Material Sciences

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16N calibration and background studies for SNO+
(2022-12-15) Khaghani, Pouya
SNO+ is a multipurpose scintillator based neutrino experiment which is located 2km underground at SNOLAB, Creighton mine, Sudbury. The primary physics goal of the experiment is the search for the elusive process of neutrino-less double beta decay with 130Te loaded into the liquid scintillator cocktail. In addition, SNO+ will be able to detect low energy solar neutrinos, geo- and reactor-antineutrinos, as well as supernova neutrinos. SNO+ has completed its water phase in 2019. During the water phase SNO+ made measurements of 8B neutrinos, and improved the limits on the lifetime of nucleon decay. Aside from the physics goals, the optical and energy calibration of the detector was accomplished in water phase. SNO+ has finished filling the detector in May 2022, and preparing for the 130Te phase. This thesis consists of author’s major contributions to the experiment: i) calibration analysis described in chapter 7, and ii) the background analyses discussed in chapter 6 and chapter 7. Chapter 5 focuses on the calibration of SNO+ detector using 16N calibration source. The tagged 6.1 MeV γ’s from 16N provided the primary energy calibration data in the water phase. Furthermore, the source was deployed externally throughout the scintillator filling process, and the data was used for various calibration purposes such as studying the scintillation light yield, verifying the reconstruction algorithms, characterizing the scintillation timing, and studying the Cherenkov signal in liquid scintillator. The second part of my analysis focuses on background analyses in SNO+. Chapter 6 describes a model that I have used to estimate the effective attenuation length of the detector in scintillator phase. The model was used to fit the tagged 214Po events in scintillator phase, and estimate the effective attenuation length. The result is consistent with other studies. Moreover, chapter 7 focuses on the external backgrounds. A set of timing and angular classifiers have been developed, and originally optimised to distinguish the external backgrounds from 0νββ signal. I have utilised these classifiers to investigate their performance for the detectable solar ν signals. The classifiers found effective, however it is demonstrated that the performance can be significantly improved by taking advantage of supervised learning methods. ROOT TMVA was used for this classification study. Furthermore, I have used the partial-fill scintillator data to estimate the level of the external backgrounds. The 2.6 MeV γ signal from the external 208Tl is identified in partial-fill. Furthermore, the level of external 208Tl γ’s from the hold-down ropes are estimated by taking advantage of their angular symmetry. The estimated result is consistent with previous measurements taken in water phase. Moreover, I have used the vertical displacements of the AV to estimate the creep rate of the hold-down rope system during the partial-fill period. This analysis is described in appendix A. Furthermore, the long-term stability tests of the Tensylon fibres are described in the second part of appendix A. Finally, the leaching model is briefly described in appendix B. I have developed this model as part of my MSc. research. During my first year of Ph.D, I had the chance to complete the model and develop a simple python tool to estimate the surface activity, and the level of leached isotopes for different filling scenarios.
Background reduction techniques and simulations for the PICASSO and PICO dark matter search experiments.
(2019-11-18) Scallon, Olivia
Dark matter is one of the most challenging mysteries of cosmology. The detection of Dark Matter is a main objective in modern experimental physics. The PICASSO and then the PICO experiments work towards the direct detection of WIMPs (Weakly Interacting Massive Particles) with superheated liquid detectors. Phase transitions in the superheated liquids are triggered by the nuclear recoil caused by the elastic collision of a dark matter particle. The phase transition in the detectors leads to the formation of a gaseous bubble. The acoustic signal of the nucleation of a bubble is recorded with piezoelectric sensors and pictures of the bubbles are taken with cameras. Many techniques are used to isolate potential dark matter signal from background signals. This thesis presents the work done for the fabrication process and purification techniques of the PICASSO detectors in the clean room at Université de Montréal. The detectors built with these new purification techniques allowed a background reduction of a factor of 10. The techniques and methods will be presented as well as the latest results from the data taken with these detectors. Simulations for the PICO experiment will also be presented. MCNP neutron background simulations from radioactive materials in the PICO detector will be presented. MCNP simulations for neutrons in the SNOLAB drift will also be presented as well as other MCNP simulations for the design and optimisation of the experiment. Finally, Geant4 muon-induced neutron simulations in the SNOLAB drift will be presented as well as Geant4 simulations for the design of a muon veto. These simulations were built entirely from scratch by using the SHIELDING physics list.
