Ali Sami Alnaser
Degree of: Doctor of Philosophy
Title: Electron Correlation Leading to Double-K-Vacancy
Production in Li-Like Ions Colliding with Helium
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
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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