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[en] CARPT technique is widely applied to studies on the dynamics of fluids and solids in the design phase of industrial equipment. This study describes the simulation, using MCNP code, of a CARPT-based methodology and uses a reduced-scale model of the Brazilian Multipurpose Reactor as reference for the simulations. The goal is to evaluate the applicability of this methodology to the study of natural circulation passive safety systems in medium-scale experiments, such as the one modelled here, by comparing previously simulated trajectories for a radioactive particle and the trajectories calculated by the methodology under the same conditions. The methodology described was proposed by VIEIRA (2009) and has the advantages of being cost-effective and easy to implement, but it was initially designed considering small-scale experiments. Different configurations for the system were tested and correspondence between simulated trajectories and those reconstructed by applying the technique was analyzed for each of them; efficiencies and errors were also discussed. Comparison between simulated and reconstructed trajectories showed similar trends between them for each configuration, but the errors found were not negligible. Configurations’ parameters that promoted the best fit between trajectories were listed and possible improvements were suggested. This is the first study on the application of CARPT technique for research reactors safety systems. (author)
[en] Scientific observations and thereby the gain of knowledge are limited by the available measurement methods and instruments. To improve the accuracy of scientific models, the development of detectors is an essential activity with the usage of state-of-the-art technology. Especially in space projects with their extensive qualification, the investigation and improvement of concepts have to start decades before the final operation. Processes around extremely dense celestial objects take place on small scales in hot environments with effective temperatures of up to 10 K that correspond to peak emissions of the thermal radiation of a few thousand electron volts. Further sources for spectral characteristics are absorption and emission features like the very common iron K- line with a rest energy of 6.4 keV and bremsstrahlung of charged particles accelerated in the strong magnetic fields. To reveal the nature of such compact celestial bodies and their vicinity that often feature variations on short time scales of a few microseconds, fast X-ray detectors are necessary. Compared to CCDs, active pixel sensors facilitate shorter readout cycles so that they are suitable to increase the time resolution of spectroscopic X-ray imagers. In the fastest possible readout - the continuous full parallel one - the spectral performance worsens drastically due to photons that hit the detector during the readout process that takes place almost all the time. Such effects can be reduced by implementing a storage for charge carriers generated by an incident photon into each pixel. One approach is the so-called Infinipix, a structure that is composed of two sub-pixels with a depleted p-channel field-effect transistor (DEPFET) each. The charge collection and the readout are interchanged between the sub-pixels after every frame. In the cause of my PhD research, three different layout variants are investigated for the first time on matrix scale. It is demonstrated that already the investigated implementation of the concept achieves an excellent spectroscopic performance of 2.4 electrons and 123 eV FWHM at 5.9 keV for a readout time per row of 5 μs, corresponding to a frame frequency of about 6 kHz even for a kilopixel sensor. The existing layout variations give the opportunity to study the influence of specific design parameters on the spectroscopic and storage performance and to propose improvements. New layout proposals are investigated by 3D simulations to extend the size of the working windows of operation voltages to further develop a DEPFET with storage to a technology level, adequate to be used in future space missions. Measurements and simulations also indicate the expected improvement, a storage within an active pixel sensor contributes to the spectral performance for high time resolutions. Resulting layout adaptions and a first small sensor in a full parallel readout mode will be fabricated to verify the outcomes of this work in the near future.
