Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35173 Publications

Nanostructures – Small and Beautiful

Gemming, S.; Facsko, S.; Erbe, A.

Overview presentation of FWIO activities.

Keywords: density functional; transport; ion-beam

  • Invited lecture (Conferences)
    Kristallographisches Oberseminar, 27.05.2011, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16715
Publ.-Id: 16715


Transport through nanostructures

Gemming, S.

DFTEM 2011 Tutorial on nanoscale electronic transport

Keywords: DFT; density functional; transport

  • Invited lecture (Conferences)
    CECAM Workshop "Density Functional Theory and Transmission Electron Microscopy" 2011, 24.-28.07.2011, Lausanne, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-16714
Publ.-Id: 16714


Density Functional Theory + Transmission Electron Microscopy - Introduction to Density Functional Theory

Gemming, S.

Workshop DFTEM 2011 - Introductory Lecture to DFT

Keywords: density functional; DFT

  • Invited lecture (Conferences)
    CECAM-Workshop "Density Functional Theory and Transmission Electron Microscopy" 2011, 24.-28.07.2011, Lausanne, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-16713
Publ.-Id: 16713


Ecto-ATPase inhibition: ATP and adenosine release under physiological and ischemic in vivo conditions in the rat striatum

Melani, A.; Corti, F.; Stephan, H.; Müller, C. E.; Donati, C.; Bruni, P.; Vannucchi, M. G.; Pedata, F.

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

Keywords: ATP; Adenosine; Microdialysis; Focal cerebral ischemia; Rat

Permalink: https://www.hzdr.de/publications/Publ-16712
Publ.-Id: 16712


Study of differences in the VEGFR2 inhibitory activities between semaxanib and SU5205 using 3D-QSAR, docking, and molecular dynamics simulations

Munoza, C.; Adasmea, F.; Alzate-Morales, J. H.; Vergara-Jaquea, A.; Kniess, T.; Caballero, J.

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

Keywords: Kinase inhibitors; VEGFR2; Semaxanib; QSAR; CoMFA; Docking; Molecular dynamics; Protein-ligand interactions; MM-GBSA

Permalink: https://www.hzdr.de/publications/Publ-16711
Publ.-Id: 16711


Radiolabeled small molecule inhibitors of VEGFR – recent advances

Kniess, T.

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

Keywords: Anti-angiogenic; tumor therapy; VEGFR; PET; tyrosine kinase inhibitors; radiolabeling

Permalink: https://www.hzdr.de/publications/Publ-16710
Publ.-Id: 16710


Module-assisted preparation of 64Cu with high specific activity

Thieme, S.; Walther, M.; Pietzsch, H.-J.; Henniger, J.; Preusche, S.; Mäding, P.; Steinbach, J.

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

Permalink: https://www.hzdr.de/publications/Publ-16709
Publ.-Id: 16709


Measurement of blood flow in rodents using radioactive microspheres

Bergmann, R.; Richter, T.; Schiller, E.; Bos, A.; Kniess, T.; Hofheinz, F.; van den Hoff, J.; Pietzsch, J.

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

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

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

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

  • Poster
    ESRR'12 - 16th European Symposium on Radiopharmacy and Radiopharmaceuticals, 26.-29.04.2012, Nantes, France
  • Abstract in refereed journal
    Quarterly Journal of Nuclear Medicine and Molecular Imaging 56(2012), 52-53

Permalink: https://www.hzdr.de/publications/Publ-16708
Publ.-Id: 16708


Formation of nanoclusters with varying Pb/Se concentration and distribution after sequential Pb+ and Se+ ion implantation into SiO2

Markwitz, A.; Carder, D. A.; Hopf, T.; Kennedy, J.; Kuei, C. T.; Mücklich, A.; Osipowicz, T.

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

Permalink: https://www.hzdr.de/publications/Publ-16707
Publ.-Id: 16707


PBF Changes In Areas Of Aspiration-Induced Acute Lung Injury Within Two Hours.

Richter, T.; Bergmann, R.; Pietzsch, J.; Ragaller, M.

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

  • Lecture (Conference)
    American Thoracic Society International Conference, 18.05.2011, Denver, USA
  • Abstract in refereed journal
    American Journal of Respiratory and Critical Care Medicine 183(2011), A6155

Permalink: https://www.hzdr.de/publications/Publ-16706
Publ.-Id: 16706


SUV-measurements and patient-specific corrections thereof in pediatric Hodgkin-lymphoma: Is there a benefit for PPV in early response assessment by FDG-PET?

Furth, C.; Meseck, R. M.; Steffen, I. G.; Schoenberger, S.; Denecke, T.; Henze, G.; Hautzel, H.; Hofheinz, F.; Großer, O.; Hundsdoerfer, P.; Amthauer, H.; Ruf, J.

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

Keywords: FDG-PET; Hodgkin lymphoma; pediatrics; response assessment; SUV

Permalink: https://www.hzdr.de/publications/Publ-16705
Publ.-Id: 16705


Suitability of bilateral filtering for edge-preserving noise reduction in PET

Hofheinz, F.; Langner, J.; Beuthien-Baumann, B.; Oehme, L.; Steinbach, J.; Kotzerke, J.; van den Hoff, J.

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

Keywords: quantification; PET; SUVmax; bilateral filtering; spatial resolution; image filtering

Permalink: https://www.hzdr.de/publications/Publ-16704
Publ.-Id: 16704


Automatic volume delineation in oncological PET. Evaluation of a dedicated software tool and comparison with manual delineation in clinical data sets

Hofheinz, F.; Pötzsch, C.; Oehme, L.; Beuthien-Baumann, B.; Steinbach, J.; Kotzerke, J.; van den Hoff, J.

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

Permalink: https://www.hzdr.de/publications/Publ-16703
Publ.-Id: 16703


Change of SUV and metabolic volume products after use of rigid coregistration algorithms in F18-FDG-PET

Steffen, I. G.; Hofheinz, F.; Grosser, O. S.; Furth, C.; Denecke, T.; Plotkin, M.; Amthauer, H.; Ruf, J.

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

  • Poster
    Annual Congress of the European Association of Nuclear Mediciene (EANM) 2011, 15.-19.10.2011, Birmingham, UK
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 38(2011), S269

Permalink: https://www.hzdr.de/publications/Publ-16702
Publ.-Id: 16702


A method for model-free recovery correction in PET

Hofheinz, F.; Langner, J.; Will, E.; Oehme, L.; Beuthien-Baumann, B.; van den Hoff, J.

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

  • Poster
    Annual Congress of the European Association of Nuclear Medicine (EANM) 2011, 15.-19.10.2011, Birmingham, UK
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 38(2011), S268

Permalink: https://www.hzdr.de/publications/Publ-16701
Publ.-Id: 16701


Synthesis and Molecular Structure of tert-Butyl 4-(2-tert-butoxy-2-oxoethyl)piperazine-1-carboxylate

Mamat, C.; Flemming, A.; Köckerling, M.

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

Keywords: piperazines; building blocks; X-ray structure

Permalink: https://www.hzdr.de/publications/Publ-16700
Publ.-Id: 16700


The Synthesis and Molecular Structure of 2-(4-Methoxybenzyl)-4-nitro-2H-indazole

Ebert, K.; Köckerling, M.; Mamat, C.

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

Keywords: indazoles; protecting group; p-methoxy benzyl; X-ray structure

Permalink: https://www.hzdr.de/publications/Publ-16699
Publ.-Id: 16699


Effect of the processing of embedded Ge nanocrystals upon the Si-SiO2 interface state and border trap density

Beyer, R.; Burghardt, H.; von Borany, J.

  • Lecture (Conference)
    14th European Conference on Applications of Surface and Interface Analysis (ECASIA'11), 05.09.2011, Cardiff, Wales

Permalink: https://www.hzdr.de/publications/Publ-16697
Publ.-Id: 16697


Determination of size and density of embedded Ge nanocrystals in SiO2 by scanning force microscopy using a tomographic approach

Beyer, R.; von Borany, J.

