen Auflösung von ca. 2 mm gemessen. Nach erfolgter Rekonstruktion werden mithilfe von Segmentierungs- und Auswertealgorithmen Einzelblaseninformationen generiert. Diese Daten werden hinsichtlich Strömungsdetails wie Blasengrößenverteilungen, radiale Gasgehalts- und Gasgeschwindigkeitsprofile, Strömungsverhalten von Kleinblasen in Abhängigkeit benachbarter Blasen u. a. weiter analysiert. Der Geschwindigkeitsinformation von Einzelblasen kommt dabei eine zentrale Rolle zu. Um diese bestimmen zu können werden detektierte Blasen aus beiden Tomographieebenen in Größe, Ort und resultierender Geschwindigkeit verglichen, sodass Blasenpaare anhand von Wahrscheinlichkeitswerten für beide Ebenen ermittelt werden. Unter Verwendung des konstruktiven Abstands sowie des zeitlichen Versatzes zwischen beiden Ebenen wird die individuelle Blasengeschwindigkeit errechnet. Neben der Geschwindigkeit in Hauptströmungsrichtung können somit auch radiale Geschwindigkeitskomponenten einer Blase ermittelt werden. Auf Basis der ermittelten Geschwindigkeiten können somit von Ort und Blasengröße abhängige Geschwindigkeitsprofile erstellt werden.
Im Ergebnis stehen analysierte Messdaten mit hohem Informationsgehalt zur Zweiphasen-CFD-Modellvalidierung zur Verfügung. Diese neu generierten Daten werden in diesem Beitrag an verschiedenen Zweiphasenregimen bei aufwärts- sowie abwärtsgerichteten Strömungen vorgestellt und diskutiert. Dazu werden neben quantitativen Ergebnissen auch qualitative Untersuchungsergebnisse von Geschwindigkeitsfeldern präsentiert.

At the Institute of Fluid Dynamics at the Helmholtz-Zentrum Dresden-Rossendorf the ultrafast electron beam X-ray computed tomography was developed in the last years to investigate two-phase flows. The tomography system works according to the scanned electron beam principle. In a recent study we investigated different gas-liquid flow regimes in a vertical pipe test rig at the TOPFLOW thermal hydraulic test facility. The study contains experiments of gas-liquid flow regimes varied with different superficial velocities for both phases and different flow directions. The obtained data is required for understanding fundamental physics of flow phenomena and for improving and validating of models for flow simulation codes.
To extract the needed data from the 3D gray value array, a new segmentation algorithm is developed. This algorithm bases on bubble detection by pixel agglomeration. The results are compared with threshold and gradient methods using two different bubble phantoms and real two-phase flow measurements. The new algorithm shows the best qualitative and quantitative results.

Detailed hydrodynamic characterization of transient multiphase flows is significant in the field of process engineering. The ultrafast X-ray tomography system ROFEX was used to analyze the complex transient multiphase flow and its hydrodynamic characteristics in monolithic structures. Introducing the applied tomography system and the particular experimental set-up, selected experiments and investigations will be explained. Furthermore several methods for the computation and visualization of gas and liquid phase distribution, the calculation of liquid holdup and the characterization of the occurring flow structures will be presented. As a conclusion a selection of achieved results and the derivable information will be summarized.

We present in this talk the first experiment of IR-FEL production driven by ELBE SRF gun.

Detailed molecular information of the Np(V) sorption species on amorphous and crystalline gibbsite were obtained for the first time by in situ time-resolved Attenuated Total Reflection Fourier-Transform Infrared (ATR FT-IR) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy under environmentally relevant conditions. The results consistently demonstrate the formation of mononuclear inner sphere complexes of the NpO2+ ion irrespective of the prevailing atmospheric condition. In particular, the impact of the presence of atmospheric equivalent added carbonate on the speciation in solution and on the surfaces becomes evident from vibrational data. Whilst the 1:1 aqueous carbonato species (NpO2CO3−) was found to become predominant in the circumneutral pH range, it is most likely that this species is sorbed onto the gibbsite surface as an inner sphere ternary surface complex where the NpO2+ moiety is directly coordinated to the functional groups of the gibbsite’s surface. These findings are corroborated by results obtained from EXAFS spectroscopy. The identification of the Np(V) surface species on gibbsite constitutes a basic finding for a comprehensive description of the dissemination of neptunium in groundwater systems.

Sponge-like Si nanostructures embedded in SiO2 were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations.