[en] In the context of the safety assessment of a possible nuclear waste repository and nuclear forensics of long-lived radionuclides, such as Pu, Np or Tc the need for methods that provide the possibility of laterally resolved surface imaging and detection of lowest amounts of these elements, arises. Such methods provide important information with regard to the geochemical behavior in the far-field of the repository and environmental monitoring. The work presented herein shows the possibilities of Resonance Ionization Mass Spectrometry (RIMS) for the ultra-trace analysis of Pu and Tc. An element-specific ionization process using multi-step resonant laser excitation is used in combination with mass spetrometric techniques allowing for a highly selective detection of long-lived radionuclides almost free of isobaric interferences. The principle of the routinely applied ultra-trace analysis of Pu in environmental samples is presented and followed by optimizations of the process that lead to a stable increase in the efficiency to 10 which makes the detection of a few hundred ag Pu in 2 g untreated sample material possible. In further development of the RIMS method, a new Tc tracer was thoroughly characterized and prepared for the application in the ultra-trace analysis of Tc. This Tc tracer was successfully used to quantify a previously unknown amount of Tc in a soil sample using RIMS, which marks the first time application of the method for this purpose. In case of a leakage and subsequent interaction of the radionuclides with the repository’s host rock, the important redox-active and immobilizing mineral phases have to be identified. This was realized by recommissioning of a commercial Secondary Ion Mass Spectrometry (SIMS) system, that was subsenquently technologically upgraded, optimized and augmented for the application of Laser-SecondaryNeutralMass Spectrometry (Laser-SNMS). Laser-SNMS utilizes the advantages of resonance ionization in combination with the lateral resolving capabilities of SIMS. Thus, the method allows for a matrix-independent ionization that neutralizes a false-positive signal in laterally resolved images, that can occur in SIMS. Beam transport and feeding of the laser light into the SIMS sample chamber as well as a linking of the timing of SIMS and laser system have been implented. After optimization of the SIMS process the system was extensively optimized and characterized for the application of Laser-SNMS by measurements of Gd. A lateral resolution of 6–9 µm and a mass resolution of ∼700 could be realized. Following this groundwork, the method was extended for the measurement of Pu using samples of specified amounts of Pu electrodeposited onto Ti-foil. This lead to efficiencies of 7·10–9·10. A small field of view containing a total of ∼2·10 atoms was analyzed with SIMS and Laser-SNMS. Whereas the SIMS measurement did not provide a signal distinguishable from background noise, a distinct Pu peak could be identified using Laser-SNMS, impressively demonstrating the strengths of the method. In a first application to samples originating from a possible repository host rock, pyrite particles contacted with Pu were analyzed with SIMS and Laser-SNMS. The effects of sample topography and matrix effects on SIMS measurements and respective advantages of Laser-SNMS were investigated and the successful application of the method to these kind of samples could be demonstrated.
[de]Im Rahmen der Endlagerforschung und Umweltüberwachung langlebiger Radionuklide wie Pu, Np oder Tc sind Methoden zur Untersuchung des geochemischen Verhaltens sowie dem Nachweis geringster Mengen, zur Nachbildung der Verhältnisse im Fernfeld eines Endlagers und im Kontext der nuklearen Forensik, wichtige Werkzeuge für die Sicherheits- und Spurenanalyse. In der vorliegenden Arbeit wird die Resonanzionisations-Massenspektrometrie (RIMS) zur Ultraspurenanalyse von Pu und Tc vorgestellt. Der mehrstufige, resonante Ionisationsprozess mittels Laserlicht in Verbindung mit massenspektrometrischen Verfahren erlaubt einen hochgradig elementselektiven und nahezu isobarenfreien Nachweis langlebiger Radionuklide. Der Prozess der routinemäßigen Analyse von Pu in Umweltproben mittels RIMS wird vorgestellt und es konnte durch Optimierung eine stabile Erhöhung der Effizienz auf 10 für den Nachweis von einigen hundert ag Pu in 2 g Probenmaterial erreicht werden. Weiterhin wurde ein neuer Tc-Tracer eingehend charakterisiert und die Methode für den Nachweis von Tc weiterentwickelt. In einer Bodenprobe konnte eine Menge von 1,5·10 Atome Tc unter Verwendung des Tc Tracers mittels RIMS quantifiziert werden, was den erstmaligen Einsatz der Methode in diesem Kontext darstellt. Zur Untersuchung des geochemischen Verhaltens bei Austritt der Radionuklide und Kontakt mit dem Wirtsgestein im Endlager werden ortsaufgelöste Messmethoden im Hinblick auf redoxaktive und immobilisierende Phasen benötigt. Hierfür wurde ein kommerzielles Sekundärionen-Massenspektrometer (SIMS) wieder in Betrieb genommen, technisch modernisiert, optimiert und für den Einsatz in der Laser-Sekundärneutralteilchen-Massenspektrometrie (Laser-SNMS) erweitert. Die