A systematic study of the Knight shift parameters has been carried out on single crystal specimens of tin and cadmium over a range from 1⁰ K to just below the melting points. The line widths observed in cadmium are approximately half the widths quoted by other workers, enabling more precise measurements to be made. These measurements show that the anisotropy of the Knight shift in cadmium changes sign between 4⁰ K and 77⁰ K. Pronounced changes in the Knight shift parameters are observed upon alloying cadmium with mercury. The temperature dependence of the isotropic Knight shift in tin can be explained by the volume effects and the phonon contributions when the temperature exceeds the Debye temperature. Comparing the temperature dependence data with pressure dependence results of other workers the explicit temperature dependence is extracted. It appears that the variation in the anisotropy of the Knight shift above the Debye temperature is largely caused by a change in lattice parameters, specifically a change in c/a ratio. Measurements of the line width at helium temperature in isotopically pure Sn¹¹⁹ and the same isotope in natural tin as a function of crystal orientation are reported. Second moments for the different crystal orientations have been computed. Analysis of the isotopically pure tin data leads to an evaluation of relative contributions, from the various shells, to the pseudo-dipolar interaction. For the isotopically pure tin, the measurements at the helium and room temperatures enable an evaluation of the spin-lattice relaxation time, T₁. T₁T is constant over the temperature range and closely isotropic. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

<p> The large double focusing mass spectrometer operating at its theoretical resolving power of more than 100,000 at the base of the peaks has been used to measure five mass spectral doublets. The resulting single and double neutron separation energies for some cadmium nuclides are much more precise than those from previous work. It is noted that striking regularities occur amongst these energies. </p> / Thesis / Master of Science (MSc)

No description available.

Zinc (Zn) and cadmium (Cd) have nutrient-type vertical distributions reflecting control driven by biological uptake in surface waters and remineralization of sinking biogenic particles at depth. Both metals show strong correlations with major algal nutrients (Cd with phosphate (PO43-) and Zn with silicic acid (Si)) in the world ocean. Through their roles as micronutrients and toxins to marine phytoplankton, Zn and Cd can influence surface biological community composition. Preserved Zn and Cd records have been employed as proxies to gain insight into nutrient distributions, circulation, and organic carbon export in the paleocean. A thorough and mechanistic understanding of the biogeochemical cycling of Zn and Cd is necessary for accurate paleoceanographic reconstructions as well as predicting alterations in metal supply to the modern surface ocean and its impacts on primary productivity due to oceanic changes. My dissertation aims to further this understanding through an investigation of Zn and Cd distributions in the subarctic northeast Pacific through samples collected along the Line P transect. A major focus of this dissertation was identifying and characterizing depletions of metals in O2-depleted waters relative to global and basin scale metal:macronutrient correlations. Dissolved Cd profiles from the subarctic northeast Pacific and the eastern North Atlantic show a deficit of Cd relative to regional Cd:PO43- relationships. Particulate Cd and Cd stable isotopes (ε112/110Cd) from low-O2 North Atlantic waters and published sedimentary data from the subarctic northeast Pacific point to a previously undocumented water-column metal removal process acting in O2-depleted waters. Metal sulphide formation, likely in association with particulate microenvironments, can explain the observed deficits. Other metals with similar sulphide coordination chemistry should also form metal sulphides if this process is occurring. Dissolved Zn from Line P showed distributions and Zn:Si relationships that are consistent with the removal of metal in O2-depleted waters through sulphide formation. A first order approximation of the Cd deficit suggests that sulphide formation may be an important sink term in the global Cd cycle. Surface and upper nutricline Zn:Si and Cd:PO43- relationships in the chronically iron (Fe)-limited subarctic northeast Pacific showed distinct trends, which differ from those seen in Fe-replete regions. Distributions suggest the formation of surface biogenic particles with high Cd:PO43- and Zn:Si, leaving surface waters depleted in metals relative to macronutrients and resulting in high metal:macronutrient ratios in the nutricline as these particles sink and are remineralized. This is consistent with understandings of phytoplankton physiology and uptake of divalent metals under Fe-limitation, and corresponds well with global data for dissolved Cd:PO43- patterns in Fe-limited regions. Subsurface high Cd:PO43- and Zn:Si may also be influenced by the advection of water enriched in trace metals. The distinct shallow remineralization horizon observed for Zn compared to Si in the subarctic northeast Pacific by this and previous work presents a fundamentally different distribution than observed in global Zn:Si compilations. Directed sampling in the subarctic northeast Pacific should help elucidate the mechanism behind the oceanographically distinct distributions in this basin. Dissolved ε112/110Cd from Line P demonstrates a remarkably uniform subarctic northeast Pacific deepwater reflecting an advected source signal. Particulate ε112/110Cd samples show an active Cd cycle, which is not imprinted upon the dissolved phase. Particulate ε112/110Cd from 200-600 m depth is among the lightest ε112/110Cd ever reported for natural telluric samples. This may be an important sink for light Cd in the global ocean, which at present is heavy with respect to known sources. Line P surface waters with very low Cd concentrations are not accurately represented by a closed-system Rayleigh model, which can describe ε112/110Cd in the Southern Ocean. This suggests spatially and/or temporally variable surface ε112/110Cd fractionation. A large difference is observed in reported dissolved ε112/110Cd at very low Cd concentrations between different instrumentations. An intercalibration is necessary to determine if this is an analytical artefact or reflects real oceanic variability. / Graduate

No description available.

<p> An attempt was made to measure the yields of the stable cadmium isotopes produced in the thermal-neutron fission of 233U and 235U using a solid-source mass spectrometer. The results for 235U fission indicate that there is structure in the mass-yield curve for the region studied which takes the form of a depression around masses 112-114. The origin of this structure is discussed in terms of the various mechanisms which have been proposed to explain the nature of the mass distribution in the symmetric region.</p> <p> The 233U study was unsuccessful because of the experimental difficulties encountered, primarily the interference from terrestrial cadmium and the low recovery of the fission products. </p> / Thesis / Master of Science (MSc)

No description available.

No description available.