Positron moderation and apparatus for low energy electron and positron spectroscopy

Peter Wilkie

    Research output: ThesisDoctoral Thesis

    387 Downloads (Pure)

    Abstract

    Surface-analysis and treatment apparatus have been variously designed, manufactured, developed, and commissioned or re-commissioned, for characterising the surfaces and efficiency of positron moderators based around 3 μm thick polycrystalline-tungsten foil. These include XPS and AES, based around a CLAM2 hemispherical analyser, electron-beam heating, ion bombardment, mass spectroscopy, UHV sample mounting, UHV manipulation, gas-handling lines, and entry-lock apparatus. The CLAM2 electron spectrometer is additionally adapted for operation as a bipolar charged-particle spectrometer. All control software, and much data-analysis software, is implemented in Labview. Apparatus and techniques for safely storing, handling, transferring into vacuum, and manipulating in vacuo, a nominally 1 mCi 22Na, UHV-compatible positron source, are designed, constructed, and implemented. The efficacy of cleaning and surface-analysis apparatus are demonstrated, with some limitations and instrument malfunction identified, and solutions implemented. Methods for passivating positron-trapping states in polycrystalline tungsten are proposed, based on the current understanding of positron moderation and trapping. Improved moderator geometries have been designed and an alternative, simpler, and easier to implement solid-gas moderator proposed.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2008

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