Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

A method allowing for position-resolved positron lifetime spectroscopy studies in large volume samples will be presented. This technique was developed at the superconducting linear accelerator ELBE (Electron linac with high brilliance and low emittance) at the Helmholtz-Zentrum Dresden-Rossendorf, Germany. A beam of continuous 16 MeV electron bunches of about 5 ps temporal width and a repetition frequency of 26 MHz was used to generate bremsstrahlung preserving the sharp timing of the electron beam. Positrons produced in the target via pair production feature a sharp time stamp for lifetime studies. They decelerate quickly and annihilate in microscopic defects. This allows for high timing resolution and high signal to background ratios due to the coincident detection of two annihilation photons. Two commercially available Lutetium Oxyorthosilicate scintillator (LSO) detectors were employed to detect the annihilation photons. These LSO detectors are already clinically used in the SIEMENS Biograph PET Scanner. Each detector consists of a crystal matrix with 13 13 pixels and a total size of 52 mm 52 mm 20 mm. The total energy resolution was measured to be 5.1% (RMS) and the timing resolution is 225 ps (RMS). Experiments resulting in position resolved lifetime measurements will be presented.

Radiation therapy is an important treatment modality in cancer therapy. New radiation species, like protons and light ions have the potential to increase tumor conformality of irradiation and to decrease normal tissue dose. Such high precision radiotherapy treatment requires efficient quality assurance techniques. Therefore, a dose monitoring system is highly desirable. Between 1997 and 2008, the in-beam Positron Emission Tomography (PET) method was used at the GSI Helmholtzzentrum fr Schwerionenforschung, Darmstadt, Germany, for monitoring the dose delivered by 12C beams. The spatial distribution of positron emitters generated via nuclear interactions is measured during and shortly after the irradiation. By means of a comparison between measured and simulated activity distribution conclusions on the accuracy of the dose deposition can be drawn. Different modalities of PET, i.e. measuring during the irradiation versus taking data after the treatment have been compared. Recent investigation and limits of the PET method used for in-vivo dose monitoring at ion beams will be presented and discussed. Due to inherent physical restrictions of this method, a direct quantification of the delivered dose is not feasible. Therefore, another approach based on dose monitoring by detection of prompt gamma rays is currently under investigation. In contrast to PET this method relies on the detection of prompt gamma rays between 0 and 10 MeV emitted almost instantaneously during the therapeutic irradiation. To measure these photons a Compton camera design was evaluated with respect to the special requirements and conditions that arise from this application. Different concepts were compared by means of simulation. The complete chain from simulation based on the treatment plan to the iterative reconstruction of the data was developed and is now under optimization. First measurements have been successfully performed with radioactive sources and ion beams.

Ion beams offer advantages over conventional treatment modalities, such as photons. Because of the way ions deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the collateral damage to the surrounding healthy tissue. However, small changes in the irradiated volume will lead to a misalignment of the deposited dose maximum and the tumor. Therefore, a dose monitoring system is highly desirable. Positron Emission Tomography (PET) was clinically applied for example between 1997 and 2008 at the GSI Helmholtzzentrum fr Schwerionenforschung, Darmstadt, Germany, for monitoring the dose delivered by 12C beams. Due to inherent limitations of this method, a direct quantification of the delivered dose is not feasible. Therefore, another approach currently under investigation monitors the dose by means of the detection of prompt gamma-rays. A Compton camera may be a feasible technical solution for such a monitoring system. A first prototype for imaging radioactive sources has been developed. Results of simulations used for the optimization of the detector configuration will be presented as well as an approach for the reconstruction.

In ion beam cancer therapy, range verification in patients using positron emission tomography (PET) requires the comparison of measured with simulated positron emitter yields. We found that 1) changes in modeling nuclear interactions strongly affected the positron emitter yields and that 2) Monte Carlo simulations with SHIELD-HIT10A reasonably matched the most abundant PET isotopes 11C and 15O. We observed an ion-energy (i.e., depth) dependence of the agreement between SHIELD-HIT10A and measurement. Improved modeling requires more accurate measurements of cross section values.

no abstract available

The use of cementitious materials is foreseen to immobilize long–lived intermediate level wastes that may contain significant amounts of 237Np. Predicting the release of Np from a cement–based repository requires an adequate understanding of its interaction with the main sorbing components of cement. Although Np(IV) will prevail under repository conditions after depletion of oxygen, Np(V) is expected to control the chemistry of neptunium in the early stage after repository closure as well as in the presence of oxidizing waste forms (i.e. high content of NO3–). Moreover, little is known on the stability of Np(VI) under hyperalkaline conditions, resulting in a rather ill–defined Np(V/VI) redox chemistry in cementitious environments.
Evaluation of XANES data from Np(V)–doped calcium silicate hydrates (C–S–H phases) and hardened cement paste (HCP) under anoxic and under oxidizing conditions (provided by 510–3M NaClO) clearly indicated the predominance Np(V) and Np(VI), respectively. Two different neptunyl moieties were also observed by EXAFS, with significantly shorter Np–Oax and Np–Oeq obtained for samples with NaClO (1.79–1.85 Å and 2.24–2.25 Å) compared to samples under anoxic conditions (1.88–1.89 Å and 2.39 Å), thus confirming the oxidation of Np(V) to Np(VI) in the presence of NaClO. The strong EXAFS features resulting from the neptunyl–oxygen coordination hamper the signal of atoms beyond their coordination sphere in Np(V/VI)–doped C–S–H and HCP samples. Nevertheless, Np–Oeq distances as well as evaluation of the Si–shells provided some evidence for an incorporation mechanism taking place in the C–S–H structure. In contrast to Np(V), the molecular environment of Np(VI) in C–S–H phases depends not only on the Ca:Si ratio of these phases but also on the pH of the solution, likely reflecting the differences between the hydrolysis scheme of both Np redox states under these pH conditions.
EXAFS data confirmed the predominance of aqueous Np(VI) species (as NpVIO2(OH)42–) in hyperalkaline and oxidizing tetramethylammonium hydroxide (TMA–OH) solutions. Under anoxic conditions and in the presence of CO32– (as impurity of TMA–OH), the predominance of a mixed Np(V)–OH–CO3 species was indicated by EXAFS. These Np(V/VI) aqueous species are not considered in the current NEA thermodynamic selection and therefore deserve further attention.

Lysinibacillus sphaericus JG-B53 was isolated from the uranium mining waste pile Haberland near Johanngeorgenstadt, Germany. Previous studies have shown that many bacteria that have been isolated from these heavy metal contaminated environments possess surface layer proteins (S-layers) which enable the bacteria to survive by binding metals with high affinity. Conversely, essential trace elements are able to cross the filter layer and reach the interior of the cell. This is especially true of the S-layer of Lysinibacillus sphaericus JG-B53 which is therefore of high interest for both environmental studies and technical applications. Particularly the latter due to the high amounts isolatable from biomass and the outstanding recrystallisation and metal binding properties.
In this study, S-layer protein gene sequences encoded in the genome of L. sphaericus JG-B53 were identified using next generation sequencing (NGS) technology followed by bioinformatic analyses. The genome of L. sphaericus JG-B53 encodes at least 8 putative S-layer protein genes with distinct differences. Using mRNA analyses the expression of the putative S-layer protein genes was studied. The functional S-layer protein B53 Slp1 was identified as dominantly expressed S-layer protein in Lysinibacillus sphaericus JG-B53 by mRNA studies, SDS PAGE and N-terminal sequencing. B53 Slp1 is characterised by square lattice symmetry and a molecular weight of 116 kDa.
The S-layer protein B53 Slp1 shows a high similarity to the functional S-layer protein of Lysinibacillus sphaericus JG-A12, being isolated from the same uranium mining waste pile Haberland described by previous research. These similarities indicate horizontal gene transfer and DNA rearrangements between these bacteria. The presence of multiple S-layer gene copies may enable the bacterial strains to quickly adapt to changing environments.

In this work, the influence of air pressure during the annealing of Ge quantum dot (QD) lattices embedded in an amorphous Al2O3 matrix on the structural, morphological and compositional properties of the film is studied. The formation of a regularly ordered void lattice after performing a thermal annealing process is explored. Our results show that both the Ge desorption from the film and the regular ordering of the QDs are very sensitive to the annealing parameters. The conditions for the formation of a void lattice, a crystalline Ge QD lattice and a disordered QD lattice are presented. The observed effects are explained in terms of oxygen interaction with the Ge present in the film.

Helmholtz-Beamline at XFEL

Nowadays, the development of new materials is often associated with specific properties of functionalized nanostructures. X-ray investigations are a very important tool to find the link between the functional (magnetism, luminescence) and the corresponding structural properties (size, orientation etc.) that are generating this function and to explain the underlying physical processes. This knowledge makes it possible to design new materials with specific properties.
Modern synchrotron sources give us the possibility to study the nanostructure during deposition. A sputtering chamber mounted on a six-circle goniometer allows an insight into the growth of nanostructures using different scattering and diffraction methods. We report on an in-situ X-ray investigation of a self-assembled growth of Ge nanocrystals embedded in a dielectric matrix forming a BCC-like super structure. A single some 100nm thick Ge+Al2 O3 layer using magnetron sputtering was deposited at an elevated substrate temperature. The self-assembly during growth or subsequent annealing results in the formation of a well ordered three-dimensional BCC-like quantum dot lattice within the whole deposited volume. The parameters of the formed super structure can be directly influenced by changing the deposition parameters. The self-ordering of the quantum dots is explained by diffusion mediated nucleation and surface morphology effects.

Objectives : [¹⁸F]fluspidine (FPD) is a new σ₁ receptor radioligand for imaging of cancer and neuropsychiatric diseases which consists of two enantiomers of different kinetics and affinity. Biodistribution, organ doses (ODs) and effective dose (ED) of (S)-(-)-FPD# (Ki=2.3nM) and (R)-(+)-FPD## (Ki=0,52nM) were determined in mice to assess the radiation risk to humans.

Methods : 28#/22## female CD1 mice (29.8±2.2g#/29.3±1.9g##) were injected with 0.35±0.08MBq# and 0.39±0.05MBq## FPD into tail vein. At 5, 15, 30, 45, 60, 90, 120, 180 and 240 min. p.i. they were sacrificed and organ masses and activity determined. The fractions of activity were displayed as %ID. Time and mass were scaled to human magnitude. Using OLINDA/EXM, the cumulated activity in source organs and ODs were calculated.

Results : For (S)-(-)-FPD the adrenals received the highest OD [µSv/MBq] (36.0), followed by the kidneys (35.6). The highest contribution to ED (ICRP103, [µSv/MBq]) was by lungs (3.7) and upper large intestine (2.0). For (R)-(+)-FPD the lungs receive the highest OD (45.5), followed by the kidneys (27.6). The highest contribution to ED was by lungs (5.5) followed by ovaries (2.0). The estimated ED is 16.7#/18.4##. Considering 40% underestimation in preclinical dosimetry [1] for 300MBq of FPD i.v. the expected ED to humans is 8.4# and 9.2## [mSv].

Conclusions : Considerable differences in ODs were observed between the enantiomers. However, the putative ED to humans is within the range of what is caused by other ¹⁸F-labeled compounds. The results support the further development of the radioligands as a clinical tool for brain and cancer PET-imaging.

[1] Sattler B, …, Sabri O. Incorporation dosimetry of F-18-Flubatine - Comparison of animal model data with first-in-man results J. Nucl. Med. 2012; 53(suppl): 1503.

Research Support: The trial is funded by the german research organization (AO599719)

Objectives : (+)-[¹⁸F]flubatine is the mirror image isomer of (-)-[¹⁸F]flubatine, which is successfully used for neuroimaging of alpha4beta2 nAChRs in human. To assess the radiation risk by this new radioligand, biodistribution, organ doses (OD) and the effective dose (ED) were determined in piglets.

Methods : Whole body dosimetry was performed in 3 female piglets (age: 43±1.2d, weight: 14±1.0kg). The animals were anesthetized and sequentially PET-imaged up to 5h post i.v. injection of 183.5±9.0MBq on a SIEMENS Biograph16 PET/CT-system on 7 bed positions (BP) per frame, 1.5 to 6 min/BP, CT-attenuation correction (AC) and iterative reconstruction. All relevant organs were defined by volumes of interest. Exponential curves were fitted to the time-activity-data (%ID/g, and %ID/organ). Time- and mass-scales were adapted to the human order of magnitude. The ODs were calculated using the adult male model with
OLINDA. The ED was calculated using tissue weighting factors as published in the ICRP103.

Results : The highest OD [µSv/MBq] was received by urinary bladder (71.7±26.3) and kidneys (45.1±6.5). The highest contribution to ED [µSv/MBq] was by urinary bladder (2.9±1.1) and lungs (1.7±0.02). The estimated ED to humans is 14.3±0.3.

Conclusions : Considering 40% underestimation of the ED to humans by preclinical dosimetry [1], the expected ED to humans after 300MBq i.v. is 7.2 mSv, which is about the ED by (-)-[¹⁸F]flubatine (6.8 mSv/300MBq) and well within the range of what other F-18-labeled compounds cause to humans. This risk assessment encourages to transfer (+)-[¹⁸F]flubatine from preclinical to clinical study phases and to further develop as a clinical tool for PET imaging of the brain.

[1] Sattler B, …, Sabri O. Incorporation dosimetry of F-18-Flubatine - Comparison of animal model data with first-in-man results. J. Nucl. Med. 2012; 53(suppl): 1503.

Research Support: The trial is partly co-funded by Strahlenschutzseminar in Thüringen e.V. and by Helmholtz Validation Fonds.

Objectives: Alpha7 nicotinic acetylcholine receptors (α7 nAChRs) play an important role in many neuropsychiatric diseases and various types of cancer [1]. [¹⁸F]NS10743, a promising and highly competetive α7 nAChR radioligand [1], has been successfully radiolabeled with high specific activity and radiochemical purity using a manual single-mode microwave device [2]. However, the palladium-catalyzed reduction of the remaining aromatic nitro-precursor (NS10796) to amine raises pharmaceutical restrictions and impedes the development of an automated radiosynthesis system. Here we report first results of a modified Discover CEM^® microwave-based automated radiosynthesis of [¹⁸F]NS10743, which is followed by a direct RP-HPLC separation of the product from the respective nitro precursor.
Methods: The reference compound NS10743 and the corresponding nitro-precursor NS10796 were separated by different analytical RP-HPLC conditions (Multospher 120 RP 18 AQ, ReproSil-Pur 120 CN, Lichrospher 60 RP Select B, ReproSil Gold 120 C18) using (26-95%) ACN with 10 mM NH4OAc in water. F-18 microwave-assisted nucleophilic substitution of the nitro-precursor (3.0-4.0 mg) was conducted using Kryptofix^® 2.2.2 (K222) as phase transfer catalyst. Reaction variables such as solvent system, reaction temperature, and time as well as microwave settings such as synthesis mode, applied power and cooling cycles were systematically optimized. Labelling yields were calculated based on radio-TLC and used to estimate the reproducibility of the microwave-based automated reactor. Semi-preparative RP-HPLC columns were chosen based on previous analytical tests, the desired product [¹⁸F]NS10743 separated from the precursor, purified with a Sep-Pak C18 cartridge and eluted with MeOH. Radiochemical purity was determined by radio-TLC and analytical radio-HPLC.

Figure. Analytical RP-HPLC separation of NS10743 from the corresponding nitro-precursor NS10796 using Reprosil-Pur 120 CN column (left) and one-step one-pot radiosynthesis of [¹⁸F]NS10743 (right).
Results: Optimal separation of NS10743 from the nitro-precursor NS10796 was obtained using the RP-HPLC Reprosil-Pur CN column and the related semi-preparative column using 26% ACN with 10 mM NH4OAc in water. NS10743 was eluted in front of NS10796 at low flow rates of 0.8 and 1.2 mL/min in analytical and semi-preparative RP-HPLC systems, respectively. Radiofluorination of NS10743 was successfully achieved using power cycling synthesis mode with 24 cooling cycles in DMF (140-158 °C) at a microwave radiation of 75 W for 15 min (Figure). Labelling efficiencies of ≥54% and radiochemical purity of ≥99% were achieved under these conditions, rendering a moderate-to-good reproducibility of the microwave cavity.
Conclusions: We achieved a promising one-step one-pot radiosynthetic route for the radioligand [¹⁸F]NS10743, avoiding the palladium-catalyzed reduction step. The microwave-based automated system module showed a moderate-to-good reproducibility, which encourages the further coupling with the automated system.
Acknowledgements: The work was financially supported by DFG (DE 1165/2-1).
References: [1] Brust P, Deuther-Conrad W(2012) Neuroimage Clinical Applications (Bright P., ed.) InTech - Open Access Publisher, 533-558. [2] Deuther-Conrad W, et al. (2011) Eur J Nucl Med Mol Imaging, 38, 1541–49.

Objectives: The cannabinoid receptor type 1 (CB₁) has been intensively investigated but much less is known about the role and distribution of the cannabinoid receptor type 2 (CB₂) in the central nervous system. Recently, we reported the synthesis and radiofluorination of a novel N-aryl-oxadiazolyl-propionamide for non-invasive imaging of CB₂ with PET. However, the radiolabelling yields were unsatisfactory [1]. Thus, medicinal chemistry approaches were taken to develop fluorinated CB₂ derivatives of 1 without compromising biological activity or selectivity. Radiofluorination and first biological evaluation were performed for the most promising CB₂-selective ligands.