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

Keywords: nanocrystals; silicondioxide; scanning force microscopy

  • Lecture (Conference)
    14th European Conference on Applications of Surface and Interface Analysis (ECASIA'11), 06.09.2011, Cardiff, Wales
  • Surface and Interface Analysis 44(2012), 1018-1021
    DOI: 10.1002/sia.5007

Permalink: https://www.hzdr.de/publications/Publ-16696
Publ.-Id: 16696


Organ culture of rat arteries for experimental studies of radiation-induced vascular dysfunction in vitro / in situ

Ullm, S.

kein Abstract verfügbar

  • Diploma thesis
    Technische Universität Bergakademie Freiberg, Fakultät Chemie und Physik, 2011
    85 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16695
Publ.-Id: 16695


SPIRIT- Ion Beam Applications for Europe

Möller, W.

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

Keywords: Ion Technologies; Transnational Access

Permalink: https://www.hzdr.de/publications/Publ-16694
Publ.-Id: 16694


THEREDA – A thermodynamic database for increasing confidence in waste disposal

Richter, A.; Bok, F.; Brendler, V.

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

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

Keywords: thermodynamic database; THEREDA; sorption database; RES3T; geochemical modeling

  • Abstract in refereed journal
    Mineralogical Magazine 76(2012), 2283
  • Lecture (Conference)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-16693
Publ.-Id: 16693


Neue zellpenetrierende Phosphopeptide für die molekulare Bildgebung

Richter, S.

kein Abstract verfügbar

  • Doctoral thesis
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, 2011
    150 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16692
Publ.-Id: 16692


Molekulare Charakterisierung der Rezeptortyrosinkinase EphB4 an humanen Melanomzellen

Hoche, T.

kein Abstract verfügbar

  • Other
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Biologie, 2011
    39 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16691
Publ.-Id: 16691


NO-Donoren als potentielle Radioprotektoren bei strahleninduzierter vaskulärer Dysfunktion

Bechmann, N.

kein Abstract verfügbar

  • Other
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Chemie, 2011
    81 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16690
Publ.-Id: 16690


Sekretion und funktionelle Bedeutung von extrazellulärem S100A4-Protein im humanen Melanom

Tandler, N.

kein Abstract verfügbar

  • Other
    Technische Universität Bergakademie Freiberg, Fakultät Chemie und Physik, 2011
    73 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16689
Publ.-Id: 16689


Magnetismus und Leitfähigkeit - Zwei untypische Supraleiter: 1) Vom Halbleiter zum Supraleiter in Ga-dotiertem Ge ; 2) Supraleitung & Magnetismus in nanostrukturiertem Bi3Ni

Skrotzki, R.

  • Lecture (others)
    Mitarbeiterseminar, Institut für anorganische Chemie II, Arbeitskreis Prof. Ruck, 27.-27:01:2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16688
Publ.-Id: 16688


Nachweis von Eicosanoiden mittels LC-MS.

Sehn, F.

kein Abstract verfügbar

  • Other
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Chemie, 2011
    69 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16687
Publ.-Id: 16687


Relaxation dynamics in graphene excited with low photon energies

Winnerl, S.; Mittendorff, M.; Schneider, H.; Helm, M.; Orlita, M.; Potemski, M.; Winzer, T.; Malic, E.; Knorr, A.; Berger, C.; de Heer, W. A.

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

Keywords: Relaxation dynamics; graphene; ultrafast spectroscopy

  • Lecture (Conference)
    Graphene Week, 03.-08.06.2012, Delft, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-16686
Publ.-Id: 16686


Relaxation dynamics in Landau-quantized graphene probed in the mid-infrared range

Mittendorff, M.; Winnerl, S.; Schneider, H.; Helm, M.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.

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

  • Lecture (Conference)
    DPG Frühjahrstagung, 29.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16685
Publ.-Id: 16685


Untersuchung von Molekülinteraktionen mittels Oberflächen-Plasmon-Resonanz

Lenk, J.

kein Abstract verfügbar

  • Other
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Chemie und, 2011
    64 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16684
Publ.-Id: 16684


Carrier relaxation in Landau-quantized graphene

Mittendorff, M.; Winnerl, S.; Schneider, H.; Helm, M.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.

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

Keywords: Landau quantization; relaxation dynamics; pump-probe; magnetic field; epitaxially grown

  • Poster
    Graphene Week 2012, 04.-08.06.2012, Delft, the Netherlands

Permalink: https://www.hzdr.de/publications/Publ-16683
Publ.-Id: 16683


Interaction of the receptor for advanced glycation endproducts (RAGE) with extracellular S100A4 modulates malignancy and radiation response of melanoma.

Haase-Kohn, C.; Pietzsch, J.

wird nachgereicht

  • Poster
    Keystone Symposia on Molecular and Cellular Biology, 06.-11.03.2011, Keystone, Colorado, USA

Permalink: https://www.hzdr.de/publications/Publ-16682
Publ.-Id: 16682


Opredelenie termodinamicheskikh uslovii metamorfizma Kasakhskoj Svity dokembriya armenii po amfibolovomu termobarometru

Aghamalyan, V. A.; Schulz, B.; Renno, A. D.; Lange, J.; Lorsabyan, T. K.

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

Keywords: Petrology; Armenia; Kasakh Suite; Geothermobarometry

  • Uchenie Zapiski Erevanskogo Gosudarstvennogo Universiteta (2011)3, 3-8

Permalink: https://www.hzdr.de/publications/Publ-16681
Publ.-Id: 16681


Optical afterburner for a SASE FEL: First results from FLASH

Foerst, M.; Gensch, M.; Riedel, R.; Tavella, F.; Schneidmiller, E. A.; Stojanovic, N.; Yurkov, M. V.

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

Keywords: X-ray photondiagnostic; THz; SRF accelerator; THz based electron bunch diagnostic

  • Open Access Logo Contribution to proceedings
    IPAC 2011, 04.-09.09.2011, San Sebastian, Spain
    Proceedings of IPAC

Permalink: https://www.hzdr.de/publications/Publ-16680
Publ.-Id: 16680


Control of vortex pair states by post-deposition interlayer exchange coupling modification

Wintz, S.; Strache, T.; Körner, M.; Bunce, C.; Banholzer, A.; Mönch, I.; Mattheis, R.; Raabe, J.; Quitmann, C.; McCord, J.; Erbe, A.; Lenz, K.; Fassbender, J.

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

Keywords: magnetic vortex; x-ray microscopy; interlayer exchange coupling; ion beam modification

Permalink: https://www.hzdr.de/publications/Publ-16679
Publ.-Id: 16679


Applications of ion beams in Nanotechnology

Facsko, S.

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

Keywords: ion beams; nanopatterning

  • Lecture (others)
    Dies academicus timisorensis, 26.-27.05.2011, Timisoara, Romania

Permalink: https://www.hzdr.de/publications/Publ-16678
Publ.-Id: 16678


Strength and limitations of continuum equations for sputter induced pattern formation

Facsko, S.; Keller, A.; Liedke, B.; Heinig, K.-H.

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

Keywords: pattern formation

  • Invited lecture (Conferences)
    INTERNATIONAL CONFERENCE on Ion-Beam Induced Nanopatterning of Materials, 06.-10.02.2011, Bhubaneswar, Indien

Permalink: https://www.hzdr.de/publications/Publ-16677
Publ.-Id: 16677


Electrical Characterization of Short DNA Fragments

Wieser, M.; Liu, S.-P.; Weisbrod, S.; Tang, Z.; Marx, A.; Scheer, E.; Erbe, A.

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

Keywords: DNA; molecules; molecular electronics; conductance; MCBJ; Mechanically Controllable Break Junction

  • Poster
    DPG Frühjahrstagung 2011, 13.-18.03.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16676
Publ.-Id: 16676


Atomistische Simulation der Selbstorganisation bei der Ionenstrahlerosion

Kranz, A.; Heinig, K.-H.; Liedke, B.

