Spin-tagged electron-hydrogen scattering: Ionization in the near threshold region.
Item
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Title
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Spin-tagged electron-hydrogen scattering: Ionization in the near threshold region.
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Identifier
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AAI9218280
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identifier
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9218280
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Creator
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Tang, Fu-Ching Frank.
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Contributor
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Adviser: Michael S. Lubell
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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, Atomic
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Abstract
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Electron-hydrogen atom scattering continues to remain an interesting subject for study, first because of the relative simplicity that characterizes the three-body problem, and second because of the complexity introduced by the long-range nature of the electromagnetic interaction. As the precursor to many-body physics, in which closed-form analytical solutions do not exist, it is apparent that a detailed understanding of the electron-hydrogen problem is extremely desirable. In order to provide improved sensitivity for testing theoretical approximations methods, I carried out an experiment in which spin served to tag the electrons, thereby reducing the ambiguities introduced by the identical nature of the projectile and target electrons. Stated somewhat differently, the use of polarized particles helped to distinguish the direct and exchange scattering channels, in the absence of which, tests of the predictive capabilities of theoretical approximation are often blurred.;I performed the experiment using a high-intensity beam of polarized electrons originating from a GaAs photoemission source and a highly-dissociated beam of polarized hydrogen atoms produced by an rf discharge and a magnetic hexapole selector. For incident electron energies ranging from 13.6 eV to 15.0 eV, I investigated total impact ionization using electrons with a characteristic energy spread of approximately 100 meV. The quantity I determined was the cross-section asymmetry A{dollar}\sb{lcub}\rm I{rcub},{dollar} defined by A{dollar}\sb{lcub}\rm I{rcub}{dollar} = ({dollar}\sigma(\uparrow\downarrow) - \sigma(\uparrow\uparrow){dollar}) / ({dollar}\sigma(\uparrow\downarrow)+\sigma(\uparrow\uparrow){dollar}), where {dollar}\sigma(\uparrow\downarrow){dollar} and {dollar}\sigma(\uparrow\uparrow){dollar} correspond respectively to the total cross sections for incident and target spins antiparallel and parallel. The source of polarized electrons provided typically several tens of nA of electrons in the interaction region with a polarization of 35%. The atomic hydrogen beam was characterized in the interaction region by a density of 1-2 {dollar}\times{dollar} 10{dollar}\sp{10}{dollar} atoms/cm{dollar}\sp3{dollar} and polarization of 0.515. Frequent reversal of the electron polarization direction allowed the determination of the asymmetry.;The value of A{dollar}\sb{lcub}\rm I{rcub}{dollar} was found to be of the order of 0.4 for the energy range investigated, in agreement with previous measurements. As function of energy, A{dollar}\sb{lcub}\rm I{rcub}{dollar} was not inconsistent with the Wannier picture, although additional data are needed to justify this conclusion completely.
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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.