An investigation into bioleaching of uranium and rare earth elements from quartz-pebble conglomerate ores from Elliot Lake, Ontario
(Laurentian University of Sudbury, 2014-08-29) Williamson, Aimee Lynn
Biogeochemical mineral dissolution, the microbial-assisted dissolution of minerals, is an effective method for economically promoting the release of metals of interest from ores and mine waste materials. As the low-grade ores of the Elliot Lake region may be suitable for development of a sustainable heap-leach method for the extraction of U and REEs from the low-grade host mineralization, this thesis is focused on the geochemical and biological process simulation monitoring of the biogeochemical release of elements to the leaching solutions. The response of the retired heap material to a variety of passive closure strategies is also addressed. A series of biogeochemical mineral dissolution experiments have provided a detailed understanding of the biogeochemical mineral dissolution process, with the investigation of passive approaches to prepare for decommissioning to determine suitability to the ore materials from the study site. The chemical analyses of effluents collected throughout the experimentation, coupled with mineralogical and geochemical analyses of the feed and residual mineral material has enabled an understanding of the chemical controls of the overall biogeochemical mineral dissolution process for Fe, U, and Th, together with the preferential leaching release patterns for REEs, to be obtained. A mechanism describing U retention in secondary coatings has been proposed, with a passive approach to closure using inhibition and encapsulation methods being demonstrated, along with a determination of the potential for ongoing radionuclide release from a simulated heap upon decommissioning. The laboratory research in this study has shown that biogeochemical mineral dissolution, followed by waste material encapsulation, can be successfully applied to heap-leach pads potentially, enabling the economic recovery of U, Th, and selected REEs to solution for subsequent metallurgical collection. The studies strongly support the concept of sustainable development for heap-leach operations in the Elliot Lake region.
Optimisation and use of bivalve mollusk shells as monitors and indicators for chemical and biotic stress detection
(2022-08-26) Zuykov, Mikhail
Bivalve mollusk shells are used traditionally as monitors for chemical stress detection via elemental analysis of a whole multilayered shell or its single layers. The central shell part, as suggested by some authors, has a perspective to be used as a bioarchive of environmental records. Shells as indicators of water pollution with xenobiotics and animals’ infestation with pathogens/parasites are cursorily studied. The aim of this dissertation was to increase our knowledge of bivalve shells, as environmental indicators and monitors, based on their preservation and micromorphology data. Studied chemical stressors include silver and copper in dissolved and nanoparticulate form, and actinides ( 232Th, 241Am) in dissolved form. Studied biotic stressors include pathogenic photosynthetic microalgae Coccomyxa sp. and unknown shell borers. Shells obtained from control and contaminated/infested freshwater and marine bivalves, and shells obtained after laboratory and field-based experiments, were examined by optical, digital and electron microscopy, mass spectrometry, X-ray powder diffraction, γ-spectrometry and α-tracks autoradiography. Where applicable, bivalves’ soft tissues and biological liquids were examined. The most important findings are: 1, the amount of pollutants on the external shell surface depends on its preservation and micromorphology; 2, doughnut shape structures (DSS) were found on the surface of aragonite tablets (nacre) if mussels were exposed to low concentrations of silver (in the form of ions and nanoparticles); 3, infestation of M. edulis with pathogenic photosynthetic microalga Coccomyxa sp. promotes the formation of L-shaped shell deformity (LSSD); 4, infestation with Coccomyxa was experimentally confirmed for mussels pre-exposed to copper; 5, the old (previously secreted) layers of nacre can be transformed to aragonitic lenses of prisms (ALPs) due to early unknown physicochemical mechanism in response to shell attacks with boring organisms. In order to improve environmental monitoring protocols which use bivalves it was recommended: (a) to collect marine blue mussels (Mytilidae) with eroded external shell surface, whereas shells of freshwater unionid and dreissenid bivalves must have intact fleecy periostracum; and (b) to use the presence of DSS, LSSD and ALP as indicators of water pollution with metals, metals/pathogenic alga, and shell-borers, respectively.