Während Ionenbestrahlung von Festkörpern kann es zur Bildung von Oberflächenstrukturen wie Ripples und Nanodots kommen. Diese Bildung wird mit Computerexperimenten untersucht werden. Dabei wird eine zweistufige Simulationsmethode eingesetzt, die im ersten Schritt die Kollisionskaskade eines Ioneneinschlages mit Binary Collision Approximation berechnet und im zweiten Schritt die Defektkinetik mittels kinetic Monte Carlo simuliert. Diese beiden Stufen werden für jeden Ioneneinschlag wiederholt. Dabei ergeben sich zwei mögliche Ansätze, die Simulationsergebnisse zu untersuchen.
Zum einen kann überprüft werden, inwieweit die simulierte Oberfläche verfügbaren Kontinuumsmodellen für die Musterbildung genügt. Der Vorteil der Simulation gegenüber dem Experiment besteht darin, dass man die volle zeitliche Entwicklung der Oberfläche anstelle einzelner Momentaufnahmen bekommt. Damit können unmittelbar bestehende Theorien bewerten werden.
Zum anderen kann man während der Simulation die Bewegung jedes einzelnen Atoms verfolgen. Dadurch kann man die Wahrscheinlichkeiten registrieren, mit denen die Atome in die unterschiedlichen Richtungen springen. Daraus kann der Massestrom und dessen Divergenz berechnet werden. Da die Divergenz des Massestroms nach dem zweiten Fick'schen Gesetz der Diffusion proportional zur zeitlichen Änderung der Konzentration und damit zur zeitlichen Änderung der Oberflächenhöhe ist, kann man damit Aussagen über die treibenden Mechanismen bei der Musterbildung treffen.
In diesem Vortrag sollen beide Ansätze vorgestellt und anhand eines Beispiels erläutert werden.

During ion beam irradition it is possible to observe the formation of surface structures like ripples and nanodots. This formation is examined by computer experiments. Therefore, a two step simulation method is used which calculates the collision cascade of one ion impact by binary collision approximation in a first step followed by the simulation of the defect kinetic via kinetic Monte Carlo. These two steps are repeated for each ion impact. There are two task possible to analyse the simulation results.
On the one hand, one can examine how good the simulated surface satisfies available continuum models of pattern formation. As an advantage of the simulation over experiments one can get the full temporal evolution of the surface instead of only snapshots. Therefore, existing theories can be evaluated immediately.
On the other hand, the movement of every single atom can be tracked so that one can register the probabilities of jumps of an atom into different directions. With this jump rates, the mass current and its divergences can be calculated. As the divergence of the mass current is proportional to the temporal change of surface height - this is indirectly implied by Fick's law of diffusion - statements about the driving mechanisms of pattern formation are possible.
Here, both tasks are presented and explained with the help of an example.

Keywords: atomistic simulation; BCA; kMC; ripples; mass current

  • Lecture (others)
    Spring meeting of the DFG FOR 845 "Selbstorganisierte Nanostrukturen durch niederenergetische Ionenstrahlerosion", 01.-02.02.2011, Siegen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16675
Publ.-Id: 16675


Lokalanalytische Ressourcenanalytik

Renno, A. D.; Merchel, S.; Munnik, F.; Fassbender, J.

eingeladener Beitrag ohne Abstract

Keywords: resource analytics; ion beam analysis; PIXE; PIGE

  • Contribution to external collection
    in: ACAMONTA – Zeitschrift des VFF und der TU Bergakademie Freiberg 18, Freiberg: Freunde und Förderer der TU Bergakademie Freiberg, 2011, 24-26

Permalink: https://www.hzdr.de/publications/Publ-16673
Publ.-Id: 16673


Silica-stabilized actinide(IV) colloids at near-neutral pH

Zänker, H.; Weiss, S.; Hennig, C.; Dreissig, I.

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

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

Keywords: Colloids; nanoparticles; tetravalent actinides; silica

  • Lecture (Conference)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada
  • Open Access Logo Abstract in refereed journal
    Mineralogical Magazine 76(2012)6, 2581

Permalink: https://www.hzdr.de/publications/Publ-16671
Publ.-Id: 16671


Smart Kd-concept based on Surface Complexation Modeling

Stockmann, M.; Brendler, V.; Schikora, J.; Britz, S.; Flügge, J.; Noseck, U.

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

  • Lecture (Conference)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada
  • Abstract in refereed journal
    Mineralogical Magazine 76(2012)6, 2412

Permalink: https://www.hzdr.de/publications/Publ-16670
Publ.-Id: 16670


Numerical Integrator for Continuum Equations of Surface Growth and Erosion

Keller, A.; Facsko, S.; Cuerno, R.

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

  • Book chapter
    Sarhan M. Musa: Computational Nanotechnology: Modeling and Applications with MATLAB, Boca Raton: CRC Press, 2011, 978-1439841761, 189-215

Permalink: https://www.hzdr.de/publications/Publ-16669
Publ.-Id: 16669


Temperature Impact on the Sorption of Selenate onto Anatase

Franzen, C.; Jordan, N.; Müller, K.; Meusel, T.; Brendler, V.

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

Keywords: Selenate; Se(VI); Anatase; Sorption; HighTemperatures

  • Open Access Logo Contribution to proceedings
    HiTAC - High Temperature Aqueous Chemistry, 09.11.2011, Karlsruhe, Deutschland
    Proceedings of the International Workshops ABC-Salt (II) and HiTAC 2011, Karlsruhe: KIT Scientific Publishing, 978-3-86644-912-1, 163-164

Permalink: https://www.hzdr.de/publications/Publ-16668
Publ.-Id: 16668


Radiotracer studies on the kinetics and equilibrium characteristics of adsorption of humic matter

Lippold, H.; Lippmann-Pipke, J.

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

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

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

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

  • Lecture (Conference)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada
  • Abstract in refereed journal
    Mineralogical Magazine 76(2012), 2015-2015

Permalink: https://www.hzdr.de/publications/Publ-16667
Publ.-Id: 16667


Fracture mechanics characterisation of forged base metal ring of the decommissioned reactor pressure vessel of NPP Greifswald WWER-440 unit 4

Viehrig, H.-W.; Houska, M.; Altstadt, E.; Kuechler, R.

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

Keywords: reactor pressure vessel steel; neutron irradiation; fracture toughness; Master Curve approach; non-homogeneous steel; SINTAP; multimodal approach

  • Lecture (Conference)
    25th Symposium on Effects of Radiation on Nuclear Materials, 15.-17.06.2011, Anaheim, USA
  • Contribution to external collection
    in: ASTM STP1547, West Conshohocken: ASTM International, 2012, 978-0-8031-7533-4, 69-84

Permalink: https://www.hzdr.de/publications/Publ-16666
Publ.-Id: 16666


Long term irradiation phenomena in RPV steels - the LONGLIFE project

Altstadt, E.; Bergner, F.; Hein, H.

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

Keywords: Reactor Pressure Vessel Steel; Irradiation Embrittlement; Long Term Operation

  • Invited lecture (Conferences)
    25th Symposium on Effects of Radiation on Nuclear Materials, 15.-17.06.2011, Anaheim, USA

Permalink: https://www.hzdr.de/publications/Publ-16665
Publ.-Id: 16665


Numerical and experimental modelling of VGF-type buoyant flow under the influence of travelling and rotating magnetic fields

Galindo, V.; Niemietz, K.; Pätzold, O.; Gerbeth, G.

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

Keywords: Fluid flows; Magnetic fields; Vertical gradient freeze technique; numerical simulation

  • Lecture (Conference)
    5th International Workshop on Crystal Growth Technology, 26.-30.06.2011, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-16664
Publ.-Id: 16664


Safety Monitoring of Components and Materials of Nuclear Power Plants

Gokhman, A. R.; Bergner, F.

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

  • Contribution to proceedings
    NATO Advanced Research Workshop on Nanodevices and Nanomaterials for Ecological Security, 20.-23.06.2011, Riga-Jurmala, Latvia
    Nanodevices and Nanomaterials for Ecological Security (Eds. Y.N. Shunin and A.E. Kiv), NATO Science for Peace and Security Series B: Physics and Biophysics, Dordrecht: Springer, 978-94-007-4118-8, 325-338

Permalink: https://www.hzdr.de/publications/Publ-16663
Publ.-Id: 16663


Preliminary multi-method spectroscopic approach for the uranium(VI) hydrolysis at temperatures up to 60°C

Steudtner, R.; Müller, K.; Meusel, T.; Brendler, V.

