School of Graduate Studies - Theses

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Early educational history of Norfolk County
(University of Toronto Press, 1926) Bannister, John Arthur
Photoproton Reactions In Medium-Weight Nuclei
(1966) Dawson, Donald James; Prentice, J.D.; Department of Physics
The angular distributions, energy spectra and integrated yields of photoprotons were measured for nine medium-weight nuclei with atomic number between 28 and 50 in order to test the predictions of the Independent Particle Model of nuclear photodisintegration. Thin metallic foils of natural isotopic abundance were irradiated with a bremsstahlung spectrum of energy 22 MeV. The photoprotons emitted by the targets were detected at angles of 45, 60, 90, 120 and 145 degrees with respect to the direction of the photon beam by means of silicon surface barrier detectors. By using pulse amplitude discrimination, pulse heights from the intense electron background were kept below the level of a four MeV proton for most of the target elements. The detection system was calibrated for energy with the alpha particles from a Ra source. Photoproton energy spectra were thus obtained at each of the five angles of observation for each of the nine target elements. The results of the measurements are discussed in terms of the "resonance direct" interaction theory of Wilkinson. It is found that some extensions to this model are required to explain the experimental data.
Re-situating Learning
(1967) Dharamsi, Karim
In this dissertation I examine the Theory-Theory (T-T). I argue that T-T represents the orthodox conception of learning in today's psychological literature. T-T theorists hold that human beings come "equipped" with innate representations that are "a theory." Theorists believe that this innate theory guides our relations to the world. If T-T theorists are correct, learning amounts to theory-revision. Hence, T-T brings together (roughly) two commitments: (1) innate knowledge and (2) theory-revision. In this dissertation, I show that T-T depends on a reading of Plato's Meno to buttress its commitment to innate knowledge. For (2), T-T depends on aspects of W. V. Quine's philosophy. Theorists think that Quine's naturalised epistemology is central to their position. I show that T-T's dependence on Meno depends on a rough interpretation of the dialogue. Furthermore, I suggest while in some sense Quine's philosophy can accommodate innate knowledge, T-T theorists do not make a sufficient case for such an accommodation. By reconsidering Meno I wish to question T-T's dependence on what may not be in fact a case for innate knowledge. Later I show that no clear case has been made that Quine's philosophy is compatible with the sort of innate knowledge theorists require. I suggest that re-thinking Plato's dialogue cannot save T-T. For T-T theorists must provide a clear case of how innate knowledge is clearly compatible with Quine's philosophy. I argue that too much requires reworking in T-T, and that such a reworking is not necessary because an alternative conception of learning is possible. As an alternative, I argue that learning depends on factors that are not primarily innate but social. In terms of the social aspects of learning, I argue that an important condition of human learning involves being initiated into a set of social practices. Those practices are constitutive of meaningful behaviour that is inherently tied to the histories of those who live and work within these boundaries. Here we can read "history" as "having a tradition." This latter position stands, I suggest, in stark contrast to the view of T-T theorists and is far more plausible in providing an account of learning.