Methods: The reference compounds 2 (X² = -¹⁹F) and 3 (Y² = -¹⁹F) were achieved via a modified synthetic procedure [2] from the respective benzoic acid, succinic anhydride and N-alkyl-3-amino-carbazole. SAR studies were performed by varying both N-carbazole and amide-oxadiazole chain lengths. In addition to this, the substitution pattern of the aromatic region has been investigated. Distribution coefficients (LogD, pH = 7.2) were experimentally determined for 2 and 3 using a RP-HPLC method. Aliphatic [X¹ = LG, Y¹ = -H (LG = leaving group)] and aromatic (X¹ = -H, Y¹ = -LG) radiofluorinations of 1 were performed in AcCN using Kryptofix® 222 (K₂₂₂) as phase transfer catalyst (PTC). The reaction conditions were optimized by varying the amount of PTC and precursor 1 (X¹ or Y¹ = -LG). For in vitro and in vivo studies, ¹⁸F-2 in isotonic saline solution containing 5% EtOH, was used. Rat spleen slices were incubated with ¹⁸F-2 in absence and presence of CB_1/2-specific ligands. Ex vivo autoradiographs were obtained from brain and spleen of CD-1 mice after i.v. injection of 30 MBq of ¹⁸F-2.

Figure 1. Radiofluorination of N-aryl-oxadiazolyl-propionamide precursors 1; Ki = inhibition constant

Results: The N-ethyltosylate-carbazole 1 (X¹ = -OTs, Y¹ = -F) was the best choice for aliphatic radiofluorination. Although several LG were implemented (compound 1, X¹ = H, Y¹ = -LG), aromatic radiofluorination was only successfully achieved using the ammonium salt 1 (Y¹ = Me₃N⁺I^–) as precursor. Under optimized conditions, similar radiolabelling efficiencies (>50%), high radiochemical purities (>97%) and specific activities >250 GBq/µmol were obtained for ¹⁸F-2 and ¹⁸F-3. Increasing amounts of K₂₂₂ lead to a decrease of the labelling efficiencies for ¹⁸F-2. LogD values of 3.8 and 4.4 for 2 and 3, respectively, suggest a good blood-brain barrier penetration. Autoradiography of spleen slices showed high inhibition of ¹⁸F-2 binding (≥–74%) by the CB₁/CB₂-specific CP55,940 and by CB₂-specific ligands (JTE 907, GP1a, SR144528). Notably, no inhibition by the CB₁-specific SR141716A was observed indicating highly selective CB₂ binding of ¹⁸F-2. Ex vivo autoradiographs at 30 min p.i. showed heterogeneous radiotracer distribution in spleen (%ID/g = 6.96), comparable to the in vitro distribution of [³H]CP55,940, and low uptake and homogenous radiotracer distribution in brain (%ID/g = 1.49).

Conclusions: Fluorinated derivatives of 1 have been synthesized and the compounds with the best pharmacological properties were further investigated. Direct nucleophilic ¹⁸F-substitutions successfully delivered highly selective CB₂ radioligands ¹⁸F-2 and ¹⁸F-3. Biological evaluation of ¹⁸F-2 suggests specific CB₂ binding in vivo, which makes the compound a promising candidate for further evaluation.
Acknowledgements: This work has been supported by the DFG (project BR 1360/12-1).
References: [1] Rühl T, et al. (2012), Org Med Chem Lett, 2:32 [2] Cheng Y, et al. (2008), J Med Chem, 51, 5019-5034.

Objectives: The particular properties of intracellular signalling triggered by activation of neuronal and non-neuronal α7 nicotinic acetylcholine receptors (nAChR) establishes the involvement α7 nAChR in a host of pathological conditions including brain and cancer diseases. Recent approaches to clinically use the potential of α7 nAChR as diagnostic target by quantitative imaging by PET interfere with insufficient characteristics of the available radiotracers. From a series of highly affine and α7 nAChR-specific oxadiazolyl-diazabicyclononanes we have chosen fluoro-phenyl- and N-fluoroethyl-indole-substituted ligands for radio-labelling and comparative preclinical investigation of the respective radiotracers [¹⁸F]NS10743 [1] and [¹⁸F]NS14490.

Methods: [¹⁸F]NS14490 was synthesized by both a two-step labelling process starting from the indole NS14540 via [¹⁸F]fluoroethyltosylate 1 as well as a one-step nucleophilic substitution of a tosylate precursor 2 using K[¹⁸F]F-Kryptofix 222-carbonate complex (Fig.1). Stability and partition coefficient (shake-flask method) at pH 7.2 as well as in vitro affinity towards α7 nAChR were analyzed. The specific in vitro binding of [¹⁸F]NS14490 assessed by autoradiography of mice and pig brain was compared with [¹²⁵I]α-bungarotoxin as reference. Biodistribution of [¹⁸F]NS14490 was investigated in female CD-1 mice at 5, 15, 30, and 60 min p.i. Radiotracer metabolism in vivo was studied by radio HPLC analysis of mice plasma, brain, and urine samples (30 and 60 min p.i.). Target specific binding of [¹⁸F]NS14490 in brain was shown by pre-administration of specific α7 nAChR ligands SSR180711 and NS6740 (10 mg/kg i.p., 10 min before [¹⁸F]NS14490). A preliminary dynamic PET study was performed in one female piglet.

Results: [¹⁸F]NS14490 was obtained by two-step and one-step radiosyntheses with labelling yields of ~7% and ~70%, respectively. The product of the further used one-step procedure was obtained with 36 ± 3% RCY at A_s ~150 GBq/µmol and a radiochemical purity of >98% within ~2.5 hours (n=13). [¹⁸F]NS14490 was stable for at least 120 min in both TRIS buffer and PBS. LogD_octanol/PBS of 1.11 ± 0.02 (n=12) and logD_{cyclohexane/PBS} = -2.05 ± 0.03 (n=3) were determined. The α7 nAChR binding affinity of NS14490 (K_i=2.5 nM) is considerably higher than assessed for NS10743 (K_i=11.6 nM [1]). The distribution of [¹⁸F]NS14490 binding in mice and pig brain matches the expression of α7 nAChR in these species. Compared to [¹⁸F]NS10743, a much lower fraction of [¹⁸F]NS14490 passed the blood-brain barrier (BBB) in mice (SUV 1.76 [2] vs. 0.05 at 5 min p.i.). Notably, pre-administration of NS6740 significantly reduced brain uptake of [¹⁸F]NS14490 in mice (-30% at 60 min p.i.; p-value <0.005), and the maximum SUV of [¹⁸F]NS14490 in pig brain (~0.6) was about tenfold higher than in mice. [¹⁸F]NS14490 is metabolically more stable than [¹⁸F]NS10743 [2] with 55% vs. 40% of total activity in plasma accounting for the respective parent radiotracer at 60 min p.i. , and the chromatographic analysis of brain samples revealed that none of the radiometabolites of [¹⁸F]NS14490 detected in plasma crossed the BBB.

Conclusion: Radiofluorination of the novel oxadiazolyl-diazabicyclononane analogue NS14490 was achieved and optimized. [¹⁸F]NS14490 was obtained with high RCY and A_s. Although biodistribution data indicate lower brain uptake of [¹⁸F]NS14490 in comparison to [¹⁸F]NS10743 in mice, the tenfold higher SUV in pig as well as the target specific binding shown by blocking studies in mice prompt us to continue with the preclinical evaluation of [¹⁸F]NS14490.

Acknowledgements: The work was financially supported by DFG (DE 1165/2-1). We would like to thank Jonni Heberg, Tove Thomsen, and Gitte Friberg for technical assistance.
References: [1] Deuther-Conrad, W, et al (2009) Eur J Nucl Med Mol Imaging, 36, 791-800.

Objectives: It is widely accepted that σ₁ receptors represent a novel biological target for the possible pharmacological treatment of cancer and several brain diseases, e.g. depression and neurodegeneration. From a series of σ₁-specific racemic ¹⁸F-fluoroalkylated spirocyclic piperidines^1-3 we have chosen the superior [¹⁸F]fluspidine [1] for detailed investigation of the (R)-(+)- and (S)-(–)-enantiomers (K_i: 0.52 nM; 2.3 nM) to identify their individual potential for disease-related imaging studies in humans.

Methods: The racemic tosylate precursor of [1] was enantioseparated by semi-preparative chiral HPLC on immobilized cellulose-tris-(3,5-dimethylphenyl)-carbamate as stationary phase. Automated radiosynthesis of (R)- and (S)-[1] was accomplished by nucleophilic substitution using K[¹⁸F]F-Kryptofix 222-carbonate complex (Figure 1) and organ distribution studies were performed in CD-1 mice to obtain organ-specific time activity data (%ID/g). Brain pharmacokinetics of the two enantiomers was confirmed by dynamic PET studies in pigs. Additionally, the highly selective σ₁ receptor agonist SA4503 was used in blocking studies to assess target specificity. SUV values were calculated for 24 MR-defined brain regions. Using a metabolite-corrected plasma input function compartment modelling was applied to estimate the distribution volume of both enantiomers.

Figure 2. PET time-activity curves for (S)- and (R)-[1] in pig brain (baseline and blocking conditions)

Results: Enantiomerically pure (R)- and (S)-tosylate precursors were obtained with high enantiomeric excess of >98 % and >96 %, respectively. (R)- and (S)-[1] were synthesized within ~70 min with RCY of 35-45% (EOS), RCP of >99%, and A_s of 650 and 870 GBq/µmol, respectively. In mice, both radiotracers readily passed the blood-brain barrier. However, large differences in brain pharmacokinetics of the two enantiomers were found with continuous increase of brain uptake of (R)-[1] (3.57 %ID/g at 5’, 6.01% ID/g at 240’ p.i.) in comparison to (S)-[1] with higher initial brain uptake (4.35 %ID/g at 5’ p.i.) and rapid clearance (1.04% ID/g at 240’ p.i.). Dynamic PET studies in pigs confirmed these enantiomer-related differences in brain uptake kinetics. Under baseline conditions, the initial uptake of (S)-[1] in brain was higher than that of (R)-[1] (e.g. SUV_{max, Cerebellum} ~3.4 vs. ~2.9). Clearance of (S)-[1] from brain was fast (SUV_Cerebellum ~1.1 at 95-120’ p.i.) whereas the uptake of (R)-[1] remained close to the initial level (SUV_Cerebellum ~2.5 at 95-120’ p.i.). In comparison to baseline data, application of σ₁ specific SA4503 reduced the uptake of (S)- and (R)-[1] in the target region cerebellum by initially 40% and 15% (SUV_max ~2.0 and ~2.5, respectively) and at later measurement periods significantly by ~80% (SUV ~0.2 and ~0.6 at 95-120’ p.i., respectively). Washout kinetics and SUV values determined under blocking conditions indicate both target specificity of the binding as well as minor nonspecific binding of the two radiotracers.

Conclusions: We successfully developed and validated an automated synthesis of the two enantiomers of [1]. The pharmacokinetics of (S)-[1] as investigated in two different animal models suggests that this radiotracer is most suitable for upcoming studies of depression-related changes in receptor expression in human brain. The irreversible-like binding behaviour of (R)-[1] may have advantages for tumor imaging.
Acknowledgements: Supported by DFG (STE 601/10-2, WU 176/7-2) and NIH (T32 EB004822).
References: [1] Fischer S, et al (2011) Eur J Nucl Med Mol Imaging, 38, 540-551. [2] Maisonial A, et al (2011) ChemMedChem, 6, 1401-1410. [3] Maisonial A, et al (2012) Bioorg Med Chem, 20, 257-269

An outline of current status of development of transport solutions for pin-power reconstruction in DYN3D is presented. Presently, an advanced method of current coupling collision probability with flux expansion in zones is being developed and tested for cylindrical geometry. Results of test calculations for cylindrical cell shows very good agreement with the results obtained with Monte Carlo method. This very convincing results encourage the development of a two dimensional solver and the implementation of this advanced pin power calculation method into DYN3D as further steps.

The advanced multi-group nodal diffusion code DYN3D is currently being extended to the analysis of Sodium-cooled Fast Reactor (SFR) cores. Thermo-physical properties of sodium (such as thermal conductivity, density, viscosity, etc.) were included into the thermal-hydraulics module database. The development of thermo-mechanical model (to account for the core thermal expansion effects) is planned for the near future. The main objective of this study is to demonstrate the feasibility of using DYN3D for the modeling of SFR cores. For this purpose, a 2D model of the mixed oxide fuel (MOX) European Sodium Fast Reactor (ESFR) core was considered. 2D full core depletion calculations were performed using Serpent-DYN3D code sequence and the results were compared with those obtained from a 2D full core Monte Carlo solution. Very good agreement between the codes was observed for the core integral parameters and power distribution at beginning of life (BOL) and end of life (EOL).

Objectives: The vesicular acetylcholine transporter (VAChT) is a transmembrane protein located in presynaptic vesicles of cholinergic neurons and is discussed to be an interesting target for PET imaging of neurodegenerative disorders. Previous developments of VAChT radiotracers are based on vesamicol (trans-2-(4-phenylpiperidino)cyclohexanol) and are focused on structural modifications in order to keep the high affinity of vesamicol to VAChT and to lower the affinity to σ₁ and σ₂ receptors, two off-targets which are also addressed by vesamicol. The moderate selectivity of several VAChT-ligands is one of the limiting factors for a successful application as radiotracer. Based on numerous literature data and our own intensive synthetic work in this field, we observed that structural modifications based on single-target structure affinity considerations are rarely successful. Therefore, we synthesized different series of systematically modified vesamicol analogs as basis for the development of a 3D-QSAR model, which will consider for the first time the affinity to VAChT as well as to the σ₁ and σ₂ receptors.

Methods: Nucleophilic ring opening of an epoxide precursor with a secondary amine was used to synthesize a large number of vesamicol derivatives. By varying the epoxide precursor, structural modifications in ring A of the vesamicol skeleton were realized (left part of the figure). Due to the selection of different amines, the rings B and C were sterically or electronically modified (right part of the figure). The binding affinities to VAChT were determined with competitive binding experiments using preparations of PC12 cells stably transfected with ratVAChT cDNA and (-)-[³H]vesamicol. To determine the binding affinity to the sigma receptors, rat cortex membranes and (+)-[³H]pentazocin for σ₁ and rat liver membranes and [³H]DTG for σ₂ receptors were used.

Results: So far we synthesized 55 derivatives belonging to the four classes of vesamicols, F-benzoylvesamicols, benzovesamicols and azavesamicols (Fig.) and determined their binding affinity to VAChT, σ₁ and σ₂ receptors. A few of them such as benzovesamicol or FBT are already known and were used as reference compounds. Interestingly, the VAChT binding data obtained by our test system differ to some extent from the values reported in literature. Therefore, VAChT binding data of selected vesamicol derivatives obtained either with PC12 cells or membranes of pig and/or rat brain are compared and differences of K_i values are discussed. The use of preparations obtained by freezing and thawing of PC12 cells stably transfected with ratVAChT cDNA and (-)-[³H]vesamicol was found to be the most practicable and reliable method. As a preliminary trend we could observe that modifications in ring B and C led to a loss of VAChT affinity, whereas modifications in ring A partly increased VAChT affinity, which was however often accompanied by an increase in σ₁/σ₂ receptor affinity.

Figure. Vesamicol as chemical lead and derived new analogs

Conclusion: Based on our previous results, we have to conclude that VAChT affinity suitable for PET imaging correlates often with significant off-target affinity to the σ₁ and σ₂ receptors.
Acknowledgment: Supported by DFG (WE 2927/4-1).

Objectives: (±)-[¹⁸F]Fluspidine represents a novel ligand with high binding affinity and selectivity toward σ₁ receptors [1,2]. With the aim to identify the individual potential of the two enantiomers of (±)-[¹⁸F]fluspidine for particular disease-related imaging studies, this racemate as well as its tosylate precursor needed to be enantioseparated. Therefore, we performed an extensive chiral HPLC study with different chiral stationary phases (CSPs) and eluent modes.

Methods: The use of the immobilized polysaccharide type column Chiralpak IA (Chiral Technologies Europe, Daicel) offered the possibility to study various solvents, which are not common for HPLC. We used mixtures of several alkenes with ethers, esters, alcohols and chlorinated solvents as NP mode eluents. ACN and MeOH as organic modifier mixed with aqueous TEA/AcOH or NH₄OAc as buffers were used in RP mode. Working with this column type in the polar ionic mode by using 100% ACN or MeOH with TEA/AcOH was possible as well. Furthermore, we studied the enantioselectivity on different coated polysaccharide phases (cellulose and amylose based), a Pirkle-type CSP (with pi-acceptor-donor character) and a glycopeptide CSP (teicoplanin derived; Dr. Maisch, Germany). The identification of the enantiomers was carried out with a chiral detector (OR 2090, JASCO) and is based on the measurement of optical rotation.