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

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

Keywords: U(VI); TRLFS; ATR FT-IR; high temperature

  • Contribution to proceedings
    HiTAC - High Temperature Aqueous Chemistry, 09.11.2011, Karlsruhe, Deutschland
    Proceedings of the International Workshops ABC-Salt (II) and HiTAC 2011: KIT Scientific Publishing, 978-3-86644-912-1, 177-178
  • Poster
    DMG-DGK-BMBF-ImmoRad Workshop "From atomistic calculations to thermodynamic modelling, 18.-22.02.2013, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16662
Publ.-Id: 16662


Cluster Dynamics Study of Defect Evolution in Neutron-Irradiated Dilute and Concentrated Fe-Cr Alloys

Gokhman, A. R.; Bergner, F.; Birkenheuer, U.; Ulbricht, A.

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

Keywords: Cluster dynamics; neutron irradiation; chromium iron alloys; defects

  • Open Access Logo Contribution to proceedings
    25th Research Workshop Nucleation Theory and Applications, 16.-23.04.2011, Dubna, Russia
    Nucleation Theory and Applications XIII, Dubna: JINR, 978-5-9530-0301, 259-267

Permalink: https://www.hzdr.de/publications/Publ-16661
Publ.-Id: 16661


XAS Study of dense U1-YAmYO2-X (Y=0.10; 0.15; 0.20) compounds

Prieur, D.; Martin, P. M.; Jankowiak, A.; Gavilan, E.; Scheinost, A. C.; Leorier, C.; Herlet, N.; Dehaudt, P.; Laval, J.-P.; Blanchart, P.

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

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

Keywords: Americium; Transmutation; XAS; Oxygen potential

  • Contribution to proceedings
    Actinide XAS 2011, 02.-04.03.2011, Harima Science Garden City, Japan
    Proceedings of the Actinide XAS 2011

Permalink: https://www.hzdr.de/publications/Publ-16660
Publ.-Id: 16660


Spectroscopic Characterization of Eu(III) and Am(III) Complexes with Small Organic Molecules at Elevated Temperatures

Barkleit, A.; Geipel, G.; Acker, M.; Taut, S.

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

Keywords: Americium; Europium; Lactate; Salicylate; TRLFS; High Temperatures

  • Poster
    HiTAC Workshop, 09.11.2011, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16659
Publ.-Id: 16659


Hardening and microstructure of neutron- and ion-irradiated Fe-Cr alloys

Heintze, C.; Altstadt, E.; Bergner, F.; Hernández Mayoral, M.; Xie, M.; Birkenheuer, U.

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

  • Lecture (Conference)
    OECD Nuclear Energy Agency International Workshop on Structural Materials for Innovative Nuclear Systems (SMINS-2), 31.08.-03.09.2010, Daejeon, Republic of Korea

Permalink: https://www.hzdr.de/publications/Publ-16658
Publ.-Id: 16658


Ion beam processing of surfaces and interfaces – Modeling and atomistic simulations

Liedke, B.

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

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

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

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

Keywords: kMC; BCA; TRIM; TRIDYN; TRIDER; self-organization; ripples; IBS; interface mixing; bilayers; bimetals; multilayers

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-012 2011
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-16657
Publ.-Id: 16657


Numerical simulation of the insulation material transport in a PWR core under loss of coolant conditions

Höhne, T.; Grahn, A.; Kliem, S.; Rohde, U.; Weiss, F.-P.

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

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

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

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

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

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

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

Keywords: CFD; Fibre; Core; PWR

Permalink: https://www.hzdr.de/publications/Publ-16656
Publ.-Id: 16656


Ripples and dots generated by lattice gases

Ódor, G.; Liedke, B.; Heinig, K.-H.; Kelling, J.

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

Keywords: Ripple; Dot; KPZ; Kuramoto–Sivashinsky; Mullins–Herring; Lattice gas; Coarsening; Scaling; PSD

Permalink: https://www.hzdr.de/publications/Publ-16655
Publ.-Id: 16655


Nanoscale characterization of ODS Fe-9%Cr model alloys compacted by spark plasma sintering

Heintze, C.; Hernández-Mayoral, M.; Ulbricht, A.; Bergner, F.; Shariq, A.; Weissgärber, T.; Frielinghaus, H.

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

  • Lecture (Conference)
    DIANA I: 1st International workshop on dispersion strengthened steels for advanced nuclear applications, 04.-08.04.2011, Aussois, France

Permalink: https://www.hzdr.de/publications/Publ-16654
Publ.-Id: 16654


Response of human mesenchymal stem cells to nanopatterned surfaces

Keller, A.; Andersen, O. Z.; Foss, M.; Facsko, S.; Kraft, D. C.; Besenbacher, F.

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

  • Lecture (Conference)
    Nanoscale Pattern Formation at Surfaces, 18.-22.09.2011, El Escorial, Spanien

Permalink: https://www.hzdr.de/publications/Publ-16653
Publ.-Id: 16653


The contributions of defect kinetics and sputtering to pattern formation

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.

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

Keywords: Ripples; TRIDER; TRIM; KMC; Monte-Carlo; atomistic simulation; ion beam irradiation; self organization

  • Lecture (Conference)
    Nanoscale Pattern Formation at Surfaces Congress, 18.-22.09.2011, El Escorial, Madrid

Permalink: https://www.hzdr.de/publications/Publ-16652
Publ.-Id: 16652


Surface patterning by ion bombardment: predictions of largescale atomistic simulations

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.

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

Keywords: TRIM; TRIDER; ripples; ion beam irradiation; sputtering; BCA; KMC; Monte-Carlo

  • Lecture (Conference)
    75. Jahrestagung der DPG und DPG Frühjahrstagung, 13.-18.03.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16651
Publ.-Id: 16651


Interaction of selenite with iron sulphide minerals: a new perspective

Breynaert, E.; Dom, D.; Scheinost, A. C.; Kirschhock, C. E. A.; Maes, A.

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

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

Keywords: selenium; exafs; xanes; redox; pyrite

  • Invited lecture (Conferences)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada
  • Lecture (Conference)
    Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, 22.-25.10.2012, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-16649
Publ.-Id: 16649


XRD and XAS structural characterization of mixed-valence plutonium(III,IV) oxalate hydrates used to obtain controlled particle shape of plutonium oxide

Tamain, C.; Arab-Chapelet, B.; Martin, P. M.; Rivenet, M.; Scheinost, A. C.; Grandjean, S.; Abraham, F.

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

Keywords: plutonium; exafs; xanes; nuclear fuel; mox

  • Contribution to proceedings
    Plutonium Futures - The Science 2012, 15.-20.07.2012, Cambridge, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-16648
Publ.-Id: 16648


Oxide Minerals in Soils

Kaempf, N.; Scheinost, A. C.; Schulze, D. G.

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

Keywords: oxides; minerals; soil; xrd

  • Book chapter
    Pan Ming Huang, Yuncon Li, Malcolm E. Sumner: Handbook of Soil Sciences: Properties and Processes, Part III: Soil Mineralogy, USA: CRC Press, Taylor & Francis Group, 2011, 1439803056, 22

Permalink: https://www.hzdr.de/publications/Publ-16647
Publ.-Id: 16647


Lasermodifikation von TCOs

Hauschild, D.; Vinnichenko, M.

No abstract available.

  • Lecture (Conference)
    5. Fachtagung Transparent leitfähige Schichten (TCO), 28.-30.11.2011, Neu-Ulm, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16646
Publ.-Id: 16646


Nanohole Pattern Formation on Germanium Induced by Focused Ion Beam and Broad Beam Ga+ Irradiation

Fritzsche, M.; Mücklich, A.; Facsko, S.

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

Permalink: https://www.hzdr.de/publications/Publ-16645
Publ.-Id: 16645


Die Jagd nach dem Weltrekord - Forschung in hohen Magnetfeldern

Wosnitza, J.

es hat kein Abstract vorgelegen!

  • Invited lecture (Conferences)
    Vorlesung in der Reihe "Physik am Samstag" der Fachrichtung Physik der TU Dresden, 03.12.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16644
Publ.-Id: 16644


World record race - Research at high magnetic fields

Wosnitza, J.

  • Invited lecture (Conferences)
    SFB/Transregio 21 Workshop 2011 "Common perspectives of mesoscopic systems and quantum gases", 13.-16.11.2011, Günzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16643
Publ.-Id: 16643


de Haas-van Alpen investigations of iron pnictides: first results

Wosnitza, J.