Specific Heat Measurements Of Some Solid Gases In A Helium-3 Cryostat
(1967) Burford, John C.; Graham, G.N.; Department of Physics
The specific heats of solid CO, NO, 0₂, N₂, and some dilute mixtures of 0₂ in CO and N₂ in the temperature range 0.6⁰ to 4⁰K are reported. The measurements were made in a mechanical heat switch calorimeter in a He⁴ cryostat to which had been added a He³ stage. A commercial germanium resistance thermometer was used which was calibrated against the He³ and He⁴ vapor pressure scales. The specific heats of CO and NO were measured in an attempt to settle the question as to the origin of the residual entropy of these two substances. For these cases, there exists a discrepancy between the entropy calculated from spectroscopic data (Sspec) and that calculated from specific heat data (Scal); the difference Spec‐s cal being called the residual entropy. For many years, the usually accepted explanation for the appearance of a positive, finite value of the residual entropy in the cases of CO and NO has been in terms of ‘frozen-in’ non-equilibrium states of the crystal. For these cases, it was assumed that the orientation of the molecules becomes frozen—in at a high temperature because the forces tending to produce orientational order are insufficient to overcome the high potential barriers to molecular rotation in the crystal. In this way, the disorder persists to the absolute zero, resulting in the observed value of the residual entropy. Recently, considerable doubt as to the validity of this kind of argument has been raised, especially because molecular rotation in solid CH₄ has been demonstrated even at 1.8⁰K from a recent spin—lattice relaxation study. In an attempt to find a specific heat anomaly which could remove the residual entropy, this study of CO and NO was undertaken. No anomalous behavior in either case was revealed down to 0.6⁰K. It is pointed out that our present incomplete knowledge of molecular rotation in solids at low temperatures needs to be improved by extensive infrared absorption, spin—lattice relaxation, and other studies in order to be in a better position to understand the origin of the residual entropy in those few simple substances for which such an effect persists. During the course of this work, a sample of CO was found to have been contaminated with CO₂ and air. The specific heat measurements on this sample revealed a rather broad anomaly, not accounted for by the Debye theory. A subsequent experiment in which more oxygen was deliberately added to the sample showed that the anomaly was caused by the oxygen impurity. A further experiment in this series in which oxygen was added to a nitrogen host was performed and the results allowed certain conclusions to be made regarding the origin of the anomaly. The concentrations of oxygen were very low, generally a few tenths percent. The results may be interpreted in terms of a model consistent with the low-lying rotational energy levels of the oxygen molecule. The observed anomaly was in excellent agreement with the Schottky anomaly for a system containing two levels with a degeneracy ratio, upper to lower, of 2:1, and an energy spacing of 5.14⁰.
Baman spectra of some simple molecules in condensed phases
(1967) Blumenfeld, S. Morray; Welsh, H.L.; Department of Physics
Spectroscopic studies of gases at low densities allow the determination of the intramolecular properties of free molecules. To investigate intermolecular properties, the molecules must be allowed to Interact with one another. One way of causing this interaction is to compress the gases to high pressures. The progressive changes which occur in the spectrum as the density is increased can be ascribed to the action of intermolecular forces during collisions.
An investigation of symmetry breaking in elementary particle physics
(1968) Copley, L.A.; Masson, D.; Department of Physics
The study of approximate symmetries in strong interaction physics has recently been the subject of immense theoretical interest. The group theoretical treatment of their breaking mechanisms and effects has already received exhaustive analysis. Here we go a step beyond this treatment in the hope of obtaining a clearer understanding of the underlying dynamics. This is done by considering three distinct approaches to the prob1em of calculating, within a broken symmetry scheme, the dynamical parameters of a given hadronic system.
Magnetic Moment of Iron - Nickel Invar Alloys Between 4 And 80 K
(1969) Cochrane, R.W.; Graham, G.; Department of Physics
The magnetic moment of several ferromagnetic f.c.c. iron—nickel alloys in the invar region has been investigated at low temperatures as a function of both the magnetic field and the temperature. A vibrating sample magnetometer has been constructed for these measurements with a relative sensitivity of three parts in 10(5). Such data resolution has permitted a detailed analysis of the temperature dependence of the measurements resulting from contributions at constant volume from spin wave and single particle excitations together with a term describing the effects of volume change on the magnetization. Because of the very large and negative thermal expansion of commercial invar (Meincke and Graham, 1963), this latter contribution is very significant. When the single particle and volume terms are considered in conjunction with other thermodynamic data, they suggest that the invar alloys can be interpreted on a rigid band model. Consequently, this model has been analyzed with the result that the static magnetoelastic anomalies can be understood on the basis of an approach to instability of the ferromagnetic state occasioned by the shape of the density of states.
Electromagnetic decay of states of high spin and high isospin in fluorine-19
(1969) Aitken, J. H.; Litherland, A. E.; Physics
The lowest Jπ =11/2+ state and the lowest two T = 3/2 states In 19F have been located among a number of new resonances in the 15 N(α,γ)19F reaction. The spins and radiative widths of these three new levels have been established by measurements of angular distribution and yield of γ-radiation. Their isospin is inferred from their spins, excitation energies, radiative widths and decay schemes. Measured transition matrix elements are compared with those calculated from shell-model wavefunctions which Include all (sd)3 configurations. Disagreements between 3 experiment and theory indicate that the (sd) description is inadequate for some of the positive parity states in 19F above about 4 MeV in excitation. Arguments are presented for the inclusion of (p) -2 (sd) 5 configurations to account for the properties of these states. The new 11/2+ level and the 7/2+ level at 4.38 MeV (whose spin has been definitely established in the course of this work) are discussed also in terms of a simple adiabatic rotational model for 19F. This model is found to account reasonably well for the excitation energies and transition probabilities of the lowest levels of spins 1/2 to 13/2.
