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[en] With the start of the Large Hadron Collider (LHC) at CERN it is now possible to study physics at the TeV-scale for the first time. At this unprecedented energy range it is expected that the Standard Model of particle physics will reach its limits and new phenomena can appear. One of the main goals of the ATLAS experiment is the search for physics beyond the Standard Model. This includes observing supersymmetric particles, which are predicted to have masses of several hundred GeV up to a few TeV. The subject of this thesis is the search for supersymmetric particles in final states with jets and missing transverse energy and the evaluation of the ATLAS discovery potential for supersymmetric particles in the Minimal Supersymmetric Standard Model (MSSM) parameter space for these channels. Different centre-of-mass energies of √(s)=14 TeV, 10 TeV and 7 TeV are assumed. For many R-parity conserving SUSY models, the decay of supersymmetric particles leads to detector signatures characterized by missing transverse energy and multi-jets, sometimes accompanied by leptons. In this thesis, SUSY searches with ≥2-6 jets and 0-2 leptons (electrons, muons) are studied, with a focus on 0-lepton channels, that are expected to be sensitive in large areas of the SUSY parameter space. The search strategies for supersymmetric particles are applied on a sets of differently constrained SUSY models and on several hundred SUSY signals, generated within the pMSSM subspace of the MSSM. The goal of this work is to explore the reach of the performed SUSY searches for completely different decay signatures. It will be shown that the ATLAS SUSY searches cover a large parameter space of SUSY models. The first p-p collisions at a centre-of-mass energy of √(s)=7 TeV in March 2010 allow a comparison of the measured data with the Monte Carlo predictions, in order to see how well the detector response is understood in the context of SUSY specific variables used in the 0-lepton analyzes. All measurements are found to be in agreement with the Standard Model expectations within the associated systematic uncertainties. The results indicate that the ATLAS SUSY searches cover a large parameter space and it is possible to discover or exclude some SUSY models already with a few pb-1 of integrated luminosity.
[en] This work was carried out aiming to design and characterise 9-12% Cr steels with tailormade microstructures for applications in fossil fuel fired power plants. The investigations concentrated in the design and characterisation of heat resistant steels for applications in high oxidising atmospheres (12% Cr) and 9% Cr alloys for components such as rotors (P91). ThermoCalc calculations showed to be a reliable tool for alloy development. The modeling also provided valuable information for the adjustment of the processing parameters (austenisation and tempering temperatures). Two 12% Cr heat resistant steels with a fine dispersion of nano precipitates were designed and produced supported by thermodynamic modeling (ThermoCalc). A detailed characterisation of the microstructure evolution at different creep times (100 MPa / 650 C / 8000 h) was carried out by scanning transmission electron microscopy (STEM). The results of the microstructure analysis were correlated with the mechanical properties in order to investigate the influence of different precipitates (especially M_2_3C_6 carbides) on the creep strength of the alloys. Precipitation of Laves phase and Z-phase was observed after several hundred hours creep time. Very few Z-phase of the type Cr(V,Ta)N nucleating from existing (V,Ta)(C,N) was observed. Both alloys show growth and coarsening of Laves phase, meanwhile the MX carbonitrides present a very slow growth and coarsening rate. Alloys containing Laves phase, MX and M_2_3C_6 precipitates show best creep properties. The influence of hot-deformation and tempering temperature on the microstructure evolution on one of the designed 12% Cr alloys was studied during short-term creep at 80-250 MPa and 650 C. Quantitative determination of dislocation density and sub-grain size in the initial microstructure and after creep was investigated by STEM combined with the high-angle annular dark-field detector (HAADF). A correlation between microstructure evolution and creep response was established. All crept samples showed a significant increase of sub-grain size and a reduction of the dislocation density. Hot deformed samples showed better creep strength than non hot-deformed samples, due to homogenisation of the microstructure. The tempering temperature affected the dislocation density and the sub-grain sizes, influencing the creep behaviour. 9% Cr alloys were designed supported by ThermoCalc. Two sets of alloys were produced: 9% Cr alloys with 0.1 % C and 0.05% C and 9% Cr alloys containing ∝ 0.03% Ti again with 0.1% C and 0.05% C (always wt%). Microstructure investigations showed good agreement with the predicted phases of the thermodynamic modeling. The volume fraction of precipitated M_2_3C_6 carbides is directly related to the carbon content of the alloys. Hardening of the Ti-containing alloys by precipitation of fine dispersed Ti-based MX particles was achieved. The precipitation of these carbides was limited to the austenisation and tempering treatment used. The microstructure evolution (sub-grain and particle size) during creep at 650 C / 100MPa was investigated by STEM-HAADF. The sub-grain size evolution and the coarsening of precipitates (MX carbonitrides, M_2_3C_6 and Laves phase) were more pronounced for Ti-containing alloys. 9Cr alloys without Ti and with low carbon content presented the highest creep strength of all investigated alloys.