  • Invited lecture (Conferences)
    Kick-off meeting of the SPP 1458 "High-temperature superconductivity in iron pnictides, 24.-25.02.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16642
Publ.-Id: 16642


Monte-Carlo simulation to optimize SPECT-hardware dedicated to in-beam control of particle therapy

Rohling, H.; Dersch, U.; Fiedler, F.; Golnik, C.; Kormoll, T.; Müller, A.; Schöne, S.; Enghardt, W.

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

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

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

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

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

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

  • Poster
    ICTR-PHE 2012 - International #Conference on Translational Research in Radiation Oncology, 27.02.-02.03.2012, Genf, Schweiz
  • Radiotherapy and Oncology 102(2012), S46

Permalink: https://www.hzdr.de/publications/Publ-16641
Publ.-Id: 16641


Curium(III) speciation studies with cells of a groundwater strain of Pseudomonas fluorescens

Moll, H.; Lütke, L.; Barkleit, A.; Bernhard, G.

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

Keywords: curium; Pseudomonas fluorescens; bacteria; fluorescence spectroscopy; TRLFS; complexation

Permalink: https://www.hzdr.de/publications/Publ-16640
Publ.-Id: 16640


Application of Different Nuclides in Retrospective Dosimetry

Konheiser, J.; Mittag, S.; Viehrig, H.-W.

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

Keywords: fluence calculations; Nonte-Carlo program; retrospective dosimetry; Niobium; Nickel; Technetium

  • Journal of ASTM International 9(2012)3

Permalink: https://www.hzdr.de/publications/Publ-16639
Publ.-Id: 16639


Das Hochfeld-Magnetlabor Dresden: Rekorde in Rossendorf

Uhlarz, M.

  • Lecture (Conference)
    Tag der Wissenschaften 2011 am BSZ Radebeul, 08.06.2011, Radebeul, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16638
Publ.-Id: 16638


Development of a soft-magnetic shield for magnetic prostheses

Uhlarz, M.

  • Lecture (Conference)
    MAGISTER M30 Meeting, 16.-17.06.2011, Edingburgh, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-16637
Publ.-Id: 16637


Magnetic characterization of implantable magnetic scaffolds and powders: Activities at HZDR

Uhlarz, M.

  • Lecture (Conference)
    MAGISTER M30 Meeting, 16.-17.06.2011, Edingburgh, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-16636
Publ.-Id: 16636


Superposition of ferromagnetic and antiferromagnetic spin chains in the quantum magnet BaAg2Cu[VO4]2

Tsirlin, A. A.; Müller, A.; Lorenz, B.; Skourski, Y.; Rosner, H.

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

Permalink: https://www.hzdr.de/publications/Publ-16635
Publ.-Id: 16635


Magnetic properties and exchange integrals of the frustrated chain cuprate linarite PbCuSO4(OH)2

Wolter, A. U. B.; Lipps, F.; Schäpers, M.; Drechsler, S.-L.; Nishimoto, S.; Vogel, R.; Kataev, V.; Büchner, B.; Rosner, H.; Schmitt, M.; Uhlarz, M.; Skourski, Y.; Wosnitza, J.; Süllow, S.; Rule, K. C.

We present a detailed study in the paramagnetic regime of the frustrated s = 1/2 spin-compound linarite PbCuSO4(OH)2 with competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions. Our data reveal highly anisotropic values for the saturation field along the crystallographic main directions, with ∼7.6, ∼10.5, and ∼8.5 T for the a, b, and c axes, respectively. In the paramagnetic regime, this behavior is explained mainly by the anisotropy of the g factor, but leaving room for an easy-axis exchange anisotropy. Within the isotropic J1-J2 spin model, our experimental data are described by various theoretical approaches, yielding values for the exchange interactions J1 ∼ −100 K and J2 ∼ 36 K. These main intrachain exchange integrals are significantly larger as compared to the values derived in two previous studies in the literature and shift the frustration ratio α = J2/|J1| ≈ 0.36 of linarite closer to the one-dimensional critical point at 0.25. Electron spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements further prove that the static susceptibility is dominated by the intrinsic spin susceptibility. The Knight shift as well as the broadening of the linewidth in ESR and NMR at elevated temperatures indicate a highly frustrated system with the onset of magnetic correlations far above the magnetic ordering temperature TN = 2.75(5) K, in agreement with the calculated exchange constants.

Permalink: https://www.hzdr.de/publications/Publ-16634
Publ.-Id: 16634


B-T phase diagram of CoCr2O4 in magnetic fields up to 14 T

Pronin, A. V.; Uhlarz, M.; Beyer, R.; Fischer, T.; Wosnitza, J.; Gorshunov, B. P.; Komandin, G. A.; Prokhorov, A. S.; Dressel, M.; Bush, A. A.; Torgashev, V. I.

We have measured the magnetization and specific heat of multiferroic CoCr2O4 in magnetic fields up to 14 T. The high-field magnetization measurements indicate a new phase transition at T = 5–6 K. The phase between T and the lock-in transition at 15 K is characterized by magnetic irreversibility. At higher magnetic fields, the irreversibility increases. Specific-heat measurements confirm the transition at T , and also show irreversible behavior. We construct a field-temperature phase diagram of CoCr2O4.

Permalink: https://www.hzdr.de/publications/Publ-16633
Publ.-Id: 16633


Recent Topics of Organic Superconductors

Ardavan, A.; Brown, S.; Kagoshima, S.; Kanoda, K.; Kuroki, K.; Mori, H.; Ogata, M.; Uji, S.; Wosnitza, J.

Recent developments in research into superconductivity in organic materials are reviewed. In the epoch-defining quasi-one-dimensional TMTSF superconductors with Tc ~ 1 K, Tc decreases monotonically with increasing pressure, as do signatures of spin fluctuations in the normal state, providing good evidence for magnetically-mediated pairing. Upper critical fields exceed the Zeeman-limiting field by several times, suggesting triplet pairing or a transition to an inhomogeneous superconducting state at high magnetic fields, while triplet pairing is ruled out at low fields by NMR Knight-shift measurements. Evidence for a spatially inhomogeneous superconducting state, Fulde–Ferrel–Larkin–Ovchinnikov state, which has long been sought in various superconducting systems, is now captured by thermodynamic and transport measurements for clean and highly two-dimensional BEDT-TTF and BETS superconductors. Some of the layered superconductors also serve as model systems for Mott physics on anisotropic triangular lattice. For example, the Nernst effect and the pseudo-gap behavior in NMR relaxation are enhanced near to the Mott transition. In the case of increasing spin frustration, the superconducting transition temperature is depressed, and antiferromagnetic ordering is eliminated altogether in the adjacent Mott insulating phase. There is an increasing number of materials exhibiting superconductivity in competition or cooperation with charge order. Theoretical studies shed light on the role of spin and/or charge fluctuations for superconductivity appearing under conditions close to those of correlation-induced insulating phases in the diversity of organic materials.

Permalink: https://www.hzdr.de/publications/Publ-16632
Publ.-Id: 16632


Temperature dependence of the London penetration depth in Pr2CuO4 from millimeter-wave optical experiments

Pronin, A. V.; Fischer, T.; Wosnitza, J.; Ikeda, A.; Naito, M.

We have investigated the in-plane penetration depth, λ(T), of nominally undoped superconducting Pr2CuO4 films (Tc = 27.5 K) by measuring the phase-sensitive millimeter-wave transmission at temperatures between 2 and 30 K. The overall temperature dependence of the superfluid density, ns = λ2(0 K)/ λ2(T), resembles the behavior typical for the cuprate superconductors [ns(T) / ~ 1 (T/Tc)2]. However, a closer look on the penetration depth at low temperatures reveals flattening of its temperature dependence. We find λ(T) / Tn with n = 2.8 ± 0.2.

Permalink: https://www.hzdr.de/publications/Publ-16631
Publ.-Id: 16631


Dinuclear complexes of tetravalent cerium in an aqueous perchloric acid solution

Ikeda-Ohno, A.; Tsushima, S.; Hennig, C.; Yaita, T.; Bernhard, G.

Primary aquo species of tetravalent cerium (Ce(IV)) in perchloric acid has been identified as a single oxo-bridging dinuclear complex, not a mononuclear one, by extended X-ray absorption fine structure (EXAFS) spectroscopy combined with density functional theory (DFT) calculations.