SNO+ sensitivities to pre-supernova and supernova neutrinos
(2021-09-10) Rumleskie, Janet
Core-collapse supernovae (CCSNe) deposit heavy elements into the surrounding interstellar medium, affect the chemical evolution of galaxies, and lead to the formation of exotic bodies such as neutron stars and black holes. Neutrinos are also generated deep in the core of the CCSN over the timescale of tens of seconds and possess an imprint of the unconfirmed core-collapse mechanism. The progenitor stars to CCSNe also emit neutrinos in the final hours prior to collapse, albeit with an order of magnitude lower intensity and energy. A pre-supernova monitor and alert system was developed for the SNO+ detector based on inverse beta decay events. Such an alert will warn SNO+ and other neutrino experiments to maintain uptime to detect neutrinos from the impending supernova. Assuming the bestcase progenitor model, neutrino hierarchy, and background rates, the pre-supernova alert is expected to alarm for candidates as early as 100 hours prior to a supernova and up to a distance of 640 pc. Details of the construction and sensitivity of the pre-supernova monitor are presented within this thesis. The event rate from the next galactic supernova in SNO+ will depend on distance, but could exceed typical detector operating rates by an order of magnitude. The SNO+ data acquisition was stress-tested in this thesis with an embedded light injection source and compared to simulations characterizing the SNO+ detector’s response to CCSNe. These tests revealed SNO+ will experience data loss for any CCSN closer than 1.4 kpc. In addition, the SNO+ detector is expected to collect data from the neutronization burst of Betelgeuse before the data acquisition is overwhelmed. Using the detector simulations, a programmable laser diode was also prepared to emulate the light expected in SNO+ from supernova neutrinos. This light source is more dynamic and isotropic than the embedded source and will eliminate many of the uncertainties from the embedded source. It will be deployed in the future.
Study of quantum phase transitions and topological phases in chains and ladders
(2022-07-28) Pandey, Toplal
The ground-state phase diagrams and order parameters of low-dimensional quantum models are analyzed. Those models in their spin representation are the dimerized spin-1/2 XY and XYZ chains, and the two-leg ladders with anisotropy and three different dimerization patterns, in the presence of uniform and staggered transverse fields. The analysis is done by using the effective quadratic fermionic Hamiltonian of models, resulting from the Hatree-Fock mean-field approximation. In the fermionic representation, those models are equivalent to the generic Kitaev -Majorana chains/ladders with the proper parametrizations. An exact solvable model, the XY chain has a rich phase diagram, and its distinct phases are identified by the local and nonlocal (string) order parameters. We have calculated all the local order parameters (spontaneous magnetization) and the nonlocal order parameters within the same systematic framework, along with the winding numbers for all regimes of the phase diagram. By combining the exact and the meanfield methods, the local and string order parameters on the phase diagram of the XYZ chain, are identified and calculated. We found similar qualitative pictures on the phase diagrams of XY and XYZ chains, where the corresponding parameters of the latter model are renormalized by the interaction ∆ = Jz/J. For both models, the topological nontrivial phase is shown to have a peculiar oscillating order with the period of a four lattice spacing, not reported before and awaiting for its experimental confirmation. The detailed analysis of patterns of the string order is given. Moreover, the trivial phases of both the cases are investigated by local order parameters (components of spontaneous magnetization). The special XXZ limit of the model with additional U(1) symmetry is in agreement with the Lieb-Schiltz-Mattis theorem and its extensions, plateaus of magnetization, and some additional conserving quantities. We have shown that within the XYZ chain, where the plateaus are smeared, the robust oscillating string order parameter is continuously connected to its XXZ limit. Also, the nontrivial winding number and zero-energy localized Majorana edge states, as additional attributes of the topological order, are robust in that phase, even off the line of U(1) symmetry. The phase diagram of the isotropic two-leg ladder is investigated by calculating the field-induced magnetization at each point along the external field. In the phase diagram, the two kind of phases, gapped plateau and gapless Lutinger liquid, (LL) are identified. In the applied uniform field, those models are in agreement with the quantization conditions of the magnetization plateaus. The existence of the mid-plateau in the staggered ladder with columnar field, we report for the first time is an indication of a new spin gapped phase in this type of spin structure. For the staggered and columnar ladder, the alternating field only modifies the phase boundaries of the phase diagram. The ladder with the rung dimerization and columnar field exhibits additional quantum phase transition by closing and re-opening the zero-plateau and mid-plateau gapped phases with respect to the alternating field. The Hatree-Fock mean-field Hamiltonian of the ladders with an anisotropy and two dimerization patterns, map onto the sum of two quadratic Majorana Hamiltonians, which are dual to a sum of two (even/odd) XY quantum chains in the alternating transverse fields. The mapping between the effective Hamiltonian of the ladder and the pair of the dual XY chains considerably simplifies calculations of the order parameters, and analyses of the hidden symmetry breaking. The ground state phase diagram of the staggered ladder contains nine phases: four of them are conventional antiferromagnets, while the other five possess the non-local brane orders. Using the dualities and the newly found exact results for the local and string order parameters of the transverse XY chains, we were able to find analytically all the magnetizations and the brane order parameters for the staggered case, as well as the functions of the renormalized couplings of the effective Hamiltonian. The columnar ladder has three ground-state phases, and it does not possess a magnetic long-range order. The brane order parameters for these phases are numerically calculated from the Toeplitz determinants. We expect this study to motivate the search for the real spin-Peierls anisotropic ladder compounds, which can undergo the predicted quantum phase transitions with a gap closure and distinct brane orders.