[en] This paper studies the behavior of Aliquat 336 in the Molybdenum extraction from basic solutions from the process of Codelco Norte ion exchange applied at the pilot level. The results obtained in the study show that a stage is required previous conditioning of the organic phase with sulfuric acid, also show that it is required to feed the Elution Extraction stage with a content less than 1 g/L of Molybdenum to obtain greater efficiency in the extraction process of this element. From the point of view of the kinetics, in the extraction stage the equilibrium reached 30 seconds with 41.32%, while in the Re-extraction stage the balance was reached at 300 seconds with 90.59%. The Mc Cabe Thiele diagram shows that 3 stages are required to achieve extract Molybdenum from basic solutions (pH≅10) with a concentration of 1,120 mg/L up to 56 mg/L which represents an efficiency of 95%. Various re-extractants were evaluated on ammonium base, obtaining higher percentages of re-extraction with Ammonium Chloride. The diagram of Mc Cabe Thiele in the Retraction stage shows that 2 stages are required, obtaining an advance of 4 g/L from an organic loaded with 449 mg/L of Mo, with a 95% efficiency. According to the results obtained, it is possible to obtain solutions Molybdenum concentrates from basic solutions through the use of Aliquat 336. It is important to note that this is the first study carried out in these pH conditions, so this work will serve as a basis for future research in the extraction of Molybdenum from alkaline solutions
[en] Joints between carbon steel and Alloy 600, containing Alloy 82 weld metal, were exposed to two steam-hydrogen environments considered to simulate exposure to primary water conditions in a Pressurized Water Reactor (PWR) or Canada Deuterium Uranium (CANDU) reactor. The welds were found to have elevated and variable iron contents due to dilution by carbon steel during welding. This gave the Alloy 82 weld, near the inner surface of the component, an iron content approaching that of Alloy 800. A potentially protective external iron oxide film formed on the inner surface of the weld. However, the chromium content throughout the weld is below that which would form an external chromium oxide. The results indicate that low chromium content causes internal oxidation throughout the weld and potentially below the external iron oxide which could lead to Primary Water Stress Corrosion Cracking (PWSCC). (author)
[en] This thesis is dedicated to the development of a Monte Carlo neutron transport solver based on the subgroup (or multiband) method. In this formalism, cross sections for resonant isotopes are represented in the form of probability tables on the whole energy spectrum. This study is intended in order to test and validate this approach in lattice physics and criticality-safety applications. The probability table method seems promising since it introduces an alternative computational way between the legacy continuous-energy representation and the multigroup method. In the first case, the amount of data invoked in continuous-energy Monte Carlo calculations can be very important and tend to slow down the overall computational time. In addition, this model preserves the quality of the physical laws present in the ENDF format. Due to its cheap computational cost, the multigroup Monte Carlo way is usually at the basis of production codes in criticality-safety studies. However, the use of a multigroup representation of the cross sections implies a preliminary calculation to take into account self-shielding effects for resonant isotopes. This is generally performed by deterministic lattice codes relying on the collision probability method. Using cross-section probability tables on the whole energy range permits to directly take into account self-shielding effects and can be employed in both lattice physics and criticality-safety calculations. Several aspects have been thoroughly studied: • The consistent computation of probability tables with a energy grid comprising only 295 or 361 groups. The CALENDF moment approach conducted to probability tables suitable for a Monte Carlo code. • The combination of the probability table sampling for the energy variable with the delta-tracking rejection technique for the space variable, and its impact on the overall efficiency of the proposed Monte Carlo algorithm. • The derivation of a model for taking into account anisotropic effects of the scattering reaction consistent with the subgroup method. In this study, we generalize the Discrete Angle Technique, already proposed for homogeneous, multigroup cross sections, to isotopic cross sections on the form of probability tables. In this technique, the angular density is discretized into probability tables. Similarly to the cross-section case, a moment approach is used to compute the probability tables for the scattering cosine. • The introduction of a leakage model based on the B1 fundamental mode approximation. Unlike deterministic lattice packages, most Monte Carlo-based lattice physics codes do not include leakage models. However the generation of homogenized and condensed group constants (cross sections, diffusion coefficients) require the critical flux. This project has involved the development of a program into the DRAGON framework, written in Fortran 2003 and wrapped with a driver in C, the GANLIB 5. Choosing Fortran 2003 has permitted the use of some modern features, such as the definition of objects and methods, data encapsulation and polymorphism. The validation of the proposed code has been performed by comparison with other numerical methods: • The continuous-energy Monte Carlo method of the SERPENT code. • The Collision Probability (CP) method and the discrete ordinates (SN) method of the DRAGON lattice code. • The multigroup Monte Carlo code MORET, coupled with the DRAGON code. Benchmarks used in this work are representative of some industrial configurations encountered in reactor and criticality-safety calculations: • Pressurized Water Reactors (PWR) cells and assemblies. • Canada-Deuterium Uranium Reactors (CANDU-6) clusters. • Critical experiments from the ICSBEP handbook (International Criticality Safety Benchmark Evaluation Program). (author)
