Candidate: Ali Sami Alnaser

Degree of: Doctor of Philosophy

Department: Physics

Title: Electron Correlation Leading to Double-K-Vacancy Production in Li-Like Ions Colliding with Helium

Committee:
Dr. John Tanis, Chair
Dr. Thomas Gorczyca
Dr. Emanuel Kamber

Date: Friday, May 24, 2002, 2:00 p.m. – 4:00 p.m.
202 Everett Tower, Bradley Commons Room

Abstract:
Single and double K-shell vacancies in Li-like like ions colliding with neutral helium target have been investigated using high-resolution Auger projectile spectroscopy. Be+, B2+, C3+ and O5+ Li-like ions were produced and accelerated to intermediate-to-high collision velocities where perturbative models are expected to be valid, using the Tandem Van de Graaff accelerator at Western Michigan University.

Double-K-vacancies in atomic systems or so-called "hollow ions" can be induced by different mechanism in ion-atom collisions. For intermediate-to-high velocity atomic collisions where the collision time is small, the projectile ion can interact with only one of the target electrons transferring it to an excited state or the continuum to produce a K vacancy. By subsequent rearrangement of the remaining ion, in which electron correlation plays an important role, the second K electron may be excited or ejected. This process is referred as TS1 (two-step with one projectile interaction). Additionally, at lower projectile velocities, the projectile may interact with each of the target electrons independently to produce two-K-vacancies. This process is referred as TS2 (two-step with two projectile interactions).

Plane-Wave Born approximation (PWBA) was used to calculate the cross sections of the single-K-shell excited states, and was used to compare with the measured ones.

The collision velocity dependence of the ratio of double-to-single K-shell vacancies was used to help determine the mechanisms responsible for the hollow state production in the different Li-like ions.

Different electron correlation effects were inferred from the spectral features of the formed hollow states. The variation of these effects were also investigated as a function of the collision velocity and the atomic number of the Li-like ion.

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