No description available.

No description available.

No description available.

The purpose of this investigation was to study the thermoelectric effects in a single crystal of antimony at liquid-helium temperatures.

The presence of a moderately strong magnetic field, uniform and static, in the irradiated medium modifies the spatial distribution of events. The imposition of a magnetic field produces elecron helices, characterised by their radii and pitches. The differential and integral distribution of track lengths, corresponding to electrons slowing down in water in a magnetic field, have been computed as function of radii and pitches for 200 kVp X-rays and for ⁶⁰ Co gamma-rays. Theoretical work has shown that the probability of energy deposition in a smaller volume of the absorbing medium has been significantly increased as a result of the presence of a magnetic field during photon irradiation. The distributions of track lengths as function of electron radii and pitches have been studied in strong magnetic fields (1 - 20 Tesla). The trajectories of an electron moving in water for different emission angles (up to π/2) and for magnetic fields of 5 and 10 Tesla, have been computed. The data for stopping powers used in this study, cover electron energies of 30 eV to 1200 keV (initial energy). In the presence of a magnetic field, each electron spiral has enclosed a conical volume. As the magnetic field increases, so the volume enclosed by the spiral decrease resulting in a substantial increase in the number of hits (events) compared with events in the same volume in the absence of a magnetic field. The experimental work started with the study of the characteristics of a spherical walled proportional counter. The frequency density, y.f(y), energy probability density, y^2f(y), distributions and their averages overline Y_F and overline Y_D respectively, have been computed on the basis of the pulse height distribution of low-LET radiation. Gamma rays from ¹³⁷Cs and ⁶⁰Co have been used with and without a magnetic field. Transverse magnetic fields of 0.0304, 0.13, 0.24 and 0.34 Tesla as well as a longitudinal magnetic field of 0.0304 Tesla have been used in microdosimetric measurements. An average sphere diameter of 2 μm has been simulated for the purpose. In the presence of the transverse magnetic fields, an increase of up to ~ 45% and ~ 78% has been obtained in the values of overline Y_F and overline Y_D respectively for ^137Cs gamma rays. For ^60Co gamma rays the values of both overline Y_F and overline Y_D increase by up to about 97%. For the longitudinal magnetic field when compared with the corresponding transversal magnetic field, a substantial increase in the value of overline Y_F has been found for ^137Cs gamma rays and a less significant increase for ^60Co gamma rays. Also, a significant increase in overline Y_D has been obtained for both indirectly ionizing radiations.

Graduate / 0607

Graduate / 0607

No description available.

No description available.

Hydrogen fuel cell applications are set to ameliorate the world's energy woes, yet there still exists problems that need to be overcome in terms oftheir fuelling. While compressed storage, cryogenic storage, chemical storage, and adsorptive storage solutions exist, none meet the requirements that are needed to facilitate a replacement for the gasoline powered automobile. Metal hydrides have been long studied as an alternative method for storing hydrogen safely and efficiently, with significant developments being made in advanced alloys. While this research is beneficial, it was theorized that an externally applied magnetic field might augment the storage properties of existing magnetically susceptible metal hydrides, without trial and error alloy development. Constant volume hydrogen absorption experiments were conducted using LaNi5 in order to test this theory. A known amount of LaNi5 was exposed to hydrogen, with the absorption equilibrium data collected over a period of 6 hours. An equal sample was then exposed to hydrogen with a 0.7 Tesla applied field applied to the sample. There was a distinct difference between the absorption curves of the two equal samples, with the sample under the influence of the magnetic field achieving an absorption of only 0.60% wt. in comparison with the unmodified sample which absorbed 0.88% wt. It was concluded that the presence of an externally applied magnetic field has a negative effect on the overall capacity of LaNis through the prevention of a shift in the inner lattice structure of LaNis that would otherwise permit an increased hydrogen capacity. This effect while negative in terms of overall storage capacity could have a possible benefit in terms of the desorption of the stored hydrogen, as the magnetic field could be used in lieu of an increase in temperature in order to drive the hydrogen from the fully filled structure. / Thesis / Master of Applied Science (MASc)