[en] Study of quench cooling is very important in nuclear reactor safety for limiting the extent of core damage during the early stages of severe accidents after Loss of Coolant Accidents (LOCA). Quench of a hot dry surface involves the rapid decrease in surface temperature resulting from bringing the hot surface into sudden contact with a coolant at a lower temperature. The quench temperature is the onset of the rapid decrease in the surface temperature and corresponds to the onset of destabilization of a vapor film that exists between the hot surface and the coolant. Re-wetting the surface is the establishment of direct contact between the surface and the liquid at the so-called re-wetting temperature. Re-wetting is characterized by the formation of a wet patch on the surface which then spreads to cover the entire surface. Situations involving quench andre-wetting heat transfer are encountered in a number of postulated accidents in Canada Deuterium Uranium (CANDU) reactors, such as re-wetting of a hot dry calandria tube in a critical break LOCA. This accident results in high heat transfer from the calandria tube to the surrounding moderator liquid which can cause the calandria tube surface to experience dryout and a subsequent escalation in the surface temperature. If the calandria tube temperature is not reduced by initiation of quench heat transfer, then this may lead to subsequent fuel channel failure. In literature very limited knowledge is available on quench and re-wetting of hot curved surfaces like the calandria tubes. In this study, a Water Quench Facility (WQF) has been constructed and a series of experiments were conducted to investigate the quench and re-wetting of hot horizontal tubes by a vertical rectangular water multi-jet system. The tubes were heated to a temperature between 380-800°C in a controlled temperature furnace then cooled to the jet temperature. The temperature variation with time in the circumferential and the axial directions of the tubes has been measured. The two-phase flow behavior and the propagation of the re-wetting front around and along the tubes were simultaneously observed by using a high-speed camera. The effects of several parameters on the cooling process have been investigated. These parameters include: initial surface temperature, water subcooling (in the range 15- 80°C), jet velocity (in the range 0.15-1.60 m/s), tube solid material (brass, steel and Alumina), surface curvature, tube wall thickness, jet orientation and number of jets. The variables studied include the re-wetting delay time (time to quench after initiating the cooling process), there-wetting front propagation velocity, the quench and re-wetting temperatures, the quench cooling rates and the boiling region size. The quench and the re-wetting temperatures as well as the re-wetting delay time were found to be a strong function of water subcooling. The quench and re-wetting temperatures increase with increasing water subcooling. The rewetting delay time decreases with increasing the water subcooling, decreasing initial surface temperature, increasing liquid velocity and decreasing the surface curvature. There-wetting front velocity is mainly dependent on the initial surface temperature and water subcooling. The re-wetting velocity increases by decreasing the initial surface temperature and by increasing the water subcooling. Decreasing the surface curvature was found to also increase the re-wetting front velocity. Correlations of the phenomena studied have been developed and provided good prediction of the experimental data collected in this study and data available from literature. The. results of this study provide novel knowledge and an experimental database for mechanistic modeling of quench heat transfer on calandria tube surfaces that experience dryout and film boiling. (author)
[en] Several instrumentation equipment (pressure transmitters, flow and level) are used in a nuclear power plant. To make sure of the correctness of their reading, it is essential to calibrate periodically these equipment. These systematic interviews represent a very high workload, generate exposures, radiological information for the staff and represent a risk of error in the execution. Based on the experience gained over the years by several nuclear power plants, it has been shown that the majority of calibrations performed on these equipment s are not required since they usually keep their calibration. However, any transmitter can possibly develop errors and it is preferable to to quickly detect this failure. Given these facts, the nuclear industry has developed new technologies that enable online monitoring of instrumentation equipment. This surveillance is based on non-intrusive techniques that evaluate the performance of the equipment, allowing among others to detect the drift of a transmitter. By using these technologies, it is thus possible to focus maintenance efforts on equipment for which observations are deemed necessary. Despite a number of online monitoring systems (SSL) are already in use at some plants (Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) ), this technology is still not widely used in the nuclear industry. It is also noted that such systems are not widely used in CANDU power plants. The objective of this project is to validate the implementation of an SSL in a nuclear power plant (CANDU 6) in order to increase the interval for calibration of instrumentation equipment. An application project has first been done to evaluate the performance of an SSL. In the frame of this project, the mathematic algorithm Instrumentation and Calibration Monitoring Program (ICMP) developed by Electric Power Research Institute (EPRI) has been adapted and tested with data from a power station (CANDU 6). The results showed that when a transmitter presented a drift, SSL was able to detect in the vast majority of cases studied.
