Date of Award

1990

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Physics

Keywords

Physics, Atomic.

Supervisor

McConkey, J. W.,

Rights

info:eu-repo/semantics/openAccess

Abstract

Electron impact excitation of the rare gases has been studied via a series of polarisation correlation Stokes parameter measurements performed on an electron-photon coincidence apparatus. The Stokes parameters yield fundamental information on the magnitudes and relative phases of the scattering amplitudes which describe the scattering process, and also yield basic information about the elements of the density matrix describing the excited atomic state. Use of an in-plane polarisation analyser allowed a detailed study of the relative so-called "height" of the excited state charge cloud immediately following the electron-atom collision. A breakdown of the reflection symmetry, with respect to the scattering plane, in the excitation process can be caused by a spin flip of the exciting electron, and would give a non-zero height parameter. Hence measurements of the charge cloud height parameter allowed a detailed analysis of the influence of spin in the excitation process. Of critical importance to the performance of these measurements and the proper analysis of the experimental results is the definition of the scattering plane. Since the finite volume of the interaction region formed by the intersection of electron and gas beams can have depolarising effects, models which numerically simulate these effects and those due to the finite acceptance angles of the detectors have been developed. It was found that these "finite volume" effects were significant, under realistic experimental parameters, only at small angles ($<$5$\sp\circ$) and at angles where the P$\sb1$ parameter approaches $-$1. The atomic species studied were Ne, Ar, Kr, and Xe for electron scattering angles up to 50$\sp\circ$ and impact energies between 30 and 80 eV. Kr and Xe targets have naturally occurring isotopes with non-zero nuclear spin and in both cases the natural lifetimes of the excited states are long enough for complete hyperfine relaxation prior to photon decay. This causes depolarisation which must be taken into account. After carefully taking into account these two depolarising effects very good agreement was found with theoretical predictions, in particular with distorted-wave Born approximation calculations. Within experimental error the height parameter was found to be zero and hence no evidence for spin flip of the exciting electron was found. This resolves the previous disagreement between a number of experimental groups and the theoretical predictions.Dept. of Physics. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1990 .C677. Source: Dissertation Abstracts International, Volume: 52-11, Section: B, page: 5882. Chair: J. W. McConkey. Thesis (Ph.D.)--University of Windsor (Canada), 1990.

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