Results: The tosylate precursor could be best enantioseparated with the Chiralpak IA column using 90% n-hexane/THF/0.1% DEA. At a flow rate of 1mL/min the (–)-enantiomer eluted with t_R=13.9 min in front of the (+)-enantiomer with t_R=32.4 min. This remarkable separation is appropriate for a semi-preparative separation of the precursor compound to provide enantiomerically pure precursor compounds for the radiosynthesis of (S)-(–)-[¹⁸F]fluspidine and (R)-(+)-[¹⁸F]fluspidine. In contrast to the results obtained with the tosylate, the corresponding fluoro compound fluspidine could not be enantioseparated with the Chiralpak IA column. Also most of the other columns investigated were not successful. Exclusively, the Reprosil-Chiral OM column (comparable to Chiralcel OD) was appropriate to separate the fluspidine enantiomers sufficiently in NP mode using 97% n-hexane/isopropanol/0.1% DEA (Figure). This method was transferred to the automated radiosynthetic procedure to analyze the enantiomeric purity of (S)-(–)-[¹⁸F]fluspidine and (R)-(+)-[¹⁸F]fluspidine, which was higher than 97%.

Figure. Analytical enantioseparation of (±)-fluspidine (left) and verification of (R)-(+)-[¹⁸F]fluspidine after radiosynthesis (right) on Reprosil-Chiral OM with 97% n-hexane/isopropanol/0.1% DEA

Conclusion: We successfully developed two chiral HPLC methods for enantioseparation of fluspidine and its tosylate precursor. Furthermore, we have repeatedly shown, that it is not predictable which chiral phase will be suitable to separate the enantiomers of a compound even if the derivatives are structurally related.

Acknowledgment: Supported by DFG (STE 601/10-2, WU 176/7-2).
References: [1] Fischer S, et al (2011) Eur J Nucl Med Mol Imaging, 38, 540-551. [2] Maisonial A, et al (2012) Bioorg Med Chem, 20, 257-269.

Objectives: Pre- and postsynaptic modulation of different neurotransmitter systems and further non-neuronal mediators connect α7nAChRs to brain development, learning and memory, sleep, pain perception, reward, drug dependency and various neuropsychiatric diseases. Recent approaches to use α7 nAChR as target for neuroimaging interfere with insufficiencies of the available radiotracers connected to a rather low receptor density in brain¹. From a series of highly affine and α7nAChR-specific oxadiazolyl-diazabicyclononanes we have chosen fluoro-phenyl- and N-fluoroethyl-indole-substituted ligands for radiolabelling and comparative preclinical investigation of the respective radiotracers [¹⁸F]NS107432 and [¹⁸F]NS14490.

Methods: [¹⁸F]NS14490 was synthesized by one-step nucleophilic substitution of an unlabelled tosylate precursor (Fig.). Stability against defluorination and partition coefficient (shake-flask method, pH 7.2) and in vitro affinity towards α7nAChR and other nAChR were investigated. [¹⁸F]NS14490 receptor autoradiography of mice (Fig.) and pig brain was compared with [¹²⁵I]bungarotoxin as reference. In female CD-1 mice biodistribution (5´, 15´, 30´, 60´ p.i.) was investigated, and [¹⁸F]NS14490 metabolism was studied by radio-HPLC (plasma, brain, urine; 30´, 60´ p.i.). Target specific binding of [¹⁸F]NS14490 was demonstrated by pre-administration (10´ before radioligand) of highly specific α7nAChR ligands (SSR180711, NS6740; 10 mg/kg). A preliminary dynamic PET study was performed in female pig (Fig.).

Results: [¹⁸F]NS14490 was obtained within 2-2.5h with RCY of 36%±3% (n=13), RCP >98%, and A_s ~150 GBq/µmol. It was stable for >2h in TRIS-buffer and PBS. LogD_octanol/PBS of 1.11±0.02 (n=12) and logD_{cyclohexane/PBS} of -2.05±0.03 (n=3) were determined. The α7 binding affinity of NS14490 (2.5 nM) is considerably higher than assessed for NS10743 (11.6 nM²). [¹⁸F]NS14490 binding in mice and pig brain matches the expression of α7nAChR in these species. No receptor-free reference region was identified. Almost similar striatum-to-cerebellum ratios (~1.3) were obtained in pig autoradiography and dynamic PET studies with [¹⁸F]NS14490 and [¹⁸F]NS10743². However, compared to [¹⁸F]NS10743, a much lower fraction of [¹⁸F]NS14490 passed the blood-brain barrier (BBB) in mice (SUV 1.22 vs. 0.05 at 5´ p.i.). Notably, pre-administration of NS6740 significantly reduced the brain uptake of [¹⁸F]NS14490 in mice (30% at 60´ p.i.; p< 0.005) and the maximum SUV of [¹⁸F]NS14490 in pig brain (~0.6) was an order of magnitude higher than in mice. [¹⁸F]NS14490 is metabolically more stable than [¹⁸F]NS10743² with 55% vs. 40% of total activity in plasma accounting for parent compound at 60´ p.i. Chromatographic analysis of brain samples revealed that no radiometabolites of [¹⁸F]NS14490 crossed the BBB.

Conclusion: Radiofluorination of the novel oxadiazolyl-diazabicyclononane analogue NS14490 was achieved and optimized. [¹⁸F]NS14490 was obtained with high RCY, RCP and A_s. Although biodistribution data indicate lower brain uptake of [¹⁸F]NS14490 in comparison to [¹⁸F]NS10743 in mice, the more than ten-fold higher SUV in pig and the target specific binding shown by blocking studies in mice prompt us to continue with the preclinical evaluation of [¹⁸F]NS14490.
Acknowledgements: Supported by DFG (DE1165/2-1).

References: ¹Brust P, Peters D, Deuther-Conrad W (2012) Curr Drug Targets 13, 594-601.
²Deuther-Conrad W et al. (2009) Eur J Nucl Med Molec Imaging, 36, 791-800.

PET is a well-established neuroimaging method in identifying AD. An ideal PET biomarker for AD should allow a reliable estimation of disease risk and rate of disease progression long before first symptoms are clinically diagnosed. The main pathologic processes of AD, deposition of β-amyloid, hyperphosphorylated tau protein, degeneration of cholinergic and other neurons, precede clinical symptoms by years providing potential targets for the identification of individuals at risk for AD.
In the last few years, several PET tracers targeting β-amyloid in AD have been developed, such as [¹¹C]PIB, [¹⁸F]florbetaben, [¹⁸F]florbetapir, [¹⁸F]flutemetamol. The suitability of these PET radiopharmaceuticals to differentiate AD patients and patients with mild cognitive impairment (MCI) from control subjects has been demonstrated. However β-amyloid deposition has been found in about 20% of normal elderly subjects. Therefore other potential neuroimaging biomarkers, for instance based on radiopharmaceuticals for the cholinergic system may be of interest.
Loss of nicotinic acetylcholine receptors (nAChRs) is a major contributor to the cognitive deterioration in AD. The α4β2-nAChR subtype is thought to be the most severely reduced in the onset of AD. Using 2-[¹⁸F]F-A85380 PET we showed a significant decline in α4β2-nAChRs in early AD which correlated significantly with the loss of cognitive function. Because this tracer is not suitable as a biomarker in a routine clinical set-up for early AD-diagnosis we developed the new radiotracer (-)-[-[¹⁸F]flubatine with faster kinetics, significantly improved brain uptake and better image quality.
Our further attempts for development of PET biomarkers include the α7nAChR and σ₁ receptors as targets, as both are suggested to be involved in early AD. [¹⁸F]NS10743 and [¹¹C]NS14492 are radioligands which show high brain uptake, regional distribution and dose-dependent blockade in accordance with α7nAChR expression pattern in animal PET studies and are promising for in vivo mapping and quantitative imaging of α7nAChR in AD. For PET imaging of σ₁ receptors a series of fluoroalkyl substituted spirocyclic piperidines was developed and (S)-[-[¹⁸F]fluspidine has been selected as the most promising for molecular imaging in human.
Taken together, there is optimism that it might be possible in future to improve early neuroimaging diagnosis of AD as a multifactorial disorder by a multi-tracer PET imaging strategy, with important implications for early preventive/therapeutic interventions.

A fundamental problem in light-matter interaction is the coupling of an intense, monochromatic electromagnetic wave with a quantum mechanical two-level system. One effect related to this is the Autler-Townes or AC Stark effect. Originally observed and described in molecular spectroscopy the effect refers to a splitting of an energy level that is resonantly coupled via intense radiation to an adjacent level, i.e. the states get ”dressed” by the light-matter interaction. We investigate this effect using a free-electron laser (FEL) driven intra-excitonic transition between the heavy-hole 1s and 2p states in a semiconductor multiple quantum well. We have observed distinct intensity- and wavelength dependent Rabi sidebands of the 1s exciton line in the terahertz (THz) regime when the FEL was tuned around the 1s-2p transition [1]. Temperature-dependent measurements have been done and a clear Rabi-sideband behavior is observable up to 200 K where the thermal energy already exceeds the exciton binding energy by a factor of 1.7 [2]. A threefold NIR transmission change at 200 K on picosecond timescales could be promising for optical modulators with Peltier-cooling. We also present measurements at higher THz fields exploring the regime beyond the rotating-wave approximation (RWA), where the Rabi energy is comparable to the transition energy. Theoretical calculations support the understanding of the underlying processes especially for the high-field measurements.
[1] M. Wagner, H. Schneider, D. Stehr, S. Winnerl, A. M. Andrews, S. Schartner, G. Strasser, and M. Helm, Phys. Rev. Lett. 105, 167401 (2010)
[2] M. Wagner, M. Teich, M. Helm, and D. Stehr, Appl. Phys. Lett. 100, 051109 (2012)

A fundamental problem in light-matter interaction is the coupling of an intense, monochromatic electromagnetic wave with a quantum mechanical two-level system. One effect related to this is the Autler-Townes or AC Stark effect. Originally observed and described in molecular spectroscopy the effect refers to a splitting of an energy level that is resonantly coupled via intense radiation to an adjacent level, i.e. the states get ”dressed” by the light-matter interaction. We investigate this effect using a free-electron laser (FEL) driven intra-excitonic transition between the heavy-hole 1s and 2p states in a semiconductor multiple quantum well. We have observed distinct intensity- and wavelength dependent Rabi sidebands of the 1s exciton line when the FEL was tuned around the 1s-2p transition [1]. We also present measurements at higher electric fields exploring the regime beyond the rotating-wave approximation (RWA), where the Rabi energy is comparable to the transition energy. Theoretical calculations support the understanding of the underlying processes, which is especially interesting for the regime beyond the RWA. Also temperature-dependent measurements have been done and a clear Rabi-sideband behavior is observable up to 200 K where the thermal energy already exceeds the exciton binding energy by a factor of 1.7 [2]. A threefold NIR transmission change at 200 K on picosecond timescales could be promising for optical modulators with Peltier-cooling.
[1] M. Wagner, H. Schneider, D. Stehr, S. Winnerl, A. M. Andrews, S. Schartner, G. Strasser, and M. Helm, Phys. Rev. Lett. 105, 167401 (2010)
[2] M. Wagner, M. Teich, M. Helm, and D. Stehr, Appl. Phys. Lett. 100, 051109 (2012)

The M1 excitations in the nuclide 90Zr have been studied in a photon-scattering experiment with monoenergetic and linearly polarized beams from 7 to 11 MeV. More than 40 Ji^pi = 1+ states have been identified from observed ground-state transitions, revealing the fine structure of the giant M1 resonance with a centroid energy of 9 MeV and a sum strength of 4.17(56) mu_N^2 . The result for the total M1 strength and its fragmentation are discussed in the framework of the three-phonon quasiparticle-phonon model.

The transition from mild sedation to deep anaesthesia is marked by the phenomenon of burst suppression (BS). FDG-PET studies show that the cerebral metabolic rate for glu-cose (CMRglc) declines dramatically with onset of BS in the adult brain. Global CMRglc increases substantially in the post-natal period and achieves its maximum in preadoles-cence. However, the impact of post-natal brain development on the vulnerability of CMR-glc to the onset of BS has not been documented.
Therefore, cerebral blood flow and metabolism were measured using a variant of the Kety-Schmidt method, in conjunction with quantitative regional estimation of brain glucose uptake by FDG-PET in groups of neonate and juvenile pigs, under a condition of light sedation or after induction of deep anaesthesia with thiopental. Quantification of simultaneous ECoG recordings was used to establish the correlation between anaesthesia-related changes in brain electrical activity and the observed cerebrometabolic changes.
In the condition of light sedation the magnitude of CMRglc was approximately 20% higher in the older pigs, with the greatest developmental increase evident in the cerebral cortex and basal ganglia (P < 0.05). Onset of BS was associated with 20-40% declines in CMR-glc.
Subtraction of the mean parametric maps for CMRglc showed the absolute reductions in CMRglc evoked by thiopental anaesthesia to be two-fold greater in the preadolescent pigs than in the neonates (P < 0.05). Thus, the lesser suppression of brain energy demand of neonate brain during deep anaesthesia represents a reduced part of thiopental suppressing brain metabolism in neonates.

We present the results of velocity measurements obtained by ultrasonic Doppler velocimetry and local potential probes in the flow of GaInSn eutectic melt driven by a two phase inductor in a cylindrical container. This type of flow is expected in a recent modification to the floating zone technique for the growth of small-diameter single intermetallic compound crystals. We show that the flow structure can be changed from the typical two toroidal vortices to a single vortex by increasing the phase shift between the currents in the two coils from 0 to 90 degrees. The latter configuration is thought to be favourable for the growth of single crystals. The flow is also computed numerically and a reasonable agreement with the experimental results is found. The obtained results may be useful for the design of combined two-phase electromagnetic stirrers and induction heaters for metal or semiconductor melts.

We use a focused helium ion beam microscope to controllably remove material from Pt-capped thin film multilayers with perpendicular magnetic anisotropy. The dose range required to remove several nm of the cap layer is the same as that required to induce a spin reorientation transition. Milling depth for Pt is found to scale with the logarithm of ion dose, with very high removal yields of hundreds of atoms per He ion at low doses. While the deposited energy is of order of previous broadbeam helium irradiations, the current density impacting on the surface of the sample is several tens of A/cm2, orders of magnitude higher. Patterning of the platinum capping layer with 20 nm resolution is demonstrated.

Point contact spin transfer devices combining out-of-plane and in-plane magnetized layers are promising candidates for spin transfer oscillators, in that they can achieve high-power and close to zero field operation [1][2]. We present recent experimental results on spin transfer torque oscillators combining both out-of-plane (CoFe/Pd) and in-plane (CoFe) magnetized layers. The device structure is such that the in-plane layer is lithographically patterned (to serve as a nanopillar/point contact) whereas the out-ofplane layer is extended. We find that, unlike previously reported point-contact devices where both ferromagnetic layers were extended [2], microwave oscillations are excited at zero applied field. We investigate how the high frequency dynamics are affected as a function of in-plane applied magnetic fields. As the in-plane field is increased, the current frequency dependence changes from negative (red-shift) to positive (blue-shift) slope. This occurs as the magnetisation direction of the out-of-plane layer nears its anisotropy field which is determined from MR curves. High frequency oscillations persist beyond the anisotropy field of the out-of-plane magnetised layer.
In order to gain insight to the observed response of the system, we calculated current-field phase diagrams for both layers by numerical integration of the LLG equation, taking into account the Slonczewski spin Transfer torque including the spin transfer asymmetry characterized by the coefficient λ [3]. According to These calculations, dynamics in the in-plane layer are only expected when the initial magnetisation is aligned antiparallel to the applied field, while oscillations of the out-of-plane layer are not expected with an in-plane applied field above the anisotropy field. Since the observed microwave spectra seem not to be adequately explained by individual layer dynamics it may be necessary to account for dynamics of both layers simultaneously.

A.M.D. and C.F. acknowledge financial support from the Swiss National Foundation Ambizione grant (PZ00P2_131808).
References:
[1] Houssameddine, D. et al., Nature Mat. 6, 447 (2007).
[2] Rippard, W.H., et al., Phys. Rev. B. 81, 014426 (2010).
[3] Slonczewski, J.C., J. Magn. Magn. Mater. 247, 324 (2002).

Thermodynamic sorption models (TSMs) offer the potential to improve the incorporation of sorption in environmental modelling of contaminant migration. One specific application is safety cases for radioactive waste repositories, in which radionuclide sorption on mineral surfaces is usually described using distribution coefficients (Kd values). TSMs can be utilised to provide a scientific basis for the range of Kd values included in the repository safety case, and for assessing the response of Kd to changes in chemical conditions. The development of a TSM involves a series of decisions on model features such as numbers and types of surface sites, sorption reactions and electrostatic correction factors. There has been a lack of consensus on the best ways to develop such models, and on the methods of determination of associated parameter values. The present paper therefore presents recommendations on a number of aspects of model development, which are applicable both to radioactive waste disposal and broader environmental applications.
The TSM should be calibrated using a comprehensive sorption data set for the contaminant of interest, showing the impact of major geochemical parameters including pH, ionic strength, contaminant concentration, the effect of ligands, and major competing ions. Complex natural materials should be thoroughly characterised in terms of mineralogy, surface area, cation exchange capacity, and presence of impurities. During the application of numerical optimisation programs to simulate sorption data, it is often preferable that the TSM should be fitted to the experimentally determined Kd parameter, rather than to the frequently used percentage sorbed. Two different modelling approaches, the component additivity and generalised composite, can be used for modelling sorption data for complex materials such as soils. Both approaches may be coupled to the same critically reviewed aqueous thermodynamic data sets, and may incorporate the same, or similar, surface reactions and surface species. The quality of the final sorption model can be assessed against the following characteristics: an appropriate level of complexity, documented and traceable decisions, internal consistency, limitations on the number of adjustable parameter values, an adequate fit to a comprehensive calibration data set, and capability of simulating independent data sets. Key recommendations for the process of TSM development include: definition of modelling objectives, identification of major decision points, a clear decision making rationale with reference to experimental or theoretical evidence, utilisation of a suitable consultative and iterative model development process, testing to the maximum practicable extent, and thorough documentation of key decisions. These recommendations are consistent with international benchmarks for environmental modelling.