Keywords: Tetravalent cerium; Dimer; XAS; EXAFS; DFT calculations

Permalink: https://www.hzdr.de/publications/Publ-16630
Publ.-Id: 16630


Field-induced gap in a quantum spin-1/2 chain in strong magnetic fields

Zvyagin, S.

Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions that exhibits a field-induced spin gap, are probed by means of high-frequency electron spin resonance spectroscopy in pulsed magnetic fields up to 64 T. In particular, we report on a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations in the magnetic excitation spectrum) to a spin-polarized state with magnon excitations (Fig. 1). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG calculations for spin-1/2 Heisenberg chain with a staggered transverse field [1]. Such a behavior appears to be a general feature of the high-field excitation spectrum of quantum spin-1/2 chain systems with alternating g-tensor and/or Dzyaloshonskii-Moriya interactions. In addition, the development of the high-field Electron Spin Resonance facilities at the Dresden High Magnetic Field Laboratory is reported.
This work was partly supported by DFG and EuroMagNET II.

  • Invited lecture (Conferences)
    International Workshop "Advanced ESR Studies for New Frontiers in Biofunctional Spin Science and Technology" (AEBST 2011), 13.-14.11.2011, Kobe, Japan

Permalink: https://www.hzdr.de/publications/Publ-16629
Publ.-Id: 16629


Biotechnologie zur Gewinnung von Ressourcen

Pollmann, K.; Kutschke, S.; Raff, J.

Vorstellung der Forschungsvorhaben Ressourcengewinnung

  • Lecture (others)
    Vorstellung beim Städtebund Silberberg, 27.01.2012, Aue, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16628
Publ.-Id: 16628


EduGATE - basic examples for educative purpose using the GATE simulation platform

Pietrzyk, U.; Zakhnini, A.; Axer, M.; Sauerzapf, S.; Benoit, D.; Gaens, M.

EduGATE is a collection of basic examples to introduce students to the fundamental physical aspects of medical imaging devices. It is based on the GATE platform, which has received a wide acceptance in the field of simulating medical imaging devices including SPECT, PET, CT and also applications in radiation therapy.
GATE can be configured by commands, which are, for the sake of simplicity, listed in a collection of one or more macro files to set up phantoms, multiple types of sources, detection device, and acquisition parameters. The aim of the EduGATE is to use all these helpful features of GATE to provide insights into the physics of medical imaging by means of a collection of very basic and simple GATE macros in connection with analysis programs based on ROOT. A graphical user interface to define a configuration is also included.

Keywords: Monte Carlo Simulation; GATE; PET; SPECT; Education; Imaging

Permalink: https://www.hzdr.de/publications/Publ-16627
Publ.-Id: 16627


Numerical simulations of CCFL experiments using a morphology detection algorithm

Höhne, T.; Darlianto, D.; Lucas, D.

In order to improve the understanding of counter-current two-phase flows and to validate new physical models, CFD simulations of 1/3rd scale model of the hot leg of a German Konvoi PWR with rectangular cross section was performed. Selected counter-current flow limitation (CCFL) experiments at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) were calculated with ANSYS CFX 12.1 using the multi-fluid Euler-Euler modeling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a SST turbulence model for each phase. In the simulation, the surface drag was approached by a new correlation inside the Algebraic Interfacial Area Density (AIAD) model. The AIAD model allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicated that quantitative agreement of the CCFL characteristics between calculation and experimental data was obtained. The goal is to provide an easy usable AIAD framework for all ANSYS CFX users, with the possibility of the implementation of their own correlations.

Keywords: Numerical simulation; CFD; CCFL; AIAD model; reflux condensation; PWR hot leg; air-water experiment

Permalink: https://www.hzdr.de/publications/Publ-16626
Publ.-Id: 16626


Image-Processing-Based Study of the Interfacial Behavior of the Countercurrent Gas-Liquid Two-Phase Flow in a Hot Leg of a PWR

Montoya, G.; Deendarlianto; Lucas, D.; Höhne, T.; Vallee, C.

The interfacial behavior during counter-current two-phase flow of air-water and steam-water in a model of a PWR hot leg was studied quantitatively using digital image processing of a subsequent recorded video images of the experimental series obtained from the TOPFLOW facility, Helmholtz-Zentrum Dresden-Rossendorf e.V. (HZDR), Dresden, Germany. The developed image processing technique provides the transient data of water level inside the hot leg channel up to flooding condition. In this technique, the filters such as median and Gaussian were used to eliminate the drops and the bubbles from the interface and the wall of the test section. A Statistical treatment (average, standard deviation, and probability distribution function (PDF)) of the obtained water level data was carried-out also to identify the flow behaviors.

The obtained data are characterized by a high resolution in space and time, which makes them suitable for the development and validation of CFD-grade closure models, e.g. for two-fluid model. This information is essential also for the development of mechanistic modeling on the relating phenomenon. It was clarified that the local water level at the crest of the hydraulic jump is strongly affected by the liquid properties.

Keywords: CFD; Hot Leg

  • Open Access Logo Science and Technology of Nuclear Installations 2012(2012), ID 209542
    DOI: 10.1155/2012/209542

Permalink: https://www.hzdr.de/publications/Publ-16625
Publ.-Id: 16625


Counter-current Flow Limitation of Gas-Liquid Two phase Flow in Nearly Horizontal Pipe

Prayitno, S.; Santoso, R.; Darlianto, D.; Höhne, T.; Lucas, D.

Experimental on the work counter current two phase flow of air and gas in nearly horizontal flows have been performed. The experiments are conducted with 50 mm inner diameter pipe, in two inclination angle setting (20° and 10° from horizontal) and smooth liquid and air inlet i.e. a porous liquid inlet and a nozzle connected with calm section for gas inlet. The effect of liquid properties are examined by using five different working fluids (Water, two different concentration of butanol and glycerin aqua solutions). As results, (1) CCFL causes a drastic change in the delivered liquid to the lower plenum. (2) The effect of inclination angle is significantly observed. The flooding gas superficial velocity needed decreases with inclination angle. (3) The liquid viscosity affects the flooding phenomena.

Keywords: counter-current flow limitation; flooding; inclined pipe; liquid properties

Permalink: https://www.hzdr.de/publications/Publ-16624
Publ.-Id: 16624


CFD studies of the insulation material transport inside the reactor pressure vessel under LOCA conditions

Höhne, T.; Grahn, A.; Kliem, S.

In 1992, strainers on the suction side of the ECCS pumps in Barsebäck NPP Unit 2 became partially clogged with mineral wool because after a safety valve opened the steam impinged on thermally-insulated equipment and released mineral wool. This event pointed out that strainer clogging is an issue in the course of a loss-of-coolant accident (LOCA). In the LOCA event inside the containment, energetic pressure waves and fluid jets would impinge upon components in the vicinity of the break and could release thermal insulation and dust. In addition, debris can be created by chemical reactions between reactive ECC solutions and the materials in the containment. These reactions may result in additional debris such as disbanded coatings and chemical precipitates being generated [1].Through transport mechanisms such as entrainment in steam/water discharge from the break and wash down due to condensate flow in the containment, a fraction of the generated debris and other material in the containment would be transported to the containment sump. Subsequently, if the ECCS is operating in the sump recirculation mode, the debris suspended in the containment sump would begin to accumulate on the sump strainers. A small part could penetrate trough the strainers and could be transported towards the core. The accumulation of this suspended debris on the sump strainers can create an almost uniform covering on the strainer, which would tend to increase the head loss across the strainer. On account of this phenomenon, modifications of the insulation material, the strainer size and the mesh size at the strainers were carried out in most of the German NPPs to assure the emergency core cooling during the sump recirculation mode. Moreover, differential pressure measurements and back flushing procedures were implemented to remove the mineral wool from the strainers, before the differential pressure exceeds a certain level. Nevertheless, it cannot be completely ruled out, that small fractions of the insulation material are transported into the RPV. During hot leg ECC injection, the fibres enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might cause a reduction of the ECC flow into the core and degradation of core cooling.
It was the aim of the numerical simulations to study where and how many mineral wool fibres are deposited at the upper spacer grid. The 3D, time dependent, multi-phase flow problem was modelled applying the CFD code ANSYS CFX. Best practice guidelines were used to specify the grid size, turbulence model and the multiphase model. The spacer grids were modelled as a strainer, which completely retains all the insulation material reaching the uppermost spacer level. In this model, which was validated against experiments at HTWS Zittau, the accumulation of the insulation material gives rise to the formation of a compressible fibrous cake, the permeability of which to the coolant flow is calculated in terms of the local amount of deposited material and the local value of the superficial liquid velocity. The CFD simulations have shown that after starting the sump mode, the ECC water injected through the hot legs flows down into the core at so-called “breakthrough channels” at the outer regions of the core, which were first recognized in UPTF experiments. In contradiction the hotter, lighter coolant rises in the centre of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the breakthrough zones. This means that the fibres are not uniformly deposited over the core cross section.
Further investigations are necessary to determine the accumulation of insulation material for a longer period of time. Also steam production in the core or re-suspension of the insulation material during back flow should be considered.