Absolute intensities and pressure effects in the infrared fundamental bands of methane and its deuterated species
(1969) Cowan, V. Michael; Welsh, H.L.; Department of Physics
The infrared fundamental bands of methane and its deuterated species have been examined in dilute mixtures with helium, at densities from ~100 to ~1000 amagat. There are a total of 24 active fundamentals for CH4, CH3D, CH2D2, CD3H, and CD4, although in some cases only groups of overlapping bands can be observed. For the thirteen separate bands or groups of hands, the density variation of the spectral profiles and the integrated intensities has been studied. The contours have been corrected for slit-width effects by an iterative procedure. There is progressive disappearance of the rotational structure with increasing density, until at the highest pressures only broad, almost featureless bands remain. For the stretching modes, the integrated intensity Ӷ decreases linearly with helium density; the relative decrease is the same for bands at ~3000 cm-l and ~2200 cm-l, and equal to 1.53 x 10~4 / amagat. For the deformation modes, the initial decrease in Ӷat low densities is followed by a region of constant or slightly increasing intensity…
Whole-rock dating of young extrusives by the potassium-argon method
(1970) Baksi, Ajoy K.; York, D.; Department of Physics
The feasibility of dating very young extrusives by the wholerock potassium-argon technique has been investigated. Rocks from the Columbia River Basalts, Oregon, Rio Grande de Santiago volcanics, Mexico, San Francisco Volcanic Field, Arizona, Hawaii and Australia have been studied. Some of the results point out the grave difficulties that can arise due to the presence of small quantities of excess argon in such rocks. ·Comparison on the ages of rocks in the age range 0 to 5 million years strongly suggest that inter-laboratory differences exist especially in the detection and measurement of small quantities of radiogenic argon. Study of a very thick extrusive of Recent age indicates that atmospheric argon may have been incorporated into the edges of the flow as it solidified. The quantity of argon present and its isotopic composition is not homogeneous throughout the lava flow. Wherever possible, the data are examined on potassium-argon isochrons. This yields information about the precision of the individual analyses. Lack of total control over the “blanks" during the argon analyses, does not allow unequivocal interpretation of the meaning of the "ages" obtained.
From Wide Angle Reflection To Leaking Mode Seismograms - A Theoretical And Experimental Study
(1970) Dampney, C.N.G.; Wilson, J.T.; Department of Physics
Seismograms observed by a detector in the wide angle reflection to leaking mode region, (the intermediate zone), exhibit a plethora of interesting features. Head waves form and interfere with directly reflected arrivals, supercritically reflected waves have unusually large amplitudes and the normal and leaking modes gradually become predominant with increasing source- receiver separation. This transition region from seismograms consisting mostly of directly reflected waves to seismograms where the total characteristics of the medium are integrated by the normal and leaking modes in therefore an important area of study. The eigenfunction expansion of an infinite medium elastic wave field in Cartesian co-ordinators is an infinite series of plane waves describing generalized rays with real and complex angles of propagation. The expansion can be modified for a place layered medium by assigning transmission factors to the rays at they encounter each interface producing further rays. The “Sherwood-Cagniard” technique, (Sherwood (1958 and 1960)), provides a methods of evaluating the eigenfunction solution for an impulsive line source. In this thesis it has been used in a modified form to give closed solution for rays which follow and ascribed sequence of transmissions and velocities in a two dimensional medium. Furthermore, this solution is shown to be easily related to cylindrically symmetric three dimensional wave propagation. The mathematical method is ideally suited to generating synthetic seismograms in the intermediate zone. The technique is developed and made systematic by a ray indexing methods for computer programming purposed. Theoretical seismograms thus computed are then compared with experimental seismograms observed on models. The transmission factor assigned to rays with a given angle of propagation are functions only of the angle between the rays’ wave-front and the interface. Thus the method is extended to plane dipping interfaces and the theoretical seismograms compared with experiment. Finally an attempt is made to generalize the technique to curved interfaces. Even here some agreement is obtained with the experimental seismograms. The experimental seismograms are measured on a calibrated two dimensional seismic model system. The system features a new construction technique with bongs glass to epoxy to form layer over a half space models with curved, dipping or horizontal interfaces.
