http://hdl.handle.net/1974/784 2013-05-25T06:40:21Z 2013-05-25T06:40:21Z Seddighin, MARYAM http://hdl.handle.net/1974/8016 2013-05-04T05:12:26Z 2013-05-02T04:00:00Z

Title: Low Energy 8B Solar Neutrinos in SNO+: Controlling and Constraining Radon Backgrounds Authors: Seddighin, MARYAM Abstract: SNOLAB located in Sudbury, Canada, is hosting a new liquid scintillator experiment for studying neutrinos which is called SNO+. Many interesting physics topics such as measuring low energy solar neutrinos and searching for neutrinoless double beta decay are expected to be performed using the SNO+ detector. SNO+ is designed to measure the solar neutrino flux at a lower energy range than SNO, and therefore it is able to study LMA-MSW oscillations at this range of energy. This research is concerned with extracting low energy 8B solar neutrinos while studying the tagging and reduction of 214Bi by 99.8%, one of the main backgrounds in the energy range of interest. Ways to measure and control radon were also studied since it is the source of the 214Bi background. Scintillation material, zinc sulfide, was selected for use in fabrication of radon detectors known as Lucas cells. The fabrication of cover gas bags employed in the SNO+ experiment to react to mine air pressure fluctuations is described and the interior radon emanation of these bags was measured and calculated. Description: Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-05-01 20:26:56.981

2013-05-02T04:00:00Z Ali, Aaron http://hdl.handle.net/1974/7991 2013-05-04T05:05:37Z 2013-04-30T04:00:00Z

Title: Gigahertz Modulation of a Photonic Crystal Cavity Authors: Ali, Aaron Abstract: Photonic crystal (PtC) cavities are an increasingly important way to create all optical methods to control optical data. Not only must the data be controlled, but interfacing it with high frequency electrical signals is particularly interesting especially if this occurs in the 1.55µm telecom band. We present an experiment that uses Rayleigh surface acoustic waves (SAWs) to modulate the frequency of the guided mode of an L3-cavity PtC created on a silicon slab. This work has the potential to interface optical and electrical signals via a mechanical strain wave operating at gigahertz frequencies. Defects are carefully designed into a triangular lattice PtC to realize a waveguide coupled optical cavity. The cavity can be experimentally accessed through grating couplers excited by polarized light at 10 degrees incidence from normal. The optical components are fabricated on a silicon-on-insulator platform, with light confined to the silicon slab region. Through transmission experiments, the L3 cavity was found to have a narrow resonance characterized by a Lorentzian distribution. A quality factor of 165 centered at 6255 1/cm (1.599µm) was measured. Aluminum interdigitated transducers (IDTs) were fabricated through a lithography liftoff process. Their ability to create SAWs requires a piezoelectric medium. As silicon does not have this property, growth of a thin ZnO film was required. The transducers were measured using a network analyzer and were found to produce Rayleigh SAWs at a frequency of 179MHz and a wavelength of 24µm. The acoustic energy traveled 70µm to the target optical device. The L3 cavity has dimensions of around 4µm a side - less than 1/2 a SAW wavelength. Modulation of the L3 PtC resonant frequency was monitored through a repeat of the transmission experiment but with RF excitation of the IDTs at the SAW frequency. A broadening of the transmission spectrum was expected. Unfortunately no change in the fitting parameters could be measured. An HF etch was used to undercut the L3 PtC such that a silicon slab suspended in air could be realized. Simulations had been conducted showing an order of magnitude increase in the quality factor was possible. Broken wirebonds on the transducers created unintended etch channels rendering the SAW non-operational. Description: Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-04-29 12:33:49.254

2013-04-30T04:00:00Z Wu, ZHIGANG http://hdl.handle.net/1974/7956 2013-04-28T05:27:51Z 2013-04-26T04:00:00Z

Title: Dissipative dynamics of atomic Bose-Einstein condensates at zero temperature Authors: Wu, ZHIGANG Abstract: In this thesis we study various dissipative processes that are associated with the flow of an atomic Bose-Einstein condensate at zero temperature. In particular, we investigate the effect of a weak correlated disorder potential on the collective dipole motion of a harmonically-confined elongated condensate. By using an extension of the Harmonic Potential Theorem, we demonstrate that the dynamics of the system can be described equivalently in terms of a disorder potential oscillating relative to a stationary condensate. This latter point of view allows the application of linear response theory to determine the drag force experienced by the condensate and to evaluate the damping rate of the centre of mass oscillation. The density response function for the elongated condensate is determined with a new local density approximation that takes into account the tight radial confinement of the atomic cloud. Our linear response theory reveals the detailed dependence of the damping rate on various system parameters. A comparison with available experimental data is only partially successful and points to the need for additional experiments. In addition to disorder induced dissipation, we also consider a variety of other problems that can be addressed by means of linear response theory. For example, we study momentum transferred to a condensate by a Bragg pulse and the energy absorption of a gas in an optical lattice that is parametrically modulated in different ways. All of these applications demonstrate the utility of linear response theory in describing the dynamics of Bose-condensed systems which are subjected to weak perturbations. Description: Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-04-26 10:54:11.915

2013-04-26T04:00:00Z Eadie, Gwendolyn http://hdl.handle.net/1974/7863 2013-03-28T04:59:06Z 2013-03-27T04:00:00Z

Title: Measuring the Mass of a Galaxy: An evaluation of the performance of Bayesian mass estimates using statistical simulation Authors: Eadie, Gwendolyn Abstract: This research uses a Bayesian approach to study the biases that may occur when kinematic data is used to estimate the mass of a galaxy. Data is simulated from the Hernquist (1990) distribution functions (DFs) for velocity dispersions of the isotropic, constant anisotropic, and anisotropic Osipkov (1979) and Merritt (1985) type, and then analysed using the isotropic Hernquist model. Biases are explored when i) the model and data come from the same DF, ii) the model and data come from the same DF but tangential velocities are unknown, iii) the model and data come from different DFs, and iv) the model and data come from different DFs and the tangential velocities are unknown. Mock observations are also created from the Gauthier (2006) simulations and analysed with the isotropic Hernquist model. No bias was found in situation (i), a slight positive bias was found in (ii), a negative bias was found in (iii), and a large positive bias was found in (iv). The mass estimate of the Gauthier system when tangential velocities were unknown was nearly correct, but the mass profile was not described well by the isotropic Hernquist model. When the Gauthier data was analysed with the tangential velocities, the mass of the system was overestimated. The code created for the research runs three parallel Markov Chains for each data set, uses the Gelman-Rubin statistic to assess convergence, and combines the converged chains into a single sample of the posterior distribution for each data set. The code also includes two ways to deal with nuisance parameters. One is to marginalize over the nuisance parameter at every step in the chain, and the other is to sample the nuisance parameters using a hybrid-Gibbs sampler. When tangential velocities, v(t), are unobserved in the analyses above, they are sampled as nuisance parameters in the Markov Chain. The v(t) estimates from the Markov chains did a poor job of estimating the true tangential velocities. However, the posterior samples of v(t) proved to be useful, as the estimates of the tangential velocities helped explain the biases discovered in situations (i)-(iv) above. Description: Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-03-26 17:23:14.643

2013-03-27T04:00:00Z