[en] In several countries utilising nuclear power plants as energy source, e.g. Finland, Germany and Sweden, the concept of direct geological disposal of spent nuclear fuel (SNF) is considered. This suggests to store SNF after discharge from the nuclear reactor for few years under water in reactor-site storing pools until transfer out of the reactor building to an interim storage facility. In case of dry interim storage, the irradiated fuel assemblies are emplaced in multi-purpose transport and storage casks, such as the CASTOR® of Gesellschaft für Nuklear-Service. Eventually, the SNF is transferred to a deep geological repository. For instance in Germany, Spain and the United States of America, multi-purpose casks with SNF are stored in dry interim storage facilities, mostly located in close vicinity to the nuclear power plants, where the SNF was discharged from. It is foreseen to keep the SNF in transport and storage casks until a final repository for high-level waste (HLW) will be in operation. Begin of operation of final repositories for HLW are expected in the next years (Finland and Sweden), respectively decades (e.g. Switzerland and other European countries). Since transport and storage casks are not licensed for final disposal, the SNF needs to be transferred into a suitable final disposal container. The integrity of the fuel claddings during the transfer from transport and storage casks to final disposal containers is of utter importance, to ensure that radionuclides (RN) will not be released by failure of the cladding tube. Already during reactor operation, the Zircaloy cladding tubes undergo different processes, such as transient elongation of the fuel rod, oxidation of the fuel- and the water-faced sides, formation of zirconium hydrides, as well as mechanical stress, which correlates with the fuel pellet swelling at higher burn-ups. Furthermore, in case of long-term safety analyses for final repositories, the contact of groundwater with the stored nuclear waste is considered. Depending on the classification of the national waste management organisations of the individual countries, at this, the cladding tube is considered as a technical barrier whose failure leads to a release of radionuclides, in particular activation products from the cladding as well as RNs from the fuel following the water penetration through the breached cladding to the SNF. In this context, various activation and fission products, such as, for example C-14, Cl-36, Cs 135 and I-129 are of significant interest due to their long half-lives, expected rapid release from the waste and high mobility in a repository system. This Ph.D. thesis addresses the occurrence of the beta and gamma radiation-emitting radionuclides Cl-36, Cs-137 and I-129, which are segregated to some extent from the fuel to the pellet-cladding interface during reactor operation. As part of these investigations, the inventory of radionuclides at the interface, respectively the inventory of the irradiated fuel and the Zircaloy cladding tube will be determined experimentally and compared to activation calculations obtained by Monte Carlo N-particle code and CINDER as well as webKORIGEN calculations. For the precise identification of the Cl-36 and I-129 inventory, it is necessary to develop a radiochemical separation process, which allows a quantitative analysis of both of the nuclides. Since Cl-36 has no and I-129 very low energy gamma-lines, an experimental inventory determination is only possible by a complex separation of these two isotopes from other radionuclides. The method developed in this work allows the profound separation and quantification of Cl-36 and I 129 from other interfering radionuclides, present in excess by many orders of magnitude in highly radioactive specimens, by using various extraction and precipitation steps. The results presented in this work provide information on the actual proportion of Cl-36 generated by neutron activation in highly radioactive waste, as well as on the amount of the initial Cl-35 impurity. Furthermore, it is shown, that I-129 is transported by a temperature driven process from the hot pellet centre to the peripheral area, adjacent to the colder cladding, resulting in the enrichment of the volatile radionuclide. In addition to the determination of Cl-36 and I-129 activities, other radionuclides (i.e. transuranium isotopes, fission and activation products) in the highly radioactive samples were determined and quantified with respect to enrichment factors in e.g. the fuel-cladding interaction layer in the spent nuclear fuel. The experimental radionuclide measurements performed within this thesis are in good agreement with values derived from calculations and are providing further knowledge on the distribution of radionuclides in spent nuclear fuel and thus also to the more accurate determination of the source term for irradiated fuel. In the second part of the thesis, different spectroscopic methods like scanning electron microscopy and energy / wavelength dispersive X-ray spectroscopy (SEM-EDS / -WDS) as well as X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) are used for the analysis of the fuel-cladding interface. Here, examinations of the occurrence of caesium / chlorine / iodine containing phases within the fuel-cladding interaction layer of different irradiated fuel-types (UO${}_X$ and mixed oxide fuel (MOX)) as well as different burn-ups (50.4 GWd/t${}_{HM}$ and 38.0 GWd/t${}_{HM}$) are performed. It is evident, that the chemistry at the interface is far more complex than often reported in the past literature, such as solely the occurrence of CsI, UO${}_2$ or a mixed compound of zirconium and uranium ((Zr, U)O${}_{2-<!--\; ???\; -->x}$). To the knowledge of the author, it is the first time that synchrotron radiation based Cl and I K edge measurements are performed on actual spent nuclear fuel fragments and Zircaloy cladding segments, resulting in an iodine-bearing compound with structural similarity to CsI and a yet to be identified chlorine-bearing compound. These measurements aim to provide a better understanding on the occurrence of iodine and chlorine-bearing agglomerates in spent nuclear fuel. The last part of the thesis focusses on possible corrosive effects of fission and activation product agglomerates on the interface layer, impacting the cladding integrity of spent nuclear fuel rods with regard to a prolonged dry interim storage. Hereto, U-O-Zr-Cs-Cl-I-containing phases are deposited on unirradiated Zircaloy and stored under inert gas and elevated temperature for an extended period of time. Afterwards the resulting samples are analysed by SEM-EDS and XPS to draw conclusions on their corrosion and embrittlement behaviour. Results obtained from this experiment indicate pitting corrosion processes on the Zircaloy cladding under the above mentioned conditions, enabled by the halogen-bearing species. Especially the role of the impurity chlorine in nuclear fuel and cladding material is highlighted by this experiment as its effects on possible cladding degradation under interim storage conditions is till now afflicted with uncertainties. However, it is evident, that more experiments are needed to elucidate this effect. The applied experimental conditions are not fully representative for the interim storage environment. The effect of radiation is not considered and a significant oxidation of the introduced UO${}_2$ was found unexpectedly, despite working under Ar atmosphere. The work of this thesis is performed in part within the EURAD work package “Spent fuel characterization and evolution until disposal”.