Surface modification of biodegradable magnesium implant materials for controlled biodegradation
(2019-06-18) Hegy, Afrah Al
Magnesium and its alloys are promising candidates to be employed as a new generation of biodegradable metals in orthopaedic applications. However, the rapid degradation rate of magnesium alloys in the physiological environment has prevented their widespread application in medicine. The main objective of this thesis was to develop surface modification strategies that control the degradation rate of magnesium alloys in physiological environments and to provide an accurate assessment and evaluation of their biocompatibility in vitro. The overall thesis is composed of three individual projects. The first project was to develop an accurate method to test the in vitro biocompatibility of magnesium alloys. In this study, the CyQUANT assay was used to quantitatively evaluate the in vitro biocompatibility of Mg AZ31 alloy by both direct and indirect methods. The results demonstrated that the CyQUANT assay provides a more complete assessment of the overall in vitro biocompatibility of biodegradable metals by combining both direct and indirect analyses. In the second project, a multilayer coating consisting of a sol-gel silica layer followed by a mesoporous silica layer and finally a layer of calcium phosphate was developed. Surface characterization showed that a uniform and stable multilayer coating was successfully deposited on the Mg AZ31 alloy. In vitro characterization of the coatings confirmed this surface modification strategy significantly decreases the degradation rate of the magnesium alloy and that it is not cytotoxic. Superhydrophobic surfaces decrease the corrosion rate of magnesium alloys, however, cell adhesion is inhibited. In the third project, a superhydrophobic magnesium alloy surface was modified with the cell adhesive molecule, MAPTrix-F-RGD and the influence of this surface modification on cell adhesion was studied. The results demonstrate that although the MAPTrixF-RGD molecule was successfully immobilized to the superhydrophobic magnesium alloy surface, cell adhesion was not improved. The complex surface topography of the superhydrophobic Mg AZ31 surface may be responsible for the observed cell behavior. This thesis demonstrates that surface modification can be used to simultaneously control both the biodegradation rate and the biocompatibility of magnesium and its alloys, making these materials promising candidates for orthopaedic applications. In addition, it has been demonstrated that cell quantification assays based on the fluorescence of cyanine dyes are an excellent method for in vitro testing of these materials in direct contact with cells.
Synthesis and characterization of novel ethylene copolymers by palladium-diimine catalysts
(2015-09-24) Xiang, Peng
Late transition metal catalysts, especially Pd-diimine catalysts, have been extensive studied for olefin polymerization. The unique characteristics of Pd–diimine catalysts, including chain walking mechanism, highly electrophilic cationic metal center with reduced oxophilicity, the capability of initiating and catalyzing olefin "living" polymerization, and the sterically tunable–diimine ligands, allow the synthesis of a range of polyolefins and olefin copolymers with special pedant functionalities and unique microstructures. The main objective of this thesis research is to synthesize different new types of polymers and polymer-grafted nanoparticles with Pd–diimine catalysts by utilizing above unique characteristics. A broad class of low-polydispersity ethylene–norbornene (E–NB) copolymers having various controllable comonomer composition distributions, including gradient, alternating, diblock, triblock, and block-gradient, was synthesized through “living”/quasi-living E–NB copolymerization facilitated with a single Pd–diimine catalyst. This synthesis benefits from two remarkable features of the Pd–diimine catalyst, its high capability in NB incorporation and high versatility in rendering E–NB “living” copolymerization at various NB feed concentrations ([NB]0) while under an ethylene pressure of 1 atm and at 15 C. A class of hyperbranched polyethylene ionomers containing positively charged tetralkylammonium ions and different counter anions were first synthesized by direct iv one-pot copolymerization of ethylene with tetralkylammonium-containing acrylate-type ionic liquid comonomers. The use of a Pd–diimine catalyst, which shows excellent stability towards the highly polar ionic