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UBC Theses and Dissertations

Nuclear orientation at very low temperatures Malakoff, Walter


One of the recently developed methods for studying nuclei depends on the orientation of the spin axes of the nuclei with respect to some axis fixed in space. Since there is an association between the angular momentum properties of a nuclear system and directional effects in the absorption or emission of radiation by such a system, this nuclear ordering is characterized by anisotropic effects in the interaction of the nuclei with radiation, whether particle or electromagnetic. This thesis encompasses the preliminary work done in assembling a system consisting of cryogenic equipment and electronics to measure the anisotropy in radiation emitted from radioactive nuclei oriented in a ferromagnetic host lattice (iron) at very low temperatures (∾0.01°K) and to observe the changes in anisotropy with changes in temperature. Chapter 1 contains a condensed account of the information that can be obtained from oriented nuclei, the methods of producing oriented nuclei and the theory required for extracting information from the observed anisotropy. Chapter 2 describes the low temperature apparatus and-includes a description of the low temperature cryostat, the Dewar vessels, the specimen assembly, the superconducting solenoid, and the polarizing solenoid. Chapter 3 deals with thermometry at low temperatures, the technique used for cooling adiabatically and the preparation of the Co⁶º specimen used for thermometry. Chapter 4 explains the function of each module of electronics used in the experimental configuration. Nuclear orientation of Co⁶º is covered in Chapter 5 and includes an analysis and discussion of results. Chapter 6 outlines the improvements to be made in the design of a new low temperature system and includes a brief summary of the future program of studies in nuclear orientation at very low temperatures.

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