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The properties of unbound nuclei 12Li and 13Li are calculated within themultistep shell model in the complex energy plane by assuming that the spectraare determined by the motion of neutrons outside the 9Li core. It is foundthat in 12Li the ground state consists of an antibound 1/2+ state and thatonly this and a 1/2− and a 5/2+ excited states are physically meaningfulresonances. Calculations suggest that there is no bound or antibound statein 13Li. / QC 20110222

At least two Cosmological phase transitions are very probable to have happened since the beginning of the universe, one of them being the electroweak phase transition responsible for the breaking of the EW symmetry. It is possible that the EW phase transition could have caused the observed baryon asymmetry of the universe and therefore provide an explanation for the baryon asymmetry problem. Furthermore, it could also have generated observable gravitational waves. Both of these possibilities however hinge on the fact that the EW phase transition had been a first-order phase transition, which it is not according to the standard model. The SM predicts a crossover transition. In this work, the EW phase transition is studied in the simplest extension to the SM in The StandardModel Effective Field Theory, by adding a φ6 operator to the scalar sector. Calculations show that it is indeed possible to have a first-order EW phase transition in this extension. Characteristic parameters of the phase transition are then calculated to generate a GW power spectrum to see if they are detectable by LISA or not. The generated GW signatures lie just outside of the LISA sensitivity region. The theoretical uncertainties in the calculations are however possibly large enough that one cannot yet exclude that the GW signals can be observed by LISA.

Vapor explosion as a result of Molten Fuel-Coolant Interactions (MFCI) postulated to occur in certain severe accident scenarios in a nuclear power plant presents a credible challenge on the plant containment integrity. Over the past several decades, a large body of literature has been accumulated on vapor explosion phenomenology and methods for assessment of the related risk. Vapor explosion is driven by a rapid fragmentation of high-temperature melt droplets, leading to a substantial increase of heat transfer areas and subsequent explosive evaporation of the volatile coolant. Constrained by the liquid-phase coolant, such rapid vapor production in the interaction zone causes pressurization and dynamic loading on surrounding structures. While such a general understanding has been established, the triggering mechanism and subsequent dynamic fine fragmentation have yet not been clearly understood. A few mechanistic fragmentation models have been proposed, however, computational efforts to simulate such phenomena generated a large scatter of results. In order to develop a mechanistic understanding of thermal-hydraulic processes in vapor explosion, it is paramount to characterize dynamics of fragmentation of the hot liquid (melt) drop and vaporization of the volatile liquid (coolant). In the present study, these intricate phenomena are investigated by performing well-controlled, externally triggered, single-drop experiments, using advanced diagnostic techniques to attain visual information of the processes. The methodology’s main challenge stemming from the opaqueness of the molten material surrounded by the vapor film and rapid dynamics of the process, was overcome by employing a high-speed digital visualization system with synchronized cinematography and X-ray radiography system called SHARP (Simultaneous High-speed Acquisition of X-ray Radiography and Photography). The developed image processing methodology, focus on a separate quantification of vapor and molten material dynamics and an image synchronization procedure, consists of a series steps to reduce the effect of uneven illumination and noise inherited of our system, further segmentation, i.e. edge detection, and extraction of image features, e.g. area, aspect ratio, image center and image intensity (radiography). Furthermore, the intrinsic property of x-ray radiation, namely the differences in linear mass attenuation coefficients over the beam path through a multi-component system, which translates the image intensity to a transient projection of the molten material morphology, was exploited. A methodology for the quantitative analysis of the x-ray images, i.e. transient maps of the fragmented melt, was developed. Its uncertainties were evaluated analytically and experimentally pointing towards the need to minimize the X-ray scattering and noise inherited from the optical system, for a more accurate quantification and a larger calibrated thickness range. Analysis of the data obtained by the SHARP system and image processing procedure developed provided new insights into the physics of the vapor explosion phenomena, as well as, quantitative information of the associated dynamic micro-interactions. The qualitative analysis, based on the matched radiograph and photographic images, describe the bubble and melt interrelated progression granting information on the phenomenological micro-interaction of the vapor explosion process. The dynamics of the initially disturbed vapor film is composed by multiple cycles, where the vapor bubble grows to a maximum diameter and collapses. X-ray radiographs show that during the first bubble expansion, the melt undergoes deformation/pre-fragmentation but does not follow the bubble interface during the subsequent expansion; suggesting no mixing between coolant and melt. Coolant entrainment occurs when the expanded bubble collapses leading to fine fragmentation of the molten material due to explosive evaporation. The vapor bubble expansion, fed by these fragments at the boundary, reaches its critical size, and start collapsing. The remaining melt is accountable for the following cycle. Bubble dynamics analysis shows a strong correlation between energetics of the subsequent explosive evaporation and the high temperature molten material drop (tin) deformation/partial fragmentation during the first bubble growth. The data suggest that this pre-fragmentation may have been responsible in providing an adequate mixing condition that promotes coolant entrainment during the bubble collapse stage. The SHARP observations followed by further analysis leads to a hypothesis about a novel phenomenon called pre-conditioning, according to which dynamics of the first bubble-dynamics cycle and the ability of the melt drop to deform/pre-fragment dictate the subsequent explosivity of the so-triggered drop. / QC 20101108