Aggressive environments contribute to the corrosion of pipe organs, which causes flaking, losing the voice and final collapse of the old century’s pipes. Additional factor is dezincification of brass (CuZn) containing more than 15 at.% of Zn in the presence of oxygen and moisture. In this approach, the nanotechnology treatment of the CuZn24 (reed organ pipes) is proposed. The conservation strategy based on two stages Pulsed Laser Deposition (PLD) followed by Plasma Immersion Ion Implantation (PIII) were performed. The brass coupons were coated with the protective oxide-films (Al2O3, SiO2, and ZnO) using PLD technique, and implanted with nitrogen ions of energy 20 keV for 200 seconds. The influence of the deposited and implanted coatings, on the corrosion phenomena, has been evaluated by exposing the coupons to the laboratory air with the high concentration of 2% acetic acid (CH3COOH), as aggressive agent. The areal density of the deposited films was measured using Rutherford Backscattering Spectroscopy (RBS). The composition and depth profiling of the sample’s elements was analyzed with Auger Electron Spectroscopy (AES). The average roughness (Ra) of the as coated and implanted specimens was measured using Dektak Stylus Profilometry in 2 and 3 dimensions. Those results were compared with the roughness measurements performed after the corrosion test. A significant improvement in the corrosion resistance with acetic acid action has been achieved by applying aluminum oxide film (30 nm) and introducing nitrogen ions into the near surface and the interphase regions. This gives a light to introduce the nanotechnology into the greatest and best sounding objects of the cultural heritage.

The present historical organs are musical instruments, which provide sound impression of divine music spanning six centuries. Unfortunately, organ pipes, traditionally made of PbSn alloys, have been severely affected by corrosion in the last couple of centuries, and particularly over the last decades. A major threat to the historical organs is harmful indoor environments. Thus, it is necessary to develop a method of protecting the organ pipes, so that the significant cultural heritage obtained over many centuries does not get lost. A new conservation concept based on nanotechnology using plasma immersion ion implantation (PIII) is proposed here for the protection of PbSn alloys exposed to high levels of acetic acid vapors. Samples of organ-pipe quality PbSn alloys with compositions were processed by PIII of either nitrogen or SF6 for different times and bias voltages. The PIII-treated specimens were subsequently studied by Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy to study the concentration/depth profiles of the implanted elements. The implant profiles were also simulated with the aid of the SRIM code. Samples were finally examined using an accelerated corrosion tests in an acetic acid ambient. Both the alloy composition and the implant dose were found to strongly influence the corrosion behavior of the PbSn alloys. The best corrosion resistance was obtained for samples consisting of Pb-Sn15-Sb10 and Pb-Sn28, after the implantation of nitrogen to a dose of1E16cm-2.It was revealed that plasma immersion ion implantation can play an important role in the corrosion prevention of the organ pipes in the acetic acid atmosphere. A protection mechanism was accordingly proposed and discussed.

Ferritisch/martensitische Cr-Stähle und deren oxiddispersionsverfestigte Varianten gehören zu den potenziellen Konstruktionswerkstoffen für Komponenten zukünftiger kerntechnischer Einrichtungen, wie z. B. Fusionsreaktoren und Spalt-reaktoren der IV. Generation, die Strahlungsfeldern mit hohem Neutronenfluss aus-gesetzt sind. Ein Hauptproblem dieser Materialgruppen ist das Auftreten des Spröd-duktil-Übergangs und dessen maßgeblich durch die Strahlenhärtung verursachte Verschiebung zu höheren Temperaturen.
In der vorliegenden Arbeit wird das Bestrahlungsverhalten von binären Fe-Cr-Modelllegierungen untersucht, die ein vereinfachtes Modell für ferritisch/martensitische Cr-Stähle darstellen. Dabei werden Bestrahlungen mit Eisenionen zur Simulation der durch Neutronen hervorgerufenen Schädigung verwendet. Die auf wenige Mikrometer begrenzte Eindringtiefe der Ionen macht es erforderlich, dass für dünne Schichten geeignete Charakterisierungsmethoden ein-gesetzt werden. Im Rahmen dieser Arbeit sind das Nano¬härte¬messungen und Transmissions¬elektronen¬mikroskopie (TEM).
Im Ergebnis liegen die bestrahlungsinduzierte Härteänderung der Schicht in Ab-hängig¬keit von Chromgehalt, Bestrahlungsfluenz und –temperatur sowie, für aus-gewählte Zustände, quantitative TEM-Analysen vor. Zusammen mit begleitenden Ergebnissen von Neutronenkleinwinkelstreuexperimenten an neutronen-bestrahlten Proben der gleichen Werkstoffe ermöglichen sie die Identifizierung von bestrahlungsinduzierten Versetzungsringen und nm-großen α’-Ausscheidungen als Quellen der Strahlenhärtung. Im Rahmen eines vereinfachten Modells, das auf Orowan zurückgeht, werden die Hindernis¬stärken dieser Gitterbaufehler für das Gleiten von Versetzungen abgeschätzt.
Darauf aufbauend erfolgt ausblickartig eine Erweiterung des Untersuchungsgegenstands auf komplexere Situationen hinsichtlich der Bestrahlungs-bedingungen und des Werkstoffs. Durch das Einbeziehen simultaner und sequentieller Bestrahlungen mit Eisen- und Heliumionen kann gezeigt werden, dass der Effekt von Helium auf die Strahlenhärtung von der Bestrahlungs-reihenfolge abhängt und dass der simultane Eintrag fusionsrelevanter Mengen von Helium zu einer Verstärkung der Strahlenhärtung führt, die auf einem synergistischen Effekt beruht. Für Cr-Stähle mit 9 % Cr und deren oxiddispersions-verfestigte Varianten wird kein grundlegend anderes Bestrahlungsverhalten beobachtet als für binäres Fe-9at%Cr. Es gibt jedoch Hinweise, dass Oxid-dispersionsverfestigung die Strahlenhärtung unter bestimmten Bedingungen reduzieren kann.
Im Ergebnis der Arbeit zeigt sich, dass Ionenbestrahlungen in Kombination mit Nanohärtemessungen zu einem vertiefenden Verständnis der Strahlenhärtung in Werkstoffen auf Fe-Cr-Basis sowie zu einer effektiven Materialvorauswahl beitragen können. Voraussetzung ist, dass der Eindruckgrößeneffekt und der Substrateffekt auf geeignete Weise in Rechnung gestellt werden.