[en] Future developments in nanophotonics require facile, inexpensive and parallelizable fabrication methods and need a fundamental understanding of the spectroscopic properties of such nanostructures. These challenges can be met through colloidal self-assembly where pre-synthesized colloids are arranged over large areas at reasonable cost. As so-called colloidal building blocks, plasmonic nanoparticles and quantum dots are used because of their localized light confinement and localized light emission, respectively. These nanoscopic colloids acquires new hybrid spectroscopic properties through their structural arrangement. To explore the energy transfer between these nanoscopic building blocks, concepts from physical optics are used and implemented with the colloidal self-assembly approach from physical chemistry. Through an established synthesis, the nanocrystals are now available in large quantities, any they receive the tailored spectroscopic properties through directed self-assembly. Moreover, the tailored properties of the colloids and the use of stimuli-responsive polymers allow a functionality that goes beyond current developments. The basics developed in this habilitation thesis can lead to novel functional devices in the field of smart sensors, dynamic light modulators, and large-area quantum devices.

[en] Here we demonstrate how a surface plasmon (SP) generated near field pattern in the vicinity of a nano-scale pin hole can be used to generate reversible topography changes in a photosensitive polymer film above the opening. This can be achieved by simply changing the polarization state of the plasmon generating incoming light. In the case of linear polarization, the near field intensity pattern causes the film to laterally expand/contract according to the direction of the polarization. For circular polarization, two pronounced rims corresponding to maxima in the topography are observed. In all cases, the topographical variation is in close agreement with the SP intensity distribution computed from finite difference time domain simulation. Our results demonstrate the versatility of using SP near fields to imprint a variety of structures into photosensitive polymer films using only a single metallic mask. (paper)

[en] We report on sub-wavelength structuring of photosensitive azo-containing polymer films induced by a surface plasmon interference intensity pattern. The two surface plasmon waves generated at neighboring nano-slits in the metal layer during irradiation interfere constructively, resulting in an intensity pattern with a periodicity three times smaller than the wavelength of the incoming light. The near field pattern interacts with the photosensitive polymer film placed above it, leading to a topography change which follows the intensity pattern exactly, resulting in the formation of surface relief gratings of a size below the diffraction limit. We analyze numerically and experimentally how the depth of the nano-slit alters the interference pattern of surface plasmons and find that the sub-wavelength patterning of the polymer surface could be optimized by modifying the geometry and the size of the nano-slit. (paper)