Methode nutzt die Vorteile der Resonanzioni-sation in Kombination mit ortsaufgelösten Messungen mittels SIMS. Durch diesen, von der Probenmatrix unabhängigen, Ionisationsprozess verhindert die Laser-SNMS falsch-positive Signale in ortsaufgelösten Verteilung, wie sie in der SIMS auftreten können. Der Strahltransport und Einkopplung des Laserlichtes in das SIMS System sowie Verknüpfung der zeitlichen Ansteuerung von SIMS und Lasersystem wurden technisch realisiert. Nach Optimierung des SIMS-Prozesses, wurde das System eingehend für den Laser-SNMS Betrieb mittels Messungen von Gd optimiert und charakterisiert, bei erreichbaren lateralen Auflösungen von 6–9 μm mit einer Massenauflösung von ∼700. Aufbauend auf diesen Erkenntnissen, wurde die Methode auf die Messung von Pu erweitert. An Elektrolyseproben mit bekannter Pu-Belegung konnten Effizienzen im Bereich von 7·10–9·10 erreicht werden. Mittels Laser-SNMS konnte noch eine Menge von ∼2·10 Atome Pu im analysierten Bereich nachgewiesen werden, in SIMS hingegen kein Signal mehr identifiziert werden, was die Stärke der Methode demonstriert. In einer ersten Anwendung der Laser-SNMS auf endlagerrelevante Proben wurden mit Pu kontaktierte Pyrit-Partikel mit SIMS und Laser-SNMS untersucht. Hierbei konnten Einflüsse von Topographie und Matrixeffekten auf SIMS-Signale sowie dahingehende Vorteile der Laser-SNMS untersucht und die erfolgreiche Anwendung der Methode auf diese Art von Proben demonstriert werden.
[en] Understanding the excitation pattern of baryons is indispensable for the understanding of non-perturbative QCD. Up to now only the nucleon excitation spectrum has been subject to systematic experimental studies, in contrast very little is known on excited states of double or triple strange baryons. A better knowledge of the baryon spectrum in the double and triple strange sector is however important to scrutinize the models developed using data on N and states. In studies of antiproton-proton collisions, the ANDA experiment is well-suited for a comprehensive baryon spectroscopy program in the multi-strange and charm sector. For final states containing a pair, cross sections of the order of b are expected, corresponding to production rates of 10=d at a luminosity L = 10 cm s. The present thesis focuses on excited states and investigates the possibility to reconstruct the reaction and its charged conjugate channel with the ANDA detector. Furthermore, first steps towards a partial wave analysis of the K and K final states are presented.
[en] The wide broadening of Lyman and Balmer lines in H or H mixed plasmas is a widely observed and studied phenomena in many kinds of different plasmas, ranging from stellar to laboratory plasmas. The source of the fast H atoms in front of the surface as well as the origin of the observed emission in laboratory plasmas is under controversial discussion. A. V. Phelps proposes a "sheath-collision" model in which H, H and H ions are accelerated in the sheath and create fast H atoms by charge transfer or dissociation interaction with gas or the metallic surface. There are a number of experiments trying to explain the broadening of the lines, but the community could only agree on the fact that the broadening is caused by the Doppler effect. Usually experiments in this field are performed in high pressure plasmas (p ≥ 1 Pa), but this makes it very difficult to analyze the Doppler-shifted emission due to the following reasons. On the one hand, the high pressure leads to emission of accelerated ions and backscattered atoms which makes the detected signal a superposition of both effects. On the other hand, the emission of ions inside the Debye sheath leads to a Stark broadening of the emitted lines and makes the analysis of the emission spectra complicated. In this thesis the two main problems of the Doppler-shifted emission of the fast atoms are investigated. First, the source of emission of the fast atoms and its properties and second, the application of the observed blue and red-shifted emission in physics of low density and low temperature plasmas. The experiments are performed in a low density plasma (p <0.05 Pa) at the PSI-2 device. The low density is used to avoid emission by ions accelerated in the sheath and emission inside the sheath in general. In a low density pure H plasma practically no Doppler-shifted emission is observed in comparison to the high pressure experiments. The line broadening begins to arise when Ar is mixed into the plasma. By varying the surface material and the applied negative potential to the surface, the experiments have proven that the source of the Doppler-shifted emission are only backscattered or reflected atoms created as a result of ion-surface interaction which exclude emission caused by charge-exchange in the sheath. Further studies presented in this thesis prove that the red-shifted emission generated by the same atoms is only caused by light or photon reflection at the metallic surface. The latter observation stimulated a development of a new Doppler-Shifted Reflectance Measurement (DSRM) diagnostic which can measure the spectral reflectance of the metallic surface in situ during the