Keywords: CFD; UPTF; ECC; RPV

  • Lecture (Conference)
    CFD4NRS-4, The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology, 10.-12.09.2012, Daejeon, Korea
  • Contribution to proceedings
    CFD4NRS-4, The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology, 10.-12.09.2012, Daejeon, Korea
    CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-16623
Publ.-Id: 16623


CFD-modelling of CCFL phenomena in a PWR hot leg model

Höhne, T.; Darlianto, D.; Lucas, D.

The detailed three-dimensional (3-D) information on the transient flow behaviour under countercurrent flow limitation (CCFL) in a pressurized water reactor (PWR) hot leg is an important issue in the reactor safety analysis. It relates to a hypothetical scenario of small break Loss of Coolant Accident (LOCA) in a PWR, and leads to the reflux-condensing mode. During this scenario, a part of the condensate flows back towards the reactor pressure vessel (RPV) in counter current to the steam. In this mode, a CCFL could occur, affecting the core cooling. Deendarlianto et al. (2011a) has already reviewed different applications of CFD codes to simulate the phenomena around the CCFL in a PWR hot leg. They indicated that there is still a lack of knowledge regarding suitable closure models for this application. In some cases empirical correlations originally obtained for one-dimensional codes were used for this multidimensional problem.

Keywords: LOCA; PWR; AIAD; CFD

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2012, 22.-24.05.2012, Stuttgart, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2012, 22.-24.05.2012, Stuttgart, Deutschland
    CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-16622
Publ.-Id: 16622


Multiphase Flows in Industrial Applications – Theory, Experiments and CFD Validation

Höhne, T.

Strong increase of usage of three-dimensional Computational Fluid Dynamics (CFD) in industrial applications because for instance
slugging,
pressurized thermal shocks,
coolant mixing,
thermal striping
cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.

Keywords: CFD; slugging; pressurized thermal shocks; coolant mixing; thermal striping

  • Invited lecture (Conferences)
    International Seminar Series 2012, Universitas Gadjah Mada, Faculty of Engineering, 30.01.2012, Yogyakarta, Indonesia

Permalink: https://www.hzdr.de/publications/Publ-16621
Publ.-Id: 16621


CFD in Safety of Nuclear Industry

Höhne, T.

Strong increase of usage of three-dimensional Computational Fluid Dynamics (CFD) in industrial applications because for instance
slugging,
pressurized thermal shocks,
coolant mixing,
thermal striping
cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.

Keywords: CFD; slugging; pressurized thermal shocks; coolant mixing; thermal striping

  • Invited lecture (Conferences)
    International Conference on Computational Modeling Validation, 14.-15.01.2012, Sydney, Australien
  • Open Access Logo Contribution to proceedings
    International Conference on Computational Modeling Validation, 14.-15.01.2012, Sydney, Australien
    CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-16620
Publ.-Id: 16620


Recent Developments in CFD Modeling of Multiphase Flows

Höhne, T.

CFD (Computational Fluid Dynamics) is the simulation of fluids engineering systems using modeling (mathematical physical problem formulation) and numerical methods (discretization methods, solvers, numerical parameters, and grid generations, etc.)
CFD made possible by the advent of digital computer and advancing with improvements of computer resources (500 Floating Point Operations per Second (flops), 1947 10 Petaflops, 2011)

Keywords: CFD; AIAD; Multiphase flow

  • Invited lecture (Conferences)
    INTERNATIONAL CONFERENCE ON COMPUTATIONAL MODELING VALIDATION, 14.-15.01.2012, Sydney, Australien
  • Open Access Logo Contribution to proceedings
    INTERNATIONAL CONFERENCE ON COMPUTATIONAL MODELING VALIDATION, 14.-15.01.2012, Sydney, Australien
    CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-16619
Publ.-Id: 16619


Modelling and Simulation of 4D GeoPET Measurements with COMSOL Multiphysics 4.2a

Schikora, J.; Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.

Our GeoPET-method allows the 4D monitoring of (reactive) transport processes in geological material on laboratory scale (Gründig et al., 2007; Kulenkampff et al., 2008; Richter et al., 2005) by quantitative imaging of tracer concentrations. Recently we have conducted a long-term 22Na+ in-diffusion experiment in an Opalinus clay drill core over aperiod of 7 months. We modelled this experiment with COMSOL Multiphysics ® 4.2a (3D convection-diffusion equation, PDE mode, PARDISO solver) for reproducing the observed spatiotemporal concentration distribution data with the following underlying equation for this anisotropie diffusion and adsorption:
8Ci ( ) 8q
cßt = \l Dc . \lCi P8t
-c [-] porosity, ci[moVm3] 22Na+concentration, D e [m2/s] tensor of the effective diffusion constant for 22Na+ in Opalinus clay, P [kg/m3 ] bulk density and 8q/8t sink term for considering the sorption. By importing GeoPET images from various time steps and applying the Optirnization Module (least square fit applying the LevenbcrgMarquardt algorithrn) to these images we efficiently deterrnined hest fit values e.g. of the diffusion tensor. Cornbined with the parameter sweep operation the sensitivity analysis is performed in parallel and covers the range of literature values for porosity and Kd values for 22Na+sorption on Opalinus cIay.
The experimental data could be reproduced quite weIl, but the obtained parameter values for diffusion parallel and normal to the bedding are slightly larger than reported in Gimmi and Kosakowski (2011). This is coherent with our observations of an emerging gas bubble in the central borehole tracer reservoir: Soil moisture tension in the partly unsaturated clay must have significantly influenccd thc transport regime by an additional advective component.
We suggest COMSOL Multiphysics ® is a powerful tool for the inverse modelling of timedependent, multidimensional experimental data as obtained by GeoPET.
References.
Gründig, M. et a1., 2007. Tomographie radiotraeer studies ofthe spatial distribution ofheterogeneous geoehemieal transport proeesses. Appl. Geochem., 22: 2334-2343.
Kulenkampff, J. et al., 2008. Evaluation ofpositron emission tomography for visualisation ofmigration proeesses in geomaterials. Phys. Chern. Earth, 33: 937-942.
Richter, M. et al., 2005. Positron Emission Tomography for modelling of geochmical transport processes in clay. Radiochirn. Acta, 93: 643-651.
Gimmi, T. & Kosakowski, G. 2011. How mobile are sorbed eations in clay and clay rocks? Environ. Sei. Techn., 45:1443-1449

  • Poster
    EGU General Assembly 2012, 22.-27.04.2012, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-16618
Publ.-Id: 16618


Influence of Temperature on the Sorption of Selenate onto Anatase

Franzen, C.; Jordan, N.; Mueller, K.