The surface speciation of uranium(VI) on maghemite (γ-Fe2O3) was elucidated at the spectroscopic level for the first time. By means of in situ ATR FT-IR measurements, the formation of uranium(VI) outer-sphere complexes was revealed under anoxic conditions and in ambient atmosphere at mildly acid conditions. This type of complexation was verified by the frequency of the ν3(UO2) mode observed for the surface species, the impact of the ionic strength of the background electrolyte on U(VI) sorption and by the high reversibility of the sorption process monitored by on line spectroscopy. The impact of carbonate ions from atmospherically derived CO2 on U(VI) sorption on maghemite was investigated. Although the surface speciation of the carbonate ions presumably change from a monodentate coordination on maghemite to a bidentate coordination in the ternary sorption system, the U(VI) speciation is not changed. A contrasting juxtaposition of comparable results obtained from maghemite and ferrihydrite reveal a basically different type of U(VI) complexation, namely outer and inner spheric coordination.

Local reversible structural changes in SrTiO3 single crystals in an external electric field are induced by oxygen redistribution. We present in-situ X-ray diffraction measurements during and immediately after electroformation. Several reflections are monitored and show an elongation of the cubic unit cell of strontium titanate. Raman investigations verify that the expansion of the unit cell involves a transition from the centro-symmetric to a lower symmetry phase. During a complete formation cycle, including the hold time of the electric field and relaxation time without field, two different dynamics are observed for the reversible transitions from cubic symmetry to tetragonal distortion: a slow one during the increase of the lattice constant in field direction and a fast one after switching off the electric field. Based on the experimental data we propose the formation of a polar strontium titanate unit cell at room temperature stabilized by the electric field, which is referred to as migration-induced field-stabilized polar (MFP) phase.

In an underground rock characterization facility, the ONKALO tunnel in Finland, massive 5–10-mm thick biofilms were observed attached to tunnel walls where groundwater was seeping from bedrock fractures at a depth of 70 m. In laboratory experiments performed in a flow cell with detached biofilms to study the effect of uranium on the biofilm, uranium was added to the circulating groundwater obtained from the fracture feeding the biofilm. The final uranium concentration was adjusted to 4.25×10–5 M. EF-TEM studies indicated that uranium in the biofilm was immobilized intracellularly in microorganisms by the formation of metabolically mediated uranyl phosphate, similar to needle-shaped Autunite (Ca[UO2]2[PO4]2•2-6 H2O) or meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O). At the Äspö HRL (Sweden) Gallionella ferruginea dominated biofilms associated with bacteriogenic iron oxides (BIOS) and groundwater were sampled from an in situ continuous flow cell. In laboratory sorption experiments UO2(ClO4)2 and NpO2(ClO4) were added to the BIOS biofilms in groundwater under aerobic conditions adjusting a final U(VI) concentration of 1.9×10-5 M. U(VI) and 3.27×10-5 M Np(V). The results showed a substantial decrease of uranium and neptunium in the groundwater of approximately 85 % and 95 %, respectively. Thermodynamic calculation of the theoretical predominant field of uranium species was performed using the analytical data of the uranium-contaminated groundwater. Under the given pH and Eh the formation of the aqueous uranium carbonate species Ca2UO2(CO3)3(aq) is predicted due to the high concentration of carbonate in the groundwater. In the BIOS biofilm the ferrous iron-oxidizing and stalk-forming bacterium Gallionella ferruginea is dominating the sorption process. The stalk represents an organic surface upon which Fe oxyhydroxides can precipitate. Under the given pH conditions the uptake of U and Np depends predominantly on the high amount of ferrihydrite precipitated onto the stalks. Conclusively, the combination of this biological material and iron oxides creates an abundant surface area for adsorption of radionuclides.