Hail Formation And Its Effect On A Model Updraft
(1970) Charlton, Robert B.; List, R; Department of Physics
The simulation of hailgrowth and its effects on cloud liquid water and energy balance is achieved by injecting hail embryos at the freezing level of a model updraft. Steady-state one-dimensional numerical models in which hail is only ascending or where it is ascending and descending are considered. The problems associated with the hail accumulation zones of former similar models are overcome by introducing a size distribution of hail embryos. Moderate concentrations of hail embryos, H to 2 per cubic meter, grow to deplete a significant fraction of the cloud's liquid water content. If this significant depletion of liquid water occurs, a hail accumulation zone is formed wherein the downward force on the cloud's updraft due to the hailstones is of the same order of magnitude as the upward buoyant force and further these zones are found to contain a maximum hail mass only three or four times greater than the vet-adiabatic liquid water content. The growth of hailstones from 0.25 or 0.50cm embryos to 3cm while ascending or U to 6cm after ascending and descending takes about lOmin in the former case and 20-30min in the latter. These growth rates are consistent with radar observations and they require only adiabatic liquid water contents (3*5gn/m* at maximum). Even larger stones are grown when they are non-spherical. The growth of large hailstones is therefore not dependent on an elaborate model of hailstone recycling within the cloud. Hail surface icing conditions and heat and mass exchange between the hailstones and the cloud air are found to be important to hailstone characteristics, the updraft's energy balance and liquid water content. Therefore, any future models of hailclouds should include the feedback mechanisms between growing hail and cloud air if moderate to heavy hail showers are to be numerically simulated. Altering the number of hail embryos or the cloud's liquid water content for the purpose of weather modification can produce positive or negative effects on hail production which are highly dependent on the hailcloud's parameters. For this reason any methods used to suppress hail should be allied with a definitive model of hail formation.
In-Vivo Neutron Activation Analysis And Associated Dosimetry
(1970) Agard, E.T.; McNeill, K.G.; Department of Physics
The use of neutron activation analysis in vivo for the measurement of calcium in the human body has proved to be a more accurate and less hazardous technique than many other methods currently used. The health hazard associated with this technique is determined in this study by a method of neutron dosimetry, based on the radiation damage in plastics caused by neutron induced fission fragments…
In Vivo Neutron Activation Analysis and Associated Dosimetry
(1970) Agard, E. T.; McNeill, K. G.; Physics
The use of neutron activation analysis in-vivo for the measurement of calcium in the human body has proved to be a more accurate and less hazardous technique than many other methods currently used. The health hazard associated with this technique is determined in this study by a method of neutron dosimetry based on the radiation damage in plastics caused by neutron induced fission fragments. The lower legs of a phantom were irradiated for 10 minutes with four 23Q 49 Pu-Be neutron sources immersed in water. The 3.1 MeV Ca gamma rays from the legs were counted by two 8" dia. by 4" Nal(Tl) scintillation detectors in the Whole Body Counter at the Toronto General Hospital. The activity was such that there was a statistical error of 2%. The reproducibility of the results was determined from a series of 10 irradiations and the standard deviation was found to be +/- 2.3%. The expected interference from the 3.1 MeV peak in 37S produced by the 37Cl(n,p)37S reaction was estimated to be about 2% and an experimental assessment of this interference showed that the contribution made by 37S to the 49Ca peak was about 4% . For the neutron dosimetry, the plastic damaged by the fission fragments was etched in a 6N solution of NaOH, and the resulting holes counted by an electrical sparking method. Experiments were carried out to find optimum processing procedures and to check the range of linearity of the system. It was found that 232th foils were adequate for determining the significant neutron dose, which was about 0.8 rem during the irradiation of the legs. If required, 235U foils may also be used to monitor thermal fluences. A comparison of fast neutron doses measured by this technique with a completely independent method at Brookhaven National Laboratories showed very good agreement.
