Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 203-207).

Thesis (M.S.)--University of Wisconsin--Madison, 1957. / Typescript. eContent provider-neutral record in process. Description based on print version record.

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The properties of sub-monolayer Helium-3 films adsorbed on two totally different but planar substrates, Mylar^† film and exfoliated graphite have been studied using NMR. The nuclear magnetic relaxation times T₁ and T₂ have been measured as functions of fractional monolayer completion, temperature, substrate plane orientation and Larmor frequency using a specially designed and constructed NMR spectrometer system. The results obtained with a Mylar film substrate are consistent3with the formation of patches of solid ³He at regions of preferential adsorption on the substrate. Measurements of T₂ m very low coverage ³He films on exfoliated graphite also indicate that the adsorbate forms areas of relatively high density solid, in agreement with the thermodynamic analysis of Elgin and Goodstein. Finally, detailed measurements of T₂ as a function of all of the above parameters at low areal densities will help us to characterise the relaxation processes for the fluid phase of ³³He on exfoliated graphite. ^†Mylar is the tradename of poly(ethelene-terephthalate) film, marketed by Du Pont.

The heavy alkaline earth hydrides consist of the Group II (alkaline earth metal) hydrides, namely CaH2, SrH2, and BaH2, which adopt the cotunnite-type structure at ambient pressure and temperature conditions. There has been much recent research interest in these compounds; in the past decade numerous experimental and theoretical studies exploring the hydrides in both applied and fundamental respects have been added to the literature. The present work constitutes a study of the heavy alkaline earth hydrides subjected to extreme pressure conditions (at ambient temperature). Specifically, pressure-dependent angle-dispersive powder x-ray diffraction and Raman spectroscopy experiments, as well as first-principles calculations, have been carried out to explore the structural stability, compressibility, and optical phonon spectra of the heavy alkaline earth hydrides. To complement the work on the hydrides, a companion study on BaF2---a structural analogue---is presented, as well as a description of some selected experimental techniques used to carry out the research. The powder x-ray diffraction results reveal that all of the heavy alkaline earth hydrides undergo a pressure-induced, first-order structural phase transition. The proposed Ni2ln structure for the high-pressure phase is based on both the results of first-principles calculations and an isostructural comparison with BaF2. The transition pressures and the proposed high-pressure structure are corroborated by the results of the Raman spectroscopy measurements. Where applicable, equation of state parameters from both the experimental and theoretical studios are reported, and a comparison of these respective parameters at ultra-high pressures (greater than 50 GPa) suggests that the experimentally observed bulk moduli are overestimated due to the presence of non-hydrostatic pressure conditions.

Work on film flow in liquid helium II is not new, but very little has been done in the temperature region below 1 degree. The present work describes a method of extending these measurements down to the very low temperature range. After a brief introduction laying the foundation of the problem in its proper framework in the field of low temperatures, the experiments and results obtained by other workers in film flow and associated phenomena are reviewed. Then the author proceeds to the development of experimental techniques used in attempting to seal gaseous helium at high pressures in glass capsules. Chapter II terminates with a full description of the so-called Heater Method with which helium 'bombs' were sealed at pressures ranging from 750 to 1100 psi. One of these capsules containing a capillary beaker, and partially filled with manganous ammonium sulfate, was used in determining film flow rates at temperatures ranging from approximately 2° to 0.6°K, The lower temperatures were obtained by adiabatic demagnetization techniques. Chapter III is a report of such experimentation. The results obtained are much like those of Ambler and Kurti, 1952, and support their contention that film flow rates do increase with decreasing temperatures in the region below one degree absolute. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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