The radioactive isotope Selenium-79 is a long-lived fission product found in nuclear waste. Due to its long half life of 3.27 ∙ 105 years, it is expected to be one of the isotopes most contributing to the potential radiation dose according to safety assessments of nuclear waste underground repositories. A detailed knowledge of the mobility and bioavailability of selenium is therefore of great importance for a safe disposal of radioactive waste.
One major process controlling selenium mobility and bioavailability is the adsorption onto mineral surfaces of both the geological and engineered barrier. High level and long-lived radioactive waste increase the temperature in the vicinity of the waste disposal site. Thus, it is important to understand to what extent this temperature increase influences the sorption of selenium.
The present study focuses on the impact of temperature on the sorption of selenate (SeO42-) onto anatase (TiO2). Because of its abundance in rocks and its well-known crystal structure, anatase represents an ideal model system for the study of sorption behaviour of Se onto transition metal oxide phases. The sorption of selenate onto anatase at different temperatures (25 °C – 60 °C) was investigated both with batch experiments and ATR FT-IR spectroscopy. In order to explain possible differences in sorption at higher temperatures, the surface of the anatase was investigated.
The sorption of Se(VI) onto anatase as a function of pH was similar at 25 °C and 60 °C, i.e. sorption decreased with increasing pH. However, the sorption capacity of anatase towards Se(VI) was lowered at a higher temperature. Furthermore, the pH value above which no Se(VI) sorption occurs was shifted to lower pH values (from pH 6.5 at 25 °C to pH 5.5 at 60 °C).
The isoelectric point of anatase (pHIEP) was located at pH 6.3 at 25 °C. At higher temperatures, the pHIEP was shifted towards lower pH with a value of 5.5 at 60 °C. In addition, the absolute values of the zeta potential were lowered at higher temperatures. Both findings were in good agreement with the batch experiments.
The observed decrease in selenate sorption at higher temperatures could be assigned to a change in the surface properties of anatase.

Keywords: Selenium; selenate; sorption; anatase; temperature

  • Lecture (Conference)
    Experimental Mineralogy Petrology and Geochemistry, 04.-07.03.2012, Kiel, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16617
Publ.-Id: 16617


THEREDA - One Database for thermodynamic and sorption data

Bok, F.; Brendler, V.; Richter, A.

For geochemical modeling of scenarios for the disposal of radioactive and (chemo)toxic waste, comprehensive and internally consistent thermodynamic data are required as well as sorption data for the surrounding host rocks. The use of different databases renders it difficult to compare results of geochemical modeling, due to incompleteness, inconsistencies, resticted ranges of variation (temperature, density, pressure), limitations in solution composition (ionic strength) and last but not least missing sorption data.
THEREDA (THErmodynamic REference DAtabase, www.thereda.de) is a project adressing these issues through high quality standards: full documentation and thus transparency of all data, internal consistency, quality assurance measures, different interaction models, comprehensiveness. It shall imporve geochemical modelling for various environmental applications, namely radiochemical waste disposal assessment.
THEREDA contains data for the three ion-ion interaction models: extendend Debye-Hückel, Specific Ion Interaction Theory, and Pitzer model. Tailored parameter files for various geochemical modeling codes are provided (PhreeqC, ChemApp, EQ3/6, Geochemist‘s Workbench). Documented benchmark calculations allow comparisons with other databases as well as between the different geochemical codes. All data, documentation and references are freely accessible via the projects homepage. Additionally, a user forum allows direct contact with the THEREDA members.
A holistic view of geochemical processes in the context of a safety analysis requires the inclusion of sorption calculations. A thermodynamically consistent treatment of these processes is only possible with surface complexation modelling (SCM). Existing SCM data from the RES³T (Rossendorf expert system for surface and sorption thermodynamics, www.hzdr.de/res3t) database is currently subjected to critical evaluation and will be included in THEREDA.

Keywords: THEREDA; RES³T; RES3T; database; thermodynamic; sorption

  • Poster
    Experimental Mineralogy Petrology and Geochemistry 2012, 04.-07.03.2012, Kiel, Deutschland
  • Contribution to proceedings
    Experimental Mineralogy Petrology and Geochemistry 2012, 04.-07.03.2012, Kiel, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16616
Publ.-Id: 16616


Different types of outer-sphere complexes of selenate ions on mineral surfaces

Jordan, N.; Ritter, A.; Heim, K.; Foerstendorf, H.

  • Lecture (others)
    Helmholtz-Koordinierungstreffen, 23.-24.01.2012, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16615
Publ.-Id: 16615


Manuskriptband für die Berliner Recycling- und Rohstoffkonferenz 2012

Dürkoop, A.; Gutzmer, J.; Faulstich, M.; Klossek, A.

Auf Basis der Rohstoffstrategie und der High-Tech Strategie 2020 der Bundesregierung (2010a, 2010b) sollen mit der vom Bundesministerium für Bildung und Forschung (BMBF) geförderten Maßnahme „r3 – Innovative Technologien für Ressourceneffizienz – Strategische Metalle und Mineralien“ konkrete Vorschläge für die Erhöhung der Versorgungssicherheit strategisch bedeutender Ressourcen in Deutschland erarbeitet werden. Unter diesen strategisch bedeutenden Ressourcen sind seltene Metalle und Industriemineralien zu verstehen, die mehr und mehr in der High-Tech-Industrie zum Einsatz kommen. Im Rahmen der Fördermaßnahme r³ wird neben zahlreichen Verbundprojekten ein übergeordnetes Begleitforschungsprojekt „INTRA r³+“ angestrebt, welches die Fördermaßnahme koordiniert, entstandenes Wissen bündelt und die Forschungspartner miteinander vernetzt. Ein zentrales Anliegen von INTRA r3+ ist die Aufbereitung und Kommunikation des entstandenen Wissens sowie die Entwicklung von gezielten Transfermaßnahmen für Akteure und Interessengruppen inner- und außerhalb des Forschungsnetzwerkes. Durch diese Maßnahmen soll der Weg zur Übertragung und wirtschaftlichen Nutzung der Projektergebnisse erleichtert werden.
Das Begleitforschungsprojekt startete im November 2011 und wird bis Januar 2016 als Serviceprogramm für r3 die Forschungsaktivitäten zur Optimierung der gesamten Wertschöpfungskette der Bereitstellung von strategischen Metallen und Industriemineralien begleiten. Koordinator des INTRA r3+ ist das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF), (siehe Punkt V). Die geförderten Verbundprojekte innerhalb des r3-Rahmenprogramms werden ab Mitte 2012 mit ihren Forschungsarbeiten für innovative Technologien zur Ressourceneffizienz beginnen.
Durch die Bündelung, Analyse und Bewertung neuer Erkenntnisse sollen im Begleitforschungsprojekt INTRA r3+ Impulse erzeugt werden, die einerseits auf eine erfolgreiche Durchführung der Verbundprojekte abzielen, anderseits die Kooperation und Vernetzung der Verbundprojekte untereinander fördern sollen. Die Verbundprojekte werden dafür in verschiedene Forschungscluster unterteilt, die wiederum von Clusterbetreuern gesteuert werden. Im Rahmen von INTRA r³+ steht den technischen Verbundprojekten auch ein Analyseservice im Gerätepool des Koordinators HIF zur Verfügung.

Keywords: Resource efficieny; rare earth elements; industrial minerals; recycling; substitution; urban-mining

  • Invited lecture (Conferences)
    Berliner Recycling- und Rohstoffkonferenz 2012, 26.-27.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16614
Publ.-Id: 16614


Specific targeting of hypoxic tumor tissue with nitroimidazole-peptide conjugates

Splith, K.; Bergmann, R.; Pietzsch, J.; Neundorf, I.

Nitroimidazole–peptide conjugates: Attachment of a nitroimidazole unit to a cell-penetrating peptide was used to create conjugates able to target hypoxic tumor tissue. In vivo studies have demonstrated the successful delivery of these conjugates to even less well-perfused hypoxic regions in solid tumors. This approach provides a targeted delivery system with the option to use it as an imaging agent or to conjugate it with therapeutics.

Keywords: antitumor agents; cell-penetrating peptides; drug delivery; hypoxia; tumor targeting

Permalink: https://www.hzdr.de/publications/Publ-16613
Publ.-Id: 16613


The impact of atmospheric carbonate on the sorption of actinyl (V/VI) ions onto gibbsite studied by in situ ATR FT-IR and EXAFS spectroscopy

Gückel, K.; Foerstendorf, H.; Rossberg, A.

The talk shows a first comparative insight into the course of the surface complex formation of U(VI) and Np(V) onto gibbsite on a molecular level studied by ATR FT-IR and EXAFS spectroscopy.

  • Lecture (others)
    HELMHOLTZ-KOORDINIERUNGSTREFFEN 2012, 23.-24.01.2012, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16612
Publ.-Id: 16612


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