Cryogenic time-resolved laser-induced fluorescence spectroscopy (cryo-TRLFS) was successfully used to identify uranium binding forms in some German mineral waters of extremely low uranium concentrations (< 2.0 µg/L). The measurements were performed at low temperature of 153 K. The spectroscopic data showed a prevalence of aquatic species Ca2UO2(CO3)3 in all investigated waters, while other uranyl–carbonate complexes, viz, UO2CO3(aq) and UO2(CO3)22- only existed as minor species. The pH value, alkalinity (CO32-), and the main water inorganic constituents, specifically Ca2+ concentrations, showed a clear influence on uranium speciation. Thermodynamic calculations of the main uranium binding form in the investigated waters indicated a good agreement with spectroscopy.

Summary about interaction of Se(IV) with maghemite

Precession has long been discussed as a complementary energy source for homogeneous dynamo action. Here we describe the present status of the preparations - theoretical predictions, velocimetry of a scale model water experiment, and engineering/construction concerns - for a liquid sodium precession experiment. Furthermore, we report recent experimental and theoretical results on the magnetorotational (MRI) and Tayler (TI) instabilities, and discuss plans for a large-scale liquid sodium experiment to study the combination of MRI and TI.

Heiße Schmelzen werden in vielen Technologien eingesetzt, beginnend beim traditionellen Stahlguss über die Elektrolyse von Aluminium bis hin zur Züchtung von Silizium-Einkristallen. In der Optimierung dieser sehr energieintensiven Prozesse liegt ein volkswirtschaftlich relevantes Einsparpotenzial. Grundlage einer optimalen Prozessführung ist aber stets die Kenntnis der relevanten physikalischen Parameter der Schmelze, zu denen neben Temperatur, Druck und Lage der Phasengrenzen häufig auch das Geschwindigkeitsfeld gehört. Ein typisches Beispiel hierfür ist der Strangguss von Stahl, dessen finale Qualität ganz wesentlich von der Strömungsstruktur in der Kokille abhängt. Die online-Bestimmung dieser Strömung während des Gießprozesses würde die Möglichkeit einer aktiven Strömungskontrolle eröffnen, mit deren Hilfe deutlich höhere Gießgeschwindigkeiten erreicht werden könnten. In diesem Beitrag werden verschiedene Messprinzipien und ihre Anwendung für Flüssigmetallströmungen besprochen. Das erste Verfahren, die Ultraschall-Doppler-Velozimetrie (UDV), beruht auf der Bestimmung der Doppler-Frequenz-Verschiebung bei der Rückstreuung an bewegten Streuteilchen. Das zweite Verfahren nutzt den Faradayschen Induktionseffekt in bewegten elektrischen Leitern unter dem Einfluss eines äußeren Magnetfeldes. Auf dieser Basis wurden mehrerer kontaktlose Messverfahren entwickelt, so z. B. zur Bestimmung von Durchflüssen in Rohrströmungen, aber auch zur tomographischen Rekonstruktion vollständiger zwei- oder dreidimensionaler Geschwindigkeitsfelder.

Objectives
Spatial heterogeneity of FDG uptake in the tumor is a promising predictor of patient outcome in various tumor entities. Different definitions have been proposed for spatial heterogeneity of tracer uptake and mathematical approaches range from simple to very sophisticated algorithms. Here we propose a simple score for visual assessment of both heterogeneity (VSHETER) and shape irregularity (VSIRREG) of FDG uptake in the primary tumor. The prognostic value of these new scores was evaluated in sarcoma patients with F18‐FDG‐PET for initial staging.
Methods
In total 56 sarcoma patients (30 m, median age 15 y, range 2‐61 y) were included retrospectively. Histological subtypes were 22 Ewing sarcomas (EWS), 17 osteosarcomas (OS) and 17 sarcomas with various subtypes (VS). Primary tumors were visually analyzed for maximum tracer uptake relative to the liver uptake (5‐score), size (3‐score), heterogeneity of FDG uptake (3‐score), irregularity of the shape of FDG uptake (3‐score) and central necrosis (yes/no). The presence or absence of metastases was also taken into account (yes/no). The metabolic tumor volume (MTV) was measured using the semi‐automatic ROVER 3D segmentation tool which is based on thresholding at the volume‐reproducible intensity threshold after subtraction of the local background. Cox proportional hazards models and corresponding hazard ratios (HR) were used to analyze the predictive value of the visual scores as well as SUVmax and MTV for overall survival (OAS) and progression free survival (PFS).
Results
40 patients (17 EWS, 15 OS, 8 VS) survived till the end of the follow‐up with OAS times ranging from 9.1 to 97.8 months (median 46.5 months). OAS of non‐survivors ranged from 2.7 to 49.6 months (median 17.1 months). A significant association with sarcoma subtype was observed for SUVmax (p<0.01), VSHETER (p=0.05) and central necrosis (p<0.01). Multivariate cox proportional hazard analysis revealed VSHETER (HR=2.4, p=0.01) and tumor subtype (VS vs EWS, HR=4.9, p<0.01) as significant predictors of PFS whereas there was no significant association of PFS with VSIRREG, central necrosis, presence of metastatses, SUVmax or MTV. OAS was associated with the presence of metastases (HR=5.1, p=0.01), VSHETER (HR=2.6, p=0.04) and tumor subtype (VS vs EWS, HR=3.2, p=0.05). Conclusion A simple visual 3‐score for heterogeneity of FDG uptake in the primary tumor provides additional power for the prognosis of sarcoma patients based on F18‐FDG‐PET. Simple visual scores are easily implemented in the routine clinical workflow.

Arterial spin labeling (ASL) permits the non-invasive measurement of quantitative values of cerebral blood flow (CBF) and is thus well adapted to study inter- and intra-subject perfusion variations whether at rest or during an fMRI task. In this study, a template approach to detect brain activation as a CBF difference between resting and activated groups was compared with a standard generalized linear model (GLM) analysis. A basal perfusion template of PICORE-Q2TIPS ASL images acquired at 3T from a group of 25 healthy subjects (mean Age 31.6±8.3 years) was created. The second group of 12 healthy subjects (mean age 28.6±2.7 years) performed a block-design motor task. The template was compared with the mean activated image of the second group both at the individual and at the group level to extract activation maps. The results obtained using a GLM analysis of the whole sequence were used as ground truth for comparison. The influences of spatial normalization using DARTEL registration and of correction of partial volume effects (PVE) in the construction of the template were assessed.
Results showed that a basal perfusion template can detect activation-related hyperperfusion in motor areas. The true positive ratio was increased by 2.5% using PVE-correction and by 3.2% using PVE-correction with DARTEL registration. On average, the group comparison presented a 2.2% higher true positive ratio than the one-to-many comparison.

Euglena mutabilis cells were used to study the influence of eukaryotic microorganisms on the migration behavior of uranium in acid mine drainage (AMD) environments. Batch sorption experiments at pH 3 and 4 were performed in Na2SO4 background solutions to mimic AMD conditions and in NaClO4 background solutions for comparison, respectively. It was found that axenic cultures of Euglena mutabilis were able to bioaccumulate more than 94 % of uranium from a 1×10­5 mol/L uranium solution. Laser induced fluorescence spectroscopy, used to identify the speciation of uranium, indicated that the bioaccumulated uranium species forming in Euglena cells or on euglenid pellicles were related to carboxylic groups and/or organophosphate groups.
In similar experiments using sterile filtrated AMD waters, obtained from a former uranium mine, reduced uranium immobilization rates for Euglena mutabilis cells were observed. However, the identified uranium speciation in both experiments was identical. The reduced rates were attributed to the competition by other cations for available sorption sites on or in the Euglena cells. The results showed that Euglena mutabilis or components of it are able to immobilize aqueous uranium and thus may be used in future as promising agent for immobilizing uranium in low pH waste water environments.

A collaborative project funded by the Federal Ministry of Education and Research (BMBF) in the framework of the R&D program "Energie 2020+" by four Universities, two Research Centres and ANSYS is coordinated by Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The project is directed towards the development and validation of CFD models of boiling processes in PWR in the range from subcooled nucleate boiling up to the critical heat flux. The work is oriented towards basic research and focused on model development, simulation and experiments on different scales. An important objective is the education and maintaining of competence in nuclear technology.

This study aimed at visualization of cyclooxygenase-2 (COX-2) protein expression in melanoma cells by confocal laser induced cryofluorescence microscopy using 4-(3-(4-methoxyphenyl)-1H-indol-2-yl)benzene-sulfonamide (C1) representative for a novel class of autofluorescent 2,3-diarylsubstituted indole-based selective COX-2 inhibitors. COX-2 expression was measured in human melanoma cell lines A2058 and MelJuso by immunocytochemistry and immunoblotting. Cellular uptake experiments using varying C1 concentrations down to 0.1 nM (with/without molar excess of celecoxib as control) were performed at 37°C. Cryofluorescence microscopy was conducted at 20 K. COX-2 protein expression was successfully visualized by C1 in A2058 cells. COX-2-negative MelJuso cells showed no specific accumulation of C1. Control experiments using celecoxib and, additionally, implemented fluorescence spectroscopy confirmed specificity of both cellular uptake and intracellular association of C1. Cryofluorescence microscopy in combination with spectroscopy allowed for visualization of COX-2 protein expression in melanoma cells in vitro using a selective COX-2 inhibitor at very low concentrations.

Fragestellung.
Zielgerichtete Therapiestrategien gegen den epidermalen Wachstumsfaktorrezeptor (EGFR) mittels Cetuximab verbessern in Kombination mit Bestrahlung das Überleben und die lokale Tumorkontrolle bei Patienten mit Plattenepithelkarzinomen (SCC) des Kopf/Hals-Bereiches. Trotz dieses Behandlungserfolgs machen auftretende Tumorresistenzen eine weitere Optimierung dieser Therapie notwendig. In unserer Studie untersuchten wir das Überleben von SCC Zellen nach Behandlung mit einem Konjugat aus Cetuximab und dem Radionuklid Yttrium-90 ([⁹⁰Y]Y-CHX-A´´-DTPA-Cetuximab).
Methodik.
In vier verschiedene humane SCC Zelllinien (FaDu, SAS, UTSCC₁₄, A₄₃₁) wurden EGFR-Hemmung und nachgeschalteter Signalmoleküle mittels Western blot und die Bindung von Cetuximab an EGFR durch Fluorochrom-markiertes Cetuximab analysiert. Das Überleben nach Behandlung mit ⁹⁰Y, [⁹⁰Y]Y-CHX-A´´-DTPA-Cetuximab (beide ca. 5–15 MBq äquivalent zu 2–6 Gy), Cetuximab-DTPA oder Cetuximab alleine oder in Kombination mit externer Bestrahlung (Röntgenstrahlen; 200 kV, 20 mA, 1.3 Gy/min; 2–6 Gy) wurde im Koloniebildungstest bestimmt. Zusätzlich wurden Adhäsions- und gammaH₂AX-Foci-Assays durchgeführt.
Ergebnis.
Obwohl Cetuximab-Behandlung zu einer Hemmung von EGFR und nachgeschalteten Signalmolekülen führte, zeigte keine der verwendeten Zelllinien eine Strahlensensibilisierung. Fluorochrom-markiertes Cetuximab blieb zellmembranständig ohne Hinweise auf Internalisierung oder Abbau. ⁹⁰Y]Y-CHX-A´´-DTPA-Cetuximab verringerte das klonogene Überleben signifikant stärker und in Abhängigkeit der EGFR-Expression als alleiniges 90Y. Zellen, die mit 90Y plus externe Bestrahlung behandelt wurden, überlebten deutlich besser als Zellen nach [⁹⁰Y]Y-CHX-A´´-DTPA-Cetuximab plus externe Bestrahlung. Das klonogene Überleben konnte mit strahleninduzierten gammaH₂AX-Foci korreliert werden. Ein Einfluss von Cetuximab auf die Zelladhäsion war nicht zu verzeichnen.
Schlussfolgerung.
Unsere Daten zeigen, dass eine Verbindung aus Cetuximab und einem Radionuklid das Überleben von SCC Zellen deutlich stärker reduziert als das unkonjugierte Radionuklid oder externe Bestrahlung. Weitere In-vitro- und In-vivo-Studien sind nötig, um zu untersuchen, inwieweit derartige Konjugate in Therapiestrategien im Rahmen einer Strahlentherapie eingebunden werden können.

Effect of He ions irradiation on three model Fe100−xCrx alloys (x = 5.8, 10.75 and 15.15) was investigated with the conversion electron Mössbauer spectroscopy. The study of the alloys irradiated with 25 keV ions revealed that the strongest effect occured in the Fe84.85Cr15.15 sample where an inversion of a short-range-order (SRO) parameter was found.

Radiolabeled antibodies (Abs) are an attractive tool for targeting and delivering particle emitters for therapy or imaging applications. The labeling of Abs with metal radionuclides requires chelating agents and can cause loss of binding to their ligands. The aim of the present approach was to design an easy-handling flow cytometric cell-based assay to evaluate Ab-binding capacity of conjugates of the therapeutic Ab Cetuximab and to verify the most promising candidate in a competitive radioactive binding experiment. The final setup for flow cytometric assessment of cellular binding capacities of epidermal growth factor receptor (EGFR)/ErbB1-directed Ab conjugates is based on (a) the selection of a robust cell line model (b) the definition of nonsaturated staining concentrations for the unconjugated reference Ab Cetuximab plus implementation of a reasonable isotype control, and (c) the calculation of relative Ab affinities based on the flow cytometric data. Two (FaDu, SAS) out of the three cell lines with different total and cell surface expression levels of EGFR turned out to be adequate models but the application of one cell line was sufficient to estimate reduced binding capacities of conjugates relative to Cetuximab. Only 1/11 conjugate Abs exhibited a fluorescence signal comparable to unconjugated Cetuximab and was applied for radiolabeling with Yttrium-90. Unaltered binding affinity of this conjugate was proven in a competitive radioactive Ab-binding study. We conclude that the flow cytometric assay is reliable and that the relative binding capacity of Cetuximab is neither affected by covalent modification with CHX-A″-DTPA (N-[(R)-2-Amino-3-(p-isothiocyanato-phenyl) propyl]-trans-(S,S)-cyclohexane-1,2-diamine-N,N,N′,N″,N″-pentaacetic acid) with a final chelator-to-Ab ratio of 5 nor by subsequent radiolabeling. [₉₀Y]Y-CHX-A″-DTPA-Cetuximab thus qualifies for preclinical treatment testing as a prerequisite for therapeutic application.

We report on the emergence of an electronic Griffiths phase in the doped semiconductor FeSb₂, predicted for disordered insulators with random localized moments in the vicinity of a metal-insulator transition. Magnetic, transport, and thermodynamic measurements of Fe(Sb_1-xTe_x)₂ single crystals show signatures of disorder-induced non-Fermi liquid behavior and a Wilson ratio expected for strong electronic correlations. The electronic Griffiths phase states are found on the metallic boundary between the insulating state (x = 0) and a long-range albeit weak magnetic order (x ≥ 0.075).

Periodic semiconductor nanostructure arrays have the potential for nano-electronic and nano-optoelectronic application. The broad ion beam erosion is a simple and potentially mass productive technique to fabricate the nanostructure patterns on semiconductor surface as it avoids conventional lithographic steps.[1] The present work reports the fabrication of horizontal silicon nanowire arrays on insulator by Xe+ ion beam erosion of Si-on-insulator substrate. [3] A periodic ripple surface pattern of the Si surface is created by irradiation with Xe+ ions and the transfer of this pattern to the oxide interface as shown in figure 1a. This procedure results in an array of disconnected parallel ordered Si nanowires. A more recent achievement concerns nanopattern of single crystal Ge substrate which is based on a “negative epitaxy”. Vacancies created during ion beam sputtering will diffuse and rearrange according to the crystallographic anisotropy of the substrate which results in orientation-dependent pattern formation of the Ge surface.
Figure 1 (a) Schematic of Si NWs array fabricated by Xe+ beam irradiation on Si-on-insulator substrate. (b)Atomic Froce Miroscopy (AFM) images showing the nanostructure and pattern fabricated on Ge (100) and Ge (111) surface based on “negative epitaxy” process. The scale is 100 nm
[1] S. Facsko et al. Science 285, (1999) 1551.
[2] C. S. Madi et al. Physical Review Letters, 106, (2011) 066101.
[3] X. Ou et al. AIP Advances, 1, (2011) 042174.