[en] This thesis describes the results from measurements of the out-of-field dose in radiotherapy. The dose outside the treatment volume has been determined in a water phantom and an anthropomorphic phantom. Measurements were performed with linac photons, passively delivered protons, scanned protons, passively delivered carbon ions as well as scanned carbon ions. It was found that the use of charged particles for radiotherapy reduces the out-of-field dose by up to three orders of magnitude compared to conventional radiotherapy with photons.
[en] The paper describes a system for the thermal decontamination of contaminated soils by microwaves. In addition to the determination of the dielectric material parameters of different soils, a focus is on antennas for the efficient coupling of the microwaves into the ground. The developed simulation model takes into account the electromagnetic-thermal interaction and makes it possible to predict optimal plant configuration, duration and costs of a sanitation measure in advance.
[de]Die Arbeit beschreibt ein System zur thermischen Dekontaminierung verseuchter Boeden durch Mikrowellen. Neben der Bestimmung der dielektrischen Materialparameter verschiedener Boeden liegt ein Schwerpunkt auf Antennen zur effizienten Einkopplung der Mikrowellen in den Boden. Das entwickelte Simulationsmodell beruecksichtigt die elektromagnetisch-thermische Wechselwirkung und ermoeglicht es, bereits im Vorfeld optimale Anlagenkonfiguration, Dauer und Kosten einer Sanierungsmassnahme vorherzusagen.
[en] On August 3rd, 1492 Christopher Columbus started his journey searching for a new route to India while sailing westwards across the Atlantic ocean - a journey that finally led to the discovery of a thitherto unknown continent and heavily affected the history of mankind during the following centuries. Some physicists might have felt just like Columbus when the Large Hadron Collider (LHC) of the European Organization for Nuclear Research (CERN) started its operation on March 30th, 2010 at a center-of-mass energy of 7 TeV, a collision energy so far unrivaled by any laboratory based collider experiment. With these first collisions a new era in the research field of particle physics has begun. At its beginning, the predictions of the Standard Model (SM) of particle physics are tested at a new energy regime. During its heyday, the discovery of the yet unobserved Higgs boson as well as the discovery of phenomena which cannot be explained within the framework of the SM may follow. The LHC is a 26.7 km long circular accelerator, located near Geneva, Switzerland, roughly 100 m below the surface. Two proton beams moving in opposite directions are accelerated to 3.5 TeV and brought to collision in the center of four large particle detectors. The collision data analyzed in this thesis has been collected with the Compact Muon Solenoid (CMS) detector. CMS is a multi-purpose particle detector, hermetically built around the collision point of the two proton beams. It is constructed with typical onion-like design of collider detectors: a silicon-based tracking system surrounded by a homogeneous electromagnetic calorimeter and a sampling hadronic calorimeter. These subdetectors are enclosed by a superconducting solenoid providing a 3.8 T magnetic field which is necessary to bend the trajectories of charged particles and thus allows a precise measurement of their momenta. The solenoid is surrounded by an iron yoke, responsible for returning the magnetic flux, as well as by the muon chambers used to identify muons traversing all of the inner detector regions without being absorbed. The SM is a relativistic quantum field theory describing twelve fundamental fermions and the interactions between them. These fermions can be grouped into six quarks and six leptons which can be further divided into three generations. All ordinary matter is made of fermions from the first lepton and quark generations while the fermions of the remaining generations can solely be produced in highly energetic particle collisions. Moreover, there are four forces acting between the fundamental particles. Besides gravitation which is not part of the SM, these are the electromagnetic, the strong and weak interaction. Designed in the late 1960s and early 1970s, the SM and the predictions deduced from it have undergone a variety of experimental tests. So far, almost all predictions have been found to be fulfilled. With a mass of 173.3 GeV/c"2, the top quark is the heaviest particle among the fundamental fermions. It has been discovered in 1995 by the CDF and D0 experiments at Fermilab's proton anti-proton collider Tevatron near Chicago, USA. At the Tevatron and the LHC, top quarks are mainly produced pairwise via the strong interaction. The measurement of the top-quark pair production cross-section at the LHC is one of the first important steps when testing the predictions of the SM at the new energy regime. Moreover, a precise knowledge of the t anti t production cross-section is the basis for interesting measurements in the top-quark sector as well as for searches for physics which cannot be explained in the context of the SM. In this thesis, the first measurement of the top-quark pair production cross-section at √(s)=7 TeV using events with an electron+jets final state is described. The production of top-quark pairs is distinguished from other physics processes by solely employing the kinematic properties of t anti t events. The analyzed dataset has been recorded with the CMS detector during the 2010 operation of the LHC and corresponds to an integrated luminosity of 35.9 pb"-"1.