At the Äspö HRL (Sweden) Gallionella ferruginea dominated biofilms associated with bacteriogenic iron oxides (BIOS) and groundwater were sampled from an in situ continuous flow cell, which has been installed in a cavity of the main access tunnel at 2200 A site, 300 m below sea level In laboratory sorption experiments UO2(ClO4)2 and NpO2(ClO4) were added to the BIOS biofilms in groundwater under aerobic conditions adjusting a final U(VI) concentration of 1.9×10-5 M. U(VI) and 3.27×10-5 M Np(V). The analysis showed a substantial decrease of uranium and neptunium in the groundwater of approximately 85 % and 95 %, respectively. Under the given pH and Eh the formation of the aqueous uranium carbonate species Ca2UO2(CO3)3(aq) is predicted due to the high concentration of carbonate in the groundwater. In the BIOS biofilm the ferrous iron-oxidizing and stalk-forming bacterium Gallionella ferruginea is dominating the sorption process.

Normal incidence ion irradiation at elevated temperatures, when amorphization is prevented, induces novel nanoscale patterns of crystalline structures on elemental semiconductors by a reverse epitaxial growth mechanism: on Ge surfaces irradiation at temperatures above the recrystallization temperature of 250°C leads to self-organized patterns of inverse pyramids. Checkerboard patterns with fourfold 2 symmetry evolve on the Ge (100) surface, whereas on the Ge (111) surface, isotropic patterns with a sixfold symmetry emerge. After high-fluence irradiations, these patterns exhibit well-developed facets. A deterministic nonlinear continuum equation accounting for the effective surface currents due to an Ehrlich-Schwoebel barrier for diffusing vacancies reproduces remarkably well our experimental observations.

It has been recently found by energy filtered transmission electron microscopy (EFTEM) that metastable SiOx≈1 films decay into a Si nanowire network embedded in SiO2 by spinodal decomposition during thermal treatment. To have a guideline for nanocomposites fabrication, the details of the morphology evolution have been studied by comparison of EFTEM images with kinetic Monte-Carlo (kMC) simulations. Pair correlation functions calculated by kMC have been adjusted to that extracted from EFTEM. This comparison allows to conclude about characteristic lengths of 3D morphologies. Combining kMC with EFTEM delivers the understanding for tailoring the properties like quantum confinement of the spongy Si

The interaction between the Pseudomonas fluorescens biofilm and U(VI) were studied using extended X-ray absorption fine structure spectroscopy (EXAFS), and time-resolved laser fluorescence spectroscopy (TRLFS). In EXAFS studies, the formation of a stable uranyl phosphate mineral, similar to autunite (Ca[UO2]2[PO4]2•2–6H2O) or meta-autunite (Ca[UO2]2[PO4]2•10–12H2O) was observed. This is the first time such a biomineralization process has been observed in P. fluorescens. Biomineralization occurs due to phosphate release from the cellular polyphosphate, likely as a cell’s response to the added uranium. It differs significantly from the biosorption process occurring in the planktonic cells of the same strain. TRLFS studies of the uranium-contaminated nutrient medium identified aqueous Ca2UO2(CO3)3 and UO2(CO3)3 4− species, which in contrast to the biomineralization in the P. fluorescens biofilm, may contribute to the transport and migration of U(VI). The obtained results reveal that biofilms of P. fluorescens may play an important role in predicting the transport behavior of uranium in the environment. They will also contribute to the improvement of remediation methods in uranium-contaminated sites.

Using molecular dynamics simulations, we study the effects induced by the impact of Bin (n≤5) clusters with energies in the range of a 3–20 keV/atom into a Ge target. The target consists of Ge including a 10% contribution of randomly distributed Bi atoms. The impacting polyatomic clusters create a long-lived melt pool at the surface. After resolidification, the surface shows a characteristic meniscuslike depression; it is caused both by the missing sputtered atoms and by the volume change of Ge upon melting and amorphization. During cooling, Bi is driven towards the center of the melt pool. A large precipitate forms at the surface (for polyatomic impact) or in the center of the molten pocket (for monatomic impact). The remainder of the resolidified amorphous zone is purified from Bi. We argue that the reason for the demixing of Bi and Ge is the thermophoretic or Soret effect which is caused by the different diffusivities of Bi and Ge in the melt. Bi is sputtered preferentially from the sample. The extent of surface modification, the amount of Bi collected on the surface, the concentration of Bi, and structure of Bi precipitates in the former melt pool are analyzed in their dependence on projectile size, impact energy, and direction.