Electron impact excitation phenomena play an important role in atomic and molecular physics. The different energy levels of an atom or molecule interact differently with incoming electrons with different energies and that affects the excitation of the energy levels of the atoms and molecules. Studies involving electron impact excitation process are generally conducted with optical emission techniques or by the electron energy loss method. In the present study, for the first time, cavity ringdown spectroscopy (CRDS) has been used to investigate electron impact excitation phenomena of electronatom collision processes. The technique, i.e., electron impact excitation-cavity ringdown spectroscopy (EIE-CRDS), was employed for the purposes of fundamental study and of real-time applications. The fundamental study which was carried out in terms of determining electron impact excitation cross section (EIECS) has been demonstrated by measuring EIECS of a few excited levels of mercury (Hg) atom. For the application side, the EIE-CRDS technique has been employed for trace element detection. This dissertation first describes the fundamentals of electron impact excitationcavity ringdown spectroscopy (EIE-CRDS); afterwards its applications are demonstrated. A novel method of measuring excitation cross sections using this EIE-CRDS technique has been explained. In this method, first the excitation of atoms are achieved by electron impact excitation process, subsequently, CRDS measured absolute number density is utilized to determine the absolute EIECS values. Steps of the method are described in detail. Applicability of the method is demonstrated by measuring EIECS of three different energy levels of Hg, namely 6s6p 3P0, 6s6p 3P1, and 6s7s 3S1, and the obtained values are in agreement with those reported in the literature. Secondly, the EIE-CRDS technique was employed to investigate the absorption spectrum of mercury atom in the vicinity of 404.65 nm, corresponding to the transition 6s7s 3S1 -> 6s6p 3P0 levels of mercury. Elemental mercury was measured using a laser of wavelength 404.65 nm. The technological feasibility of developing a portable size instrument for mercury detection was explored. Subsequently, a portable size, dual-mode, plasma-CRDS based prototype instrument, capable of real-time trace element monitoring, was developed. The design, functioning, and specifications of the instrument are also explained.

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This research is focused on explaining the concentrations of mercury found in juvenile bald eagles (Halieattus leucocephallus) as a function of the physical and anthropogenic landscape. Due to it's location in the food chain this species is susceptible to a wide range of contaminants (xenobiotics), particularly those that bioaccumulate and biomagnify as they move through the food chain. Previous research has indicated that areas in coastal environments are less susceptible to methylation than those in freshwater environments. Sampling efforts for this research were conducted in such a manner as to obtain an equivalent number of samples from the coastal plain (expected to be low mercury) and the inland regions (expected to be statistically significantly higher). In all cases, results indicated that both feather and blood mercury concentrations were higher in the inland population (Blood: Prob > t = 0.0003, Feather: Prob > t = 0.0002). Utilizing classification and regression tree models (CART), we were able to relate metrics such as the percent of deciduous forest, percent of mixed forest, percent of pasture, and percent of wetland to measured blood mercury concentrations. We also found that the best models were produced using the USGS HUC 12 watersheds (the smallest watershed produced by the USGS). Moreover, we found that metrics describing the amount and type of fragmentation within the watersheds exhibited a significant influence on measured blood mercury concentrations. Contrary to previous research, we found wetlands to be negatively associated with higher blood mercury, whereas the abundance of core forest and a larger patch density (PD) in the deciduous and mixed land cover classes was positively associated with higher blood mercury concentrations. We also found that a higher percentage of pasture was associated with higher blood mercury. / Ph. D.

This research relates Hg levels in the Common Loon (Gavia immer) to a variety of physical factors. Constructed within the framework of a GIS system, this model analyzes the spatial relationships and the influence of physical land cover factors as a function of distance from the individual loon territories. Thiessan polygons were used to generate the territory for each loon. Buffering of the thiessan polygons was done to establish the boundaries of the individual distance classes and to gather information on the percentage of individual land cover classes within each distance class. Information on precipitation was also gathered. Results from the regression analysis (R2 = 57.3% at the 150m distance class) performed on the variables suggest that the proximity of certain land use types such as cropland, shrub land, and wetlands influence the rates at which Hg is available within an individual territory. Within the 150m and 300m buffers, crop land, shrub land, and wetland exhibited the strongest relationship with the Hg levels in the common loon, with cropland exhibiting a negative relationship suggesting that the proximity of cultivated lands plays a role in decreasing the amount of available Hg in a territory. / Master of Science