The presentation gives an overview over current research topics, methods and results in research at the Institute of Fluid Dynamics at HZDR. The talk covers both research topics in nuclear reactor safety and efficient processes and described among other the development and application of advanced two-phase flow measurement techniques and computation afluid dynamics tools.

Recent progress with compact ionization chambers has opened new possibilities for isobar suppression in accelerator mass spectrometry (AMS). Separation of ³⁶Cl (t_1/2 = 0.30 Ma) at natural isotopic levels from its stable isobar ³⁶S became feasible at particle energies of 24 MeV, which are also accessible for mediumsized tandem accelerators with 3 MV terminal voltage like VERA (Vienna Environmental Research Accelerator). Investigations with an ionization chamber revealed how physics favors isobar separation even at energies below the maximum of the Bragg curve. The strong energy focusing effect at high energy losses reduces energy straggling significantly and isobar separation steadily increases up to almost full energy loss. With an optimized detection setup, sulfur suppression factors of 2 × 10⁴ have been achieved.
Refraining from the additional use of degrader foils has the benefit of high transmission to the detector (~16%), but requires a low sulfur output from the ion source. Therefore several backing materials have been screened for sulfur content. The dependence of the sulfur output on the AgCl sample size has been investigated as well.
Precision and accuracy have been thoroughly assessed over the last two years. Since drifts in the spectra are efficiently corrected by monitoring the position of the ³⁶S peak, the reproducibility for high ratio samples (³⁶Cl/Cl > 10^-12) is better than 2%. Our blank value of ³⁶Cl/Cl ≈ (5 ± 5) × 10^-16 is competitive to other labs. ³⁶Cl has become a routine AMS-isotope at VERA.
Recently we also explored novel techniques for additional sulfur suppression already in the ion source. While results with a small gas reaction cell in front of the sputter target were discouraging, a decrease in the sulfur/chlorine ratio by one order of magnitude was achieved by directing 300mW continuous wave laser beam at 445 nm towards the cathode in the ion source.

Im Rahmen eines vom BMBF geförderten Projektes beschäftigt sich die Abteilung „Reaktiver Transport“ des HZDR in Wechselwirkungsstudien mit der Komplexbildung und dem Transportverhalten von d- und f-Elementen mit makrozyklischen Chelatliganden.
Als kurzlebige Analoga für langlebige, umweltrelevante Radionuklide kommen in den Studien 56Co, 64Cu, 65Zn und 85Sr zum Einsatz. Diese werden am hauseigenen Zyklotron hergestellt. Die makrozyklischen Liganden basieren auf funktionalisierten Calix[4]arenen.
Das Komplexierungsverhalten der Calix[4]arene bezüglich der genannten Radionuklide wurde in Extraktionsstudien in flüssig-flüssig Systemen untersucht. Dabei lag der Fokus auf den Reaktionsbedingungen, unter denen eine erfolgreiche Extraktion realisierbar war. Die Extraktionswirkung der Calix[4]arene wurde mit Hilfe der Radiotracertechnik verfolgt.
Unter alkalischen Bedingungen konnten für zwei spezielle Calix[4]arene Extraktionsausbeuten von >90 % erreicht werden. Die entstandenen Komplexe wurden hinsichtlich ihres Bindungsverhaltens spektroskopisch untersucht. Weiterhin konnten Aussagen zur Reversibilität der Reaktionen getroffen werden.
Basierend auf den Reaktionsbedingungen konnten die Extraktionsversuche der Calix[4]arene bezüglich der erwähnten Radionuklide erfolgreich auf reale Wasserproben mit komplexeren Matrizes übertragen werden.

Die NUPEC “PWR Subchannel and Bundle Tests” (PSBT) waren zur Untersuchung kritischer Wärmestromphänomene in Brennelementbündeln und zur Validierung von Heißkanalcodes ausgelegt. Einige der Tests sind zur Validierung von CFD-Wandsiedemodellen geeignet. Der Vortrag präsentiert CFD-Analysen der Gasgehaltsverteilung unter Verwendung des CFD-Codes ANSYS CFX-12.1. Zunächst werden die wichtigsten Aspekte des implementierten Modells und Unsicherheiten der Modellparameter herausgestellt. Es kann gezeigt werden, dass die gemessenen querschnittsgemittelten Messwerte mit einem Satz im Rahmen der Mo-dellunsicherheiten kalibrierter Modellparameter reproduziert werden kann. Für die Reproduktion der Verteilungsmuster des Dampfgehaltes im Kanalquerschnitt muss die Modellierung der Turbulenz beachtet werden. Nur ein Turbulenzmodell, das die turbulenten Sekundärströ-mungen auflösen kann, ist in der Lage, die beobachteten Verteilungsmuster zu reproduzieren.

Eine Anforderung an das Wirtsgestein eines möglichen Endlagers für radioaktive Abfälle in tiefen geologischen Formationen ist dessen Funktion als geologische Barriere zur Herabsetzung der Mobilität von im Störfall freigesetzten Actiniden.
Zur Untersuchung des Rückhaltevermögens von Granit gegenüber Actiniden wurde in der Diplomarbeit die Sorption von U(VI) und Np(V) an Granit aus dem Untertagelabor in Äspö (Äspö Hard Rock Laboratory, Äspö HRL, Schweden) untersucht. Die Wechselwirkungen wurden in Batch-Sorptionsversuchen im Labor simuliert und beschrieben. Um den endlagerspezifischen Bedingungen und der geplanten Einlagerung von wärmeentwickelnden, hochradioaktiven Abfällen gerecht zu werden, wurde dabei der Einfluss der Korngrößen des Granits, der Einfluss der Ionenstärke des Hintergrundelektrolyten und der Einfluss der Temperatur unter anaeroben und aeroben Bedingungen ermittelt. Die Konzentration von U(VI) und Np(V) in der wässrigen Phase wird mittels Flüssigszintillation bestimmt. Der Oxidationszustand der Actinide wird durch Flüssig-Flüssig-Extraktion mit 2-Thenoyltrifluoroaceton in Xylol ermittelt. Durch Schwingungsspektroskopie (ATR FT-IR) wurde die Speziation der Oberflächenkomplexe bestimmt.

This paper documents the sedimentological setting, mineralogy, and geochemistry of several iron formation units interbedded with siliciclastic strata of the Mesoarchean Witwatersrand Supergroup, well known for its world-class conglomerate-hosted Au-U deposits. Four major iron formation beds, with associated magnetic mudstones, are present in two distinctly different lithostratigraphic associations, namely shale- and diamictite-associated iron formation. The shale association is represented by the Water Tower and Contorted Bed iron formations in the Parktown Formation of the Hospital Hill Subgroup in the lower part of the succession and the diamictite association by the Promise and Silverfield iron formations in the overlying Government Subgroup. The iron formation units have been subjected to lower greenschist facies metamorphism. Oxide (magnetite and limited hematite), carbonate, and silicate facies iron formations are recognized. The iron formations typically overlie major transgressive flooding surfaces in the succession and, in turn, form the base of progradational coarsening-upward increments of sedimentation comprising magnetic mudstone, nonmagnetic shale, and interbedded siltstone-quartzite. The upward transition from iron formation into magnetic mudstone is accompanied by a change in mineralogical composition from hematite-magnetite iron formation at the base in the most distal setting through magnetite-siderite- and siderite-facies iron formation in the transition zone to magnetic mudstone. The siderite with associated ankerite displays highly depleted 13C values, suggesting crystallization via iron respiration in presence of organic carbon. The iron formations display positive post-Archean Australian shale-normalized Eu and Y anomalies with depletion in light rare-earth elements relative to heavy rare-earth elements, indicating precipitation from marine water with a high-temperature hydrothermal component. Integration of sedimentological, petrographic, and geochemical results indicates that the shale-associated iron formation was deposited during the peak of transgression, when reduced iron-rich hydrothermal waters entered the Witwatersrand Basin over a limited vertical extent due to neutral buoyancy, with the top of the plume occurring below the photic zone. It is suggested that chemolithoautotrophic iron-oxidizing bacteria, which would have been able to exploit the difference in chemistry between the iron-enriched plume water and ambient ocean water to fuel metabolic activity in the presence of limited free molecular oxygen, were responsible for precipitation of initial ferric iron oxyhydroxides. The vertical facies associations in the iron formations most likely developed in response to the limited vertical extent of the hydrothermal plume, with (from distal to proximal) hematite preserved where the base of the plume was not in contact with the basin floor, magnetite where the plume water was in contact with bottom sediment, iron-rich carbonates where organic carbon input was high, iron-rich alumosilicates where siliciclastic input became significant in more proximal settings, and iron-poor sediment above the top of the plume. Diamictite-associated iron formations in the Witwatersrand are inferred to have been deposited in a fashion similar to the shale-associated iron formations, with the exception that major transgressions and hydrothermal plume invasion were preceded by glacial ice cover. The climate warming and increased volcanic activity required could have been related to increased tectonic activity inferred for the Witwatersrand Supergroup during deposition of the glacially associated iron formations.

The NUPEC “PWR Subchannel and Bundle Tests” (PSBT) were designed to investigate critical heat flux phenomena in rod bundles and yield data to validate hot channel codes. Some of the tests are suitable for validating a CFD wall boiling model. The paper presents CFD calculations of the void distribution tests of the PSBT benchmark using ANSYS CFX. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns. Furthermore the influence of bubble forces on the calculated void distribution is investigated.

New developments in the framework of a common project simulating subcooled boiling are described. The computational model used combines the Euler / Euler two-phase flow description with heat flux partitioning. Main achievements were a comprehensive study of the boiling process itself and a better description of the interfacial area by coupling of wall boiling with a population balance model. The paper presents validations and shows the capabilities of the model extensions. A careful calibration of correlations used in the wall boiling model is necessary to obtain agreement with the measured data. For the demonstration, DEBORA tests were used. During these tests radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size were measured.

Der Vortrag fasst den Wissensgewinn und das Fazit des Projektverbundes zusammen

Die Simulation des kritischen Wärmestromes spielt eine wichtige Rolle bei der sicheren und effektiven Auslegung von Anlagen zur Energieerzeugung. CFD-Modelle sind hierfür sehr gut geeignet, da sie es prinzipiell ermöglichen, Strömungsvorgänge unabhängig von der konkreten Geometrie in einem weiten Bereich der thermohydraulischen Parameter zu simulieren.
Ein im Rahmen des Förderprogramms "Energie 2020+" durch das Bundesministerium für Bildung und Forschung geförderten Verbundprojektes, in dem 4 Universitäten, 2 Forschungszentren sowie der Codeentwickler ANSYS zusammenarbeiten, wird durch das HZDR koordiniert. Das Projekt ist auf die Entwicklung und Validierung von CFD-Modellen für Siedevorgänge in Druckwasserreaktoren vom unterkühlten Sieden bis hin zum kritischen Wärmestrom gerichtet. Das Projekt ist auf die Grundlagenforschung orientiert und richtet sich auf die Modellentwicklung sowie die Durchführung von Experimenteten in verschiedenen Größenordnungen. Ein wichtiges Ziel ist die Ausbildung aund Aufrechterhaltung der Kompetenz in der Kerntechnik.

A collaborative project funded by the Federal Ministry of Education and Research (BMBF) in the framework of the R&D program "Energie 2020+" by four Universities, two Research Centres and ANSYS is coordinated by Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The project is directed towards the development and validation of CFD models of boiling processes in PWR in the range from subcooled nucleate boiling up to the critical heat flux. The work is oriented towards basic research and focused on model development, simulation and experiments on different scales. An important objective is the education and maintaining of competence in nuclear technology.

The NUPEC “PWR Subchannel and Bundle Tests” (PSBT) were designed to investigate criti-cal heat flux phenomena in rod bundles and yield data to validate hot channel codes. Some of the tests are suitable for validating a CFD wall boiling model. The paper presents CFD calcu-lations of the void distribution tests of the PSBT benchmark using ANSYS CFX-12.1. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncer-tainties in several model parameters. It is then shown that the measured cross sectionally av-eraged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections atten-tion has to be focussed on the modelling of turbulence in the narrow channel. Only a turbu-lence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns.

In this paper new developments in the framework of a common project simulating subcooled boiling are described. The computational model used combines the Euler / Euler two-phase flow description with heat flux partitioning. Main achievements were a comprehensive study of the boiling process itself and a better description of the interfacial area by coupling of wall boiling with a population balance model. The model extensions are validated and the present capabilities of CFD for wall boiling are investigated.

Der Erfolg zukünftiger Synchrotronstrahlungsquellen und Hochleistungs-IR-FELs wird eng mit der Entwicklung einer geeigneten Elektronenquelle verbunden sein. Einen vielversprechenden Ansatz, die dafür erforderliche Brillanz und den hohen mittleren Strom zu erzeugen, stellt der supraleitende Hochfrequenz-Photoinjektor (SRF-Gun) dar. Im Rahmen dieser Arbeit konnte die bislang einzige, an einem Elektronen-Linearbeschleuniger betriebene Quelle dieses Typs erfolgreich in Betrieb genommen sowie wesentliche Eigenschaften theoretisch und praktisch untersucht werden.

The success of future synchrotron radiation sources and high power IR free-electron lasers (FELs) largely depends on the development of an appropriate electron source. At the moment, the superconducting radio frequency photoinjector (SRF gun) seems to be a promising approach to achieve the required brightness and the high average current at the same time. Within the present thesis a SRF gun was brought into operation and essential characteristics were investigated. At the time of printing, it was the only source equipped with all components and operated at a linear accelerator.

Objectives: (-HF-18]-Flubatine (former NCFHEB) is a new tracer for neuroimaging of !l4ß2 nAChRs with PET. To assess the radiation risk, its biodistribution, organ doses (00) and effective dose (EO) were determined in pigs and compared to earlier results in mice and humans [SNM20J J No. 1454, 1459J.
Methods: For whole body dosimetry, 5 female piglets (age: 44±3.0d, weight: 13.7±1.7kg) were narcotized (20 mglkg Ketamine, 2mglkg Azaperone; 1.5% Isoflurane in 70% N20/30% 02) and sequentially imaged up to 5h post i.v. injection of 186.6±7.4MBq F1ubatine on a PET/CT-system with 7 bed positions (BP) per frame, J .5-6min/BP, CT-attenuation correction and iterative reconstruction. All relevant organs were defined by volumes of interest. Exponential curves were fitted to the time-activitydata (%ID/g, and %IO/organ). Time and mass were adapted to the human scale. The OOs were calculated using the adult male model with OLINOA. The EO was calculated using tissue weighting factors as published in the ICRPI03.
Results: The highest 00 was received by the urinary bladder (49.0± 19.4j.1SvIMBq*) and the kidneys (39.9±6. J *). The highest contribution to the EO was by the urinary bladder (2.0±0.7*) and the stornach (1.5±0.3*). The EO to humans after i.v. injection of(-)-Flubatine is 14.6±3.2*.
Conclusions: As true for other PET-Tracers, preclinical dosimetry potentially underestimates the EO to humans. The EO by F1ubatine yielded from pig-(this study) and mice-(14.2j.1SvIMBq) studies compared to human dosimetry (22.6±0.68j.1Sv/MBq) show that animal dosimetry underestimates the potential radiation exposure to humans by 35-37%. This fact needs to be considered in the assessment ofthe EO to humans prior early phase clinical trials.
Research Support: The study was supported by Strahlenschutzseminar in Thüringen e. V

To overcome the current difficulties in designing a slurry bubble column reactor with respect to the effect of particle properties, the influence of solid concentration (Cs) on the hydrodynamics of a slurry bubble column was studied experimentally using ultrafast electron beam X-ray tomography. Experiments were carried out for dP = 100 µm at Cs = 0 – 0.36 at superficial gas velocity UG = 0.02 – 0.05 m/s in a slurry bubble column of diameter DT = 0.07 m. The real time gas flow structure, average bubble diameter and average gas hold-up as a function of UG and Cs have been reported. Corresponding three-phase simulations were also performed using the Euler-Euler multi-fluid model implemented in CFX 14. The bubble size distribution was calculated using the MUSIG model. The predicted gas hold-up and bubble size distribution also show dependence on UG and Cs and agree quite well with the measurements.

Fe ions have been implanted into Si (100) single crystals using ion implantation technique. The Fe ions have been accelerated to 45 keV with a dose of 5x10(17) ion/cm(2) at room temperature. The ions have been sent to the substrate's surface at normal incidence. The temperature dependence of magnetization measurement was explored at the temperature range of 10-300 K. The implanted Si substrate was studied with Ferromagnetic Resonance (FMR) technique and Vibrating Sample Magnetometer (VSM). The FMR spectra were recorded by applying external magnetic field in different experimental geometries. FMR spectra were analyzed and the magnetic properties, which are the g-factor, effective magnetization and uniaxial anisotropy parameter, were estimated by simulation of the experimental data. The sample showed two-fold magnetic anisotropic symmetry. By fitting the Si-2p region obtained through XPS measurements it is observed that Fe and Fe compounds are present in the material.