[en] The chemokine receptor CXCR4 is a promising target for molecular imaging of CXCR4⁺ cell types, e.g. inflammatory cells, in cardiovascular diseases. We speculated that a specific CXCR4 ligand, [⁶⁸Ga]pentixafor, along with novel techniques for motion correction, would facilitate the in vivo characterization of CXCR4 expression in small culprit and nonculprit coronary atherosclerotic lesions after acute myocardial infarction by motion-corrected targeted PET/CT. CXCR4 expression was analysed ex vivo in separately obtained arterial wall specimens. [⁶⁸Ga]Pentixafor PET/CT was performed in 37 patients after stent-based reperfusion for a first acute ST-segment elevation myocardial infarction. List-mode PET data were reconstructed to five different datasets using cardiac and/or respiratory gating. Guided by CT for localization, the PET signals of culprit and various groups of nonculprit coronary lesions were analysed and compared. Ex vivo, CXCR4 was upregulated in atherosclerotic lesions, and mainly colocalized with CD68⁺ inflammatory cells. In vivo, elevated CXCR4 expression was detected in culprit and nonculprit lesions, and the strongest CXCR4 PET signal (median SUV_max 1.96; interquartile range, IQR, 1.55-2.31) was observed in culprit coronary artery lesions. Stented nonculprit lesions (median SUV_max 1.45, IQR 1.23-1.88; P = 0.048) and hot spots in naive remote coronary segments (median SUV_max 1.34, IQR 1.23-1.74; P = 0.0005) showed significantly lower levels of CXCR4 expression. Dual cardiac/respiratory gating provided the strongest CXCR4 PET signal and the highest lesion detectability. We demonstrated the basic feasibility of motion-corrected targeted PET/CT imaging of CXCR4 expression in coronary artery lesions, which was triggered by vessel wall inflammation but also by stent-induced injury. This novel methodology may serve as a platform for future diagnostic and therapeutic clinical studies targeting the biology of coronary atherosclerotic plaque. (orig.)

[en] Enhancing photoluminescence (PL) of semiconducting 2D materials is proven essential for many applications related to optoelectronics and sensing. Here, we demonstrate synergistic PL enhancement in 2D materials by incorporating silver plasmonic nanodiscs in defect-induced monolayer molybdenum disulfide (MoS₂) for luminescent quench sensing of dopamine with high accuracy and selectivity. We develop a hole-array perforated 2D MoS₂ embedded with plasmonic silver dimers to harmonize the surface plasmon resonance with the PL wavelength of monolayer MoS₂, which enhance it by 56-fold. We implemented the optimized perforated MoS₂/dimers platform as a catalytic assay for on-chip PL quenching detection of dopamine, achieving a low limit of detection of 9.3 nM. This approach opens avenues of high-performance molecular sensing applications by improving the PL emission of 2D materials. (paper)

[en] 

Background

Right ventricular (RV) dysfunction predicts adverse outcome in peripartum cardiomyopathy (PPCM). We recently demonstrated beneficial effects associated with the prolactin release inhibitor bromocriptine at different doses when added to standard heart failure therapy in PPCM. Here, we evaluated for the first time the therapeutic potential of bromocriptine particularly in PPCM patients with RV involvement.

Methods

In this study, 40 patients with PPCM were included, of whom 24 patients had reduced RV ejection fraction (RVEF < 45%). We examined the effect of short-term (1W: bromocriptine, 2.5 mg, 7 days, n = 10) compared with long-term bromocriptine treatment (8W: 5 mg for 2 weeks followed by 2.5 mg for another 6 weeks, n = 14) in addition to guideline-based heart failure therapy in patients with an initial RVEF < 45% on the following outcomes: (1) change from baseline (Δ delta) in RVEF, (2) change from baseline in left ventricular EF (LVEF), and (3) rate of patients with full LV recovery (LVEF ≥ 50%) and (4) rate of patients with full RV recovery (RVEF ≥ 55%) at 6-month follow-up as assessed by cardiac magnetic resonance imaging.

Results

Reduced RVEF at initial presentation was associated with a lower rate of full cardiac recovery at 6-month follow-up (patients with RV dysfunction: 58% vs. patients with normal RV function: 81%; p = 0.027). RVEF increased from 38 ± 7 to 53 ± 11% with a delta-RVEF of + 15 ± 12% in the 1W group, and from 35 ± 9 to 58 ± 7% with a Δ RVEF of + 23 ± 10% in the 8W group (Δ RVEF 1W vs 8W: p = 0.118). LVEF increased from 25 ± 8 to 46 ± 12% with a Δ LVEF of + 21 ± 11% in the 1W group, and from 22 ± 6 to 49 ± 10% with a Δ LVEF of + 27 ± 9% in the 8W group (Δ LVEF 1W vs 8W: p = 0.211). Full LV recovery was present in 50% of the 1W group and in 64% of the 8W group (p = 0.678). Full RV recovery was observed in 40% of the 1W group and in 79% of the 8W group (p = 0.092).

Conclusions

Despite overall worse outcome in patients with RV dysfunction at baseline, bromocriptine treatment in PPCM patients with RV involvement was associated with a high rate of full RV and LV recovery, although no significant differences were observed between the short-term and long-term bromocriptine treatment regime. These findings suggest that bromocriptine in addition to standard heart failure therapy may be also effective in PPCM patients with biventricular impairment.