Forested streams are closely linked to terrestrial catchments which affects their biogeochemical cycling and carbon inputs. Catchment disturbances alter stream water quality and food webs, including changes in productivity. Such changes in stream conditions can potentially alter consumers’ reliance on autochthonous (in-stream) or allochthonous (terrestrial) sources and mercury bioaccumulation. A recent outbreak of the spruce budworm (SBW) that feeds on spruce and fir trees has provided the unique opportunity to examine stream food web responses across watersheds experiencing a range of defoliation in the Gaspé Peninsula, Québec. This project compares streams in twelve watersheds which were selectively sprayed to control SBW and create a gradient in defoliation. Food web samples (food sources, invertebrates, fish) were analyzed for stable isotopes of carbon and nitrogen in 2019 and 2020 to characterize food web structure, and algal productivity was measured in 2019. Hierarchical partitioning models were used throughout the study to compare the contributions of various local and landscape conditions to stream responses. Models indicated that watershed defoliation contributed to increasing autochthonous production, although some invertebrates were more allochthonous in heavily defoliated watersheds, and brook diets were unaffected by defoliation. Next, food web samples were analyzed for methylmercury (food sources, invertebrates) or total mercury (fish) and trophic magnification slopes were determined for each stream food web. Mercury levels in carnivorous invertebrates and brook trout were driven by dissolved organic carbon (DOC), but not consumer autochthony or watershed defoliation. Additionally, rates of trophic magnification were not related to defoliation severity or DOC. This study found that defoliation contributed to increasing autochthonous production and invertebrate consumer allochthony. However, this disturbance did not increase consumer mercury levels or biomagnification in stream food webs. These findings suggest that intervention to reduce defoliation would mitigate algal responses and dietary shifts, but not mercury cycling as it is influenced by DOC levels in the streams of this region. / Thesis / Master of Science (MSc) / A recent spruce budworm outbreak is causing widespread defoliation of spruce and fir trees, but the impacts to stream environments, including primary production, its consumption, and contaminant levels, are largely unknown. Streams are sensitive to conditions in the surrounding terrestrial environment, as such changes can affect the diets of stream invertebrates and fish and are also linked to increased contaminant levels in aquatic organisms. Specifically, mercury is a metal that is transferred through diet and can reach toxic levels in fish. This study found that defoliation is contributing to increased algal production in streams in the Gaspé Peninsula, Québec. However, some stream invertebrates consumed more terrestrial material in streams that had heavier defoliation. Furthermore, defoliation and algal diets did not increase levels of mercury in aquatic organisms, but this contaminant was affected by increasing concentrations of dissolved organic carbon in the streams. These findings suggest that forest defoliation can alter organisms’ diets but not mercury levels.

<p> The energy bands and Fermi surface of mercury have been calculated using local and non-local pseudopotentials. The non-local pseudopotentials were an approximation in which the repulsive potentials of the outer atomic core states were explicitly represented by non-local projection operators. </p> <p> A search was made for the regions of parameter space where the pseudopotential generated a Fermi surface having a good fit to the experimental magneto-acoustic calipers and de Haas-van Alphen extremal cross sectional areas. </p> <p> De Haas-van Alphen frequencies and cyclotron masses were calculated for symmetry planes using a local pseudopotential. </p> <p> General questions of pseudopotential theory, the symmetry of the energy bands, the occurrence of degeneracies, and the influence of spin-orbit coupling are also considered. </p> / Thesis / Doctor of Philosophy (PhD)

<p> X-ray fluorescence has been used to measure levels of lead in the bone for many years. This technique is particularly important for the occupational monitoring of those exposed to lead in the workplace as it provides an indication of long term exposure and retention in the body. The measurement of kidney mercury by x-ray fluorescence has been developed recently and is currently being improved for future use in occupational monitoring.</p> <p> X-ray fluorescence detection systems conventionally employ analog-amplifier components. Recently, digital spectrometers have been developed which can replace these conventional electronics components. The digital systems offer higher throughput without major losses in resolution which translates to better precision and reduced detection limits for x-ray fluorescence measurements.</p> <p> Investigations using the DSPECplus and DSA-2000 digital spectrometers for the measurement of bone lead in phantoms showed significant improvements in precision and potential reductions in MDL compared to conventional electronics. The use of the DSA-2000 digital spectrometer in a bone lead survey was shown to improve measurement uncertainties for in vivo bone lead measurements. Investigations using the DSA-2000 for the XRF measurement of kidney mercury in phantoms also showed a significant reduction in MDL for this system by the introduction of digital spectroscopy.</p> / Thesis / Master of Science (MSc)