There is a strong controversy in the literature on the effect of particle properties which limit reliable design of slurry bubble columns. Thus, the influence of particle size (dP) and solid concentration (Cs) on the hydrodynamics of a slurry bubble column was studied experimentally using ultrafast electron beam X-ray tomography. Experiments were carried out for dP = 50 - 150 µm at Cs = 0 – 0.20 and superficial gas velocity UG = 0.02 – 0.05 m/s in a slurry bubble column of diameter DT = 0.07 m. The real time gas flow structure, average bubble diameter and averaged gas hold-up were found to be independent of dP and Cs at small particle size and low solid concentration. However, at large dP and high Cs, strong dependency on dP and Cs was observed. Corresponding three-phase simulations were also performed using the Euler-Euler multi-fluid model implemented in CFX 14. The bubble size distribution was calculated using the MUSIG model. The predicted gas hold-up and bubble size distribution also shows dependence on dP and agreed quite well with the measurements and previous studies

Multiphase flows are omnipresent in the chemical industry. The flow phenomena in multiphase reactors strongly affect the processes performance. Nonetheless, even basic information on flow patterns, flow regimes and effects of internals etc. is often not available, which is a strong obstacle for a reliable design and scale-up. Non-invasive tomographic techniques are promising measurement tools to visualize opaque multiphase flows. The contribution provides a short survey about today’s tomographic imaging techniques and introduces the principles of radiation-based tomography. In particular, two gamma-ray computed tomography designs and their application for a sparger performance studies in large bubble columns and for flow regime determination in inclined rotating fixed bed reactors is presented.

Computational fluid dynamics simulations for two-phase flows are important in different fields of engineering and science. Since two-phase flows are inherently complex, also CFD modeling development requires special attention. The validation of model implementation and the derivation of physics based models for momentum, heat, and mass transfer in two-phase flow require experiments with generation of high-resolution measurement data. This, however, is a great challenge, since most standard flow measurement tools used in single phase flow situations, are not suited for multiphase flows.
In this article we report on advanced imaging and measuring methods for two-phase flow ex-periments, which have been extensively used in the recent past to conduct experiments for two-phase flows at the Helmholtz-Zentrum Dresden-Rossendorf. In particular the application of wire-mesh sensors, ultrafast X-ray tomography, gamma ray tomography and positron emis-sion tomography will be introduced and discussed.

In the past years a growing community of measurement scientists and engineers has been struggling with new and optimized measurement and imaging techniques for process engineering applications. This research and development is mainly driven by needs in industry and fundamental science to obtain quantitative parameters from industrial processes. The commonality behind these needs is the fact, that many industrial processes are governed by multiphase flows of educts and products, whose parameters must be obtained in many places of plants and facilities. Most prominent examples of such are multiphase chemical reactors, separation units and solids processing units, thermal hydraulic circuits in nuclear reactors and solar power plants, as well as multiphase streams in mineral oil production. Moreover, there is also a constant pressure from fundamental flow mechanical science to have high resolution experimental data from multiphase flows available for the validation of CFD codes.

Tomographic imaging techniques naturally provide a good basis for multiple parameter measurements, though the requirements for high resolution in space and time, robustness with respect to harsh process conditions and cost issues are difficult to meet, particularly within one instrument or technique. Hence the field of process tomography has been seen to develop continuously since almost 30 years. Mature concepts of robust and non-intrusive tomographic imaging techniques, such as electrical resistance (ERT), capacitance (ECT) or impedance (EIT) tomography, are today constantly improved regarding particular needs of industrial applications, such as real-time monitoring and parameter extraction, 3D imaging and sensor data fusion. Now, however, they become more and more complemented by new techniques, such as electromagnetic tomography (EMT), electromagnetic flow metering with distributed sensors and industrial hard field imaging techniques. Furthermore, emerging process and environmental technologies, like carbon capture and storage, ionic liquids for chemical engineering applications, geothermal energy harvesting and new routes of mineral oil and gas production, such shale gas exploitation, deep-water offshore oil production and processing of high viscosity crudes and and oil sands, demand also new ideas and sensors from industrial process tomography.

The 4th International Workshop on Industrial Process Tomography IWPT-4 held in Chengdu, China, Sept. 21st-23rd, 2011 was a platform for specialists to present and discuss their most recent advancements in the development and application of process tomography techniques. The workshop was the fourth in a successful series of workshops held in Beijing and Hangzhou (2005), Macau (2006), and Tokyo (2009). It was organized by the International Society for Industrial Process Tomography (ISIPT) together with the Institute of Mechanics of the Chinese Academy of Science and hosted by Southwest Petroleum University.

Die Energieeffizienz großtechnischer Prozesse ist ein wichtiges Ziel von Forschungs- und Entwicklungsaktivitäten in Unternehmen und Forschungsinstitutionen. Zum einen sichern Maßnahmen zur Erhöhung der Energieeffizienz unmittelbar die Wettbewerbsfähigkeit von Unternehmen, zum anderen besteht ein gesellschaftlicher Konsens über die Notwendigkeit der Erreichung klima- und energiepolitischer Zielstellungen, insbesondere zur Reduktion der produktionsbedingten Treibhausgasemissionen. Die politischen Ziele dazu sind ehrgeizig und wurden insbesondere in Deutschland durch den im Jahr 2011 beschlossenen Umbau der Energieversorgung durch schrittweise Abschaltung der deutschen Kernkraftwerke bis 2022 und eine deutliche Steigerung der Energieerzeugung aus erneuerbaren Energiequellen neu justiert. Mit dem Umbau der Energieversorgung sind eine Reihe technischer, wirtschaftlicher und gesellschaftlicher Probleme zu lösen. Dies betrifft die effiziente Gewinnung, Speicherung und Verteilung von elektrischer Energie aus erneuerbaren Energiequellen ebenso wie ein bedarfs- und angebotsoptimiertes Netz- und Lastmanagement im Energienetz. Parallel dazu sind weitere umfassende Maßnahmen zur Senkung des Primärenergieverbrauchs durch eine Steigerung der Energieeffizienz in Wirtschaft, Privathaushalten und im Transportsektor unerlässlich.
Die Helmholtz-Gemeinschaft deutscher Forschungszentren (HGF) stellt sich dieser Aufgabe durch verstärkte Investitionen in Forschungsinfrastrukturen und eine weitere Vernetzung der Forschungsaktivitäten zwischen Helmholtz-Zentren und Universitäten. Im Hinblick auf die neuen energiepolitischen Rahmenbedingungen in der Bundesrepublik Deutschland startete die Helmholtz-Gemeinschaft deutscher Forschungszentren im Jahr 2011 eine Initiative zur Förderung neuer Themen der Energieforschung. Die in diesem Beitrag vorgestellte Helmholtz-Energie-Allianz ist ein Forschungsverbund, der Kompetenzen und Forschungsaktivitäten im Bereich der chemischen Verfahrenstechnik bündelt. Die Ziele des auf drei Jahre angelegten Forschungsvorhabens bestehen in der Weiterentwicklung von Entwurfs- und Auslegungsmethoden sowie numerischen und experimentellen Techniken zur Effizienzsteigerung chemischer Mehrphasenprozesse, die in der chemischen Produktion von herausragender Bedeutung sind.

The structural and magnetic properties of 20-nm-thick FexPt100-x films that were processed by 20 ms flash-lamp annealing were investigated. A maximum in coercivity of (10.4 ± 0.5) kOe was achieved for a composition of Fe53Pt47, which shows also a high degree of L10 chemical order. A variation of the chemical composition toward either higher or lower Fe content leads to a lowering of the coercivity, which can be attributed to a reduction in L10 ordered volume fraction. Thus, in the millisecond time regime, the fastest ordering transformation occurs for slightly Fe-rich FePt films.

YSZ (yttria-stabilized zirconia) with cubic phase is a promising nuclear material. YSZ has excellent radiation resistance and chemical stability and can be applied for the inter matrix layer of fuel cells or for the covering and storage of nuclear waste. The effect of irradiation on YSZ has been intensively investigated in recent years via single beam implantation.[1,2] Most of experimental works were performed to simulate the radiation damage from alpha particles by He+ implantation [2] or to simulate the neutron radiation damage and the damage introduced from alpha recoils by implantation of heavy ions. [1] In fact, the radiation damages created by the simultaneous dual beam implantation of Zr+ and He+ ions is much more adequate to reflect the real irradiation conditions. However this case is rarely reported in the literature due to the experimental restrictions. In this work the dual beam facility in Rossendorf is used for the investigation of the radiation damage in YSZ created either by simultaneous implantation of Zr+ & He+ or by separate single beam implantation. The samples were analyzed by a variety of methods such as Rutherford backscattering spectrometry in channeling mode, high resolution x-ray diffraction, positron annihilation spectroscopy, nanointendation and transmission electron microscopy.
The results show that the excitation by the additional Zr+ implantation can activate and enhance the out diffusion of the simultaneously implanted He. The release of He.from YSZ substrate, instead to be trapped by implantation induced vacancies generated by the heavy Zr+ ions, avoids the formation and growth of He bubbles. Such bubbles make the material hard and brittle. In this way the ability of YSZ for the stable inclusion of nuclear waste in the long term is verified. Possible mechanisms are discussed.

[1] S. Moll et al., Journal of Applied Physics 105, 023512 (1999).
[2] G. Velisa et al., Journal of Nuclear Materials 402, 87 (2010).

The resistive switching (RS) of functional oxide thin films has attracted tremendous interest recently due to its promising application as building blocks in non-volatile memory devices. [1] By applying voltage pulses, the functional oxide films are switched between different resistance states and may store information, which is the basis of resistance random access memory (RRAM). However, the RS performance of the oxides still needs improvement for a future commercial application, and the physical mechanism of the RS is not fully understood yet. The point defects, especially oxygen vacancies, play an important role on determining the electrical conduction of oxide thin films. [2] This work reports a low cost and effective approach to tune the resistive switching behavior of BiFeO3 films which have been deposited by pulsed laser deposition [3] and irradiated with low energy Ar+ ions. Due to the preferential sputtering of BiFeO3 films, oxygen vacancies as well as the surface morphology can be tuned by low energy irradiation in a controllable way to enhance the RS performance. The obvious improvement of key switching parameters, i.e. the resistance stability and retention, was observed in the irradiated BiFeO3 (Figure 1). These improvements give an opportunity to design a nonvolatile memory with a multilevel RS function which is more scalable than a memory based on bistable RS reported by most of studies [3]. The changing of the conduction mechanism in the BiFeO3 from Poole-Frenkel to space-charged-limited conduction after irradiation will be discussed. The combination of the microstructure analysis and the electrical characterization of the irradiated BiFeO3 will gain an insight into the resistive switching mechanism.

Figure 1(a) I-V characteristic curves showing a significant improvement of the stability of resistive switching in BiFeO3 film after irradiation. The distinguishable neighboring resistance states in the irradiated sample allow for designing multilevel RS memory devices based on BiFeO3 films. (b) Retention test showing the nonvolatile resistance states in irradiated BiFeO3 film on an extrapolated time scale of 10 years.

[1] R. Waser et al., Nature Materials 6, (2007) 833.
[2] D. W. Reagor et al., Nature Materials 4, (2005) 593.
[3] Y. Shuai et al., Applied Physics Letters 98, (2011) 232901.
[4] Y. Shuai X. Ou et al., Journal of Applied Physics 111, (2012) 07D906.

The periodical semiconductor nanostructure arrays have the potential for nano-electronic and nano-optoelectronic application. Comparing to the conventional low efficiency lithographic techniques broad ion beam erosion is a simple and potentially mass productive technique to fabricate the nanostructure patterns on semiconductor surface.[1] Based on a “self-organized” erosion process, periodical nanoripple, nanohole, nanodot and nanotip arrays can be created due to the interplay of different processes.[2] As the ion beam erosion is performed on Si /Ge thin layer on insulator substrate and precisely ceased when the nanopattern moves to the interface of the buried oxide layer, an array of separate nanostructure can be fabricated on insulator. This work reports the fabrication of the horizontal silicon nanowire arrays on insulator by Xe+ beam erosion of Si-on-insulator substrate [3] (figure 1a). A periodic ripple surface pattern on Si is created by ion irradiation with Xe+ at an incidence angle of 67o to the surface normal. The transfer of the pattern to the oxide interface results in an array of disconnected parallel ordered Si nanowires.The electrical doping behaviour of the fabricated Si nanowire was investigated by scanning spreading resistance microscopy (SSRM). Meanwhile, we will also report our recent discover of single crystal Ge nanopattern formation based on “negative epitaxy” process (figure 1b). The vacancies created during the ion beam sputtering will be distributed according to the crystallographic anisotropy, which results in the orientation-dependent pattern formation on single crystal Ge surface. The mechanism of this novel process will be discussed.
[1] Stefan Facsko et al. Science 285, 1551 (1999).
[2] C. S. Madi et al. Phys. Rev. Lett. 106, 066101 (2011).
[3] Xin Ou et al. AIP Advances, 1, 042174 (2011).

The periodical semiconductor nanostructure arrays have the potential for electronic and optoelectronic application. Comparing to the conventional low efficiency lithographic techniques broad ion beam erosion is a simple and potentially mass productive technique to fabricate the nanostructure patterns on semiconductor surface.[1] Based on a “self-organized” erosion process, periodical nanoripple, nanohole, nanodot and nanotip arrays can be generated due to the interplay of different processes.[2] As the ion beam erosion is performed on Si /Ge thin layer on insulator substrate and precisely ceased when the nanopattern moves to the interface of the buried oxide layer, an array of separate nanostructure can be fabricated on insulator. This work reports the fabrication of the horizontal silicon nanowire arrays on insulator by ion beam erosion of Si-on-insulator substrate [3] and the fabrication of different single crystal Ge nanopattern and nanostructure based on novel “negative epitaxy” process induced by ion beam erosion. The electrical doping behaviour of the fabricated Si nanowire and formation mechanism of the Ge nanopattern will be discussed.
[1] Stefan Facsko et al. Science 285, 1551 (1999).
[2] C. S. Madi et al. Phys. Rev. Lett. 106, 066101 (2011).
[3] Xin Ou et al. AIP Advances, 1, 042174 (2011).

Low-energy Ar+ ion irradiation has been applied to an Au/BiFeO3/Pt capacitor structure before deposition of the Au top electrode. The irradiated thin film exhibits multilevel resistive switching (RS) without detrimental resistance degradation, which makes the intermediate resistance states more distinguishable, as compared with the nonirradiated thin film. The stabilization of resistance states after irradiation is discussed based on the analysis of the conduction mechanism during the RS, which was investigated by means of temperature-dependent current–voltage measurement from room temperature to 423 K

The Cu^II complex of H₄TETP (H₄TETP = 1,4,8,11-tetraazatetradecane-1,4,8,11-tetrapropionic acid) is five-coordinate with a distorted square-pyramidal structure (τ = 0.45; i.e. the geometry is nearly half-way between square-pyramidal and trigonal-bipyramidal) and a relatively long Cu–N and a short Cu–O bond; the comparison between powder and solution electronic spectroscopy, the frozen solution EPR spectrum and ligand-field-based calculations (angular overlap model, AOM) indicate that the solution and solid state structures are very similar, i.e. the complex has a relatively low “in-plane” and a significant axial ligand field with a d_x ² _−y ² ground state. The ligand-enforced structure is therefore shown to lead to a partially quenched Jahn–Teller distortion and to a relatively low complex stability, lower than with the corresponding acetate-derived ligand H₄TETA. This is confirmed by potentiometric titration and by the biodistribution with ⁶⁴Cu-labeled ligands which show that the uptake in the liver is significantly increased with the H₄TETP-based system.

Polyoxometalates (POMs) are inorganic cluster compounds that have been shown to possess a number of pharmacological properties, including antidiabetic, antibacterial, antiprotozoal, antiviral and anticancer activities. Their molecular mechanism of action is largely unknown. However, several studies indicate that many of their activities may be due to the inhibition of enzymes, in particular, of those enzymes that are accessible from the extracellular space and do not require the penetration of cell membranes. In this review, we describe the recent progress in the preparation and optimization of POMs, and an evaluation of their use as inhibitors of different families of enzymes. The next important steps in this area of research will be to gain a better understanding of the interactions of POMs with enzymes on a structural level through an X-ray crystallographic study of enzyme–POM complexes and the analysis of structure–activity relationships. Furthermore, POMs with increased stability and in vivo half-lives have to be prepared. Surface modification may allow the targeting of POM drugs at their sites of action.

The search for new methods of cancer diagnosis is leading to the development of multimodal imaging agents that may be detected by techniques such as Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET). A new bimodal imaging agent has been prepared which can be used for dual mode detection of cancer by both MRI and PET imaging. The imaging agent consists of an azamacrocyclic ligand, 1,4-bis (2-pyridilmethyl)-1,4,7-triazacyclononane (DMP-TACN), linked to iron oxide nanoparticles through polyethylene glycol (PEG) chains (M_n ~ 600) that are attached to the nanoparticle surface by silanization. The azamacrocyclic ligands serve as complexing agents for radioactive copper (⁶⁴Cu) for PET imaging, while the iron oxide nanoparticles work both as a carrier and an imaging agent for MRI. The iron oxide nanoparticles have been synthesized by thermal decomposition from iron oleate. The functionalized nanoparticles have sizes ranging between 7–10 nm, as determined by TEM, whilst Nanoparticle Tracking Analysis (NTA) experiments suggest an average hydrodynamic diameter of 50 nm. ⁶⁴Cu labeling experiments revealed that the nanoparticles loaded with DMP-TACN have a labeling yield of around 10%. MRI experiments in rats showed the nanoparticles accumulate in the liver 15 min after intravenous administration. 64Cu labeling and breast tumor cell labeling studies are currently being performed using the new nanoparticles.