group, is key to the direct synthesis. The resulting ionomers properties including structural, thermal, and melt rheological properties have also been demonstrated. In a further study, HBPE ionomers encapsulating self-supported Pd(0) nanoparticles (NPs) as efficient and recyclable supported Pd catalysts were synthesized with a Pd–diimine catalyst. The Pd(0) NPs were immobilized on the ionomer matrix through ionic interaction directly during the copolymerization of ethylene with polymerizable ionic liquid comonomer. The resulting ionomer supported Pd(0) nanocatalysts have been utilized to catalyze carbon-carbon cross coupling reactions (Suzuki and Heck reactions) and semi-hydrogenation of alkynes. Moreover, the successful tuning of structural parameters of PE brushes in surface-initiated ethylene “living” polymerization from two types of silica nanoparticles were studied. The brush parameters that are controlled herein include brush length, density, and topology. The PE-grafted silicas with varying brush density and length are also used as nanofillers to construct polymer nanocomposites with an elastomeric ethylene-olefin copolymer (EOC) as the matrix polymer. The effects of brush length and density on the nanofiller dispersion, rheological properties, and tensile properties of the composites are examined (The preparation and characterization of the nanocomposites were carried out by K. Petrie and M. Kontopoulou at Queen’s University).
Utilization of coal fly ash and grape waste to remove toxic metal ions in mining waste waters
(2017-09-15) Appiah-Hagan, Emmanuel
In recent years, the studies of a variety of inexpensive adsorbents as alternative to the expensive activated carbon have received a lot of attention. The purpose of my research was primarily focused on the modification of Thunder Bay coal fly ash, the characterization of the pristine and modified fly ash and the application of modified fly ash for removal of metal ions from mine wastewater. Adsorption by grape wine material (GWM) was also investigated though not completed. Modification at low and elevated temperatures with 2.0 M NaOH yielded improvement in surface area, pore volume and cation exchange capacity. However, low-temperature modification was pursued leading to very efficient adsorbents named TBRM and TBFZ compared to the original fly ash named TB. The modified and unmodified fly ash was characterized using different techniques including ICP-OES, X-ray diffraction, specific surface analysis (Brunauer-Emmet- Teller), particle size distribution analysis and scanning electron microscopy. Surface area analysis revealed an increase of specific surface area from 1.24 (TB) to 64.34 (TBRM) and 68.98 (TBFZ) m2/g, respectively. Likewise, porosity was also induced in the modified fly ash. Cation exchange capacities were determined as 1.94, 23.48 and 29.23 meq/g for TB, TBRM and TBFZ, respectively. SEM-EDS and XPS were employed to confirm the adsorption of metal cations on the surface of the adsorbents. The performance of TBRM and TBFZ for the removal of Cu2+, Pb2+, Ni2+, Cr3+, Co2+ and Cd2+ from a synthetic cocktail solution (SCS) and tailing pond water (TPW) was compared to that of TB. Results indicated TBRM and TBFZ were more efficient in both SCS and TPW. A batch method was used to study the influential parameters of the adsorption process including contact time, pH effect, and kinetics and adsorption isotherms. Column studies were done to compliment the batch mode approach. Regeneration of TBFZ revealed a possible 3-cycle application. The equilibrium data were generally modeled by the Langmuir and Freundlich models. Also, the pseudo-second order model was found to explain the adsorption kinetics most effectively. Thermodynamic studies of Ni2+ and Cu2+ with TBFZ in SCS revealed that the adsorption process was spontaneous although endothermic with a decrease in entropy. The most efficient adsorbent TBFZ was converted into innovative concrete foam composite material TBFZ:FA:BA 0.22:0.33:0.45, for adsorption studies. Preliminary studies revealed a removal of more than 95 % of Cu2+, Pb2+, Ni2+, Cr3+, Co2+ and Cd2 in both SCS and TPW after 6 h of contact. However, the regeneration of TBFZ:FA:BA 0.22:0.33:0.45 was inefficient and further investigation ought to be carried out. Overall, the results indicate a significant potential of the modified Thunder Bay fly ash as an inexpensive and effective adsorbent for the removal of toxic metals from mine wastewater.

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