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<p> Near Medicine Hat, Alberta, Pleistocene deposits are exposed on numerous bluffs along the South Saskatchewan River. The Quaternary beds are very fossiliferous, yielding a large number of mammal bones and teeth. The enamel (calcium hydroxyapatite) portion of teeth within the sediments, is used to date the deposits with the electron spin resonance (ESR) dating method. The ESR age is strongly dependent on the dose rate which in turn depends on the uranium accumulation in the tooth fragments. Two U uptake models are used based on an early and a continuous, linear accumulation of uranium.</p> <p> At young, well dated sites the ESR ages are in relatively good agreement with independent estimates. For slightly older samples (approx. 100 ka), the linear U uptake model comes closer to the estimated age at one site, but at another site, the early U uptake model agrees more favourably with the estimated age. Based on the ESR ages, several older sites can be assigned to interglacial stages 7, 9 and 13, however, these ages are much younger than those determined by faunal and stratigraphic correlation (>0.5 Ma). Samples with extremely high U contents in dentine and enamel gave unreliable ESR results. These samples may have experienced a late stage of U accumulation.</p> / Thesis / Master of Science (MSc)

<p> The principal subject of this thesis is to experimentally determine the beta attenuation patterns in tooth enamel layers, and to examine the predictions of two theoretical models which are involved in the beta dose calculations of ESR dating. One of the models is based on empirical equations (Yokoyama, 1982) and employed by R.Grün (1986) in the DATA software of ESR dating, the other is based on the "one group" transport theory which was incorporated in the ROSY dating programme (B.J. Brennan, et al., 1997).</p> <p> The theoretical bases of Grün's approximation (i.e. the empirical approach) and the "one group" transport theory are discussed. Their predictions of beta attenuation under 2-π geometry are compared with the results of Monte Carlo simulations, and were then compared with the results of our experimental work, which show clear inclination to the predictions of "one group" theory and Monte Carlo. The previous experiment of Aitken et al.(1985) is also described and its flawed geometric arrangement is discussed.</p> <p> In this study, two sets of experiments are performed. The first set used pitchblende as the irradiator and employed the configuration of irradiator-absorber-detector, which is aimed to reassess the experiment of Aitken et al. (1985). The second set of our experiments used a pure beta source of 90Sr(90Y) and employed the innovative configuration of tooth enamel pellets in a hole of tooth enamel holder, which substantially solved the problem encountered in the first set (e.g. gamma background subtraction and non-2π geometry, etc.).</p> <p> Based on our experimental results as well as the discussion of Aitken et al.'s experiment, a conclusion is drawn that the "one group" theory is more reliable in predicting beta doses in ESR dating samples, and consequently, it challenges the ESR ages calculated by DATA software which employs the empirical approach. The comparison of ESR ages calculated by the two dating programmes is shown, and some revisions of published ESR ages based on DATA programme demonstrate the great significance of our experimental results.</p> / Thesis / Master of Science (MSc)

<p> The recent urban sprawl in the tectonically active region of California has prompted palaeoseismologists, to find ways of forecasting potentially hazardous earthquakes on existing faults. Electron spin resonance (ESR) can be used to date fault gouge from different regions in a fault zone thereby providing a history of fault movements in a particular region. Therefore, an earthquake frequency pattern can be established and the faults can be rated as to their potential danger. </p> <p> ESR dating of fault gouge is based on the premise that the ESR signals of quartz grains in the gouge have been completely reset by movements on the fault. The elapsed time since faulting is recorded by a gradual charge build up in the quartz corresponding to radioactive decay of radionuclides in the fault gouge matrix. The mechanism of zeroing of the ESR signals in quartz during fault activity is not well understood. In order to better comprehend the zeroing process, the variation of ESR signals, AD and age, with respect to quartz grains size were studied. These parameters are affected by induced stress to a greater extent in the smaller grain sizes. Therefore, with sufficient stress, the smallest grain sizes (smaller than a critical size) will be totally reset and define a "plateau" of equal age. This plateau criteria is used to define total resetting in a fault gouge sample and only these portions of the samples are used for dating. The establishment of an equal age plateau is confirmed for one of the fault samples collected from Southern California. </p> / Thesis / Master of Science (MS)