plasma exposition. But not only the spectral reflectance, also the polarization by light reflection and the degradation of the optical properties of the surface are measured for the first time during plasma exposition. Furthermore, the first results on the reflectance of a Rh mirror at high temperatures are presented, which can help to built-up a Charge Exchange Recombination Spectroscopy (CXRS) diagnostic at ITER. The study of emission of fast atoms in other noble gases such as He, Ne, Kr and Xe demonstrated in contrast to the previous assumptions and the experimental cross-sections a much weaker emission in comparison to Ar. It is shown that the excitation source of H by collisions with Ar at the used conditions could be limited to only two possible atomic processes: excitation by the ground state or excitation transfer from the metastable state. The latter is measured using a Tunable Diode Laser Absorption Spectroscopy (TDLAS) diagnostic installed and tested at the PSI-2 device during this thesis. The experimental results obtained in this thesis, e.g. the absolute concentration, the spatial distribution of the metastable atoms or the gas temperature along the plasma column, support the theory of excitation transfer by metastable Ar, though further theoretical and experimental studies are still required to give an answer on this unsolved problem. Nonetheless further applications of the DSRM diagnostic are weakly affected by the source of the observed emission in noble gases.
[en] The properties of the Higgs boson couplings have been studied in decays into four leptons, H ZZ* 4 ( = e, ), using proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider (LHC) in the years 2015 to 2018 at a centre-of-mass energy of 13 TeV (LHC Run 2). Measurements have been performed using different data sets corresponding to integrated luminosities of 36.1 fb, 79.8 fb and 139 fb. The cross sections for the four main Higgs boson production modes have been measured inclusively in the 4 final states as well as in exclusive phase space regions probing the Higgs boson couplings. The inclusive Higgs boson production cross section times branching ratio into 4 decays in the rapidity range || < 2.5 of 1.34±0.12 pb measured with the full set of Run 2 data set is in very good agreement with the Standard Model (SM) prediction of 1.33±0.08 pb. All measurements in exclusive phase space regions are compatible with the SM predictions as well. The sensitivity of the measurements was projected to the ultimate integrated luminosity of the high-luminosity LHC (HL-LHC) of 3000 fb. With the HL-LHC data, the precision of the cross section measurements is expected to improve by a factor four for gluon fusion production and by a factor of six for weak gauge boson fusion production and for the associated production with a weak gauge boson. The results provided input for the long-term planning of particle physics infrastructure in the 2020 European Strategy process. The tensor structure of the Higgs boson couplings to massive vector bosons and to gluons has been studied in two effective field theory approaches to probe for small beyond-SM (BSM) CP-even and CP-odd admixtures to the CP-even SM coupling. In the first analysis performed with 36.1 fb of Run 2 data, the BSM couplings are defined within the socalled Higgs Characterisation framework. From the measurements of the rates of the four main Higgs boson production modes, constraints on the CP-odd BSM coupling to gluons () and on the CP-even and CP-odd BSM couplings to heavy vector bosons ( and ) have been obtained: −0.68 < sin ·< 0.68, −0.6 < cos ·< 4.2 and −4.4
α·<4.4 at 95% confidence level (CL), where the mixing angle describes the relative contributions of the CP-even or CP-odd terms. These are the first limits on BSM Higgs boson couplings in an EFT framework based on the measurement of the Higgs boson production rates providing substantially sensitivity. The second analysis is based on the production cross section measurements in exclusive phase space regions using the full Run 2 data set (139 fb) interpreted in the so-called Standard Model Effective Field Theory (SMEFT). Constraints have been derived on the CP-even and CP-odd BSM coupling parameters to gluons (c and c), heavy vector bosons (c, c, c and c , c, c) and top quarks (c and c). The most stringent limits at 95% CL are −0.0074 < c< 0.0080 on the CP-even BSM coupling to gluons, as well as −2.4 < c< 2.4, −0.56 < c< 0.56 and −1.03 < c< 1.03 on the CP-odd BSM coupling parameters to weak gauge bosons. The constraints on the CP-even BSM couplings to weak gauge bosons are weaker. These are the first constraints on SMEFT coupling parameters using the H ZZ* 4 decay channel, which will be combined with the results in other Higgs boson decay channels. Finally, the sensitivity of kinematic variables of the final state particles for CP-odd contributions to the Higgs boson coupling in vector boson fusion production has been evaluated in the Higgs Characterisation framework. Limits of −2.56 < < 2.64 at 68% CL are expected for the full Run 2 data set. The measurement will provide the first limits on CP-violation in the H ZZ* 4 decays.