This thesis describes new results obtained from experimental studies of the extremely neutron-deficient isotopes 169Ir and 110Xe, close to the proton drip-line. The experiments use state-of-the-art equipment for nuclear spectroscopy where a large high-resolution Germanium-detector array is coupled to a high-transmission recoil separator and using the highly selective recoil-decay tagging technique. The work is based on two experiments performed at the Accelerator Laboratory of the University of Jyväskylä, Finland. The experimental techniques used are described as are the experimental set-ups. Comparison between experimental results and theoretical predictions are made. The thesis also briefly summarises the theoretical models employed to interpret the experimental results. The results for 169Ir point to a rotational-like behaviour of a moderately deformed nucleus exhibiting triaxial shape. The experimental results do not fully agree with theoretical predictions for the shape evolution of the neutron-deficient iridium isotopes, approaching the proton drip-line. The results for 110Xe indicate an emergence of enhanced collectivity near the N=Z line in the region of the nuclear chart above 100Sn. These findings are interpreted as a possible effect of increased neutron-proton isoscalar pair correlations, a residual interaction effect not accounted for in present-day nuclear models. / QC 20101116

Despite decades of research since the initial discovery of nuclear fission, numerous unresolved questions still persist. It is known empirically that fission fragments emerge with high angular momentum. The mechanism responsible for the generation of the large angular momenta observed is one of these open questions. Since the characteristics of fission fragments are not directly measurable, experimentally accessible observables are used to derive the angular momenta using nuclear model codes. One of these observables is the yield ratio between fission products produced in different isomeric states, i.e., metastable energy levels of the same nucleus. In this thesis, a study of the level density models implemented in the nuclear model code TALYS is presented. Simulated and experimental isomeric yield ratios of a large number of nuclear reactions is compared. The results show a bias in the models that favours the population of the high-spin states and that this can be produced by the overestimation of the spin width distribution. The reason for this study is to improve the models then used in the angular momentum calculation.  Moreover, the isomeric yield ratio measurement of twenty-one FFs is presented. The measurement was performed using the JYFLTRAP system at the University of Jyväskylä. The fission fragments were produced by the 32 MeV alpha-particle induced fission of 232Th. The analysis process, involving different identification and correction methods, and preliminary results are presented.

The ATLAS detector is one of the two largest experiments installed at the Large Hadron Collider at CERN, the European Organization for Nuclear Research. During the first run, the ATLAS detector recorded data at centre of mass energies of 7 TeV and 8 TeV, enabling many precision measurements and new physics searches. One important task in ATLAS is measuring the primary vertex, the interaction point of the hardest proton-proton collision in an event. In this thesis, a study of the primary vertex reconstruction performance in data and simulated events using $t\bar{t}$ and ${Z}$ events is presented. Within the statistics available, the performance in data and simulated events is found to be compatible. Motivated by the limitations of the Standard Model of particle physics, searches for supersymmetric particles are performed with the ATLAS experiment. No signal has been observed so far, and the results are used to set exclusion limits on the masses of the supersymmetric particles. As the exclusion limits are derived from analyses which each target only a single decay mode of a supersymmetric particle, the analyses might have lower sensitivity to more complex decay scenarios. In this thesis the sensitivity of one of the ATLAS searches for direct top squark pair production to models with more complex decay modes is investigated. The study concludes that the sensitivity to models where the top squark can decay via heavier charginos and neutralinos is lower than the sensitivity to models where only decays to the lightest chargino or neutralino are present.

The PANDA experiment is one of the main pillars of the Facility for Antiproton and Ion Research (FAIR), currently under construction in Darmstadt, Germany. PANDA will be a fixed target experiment designed for the study of non-perturbative phenomena of the strong interaction. Strange hyperon production is governed by m(s)  ~ 100 MeV, which corresponds to the confinement domain. Thus, hyperons are suitable probes in this energy region. This work is a simulation study focused on the feasibility of studying the production of Σ0-bar and Λ hyperons in the pbar p -> Σ0-bar Λ reaction with the PANDA detector. A 10^4 events sample simulated at p(beam) = 1.771 GeV/c is used to perform a single-tag (inclusive) and a double-tag (exclusive) event selection. From the former, it is concluded that the single-tag method does not provide with the clean signal required for spin observables extraction. In contrast, exclusive event selection provides with a signal reasonably clean from combinatorial background and completely clean from generic hadronic background events. A signal (Σ0-bar Λ) reconstruction efficiency of ε = 5.3 ± 0.2 % is obtained for exclusive event selection. The corresponding signal to background ratio is S/B(Total) ~ 6 and the significance value is ~ 21. In addition, an exclusive event selection is performed on a 10^4 events sample simulated at p_(beam) = 6 GeV/c. Almost all the generic hadronic background events are removed by the applied selection criteria. At this beam momentum, the obtained signal efficiency is ε = 6.1 ± 0.3%, the signal to total background ratio is S/B(Total) ~ 4 and the significance is ~22. Both efficiencies are smaller compared to a previous simulation study on this channel, but are large enough to enable a study of the exclusive production of the pbar p -> Σ0-bar Λ reaction at PANDA. The difference between the results of this thesis work and the previous work is attributed to the more realistic implementation of the signal production mechanism, as well as the detector and reconstruction algorithms.

NNBAR is a proposed experiment for the European Spallation Source. Thegoal of the experiment is to observe the transformation n −  ̄n. Currently a cutbased analysis is used to select signal events and discriminate against cosmic raybackground. To further increase the signal efficiency machine learning was used.Most machine learning algorithms resulted in a higher signal efficiency at the costof lowering the background rejection. However using the Linear DiscriminantAnalysis resulted in a new signal efficiency of 94% whilst having a predictedbackground rejection of roughly 100%. These results show that machine learningis a promising tool for increasing the signal efficiency at NNBAR.