<p> Field modulation techniques were used to observe the de Haas-van Alphen effect in magnetic fields up to 5.5 tesla and at temperatures below 1.1°K. A data acquisition system recorded on magnetic tape the large amount of data necessary for computer fourier analysis of the oscillations. All of the orbits predicted by Keeton and Loucks' model of the Fermi surface of mercury were at least tentatively identified. The data on the β, τ and α orbits were in essential agreement with previous work. The γ and X-face orbits were also investigated in some detail, while tentative identification was made of the μ and T-face orbits. When the data permitted, the areas were fitted to ellipsoids or hyperboloids of revolution by a least squares calculation.</p> <p> A search was made for modifications to the de Haas-van Alphen theory due to phonons. Accurate torque de Haas-van Alphen amplitude measurements were taken as a function of temperature and magnetic field. The analysis of the results revealed no systematic dependence of either the cyclotron effective mass or the Dingle temperature on temperature from 1.25°K to 4.2°K or on magnetic field from 1.5 tesla to 2.3 tesla. Thus no effects due to phonons were observed.</p> <p> A method of observing the open orbits in metallic single crystals was developed and used to observe the open orbits in mercury. The method utilized the eddy currents induced in the sample by the rotation of a magnetic field. This provided a signal which was dependent on the conductivity in the plane perpendicular to the open orbit. The torque amplitude, which indicated the number of open orbit carriers, was used to detect the angular range of the bands of open orbits in mercury. The method was experimentally simple since no special sample geometry was necessary and no electrical connections to the sample were needed.</p> / Thesis / Doctor of Philosophy (PhD)

Researching efficient removal techniques is essential due to the toxicity of heavy metals, even at low concentrations, and their pervasiveness in a variety of environmental settings. According to WHO, Mercury is one of the most dangerous pollutants for human health. It causes severe damage to the ecosystem and other living beings. But because of its favorable physical-chemical properties, it has been widely used in the industrial activities. Unfortunately, several rivers and aquifers are getting contaminated by this hazardous chemical and inevitably putting importance on how to solve this problem. Most importantly a cost effective and environmentally friendly methods are needed to get a sustainable solution to this contamination. In this study Pinecones and pecan shells were chosen because of its abundance in nature and they are completely free of cost to get. Though some of the studies has been performed to remove some heavy metals by utilizing these two agricultural waste materials, none of the previous study investigated this two-potential bio-sorbents for removing Mercury from water solutions. In addition, there is a chance that metals and other ions will coexist in the environment, which is a complicated situation where there would be a competition among the ions for active cites on the sorbent surface. This study presents the effective removal of Hg2+ at a trace level concentration through adsorption on the grounded pinecones (PC), pecan shells (PS) and Chemically modified pinecones (PC), and pecan shells (PS). The FTIR analysis showed the functional group present in each specimen and pHPZC of each sample was determined to understand the surface chemistry and reactivity of the materials. Chemical modification might result in the increased surface area, porosity, functional groups as compared to the unmodified samples. The factors affecting adsorption efficiency were pH, adsorbent dosage, ionic strength, contact time and metal concentration. The Hg2+ removal efficiency in aqueous solution was found 90-92% for PS and APC, 92-95% for APS, and 80-85% for PC at room temperature with 1 mg/mL dose and pH their optimum pH condition. However, for unmodified PC and PS, the adsorption efficiency was less for all situation as compared to the acid modified PC and PS. The base activated PC and PS were found to be less effective than even the unmodified materials. Thus, results indicate that modification of PC and PS with Nitric acid (HNO3) increases metal adsorption efficiency as compared to unmodified samples. Furthermore, all of the materials tested found to be following the Freundlich's adsorption isotherm in aqueous solutions. Besides, ionic mercury can be readily converted to organic mercury through methylation, and as organic mercury builds up in the food chain, it is very harmful to human health even at a low level. Thus, to provide appropriate protection, the US Environmental Protection Agency (EPA) has set the maximum contamination level of mercury in drinking water at 2.0 ppb. As a result, it becomes very crucial to invent a very sensitive and selective approach for monitoring the low concentration of Hg2+ in the environment. This study aims to create an incredibly sensitive assay for the detection and quantification of Hg2+ (aq) using the single-particle inductively coupled plasma mass spectrometry (spICP-MS). The well-known thymine (T)-Hg2+-T complex forms when AuNPs modified with single-stranded DNA are exposed to Hg2+ (aq) and this formation causes AuNPs to aggregate. By determining the overall reduction in the number of identified AuNPs or NP aggregates the degree of aggregation can quantified. This spICP-MS-based approach has been reported to obtain a substantially lower detection limit of 0.031 part-per-trillion (155 fM) and a larger (10,000-fold) linear range up to 1 ppb when compared to most other Hg assays that use the similar principle of aggregation-dispersion with DNA modified AuNPs. Besides, this approach showed low interference from the sample matrix. Considering the aforementioned advantages, this study focuses on quantifying aqueous Hg2+ using single stranded DNA-gold nanoparticles conjugates with the help of single-particle inductively coupled plasma mass spectrometry (spICP-MS).

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