Electromagnetic form factors and K-[pi] scattering
(1971) Curry, Paul Hedley; Moffat, J.W.; Department of Physics
This thesis is divided into two parts — Part I: Discusses the theoretical aspects of pion and nucleon form factors. A phenomenological model is developed and found to be consistent with F1V= F π Part II: Describes a model proposed by J.W. Moffat for K-π and π-π scattering. This model is shown to satisfy the postulates of s-matrix theory, except for unitarity, and is found to be in reasonable agreement with experiment.
Dynamics of precipitation zones
(1971) Clark, Terry L.; List, Roland; Department of Physics
A simple model is formulated to represent the dynamics of freely falling zones of thermodynamically inert and non-interacting precipitation sized particles in a constant density fluid. The time dependent Navier-Stokes equations of motion and continuity equations for the air and precipitation are numerically solved for two-dimensional flow in both slab and radial symmetry. Appropriate initial-boundary conditions are specified for the system. The zones' mean vertical motion, horizontal spreading, pressure support and effects of particle size distributions are investigated. Formulae are derived for radially symmetric zones of single sized particles relating the zones' vertical convective velocity and horizontal spreading velocity to an internal Froude number. Also, a formula for the zones' momentum range is derived in terms of the internal Froude number. Onset and duration of precipitation times are studied for four different initial conditions for multi-sized particle zones and were found to vary considerably from those calculated by Kessler (1967). It was noted in one particular case that particle separation for multi-sized particle zones was as large in the horizontal direction as in the vertical direction. An example calculation for an atmosphere with an exponential density profile indicates that a mean layer density for the air and a mean layer terminal velocity for the single sized particles are reasonable assumptions to make in studies of this type.
Lattice Dynamics of Some Hexachloroplatinate Compounds As Revealed By Nuclear Quadrupole Resonance
(1971) Cooke, Douglas Fraser; Armstrong, Robin L.; Department of Physics
The nuclear quadrupole resonance (NQR) frequencies (v) of the 35cl nuclei in the compounds rubidium hexachloroplatinate (Rb2PtCRl6 ) and cesium hexachloroplatinate (Rb2PtCRl6 ) were measured as functions of temperature in the range 4-500 K, under vacuum. The corresponding spin-lattice relaxation times (T1 ) were measured at the same temperatures above 60 K in Rb2PtCRl6 and above 77 K in Rb2PtCRl6. Both v and T1 were measured as functions of hydrostatic pressure in the range 1-500 kg cm-2 at four temperatures between room temperature and 380 K. A brief description of the apparatus and techniques used is presented…
Structural and quantum-diffusion studies in the near-infrared-spectra of solid hydrogen
(1972) Boggs, Steven A.; Welsh, H.L.; Department of Physics
Experimental data on the infrared spectra of the fundamental and first overtone bands of nearly pure solid orthohydrogen, of the fundamental, first, and second overtone bands of nearly pure solid parahydrogen, are applied to analyses of the energy levels of solid hydrogen and quantum diffusion. Spectra of the fundamental band of solid hydrogen with orthohydrogen concentrations in the range 75% to ~ 99% orthohydrogen were recorded at 1.05 K and ~ 5 K, i.e., above and below the order-disorder phase transition. The zero-phonon features are interpreted in terms of travelling vibrational, rotational, and orientational excitations (vibrons, rotons, and librons). The Q branches (fundamental and overtone) for ~ 100% o-H2 in the ordered state show a structured side-band, shifted by ~ 6 - 26 cm-1 from the appropriate vibrational transition frequency and due to one- and two-libron excitations; in the disordered state, this becomes a Boltzmann-modified band of half-width ~ 12 cm-1, peaked at the vibrational frequency, and due to predominantly low-energy orientational transitions of interacting o-H2 molecules. The Si(0) group of maxima in the ordered state is interpreted as the superposition of the transitions, Qi (1) + S0(O) and Qi (1) + S0 (0) + libron, where Qi (1) is an o-H2 vibron and S 0(O) is the localized rotational transition of an impurity p-H2 molecule, the J = 2 level of which is split into three sublevels by the field of the Pa3 crystal structure. Spectra of the first and second overtone bands of pure and nearly pure solid p-H2 were recorded. A number of features were observed for the first time and are interpreted in terms of the theory of Van Kranendonk. In particular, this work marks the first investigation of the second overtone region where four zero-phonon features were observed, all due to double transitions. The fundamental band of almost pure p-H2 solid was investigated for evidence of the diffusion of o-H2 impurity molecules. The absorption features in this band which are due to interacting pairs of o-H2 molecules was observed to increase as a function of time. This growth is characterized by a rate constant which has been measured as a function of temperature in the range 1.15 K to 2.10 K and concentration in the range 0.7% to 1.6% o-H2 impurity. The value and concentration dependence of the rate constant are found to be in generally good agreement with the theory of Oyarzun and Van Kranendonk. Measurements have also been made which yield the ratio of the random number of impurity pairs to the equilibrium number as a function of temperature and concentration. These data are compared with a statistical model of the diffusion process.
