Positronium reflection.
Item
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Title
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Positronium reflection.
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Identifier
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AAI9000072
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identifier
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9000072
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Creator
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Weber, Marc Herbert.
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Contributor
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Adviser: L. O. Roellig
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Date
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1989
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter
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Abstract
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A high intensity positron beam has been used to create a beam of monoenergetic positronilum (Ps) atoms. The Ps beam was directed at surfaces to measure the reflected fraction of Ps. The positron beam was based on {dollar}\sp{lcub}63{rcub}{dollar}Cu irradiated with thermal neutrons in the High Flux Beam Reactor at Brookhaven National Laboratory to obtain {dollar}\beta\sp{lcub}+{rcub}{dollar} emitting isotope {dollar}\sp{lcub}64{rcub}{dollar}Cu. Prepared as a single crystal the copper source also functions as the moderator for the positrons. The beam is accelerated and guided magnetically to a differentially pumped gas cell filled with 10{dollar}\sp{lcub}-3{rcub}torr{dollar} Ar. Positrons pick up electrons from the gas atoms to form a beam of Ps. The differential cross section is strongly forward directed. With the additional help of collimators a monoenergetic beam of Ps emanates from the cell. The Ps beam was scattered from a single crystal of LiF(100) and the reflected Ps fraction was observed as a function of the scattering angle as well as the Ps beam energy. A strong specularly reflected peak was observed. Below 8eV as much as 29% of the incident beam is reflected when the sample is heated to about 160{dollar}\sp\circ{dollar}C. At higher energies up to 56eV between 1% and 3% are reflected specularly. This thesis represents the first measurement of Ps reflection from a surface and is a major stepping stone towards the investigation of low energy Ps diffraction from ordered solid surfaces. Important new insights about surface structures can be expected from such a new probe.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
