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A Novel Design Of A Variable Energy Positron Lifetime Beam
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Book Synopsis A Novel Design of a Variable Energy Positron Lifetime Beam by : Dan Chen
Download or read book A Novel Design of a Variable Energy Positron Lifetime Beam written by Dan Chen and published by Open Dissertation Press. This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "A Novel Design of a Variable Energy Positron Lifetime Beam" by Dan, Chen, 陳丹, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled A NOVEL DESIGN OF A VARIABLE ENERGY POSITRON LIFETIME BEAM Submitted by Chen Dan for the degree of Master of Philosophy at The University of Hong Kong in December 2007 Positron annihilation lifetime spectroscopy (PALS) is known to be a sensitive method for characterizing vacancy type defects in materials and thus tends to be the most popular of the positron annihilation techniques. Conventional PALS, which is 22 normally based on the emission of positrons from Na, works only on bulk samples since the penetration depth of the positrons from this isotope is large and not controllable. In order to study the defects in thin films or at material surfaces, however, it is highly desirable to employ PALS with a slow positron beam which has the capability of varying the incident positron energy and hence the mean positron implantation depth. Such a depth profiling PALS system is referred to in the present work as Variable Energy Positron Annihilation Lifetime Spectroscopy (VEPALS). The problem of constructing a VEPALS system, however, is the absence of a start signal for a positron entering a sample when using a positron beam. One of the ways of furnishing the necessary start signal is the usage of secondary electrons emitted when the positron strikes the sample. This method, however, suffers from two drawbacks. First the efficiency of the secondary emission varies from sample to sample. Second the timing resolution is usually poor (typically 400 to 800ps) due to the variation of secondary electron energies. The new VEPALS design presented in this thesis offers a novel approach to solving these problems. It is based on the emission of secondary electrons produced when the positron beam passes through a 25nm thick carbon foil located in front of the sample. A needle of 30μm diameter is positioned on-axis right behind the foil, creating a radial electric field that deflects the secondary electrons radially outwards sufficiently so as to miss the sample and to hit a micro channel plate (MCP) detector placed down beam. The MCP signal provides the start-signal for the positron lifetime spectrometer. The design has a cylindrical symmetry that reduces the experimental complexity. Moreover the small variations in secondary electron path length results in good timing resolution (= 500eV) of the positron beam. DOI: 10.5353/th_b3955879 Subjects: Positron beams Positron annihilation Electrons - Emission
Book Synopsis A Novel Design of a Variable Energy Positron Lifetime Beam by : Dan Chen (Physist.)
Download or read book A Novel Design of a Variable Energy Positron Lifetime Beam written by Dan Chen (Physist.) and published by . This book was released on 2007 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Novel Applications Using the High Intensity Low-energy Positron Beam at NEPOMUC by : Christoph Hugenschmidt
Download or read book Novel Applications Using the High Intensity Low-energy Positron Beam at NEPOMUC written by Christoph Hugenschmidt and published by . This book was released on 2010 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Positron Annihilation by : Werner Triftshauser
Download or read book Positron Annihilation written by Werner Triftshauser and published by . This book was released on 2001 with total page 756 pages. Available in PDF, EPUB and Kindle. Book excerpt: When it comes to studying the structures and defects of materials, there is presently no technique that is superior to positron annihilation. The increasing demands for higher accuracy and reliability provide a constant stimulus to the field, and the present book relates the newest and most important scientific discoveries made in the field of positron annihilation.
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Book Synopsis Positron and Positronium Chemistry by : S.J. Wang
Download or read book Positron and Positronium Chemistry written by S.J. Wang and published by Trans Tech Publications Ltd. This book was released on 2008-11-06 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this special volume was to provide an international forum within which to present the recent progress made in positron and positronium chemistry, and to exchange new ideas in fields of research which use positrons and positronium. Volume is indexed by Thomson Reuters CPCI-S (WoS).
Book Synopsis Development of a Low Energy Positron Beam by : Sujata Vemuri
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Book Synopsis Summaries of Reports of the Electrotechnical Laboratory by : Denki Shikenjo (Japan)
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Book Synopsis Scientific and Technical Aerospace Reports by :
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Book Synopsis Particle Accelerator Physics by : Helmut Wiedemann
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