[en] The increasing energy demand has motivated the research for renewable and sustainable sources for energy generation, such as solar energy. In this aspect, the dye sensitized solar cells (DSSC) are promising due its ability of providing energy over any light intensity. Zinc oxide (ZnO) is a well-studied n type semiconductor for use in these devices because it is a nontoxic material, inexpensive and environmental friendly, besides its physical characteristics, such as: band gap of 3,7 eV. The aim of this work was to synthesize ZnO nanostructured electrodes using the methods: Successive Ionic Layer Adsorption and Reaction (SILAR), for the seeds synthesis; and Chemical Bath Deposition (CBD), for the nanostructures growth. The nanostructures were synthesized using the precursors: zinc acetate dihydrate, zinc chloride, zinc sulfate heptahydrate and zinc nitrate hexahydrate. For each precursor, the photoanodes with distinct morphologies according to the zinc salt studied, 10 µm thick and with preferential orientation along the basal axis <0002> were obtained, and also photoanodes were obtained using the particulate material filtered from the chemical bath. The photoanodes were characterized by scanning electron microscopy, atomic force microscopy, X-ray fluorescence, and X-ray diffraction. The DSSC prepared using ZnO nanostructured photoanodes showed that the charge transport mechanism was influenced by the ZnO morphology. The particulate material from the chloride and nitrate zinc salts showed similar morphology after comminution, which resulted similar DSSCs. The DSSC produced using the de zinc sulfate powder presented the best electric parameters and it was the most efficient (η = 0,71 +-0,02%). (author)
[en] Measurements of the luminosity and of top quark pair production in as-sociation with a Z boson (Z) in proton-proton collisions with the CMS experiment at the LHC are presented. The luminosity measurement of the CMS experiment is calibrated with the Van der Meer (VdM) method, based on data collected during beam separation scans. A calibration of the length scale is performed using data from constant-separation scans. The bias of the VdM method due to the assumption of factorisable proton densities of the beams is estimated with an improved method using the transverse densities as determined from beam-imaging scan data. The performance is evaluated with dedicated simulation studies. Both studies lead to a significant reduction of the systematic uncertainty for the measurement of the integrated luminosity. Measurements of Z production in proton-proton collisions at a centre-of-mass energy of 13 TeV are performed using events with three charged leptons where the Z boson is identified in its decay to two oppositely charged leptons. The first differential Z production cross section measurement as a function of kinematic properties of the Z boson is presented, based on a dataset corresponding to an integrated luminosity of 77.5fb collected in 2016 & 2017. An extended differential measurement as a function of top quark observables is presented using the full Run 2 dataset, corresponding to an integrated luminosity of 137 fb. It includes a kinematic reconstruction of the system and allows to probe the QCD production mechanism. Within current experimental uncertainties, the measured differential cross sections are found to be in good agreement with standard model predictions.