The tridentate macrocycle 1,4,7-triazacyclononane (TACN) forms stable complexes especially with Cu(II) whereby the metal ion lying out of the plane defined by the three nitrogen atoms. The donor atoms are oriented in such a way as to maximize orbital overlap and thereby produce complexes with very high stabilities. The introduction of further donor groups on the ligand skeleton, such as pyridine units, significantly influences the thermodynamic stability as well as the kinetic inertness of the metal complexes formed. We have developed a ligand scaffold based on bis(2-pyridylmethyl)triazacyclononane (DMPTACN) [1]. This structure allows for the introduction of linker groups, such as carboxylic acids, maleimide or isothiocyanate, thereby facilitating coupling of targeting molecules (see Figure).
TACN ligands containing one or two pendant 2-picolyl arms prefer the formation of square-pyramidal coordination geometry with copper(II). A hexadentate ligand with two picoline coordination groups as well as a carboxylic functionality (DMPTACN-COOH) enforces a six-coordinate copper(II) complex having a distorted octahedral structure. It has been found that relevant peptide conjugates of this hexadentate bis(2-pyridylmethyl)-TACN-acetic acid derivative can readily form radiocopper complexes under physiologically relevant conditions and show high in vivo stability. Such radiolabeled peptides are thus attractive candidates for radiopharmaceutical applications.
We want to present the synthesis of peptide conjugates with DMPTACN derivatives capable of gastrin releasing peptide receptor (GRPR) and epidermal growth factor receptor (EGFR) targeting. Both types of receptors are overexpressed on different cancer cells. In vitro binding characteristics of [⁶⁴Cu]Cu^II-labeled DMPTACN-peptide conjugates in GRPR and EGFR overexpressing cancer cells (PC-3, FaDu, A431) will be presented. Small animal PET studies confirmed a high extent of tumor accumulation in NMRI nu/nu mice bearing the human prostate tumor PC-3. Derived from that, it can be concluded that ^64CuII complexes of DMPTACN-peptide conjugates have considerable potential for tumor imaging, since these peptide derivatives can effectively display receptor-rich tissue in vivo.
[1] G. Gasser, L. Tjioe, B. Graham, M. J. Belousoff, S. Juran, M. Walther, J.-U. Künstler, R. Bergmann, H. Stephan, L. Spiccia, Bioconjugate Chem. 2008, 9, 719-730.

No abstract needed

Since the DREAMS (Dresden Accelerator Mass Spectrometry) facility went operational in 2011, constant effort was put into enabling routine measurements of long-lived radionuclides as ¹⁰Be, ²⁶Al and ⁴¹Ca. For precise AMS-measurements of the volatile element Cl the key issue is the minimization of the long term memory effect [1]. For this purpose one of the two original HVE sources was mechanically modified, allowing the usage of bigger cathodes with individual target apertures. Additionally a more open geometry was used to improve the vacuum level. To evaluate this improvement in comparison to other up-to-date ion sources, a small interlaboratory comparison had been initiated.
The long-term memory effect in the Cs sputter ion sources of the AMS facilities VERA, ASTER and DREAMS had been investigated by running samples of natural ³⁵Cl/³⁷Cl-ratio and samples containing highly enriched ³⁵Cl (³⁵Cl/³⁷Cl > 500). Primary goals of the research are the time constants of the recovery from the contaminated sample ratio to the initial ratio of the sample and the level of the long-term memory effect in the sources.
[1] R. Finkel et al., NIMB 294 (2013) 121.

In 2011 the DREAMS (Dresden Accelerator Mass Spectrometry) facility [1] based on a HVE 6 MV Tandetron went operational. Since then constant effort was put into enabling routine measurements of long-lived radionuclides such as ¹⁰Be, ²⁶Al and ⁴¹Ca. In the case of ³⁶Cl the main focus was set on understanding and minimization of the ion source memory effect, which is the key issue for precise AMS-measurements of volatile elements like Cl and I [2,3]. For this purpose, one of the two original HVE sources was mechanically modified. The new design has a more open geometry to improve the vacuum level and a modified target loading and positioning system, which allows exchanging the individual cathode aperture with each target.
To evaluate this improvement in comparison to other up-to-date ion sources, a small interlaboratory comparison had been initiated. The long-term memory effect in the four Cs sputter ion sources of VERA [3] (Vienna Environmental Research Accelerator, NEC ion source: MC-SNICS), ASTER [4] (Accélérateur pour les Sciences de la Terre, Environnement, Risques, modified HVE SO110) and DREAMS (original HVE and modified HVE ion source) [1] had been investigated by running samples of natural ³⁵Cl/³⁷Cl-ratio and samples containing highly enriched ³⁵Cl (³⁵Cl/³⁷Cl > 500).
Primary goals of the research are the time constants of the recovery from the contaminated sample ratio to the initial ratio of the sample and the level of the long term memory effect in the sources.

[1] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 (2013) 5.
[2] R. Finkel et al., Nucl. Instr. Meth. B 294 (2013) 121.
[3] M. Arnold et al., Nucl. Instr. Meth. B 294 (2013) 24.
[4] M. Martschini et al., Nucl. Instr. Meth. B 269 (2011) 3188.

Geologische Karte mit Erläuterungen des Freistaates Sachsen 1 : 25000 (Blatt 5047 Freital)

At the ELBE accelerator at the HZDR a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and for the generation of broad band and narrow bandwidth coherent THz pulses in the frequency range between 0.1 THz – 3 THz. Similar to previous work at the prototype THz pump probe facility at FLASH [1,2] the natural synchronization between light pulses generated by the same electron bunch shall be employed for fully synchronized experiments between narrow and broad band THz pulses. The pulse energies are expected to exceed the 100 microJ limit at scalable repetition rates between 1 and 200 KHz (cw), thereby the coherent THz facility will represent a worldwide unique facility. Besides user experiments the laboratory is also foreseen as a test bed for THz-based electron bunch diagnostics (arrival time, bunch form, …) on cw linear accelerators. The current status of the project and planned experiments are presented.
[1] M. Gensch et. al., The new THz undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[2] U. Fruehling, M. Wieland, M. Gensch et. al., Single-shot Terahertz-field driven Streak camera, Nature Photonics 3 (2009), 523.
[3] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch et. al., Few Femtosecond Timing at 4th Generation X-ray light sources, Nature Photonics 5 (2011), 162."

The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to 100 MV/m regime has led to a number of exciting experiments in particular in the field of non-linear THz spectroscopy and THz control experiments. One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators [1]. A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrow-bandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator-based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra-high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X-ray pulses in 4th Generation X-ray Light sources such as FLASH [2,3,and 4] and LCLS [5]. This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5]. An overview over different THz facility projects will be presented and experimental opportunities and challenges for in particular the life sciences will be discussed on the example of recent pilot experiments.

[1] G.L. Carr et. al., High power terahertz radiation from relativistic electrons, Nature 420 (2002), 153.
[2] M. Gensch et. al., New infrared undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[3] U. Fruehling et. al., Single-Shot THz-field-driven X-ray streak camera, Nat. Photon. 3 (2009), 523.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few-Femtosecond timing at Fourth-Generation X-ray Light sources, Nat. Photon. 5 (2011), 162.
[5] D. Daranciang et. al., Single-cycle terahertz pulses with > 0.2 V/angstrom field amplitudes via coherent transition radiation, Appl. Phys. Lett. 99 (2011), 141117.

Zircon and monazite from the Stolpen granite and related rhyolitic dyke show magmatic as well as post-magmatic textures. The magmatic textures are overprinted by post-magmatic fluid interaction which is indicated by elevated contents of Y, P, Th, and U in altered zircon domains. This can be observed both in the granite and rhyolite; however these processes were less intensive in the rhyolite. Patchy zoning in primary monazite from the granite also suggests fluid-induced alterations. High Ca, Pb, and Si contents and depletion in Th, as well as porous, spongy textures in monazite from the rhyolite are results of fluid-induced alterations that caused also crystallization of cheralite. Zircon and monazite from the granite are accompanied by fluorite, Y-rich and Nb-rich minerals. The alteration of primary, magmatic accessory minerals and formation of secondary minerals is interpreted as related to magmatic fluids, which origin cannot be defined precisely on the base of the present data, however their composition suggests some mantle contribution. The presence of fluorine and CO2 which promoted the transport of some HFSE and LILE accounts for their enrichment in the accessory minerals. Fluids that affected the accessory minerals from the rhyolite show different features (silica- and Ca-enrichment) and most probably came from another source

Vorstellung des technischen Konzepts und der analytischen Möglichkeiten der Super-SIMS.

Sophisticated sample preparation including the determination of stable nuclides are an essential prerequisite for high-accuracy accelerator mass spectrometry (AMS) data. Improvements in the low-level regime already paid back [1], however, some pitfalls still exist or are (re-) appearing due to recent developments:

1.) As most samples prepared for ¹⁰Be-AMS need the addition of ⁹Be in the form of a liquid solution of known ⁹Be-concentration and commercial solutions contain too much ¹⁰Be, solutions from minerals originating from deep mines have been established. Special attention has recently been paid to the preparation of such a ⁹Be-carrier by the determination of the ⁹Be-value by an interlaboratory comparison. It could be shown that deviations between different labs exist, thus, it is strongly advised to have such solutions analysed at more than a single lab to prevent incorrect ¹⁰Be-results.
2.) In our approach to analyse as many radionuclides as possible in a single meteorite sample, small changes in the established chemical separation [2] have been tested. Though, the secondary formation of partially insoluble compounds of Mg and Al by the pressure digestion is strongly influenced, thus, yielding to too low ²⁷Al-results in the taken aliquot and overall incorrect ²⁶Al-results.
Ackn.: DREAMS-team and colleagues performing ⁹Be- and ²⁷Al-measurements (BAM, GFZ, HZDR, CEREGE, TUBAF, U Cologne, VKTA). Ref.: [1] NIMB 266 (2008) 4921. [2] RCA 84 (1999) 215.

We report on an experimental analysis of the charge transport through sulfur-free photochromic molecular junctions. The conductance of individual molecules contacted with gold electrodes and the current-voltage characteristics of these junctions are measured in a mechanically controlled break-junction system at room temperature and in liquid environment. We compare the transport properties of a series of molecules, labeled TSC, MN, and 4Py, with the same switching core but varying side-arms and end-groups designed for providing the mechanical and electrical contact to the gold electrodes. We perform a detailed analysis of the transport properties of TSC in its open and closed states. We find rather broad distributions of conductance values in both states. The analysis, based on the assumption that the current is carried by a single dominating molecular orbital, reveals distinct differences between both states. We discuss the appearance of diode-like behavior for the particul!
ar species 4Py that features end-groups, which preferentially couple to the metal electrode by physisorption. We show that the energetic position of the molecular orbital varies as a function of the transmission. Finally, we show for the species MN that the use of two cyano end-groups on each side considerably enhances the coupling strength compared to the typical behavior of a single cyano group.

Seltenerdbasierte MOS Emitter zeigen bei elektrischer Anregung die für Seltene Erden typischen Lumineszenzspektren. Die Anregung erfolgt über Stoßanregung heißer Elektronen, die aber gleichzeitig zu einer Degradation des Oxides führt. Die für die Elektronen erforderliche Beschleunigungsstrecke in der Größenordnung von 10-20 nm begrenzt die Dicken- und Spannungsskalierung nach unten. Mögliche Strategien zur Optimierung von Effizienz und Betriebslebensdauer beinhalten u. a. die Verwendung von Sensitizern zur Erhöhung des Anregungsquerschnittes bzw. das Einfügen einer SiON-Pufferschicht. Anwendungsmöglichkeiten liegen in der Sensorik mittels integrierter, optoelektronischer Chips.

Neptunium ist eines der wichtigsten Radionuklide in der Problematik der Endlagerung nuklearer Abfälle. Obwohl die Np-Konzentrationen im radioaktiven Abfall aus der Energiegewinnung gering sind, zählt es aufgrund seiner hohen Halbwertszeit (2x106 Jahre), seiner physiologischen Verfügbarkeit und seiner potenziell gesundheitlichen Schadwirkung zu den gefährlichsten Nukliden [1].

Die Sorption von Neptunium an der Wasser-Mineral Grenzfläche spielt eine wesentliche Rolle in der Abschätzung seines Migrationsverhaltens in der Umwelt. Frühere Untersuchungen zeigen, dass die Np(V) Sorption an Tonmineralen durch eine Vielzahl verschiedener Faktoren beeinflusst wird, z. B. pH-Wert, Np-Konzentration, Vorhandensein anderer Kationen und Ionenstärke. Bekannte Sorptionseigenschaften wurden vorrangig mittels Batch Versuchen erhalten [2-4]. Aussagen über die Struktur und Stöchiometrie der bei der Sorption entstandenen Neptuniumkomplexe konnten bisher nur über die Modellierung von Sorptions- und thermodynamischen Daten gewonnen werden und sind durch geeignete spektroskopische Methoden zu überprüfen [4].

Die Infrarotspektroskopie kann durch die Erfassung von charakteristischen Schwingungsfrequenzen von funktionellen Gruppen (z. B. NpO2+) Informationen zur Struktur von Molekülen bzw. von Molekülkomplexen liefern [5]. In wässrigem Milieu werden diese Untersuchungen mittels der „Attenuated Total Reflection“-Technik (ATR) durchgeführt. Somit kann die Sorption von Ionen an mineralischen Phasen in situ (z. B. in Durchfluss-experimenten) eingehend studiert werden. Durch das definierte Einstellen physikalisch-chemischer Parameter der wässrigen Lösung (pH-Wert, Ionenstärke, etc.) lassen sich definierte, naturnahe Reaktionsbedingungen schaffen.
Als Modellsystem für komplexe Tonminerale soll sich diese Untersuchung mit der Np Sorption an verschieden Mineraloxiden (z. B. Al2O3, SiO2, TiO2) beschäftigen. Die zu erhaltenden IR-Spektren sind von großer Bedeutung, um die Komplexierung der NpO2+ Kationen mit den Aluminol-, Silanol- oder Titanol- Oberflächengruppen zu verstehen und dienen als Basis für spätere Untersuchungen komplexerer Mineralsysteme.

Referenzen:

[1] Kaszuba, J.P. et al. (1999) Environ. Sci. Technol. 33, 4427-4433.
[2] Li, W.J. et al. (2003) J. Colloid Interface Sci. 267, 25-31.
[3] Del Nero, M. et al. (2004) Chem. Geol. 211, 15-45.
[4] Tochiyama, O. et al. (1995) Radiochim. Acta 68, 105-111.
[5] Müller, K. et al. (2009) Environ. Sci. Technol. 43, 7665-7670.

Geplante Arbeiten:

FT-IR Durchflussexperimente zur Sorption von Np(V) an Al2O3, SiO2, TiO2 bei Variation sorptionsbestimmender Parameter (pH, Np(V)-Konzentration, Ionenstärke, Anwesenheit von anorganischen Liganden, z. B. Carbonat)

Die vorliegende Diplomarbeit entstand vom 15.04.2012 bis zum 15.10.2012 in der Abteilung Grenzflächenprozesse des Instituts für Ressourcenökologie des Helmholtz-Zentrums Dresden-Rossendorf.
Für abgebrannte Brennelemente aus Kernkraftwerken wird neben der Wiederaufarbeitung vor allem die direkte Endlagerung als Entsorgungskonzept verfolgt. Die Endlagerbehälter korrodieren während der Einlagerungszeit, sodass der uranhaltige Abfall in die Geosphäre eintreten kann und dort physikalischen und chemischen Einflüssen ausgesetzt ist. Hohe Bedeutung kommt hier der Bildung von Hydroxo- und Carbonatokomplexen des Uranyl-Ions (UO22+) zu, welche die Chemie des Urans in wässrigen Systemen (Grundwasser) dominieren.
Die einzelnen Komplexe weisen dabei je nach Zusammensetzung unterschiedliche Affinität zu natürlichen Oberflächen – wie zum Beispiel Mineraloberflächen – auf, wobei die Beschaffenheit sowohl dieser Grenzflächen als auch der Koordinationssphäre des UO22+-Ions starke Temperatur- und pH-Anhängigkeiten zeigen. In der vorliegenden Arbeit wurde vorrangig der Temperatureinfluss auf die Sorptionsprozesse des Uran(VI) an Mineraloxidoberflächen im Temperaturbereich zwischen 25 °C und 60 °C eingehend untersucht. Dies wurde mittels zweier experimenteller Ansätze bewerkstelligt: Die Infrarot-Spektroskopie liefert Informationen zu Art und Struktur der infolge Sorption gebildeten Oberflächenkomplexe, während klassische Batch-Versuche zur Betrachtung des Verteilungsgleichgewichts zwischen gelöstem und sorbiertem Uran nützlich sind. Als Modelloberflächen für natürliche Gesteine und Minerale dienten verschiedene Metalloxide wie TiO2, SiO2, α-Fe2O3, γ-Al2O3 und γ-Al(OH)3.
Die schwingungsspektroskopischen Versuche wurden im schwach sauren pH-Bereich von 5 bis 6 durchgeführt. Es konnte gezeigt werden, dass sich die Zusammensetzung der Oberflächenkomplexe in Abhängigkeit von der Temperatur stark ändert: Bei höheren Temperaturen nimmt der Anteil koordinativ gebundener Komplexe gegenüber elektrostatisch gebundenen zu. Auch zwischen den einzelnen Oxiden wurden deutliche Unterschiede festgestellt: Während z. B. bei TiO2 elektrostatisch gebundene Komplexe von U(VI) vorherrschen, sind bei α-Fe2O3 und γ-Al(OH)3 eher die koordinativ gebundenen Komplexe zu finden. Der Carbonat-Anteil in den sorbierten Komplexen nimmt mit steigender Temperatur meist ab, lediglich α-Fe2O3 zeigte hier ein abweichendes Verhalten. Auch in den Batch-Versuchen verhielten sich die untersuchten Oxide im pH-Bereich von 2,5 bis 7 recht unterschiedlich: Wurde beispielsweise bei TiO2 eine verbesserte Sorption bei höherer Temperatur gefunden, war es bei SiO2 umgekehrt, während das Verteilungsgleichgewicht zwischen Fest- und Flüssigphase bei γ-Al(OH3), γ-Al2O3 und α-Fe2O3 durch die Temperatur eher schwach beeinflusst wurde. Grundsätzlich wurde bei steigendem pH-Wert eine Verschiebung des Gleichgewichts in Richtung Festphase beobachtet, nur bei γ-Al2O3 war ein Minimum bei pH ≈ 3 zu verzeichnen.
Die im Rahmen dieser Arbeit durchgeführten Experimente konnten die Temperatur- und pH-Abhängigkeit der Sorption von U(VI)-Komplexen an verschiedenen Oxiden weiter beleuchten, aber es besteht noch ein großer Bedarf an weiteren Experimenten, insbesondere zur Untersuchung der Sorptionsvorgänge in stark saurem oder basischem Milieu.