Interpretation of Airborne EM (Electromagnetic) Measurements Based on Thin Sheet Models
(1972-10) Ghosh, Mrinal K.; West, G. F.; Physics
An airborne electromagnetic (AEM) prospecting system is used as a very rapid means of economically searching large geologically potential areas for sulphide ore bodies within the top few hundred feet of the earth's surface. This is possible because massive sulphide ores are usually much more electrically conductive than most host rocks. The system usually consists of a transmitting coil and a receiving coil flown by an aircraft. The transmitting coil generates a time-varying magnetic field in the low audio-frequency range (100-4000 hz). Any small perturbations of a component of the field are then recorded continuously as the aircraft flies along flight lines. The record over a conducting body is called an anomaly profile. The magnitude of an anomaly depends on conductivity3 size and shape of the conducting body causing it3 and the flight direction and height of the AEM system. Interpretation is based on a qualitative or quantitative comparison of the observed response (anomaly) with the responses that would be observed by the system over simple idealized conductors. Many geological conductors are somewhat sheet-like in form and dip into the earth at an appreciable angle. The extent of the sheet is often large compared to the region sensed by the system. Both for airborne and ground EM measurements the single most important model has been the (thin) half-plane. For the multitude of AEM systems actually in use even this simple model has not been fully explored. The only available data are the peak amplitudes of the vertical half-plane for 'small-scale' systems (inaccurate) and the Lockwood quadrature system, and some profiles over perfectly conducting half-planes for a variety of systems plus a few random model profiles for a few systems. The thesis contains systematic studies with several AEM systems over vertical and dipping half-planes, vertical and flat ribbons, strike limited sheets, vertical half-plane under a thin flat overburden and two parallel half-planes. Studies have been restricted to thin conductors because of modelling convenience, and to keep the number of parameters under control. While thick bodies are interesting, the simpler thin case must obviously be done first. Field and model data have been compared in a number of cases and it is found that most of the field data is explicable without further elaboration of the models. However, certain discrepancies are found even in these selected cases which indicate that additional features of the conductors may have to be taken into account (and cast suspicion on the quality of altimetry). In the cases examined, it did not seem that the conductivity of host rocks was having much influence. The study indicates that it is often possible to discriminate flat-lying conductors from dipping conductors with the present systems. Other effects such as finite extent, influence of overburden, and fringe conductors are difficult to identify from a single flight with a current AEM system.
The electromagnetic Response of a Conductive Inhomogeneity In a Layered Earth
(1973-10) Lajoie, Jules J.; West, G. F.; Physics
In this thesis, the integral equation technique is used to model the electromagnetic prospecting problem of a conductive inhomogeneity embedded in a layered earth environment. Basically, it consists of replacing the anomalous conductor, which is simplified to a finite vertical thin plate, by a surface of scattering currents. The plate is sampled on a sqare grid and the number of points is kept to a minimum by using a fifth degree spline moment function to interpolate between them. In order to bypass the numerical problems encountered when attempting to solve directly for the components of electric field at each grid point, the integral equation is expressed in terms of two potentials representing divergence free current flow through its surface. Calculations involving the layered earth are done with a new Fast Fourier transform approach which basically consists of solving this problem in the Catesian wavenumber domain, i.e. the 2-D Fourier transform of the horizontal plane. The results show that a conductive host and/or overburden will affect the amplitude, phase and width of the conductor's free air anomaly. Both the host and the overburden will cause an attenuation and phase rotation of the source fields to the plate and the anomalous fields from the plate. When the target conductor is in contact with a conductive host, the channelling of currents induced in the host is found to increase the anomaly amplitude substantially. Computation costs do not permit the generation of high accuracy type curves, but the model examples presented demonstrate the basic physics of conductive earth effects in electromagnetic prospecting.

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