[en] Gaseous C-14 Radioactive nuclides do not affect external exposure of the body because they emit only very weak beta rays, but due to their long half-life (approximately 5.730±40 years) and the nature of being absorbed through the breathing of life, management is needed at the time of release from nuclear facilities. In the case of Korea, the relevant Notice was revised to carry out the assessment of the emission of individual radionuclides from January 2001. Accordingly, it is assessed that all nuclear power plants are monitoring the emissions of C-14 and that all residents’ dose criteria set out in the relevant Notice (Nuclear Safety and Security Commission, No. 2017-36) are satisfied. Regarding the amount of individual radionuclides emitted by nuclear power plants, the estimated emission values are given in the license submission documents of individual nuclear power plants.(the estimated emission value is a reference value and the criterion for assessing the actual emission quantity is performed in accordance with the Nuclear Safety and Security Commission Notice) However, C-14 presents the same values (2.7×1011Bq/year) regardless of plant type, which applies as a reference the average emissions of C-14 actually measured from the 10 U.S. operational plants announced in 1985. In addition, it was confirmed that the emission of C-14 measured after the first cycle operation of Shin Kori Unit 3, the new plant (APR1400 model), which recently started commercial operation, was different from the expected emission (the actual emission is satisfied with all the Nuclear Safety and Security Commission Notices), and that it was necessary to consider the mechanism for the generation and release of the C-14 nuclear species. Accordingly, the emission mechanism of domestic nuclear power plants was analyzed and the emission reduction method was considered in preparation for the passage of the number of years of operation and operation of multiple units at the site. In this study, additional variables were considered that could affect the method of assessing the yield presented by the designer in the approval submission. To this end, the previous calculations from the designer were analyzed, and the detailed analysis of the neutron flux and response cross-sectional area in the reactor was conducted to review the need for improvement and compare differences to reevaluate the amount of generation. In addition, for comparative verification, neutron reactions of O-17 and N-14 in the core were additionally performed using the Monte Carlo neutron transport simulation Code(McCARD). In addition, the amount of discharge was quantified through operation within the system to the Spent Fuel Pool (SFP) inside the Auxiliary Building. However, although the calculation results were assessed to be about 15% compared to the actual amount of emissions, it was possible to determine that some of the existing assumptions would exceed the original estimate, but only possible scenarios were considered due to lack of data to quantify and evaluate to this point. Currently, Shin-Kori Unit 3 is a short-term measure to reduce C-14 emissions during the second cycle of operation, and the operation procedures have been changed, and the effectiveness of the operation will be verified after the second planned preventive maintenance period. In addition, if the operation of Shin-Kori Unit 4 (‘19. 8.29) is further identified, it is deemed possible to verify the validity of the emission evaluation of this paper based on the fact that the trend of accumulation and release of operation experiences of the new plant is further confirmed. It is also expected that the accuracy of the actual emission prediction will be higher if the emission mechanism is re-evaluated based on the N-14 value review and the emission trend based on comprehensive consideration of the re-verification of the N-14 design (the amount of presence in the coolant)
[en] To prevent fuel damage during dry storage, Spent Nuclear Fuel (SNF) management plan and related requirements should be established. Hydride issues like hydrogen reorientation and delayed hydride cracking are considered as the major deterioration mechanisms of the cladding material. Factors affecting hydrogen transport in zirconium are known as concentration, temperature, and stress. Experimental data of stress-induced hydrogen diffusion are not enough compared to the other two factors. In this study, the effects of stress-gradient on hydrogen migration in Zircaloy-4 were studied by point load tests. The tests were conducted under constant load at various peak temperature conditions. After point load tests, to compare the degree of the hydrogen diffusion with various conditions, hardness was measured along stress-gradient. Image analysis was performed to confirm the change in hydride distribution. From the results, hydrogen tends to diffuse to higher stress. Also, if the temperature is above the terminal solid solubility of dissolution, hydrogen diffuses fully along stress-gradient. In other words, the degree of stress-induced hydrogen diffusion depending on the temperature. This study is expected to help developing hydrogen transport kinetics in zirconium alloy and establishing the domestic requirements of SNF dry storage system