Für die Sicherheitsanalyse eines Endlagers für radioaktive Stoffe ist es notwendig, das Verhalten von Uran im wässrigen Medium und im Boden zu kennen. Während der Wiederaufarbeitung oder eines Störfalls, einer unkontrollierten Freisetzung, kann Uran mit organischen Säuren im Boden oder im radioaktiven Abfall in Kontakt kommen. Speziationsuntersuchungen der Systeme Uran(VI)-Citronensäure und Uran(VI)-Oxalsäure in equimolarer Konzentration (c = 10 mM) und umweltrelevanter Ionenstärke (I = 0,1 M) bestätigten zum Teil bekannte Uranspezies, wurden aber auch durch noch nicht beschriebene Komplexe erweitert. Dazu wurde die Methode der ATR FT-IR Spektroskopie verwendet. Uran(VI) und Citronensäure bilden zwischen pH 2,5 und 5 den bekannten Komplex (UO2)2(cit)22-. Zwischen pH 5 und 6,5 ist der gemischte Uranyl-Citrat-Hydroxo-Komplex (UO2)2(cit)2OH3- und oberhalb von pH 6,5 der Komplex (UO2)3(cit)3(OH)58- zu finden, welche noch nicht in der Literatur beschrieben sind. Im System U(VI)-Oxalsäure wurde zwischen pH 1 bis etwa pH 5 der bekannte Komplex (UO2)(ox) bestätigt. Oberhalb von pH 5 bis pH 8 konnte eine neue Spezies festgestellt werden, der Komplex (UO2)2(ox)2OH-. Diese Urankomplexe zeigen eine erhöhte Migrationsfähigkeit aufgrund der Löslichkeit bis hin in den basischen pH Wert (pH 8). Das Sorptionsverhalten von U(VI) wurde an den Modelloxiden Hämatit und SiO2 in Anwesenheit der o. g. Liganden untersucht. Bereits eine equimolare Konzentration von U(VI) und Citronensäure (c = 20 µM) hemmt die Sorption von Uran an Hämatit durch Komplexierung im wässrigen Medium. Bei Beladung der Hämatitoberfläche mit U(VI) entstehen durch Kontakt mit Citronensäure kurzzeitig ternäre Oberflächenkomplexe, die durch stärkere Komplexierung im wässrigen Medium wieder abgebaut werden. U(VI) und Oxalsäure bilden ebenfalls kurzzeitig einen U(VI)-Oxalat-Hämatit-Oberflächenkomplex. SiO2 bildet mit U(VI) und den organischen Liganden keinen ternären Oberflächenkomplex. Eine uranbeladene SiO2-Oberfläche neigt zur Desorption und wässrigen Komplexierung des Schwermetalls durch die organischen Liganden. Die Immobilisierung von Uran durch Sorption an Hämatit oder SiO2 wird durch Anwesenheit von Citronen- oder Oxalsäure gehemmt.
Abstract
For a reliable safety assessment of final repositories of nuclear waste, knowledge the behaviour, i.e. molecular reactions of uranium in aqueous solutions and at mineral-water interfaces is of major concern. During an accidental release, uranium may interact with organic acids and geologic material in the near- and far-field of the nuclear waste repository.
In this work the speciation of U(VI)-citric acid and U(VI)-oxalic acid in equimolar concentration (c = 10 mM) and at environmentally relevant ionic strength (I = 0.1 M) was investigated by ATR FT-IR spectroscopy. The obtained data confirm previously described uranium complexes, however, new species could be identified as well. Between pH 2.5 and 5 the known species (UO2)2(cit)22- was found. For the first time, the mixed uranyl-citrate-hydroxo-species (UO2)2(cit)2OH3- (pH 5 – 6.5) and (UO2)3(cit)3(OH)58- (> pH 6.5) were detected. These species have not been described in the literature so far. In the system U(VI)-oxalic acid between pH 1 to 5 the known species (UO2)(ox) was confirmed. Above pH 5 to pH 8 there was a new species identified, (UO2)2(ox)2OH-. The mixed uranyl-organic ligand-hydroxo-species increase the U(VI) migration behavior, because of their high solubility till pH 8.
The sorption behavior of U(VI) was investigated on the model oxides hematite and silicon dioxide in presence of above mentioned organic ligands. Equimolar concentration of U(VI) and citric acid (c = 20 µM) decrease uranium sorption on hematite through complexation in aqueous solution. A U(VI) loaded mineral oxide surface in contact with citric acid forms an intermediate ternary surface complex with citric acid and U(VI). The complexation in aqueous medium is stronger than the ternary surface complex, hence, U(VI) desorption occurs. U(VI) and oxalic acid forms also an intermediate ternary surface complex with hematite. Silica forms no ternary surface complex with U(VI) and the organic acids. An uranium loaded silica surface desorbs U(VI) und forms aquatic species with the organic acids. The immobilization of uranium through sorption on hematite and silicon dioxide is inhibited in the presence of citric- and oxalic acid.

Ziel der Arbeit war die schwingungsspektroskopische Identifizierung und Charakterisierung der Hydrolyseprodukte des Uran(VI) in wässriger Lösung und von U(VI) Oberflächenkomplexen an der Fest-Flüssig Grenzfläche bei erhöhten Temperaturen. Diese Spezies des U(VI) können mithilfe der ATR FT-IR Spektroskopie in situ untersucht werden. Anhand charakteristischer Schwingungsfrequenzen bestimmter funktioneller Gruppen, z. B. UO22+, werden somit strukturelle Informationen über die jeweilige Bindungsform auf molekularer Ebene erhalten.

Zunächst sollte im Rahmen der Masterarbeit die bisher genutzte Durchflussapparatur für ATR FT-IR spektroskopische Untersuchungen für Experimente bei erhöhten Temperaturen weiterentwickelt werden. Bei der Verwendung der Differenzspektroskopie hat die Temperaturkonstanz eine entscheidende Bedeutung, da schon Unterschiede von einigen wenigen Grad Celsius zu Instabilitäten der Basislinie und damit zu schwer interpretierbaren bis hin zu nicht auswertbaren Infrarotspektren führen. Das von Herrn Meusel entwickelte Messsystem besteht zum Einen aus einem thermostatisierbaren Block zur Präparation und Lagerung der Proben vor und während der IR Messungen. Dabei stellen die exakte Einstellung der pH-Werte als auch die Volumenänderung der Proben durch Evaporation kritische Faktoren dar. Zum Anderen gehören ein thermostatisierbarer Metallring zum Erwärmen der direkten Umgebung des ATR-Kristalls, als auch eine Durchflusszelle mit integriertem Temperatursensor zum weiterentwickelten Aufbau. Des Weiteren wurden eine Isolation der Schlauch- und Verbindungsstücke realisiert und eine detaillierte Bedienvorschrift entwickelt. Während des Zeitraumes der Masterarbeit wurde dieser Aufbau soweit optimiert, dass eine ausreichende Grundlinienstabilität über mehrstündige Reaktionszeiträume für Untersuchungen bei Temperaturen von bis zu 70°C gewährleistet wird.

Somit konnten erstmalig die U(VI)-Hydrolysereaktionen bei erhöhten Temperaturen schwingungsspektroskopisch erfasst werden. Es wurden U(VI)-Lösungen im milli- und mikromolaren Konzentrationsbereich bei 25, 40 und 60°C untersucht. Die erhaltenen IR Spektren zeigen, dass sich mit steigender Temperatur das Hydrolysegleichgewicht zu niedrigeren pH-Werten verschiebt. Des Weiteren wurde in Lösungen mit erhöhter U(VI) Konzentration und bei Temperaturen über 25°C eine geringere Löslichkeit des U(VI) beobachtet.

Ein weiterer Aufgabenschwerpunkt der vorliegenden Masterarbeit bestand in Untersuchungen zur Komplexierung von U(VI) an der Mineraloxid-Wasser Grenzfläche in Abhängigkeit der Temperatur. Als Modellmineral wurde Titandioxid (TiO2) ausgewählt. TiO2 zeigt eine hohe thermodynamische Stabilität und wurde zudem in früheren spektroskopischen Untersuchungen am IRC intensiv hinsichtlich seiner U(VI) Retentionskapazitäten untersucht. Im Rahmen der Masterarbeit wurde der Einfluss der Temperatur bis 70°C in situ und in zeitaufgelösten Experimenten ermittelt. Im Vergleich zu Sorptionsprozessen bei 25°C verlaufen die Oberflächenreaktionen bis 50°C kinetisch beschleunigt, die U(VI) Speziesverteilung an der TiO2 Oberfläche ändert sich jedoch wenig. Anhand der erhaltenen Spektren konnten ein stark gebundener innersphärischer Komplex bei geringer Oberflächenbeladung (z. B. im frühen Sorptionsstadium) und ein weniger stark gebundener außersphärischer Komplex bei hoher Oberflächenbeladung (z. B. im späten Sorptionsstadium) nachgewiesen werden. Bei Temperaturen oberhalb 50°C deuten die Ergebnisse auf eine drastische Änderung der Sorptionsprozesse hin. Während der innersphärische Komplex vermutlich kinetisch gehemmt und die Bildung des außersphärischen Komplexes nicht mehr beobachtet wird, konnte eine neue polymere Spezies identifiziert werden. Möglicherweise handelt es sich hier um eine U(VI) Oberflächenausfällung deren spektralen Charakteristika denen von U(VI) Kolloiden in Lösung und Sorptionsprozessen an anderen Mineraloxidoberflächen (Al2O3) sehr ähneln. Die Ergebnisse belegen die entscheidende Rolle der Temperatur auf die Grenzflächenprozesse, die das Migrationsverhalten von (radioaktiven) Schwermetallen in der Umwelt maßgeblich beeinflussen.

In this talk, the following topics will be discussed:

(1) Why magnetic semiconductors are important;
(2) Diluted magnetic semiconductors by ion implantation: successful cases and pit-falls;
(3) Defect-induced ferromagnetism in semiconductors: ion beam irradiation provides a controllable approach.

The correlation between colossal magnetocapacitance (CMC) and colossal magnetoresistance (CMR) in CdCr2S4 system has been revealed. The CMC is induced in polycrystalline Cd0.97In0.03Cr2S4 by annealing in cadmium vapor. At the same time, an insulator-metal transition and a concomitant CMR are observed near the Curie temperature. In contrast, after the same annealing treatment, CdCr2S4 displays a typical semiconductor behavior and does not show magnetic field dependent dielectric and electric transport properties. The simultaneous occurrence or absence of CMC and CMR effects implies that the CMC in the annealed Cd0.97In0.03Cr2S4 could be explained qualitatively by a combination of CMR and Maxwell-Wagner effect.

In the uranium mine Königstein (Saxony, Germany) the uranium production was achieved by leaching the sandstone with sulphuric acid in the past. As a consequence the geochemical nature of the deposit was changed with an increase of sulphate and heavy metals, (especially uranium) in acidic, sulfate-rich waters. Since 2001 the mine has been flooded for remediation processes. Huge mass of Ferrovum myxofaciens dominated biofilms are growing in the acid mine drainage (AMD) water as macroscopic streamers and as stalactite-like snottites hanging from the ceiling of the galleries. Microsensor measurements were performed in the AMD water as well as in the biofilms from the drainage channel on-site and in the laboratory. The analytical data of the AMD water was used for the thermodynamic calculation of the predominance fields of the aquatic uranium sulfate (UO2SO4). According to thermodynamic calculations a retention of uranium from the AMD water by forming solid uranium(VI) or uranium(IV) species will be inhibited until the pH will increase to > 4.8.
In the underground rock characterization facility tunnel "ONKALO" in Finland massive biofilms were observed attached to the fractured bedrock at a depth of 70 m. Experiments were performed in the laboratory to study the effect on the behavior of uranium in biofilms by adding uranium to the fracture water with a final uranium concentration (410-5 M) relevant for what can be expected from an injured and leaking waste canister in the far-field during a nuclear event in a HLW repository. The results obtained by analysis, microsensor measurements, TRLFS investigation, EF-TEM/EELS studies and thermodynamic calculations clearly indicate that biofilms have to be considered as microenvironments, which differ significantly from the surrounding medium. EF-TEM investigations showed that in the biofilm uranium was immobilized intracellular in bacteria by a biologically mediated uranyl phosphate formation similar to needle-shaped Autunite (Ca[UO2]2[PO4]2•2-6H2O) or meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O). In contrast, TRLFS studies of the contaminated fracture water showed aqueous uranium carbonate species, most likely (Ca2UO2[CO3]3), which was formed using the available high amount of carbonate from the water. The results are in agreement with the thermodynamic calculation of the theoretical predominance field of uranium species, formed in the uranium contaminated fracture water at the measured geochemical parameters.

Nickel-Titanium (Ni-Ti) thin film shape memory alloys (SMAs) have been widely projected as a novel material, which can be utilized in microdevices. Characterization of their physical properties and its correlation with phase transformations has been a challenging issue. In the present study, X-ray beam diffraction has been utilised to obtain the structural information at different temperatures while cooling. Simultaneously, electrical resistivity (ER) was measured in the phase transformation temperature range. The variation of ER and integral area of the individual diffraction peaks of the different phases as a function of temperature have been compared. A mismatch between the conventional interpretation of ER variation and the results of the XRD data has been clearly identified.

As part of long-term safety assessments for radioactive waste disposals, scenarios have to be considered, which lead to the mobilization of radionuclides from the waste and to their transport through the repository system. Any repository sites (such as Gorleben) the sedimentary overburden is an important barrier for radionuclide transport. For most radionuclides the transport is retarded by sorption on mineral phases. Mica and feldspars are major components of the Gorleben sediments. However, almost no sorption parameters are available (www.hzdr.de/res³t [1]) for these systems.
The WEIMAR-project (Further Development of the Smart Kd-Concept for Long-Term Safety Assessment) shall address these shortcomings. Batch sorption experiments and spectroscopic investigations will allow the assessment, the evaluation as well as the processing of sorption data for U, Np, La(III) onto muscovite and orthoclase. Generally, the amount of sorption can depend on the pH-value, ionic strength, redox potential, concentrations of the contaminant as well as of the sorbent, of complexing ligands and competing ions. All batch experiments are carried out under ambient atmosphere and with 0.01 M NaClO4 as background electrolyte.
For muscovite and orthoclase the background concentration of the sorbing elements, the tendency of wall sorption and the dissolution behavior has to be determined. For both minerals an optimal solid-to liquid ratio has to be optimized. This means that the sorption is neither too low nor too high, so the sorption has to be between 5 and 95%. All those problems will be illustrated for the case of U(VI) sorption.

This project is funded by the German Federal Ministry of Economics and Technology (BMWi) under contract number 02 E 11072B

[1] Brendler, V. et al. (2003), J. Cont. Hydrol. 61, 281-291.

Knowledge of the migration and mobility of actinides is an important issue to predict potential release of radiotoxic elements from nuclear waste repositories. Under the reducing conditions expected for the disposal zone, the tetravalent form of the actinides An (An = Th, U, Np) is predominant. Due to the low solubility at neutral pH, An(IV) are considered as immobile under these conditions. Nevertheless, high environmental mobility has been found. This fact is obviously related with the formation of An(IV) eigencolloids or the sorption on other colloids.
We report some examples of investigated colloids of An(IV) ( An= Th, U, Np): An(IV) silica colloids.
The main characteristic properties (eg. particlesize distribution, longterm monitored time stability, surfacecharge) of these colloids are presented.