Tamer Mohammad Elkafrawy

Doctoral Dissertation Announcement

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Candidate: Tamer Mohammad Elkafrawy

Degree of: Doctor of Philosophy

Department: Physics

Title: Radiative Double Electron Capture in Collisions of Fully-stripped Fluorine Ions with Thin Carbon Foils

Committee:
Dr. John A. Tanis, Chair
Dr. Thomas W. Gorczyca
Dr. Asghar N. Kayani
Dr. Murtadha A. Khakoo
Dr. Andrzej S. Warczak

Date: Thursday, November 15, 2012 11 a.m. to 1 p.m.
2202 Everett Tower

Abstract:
Radiative double electron capture (RDEC) is a one-step process in ion-atom collisions occurring when two target electrons are captured to a bound state of the projectile simultaneously with the emission of a single photon. The emitted photon has approximately double the energy of the photon emitted due to radiative electron capture (REC), which occurs when a target electron is captured to a projectile bound state with simultaneous emission of a photon. REC and RDEC can be treated as time-reversed photoionization (PI) and double photoionization (DPI), respectively, if loosely-bound target electrons are captured. This concept can be formulated with the principle of detailed balance, in which the processes of our interest can be described in terms of their time-reversed ones. Fully-stripped ions are used as projectiles in the performed RDEC experiments, providing a recipient system free of electron-related Coulomb fields. This allows the target electrons to be transferred without interaction with any of the projectile electrons, enabling accurate investigation of the electron-electron interaction in the vicinity of electromagnetic field.

In this dissertation, RDEC is investigated during the collision of fully-stripped fluorine ions with a thin carbon foil and the results are compared with the recent experimental and theoretical studies. In the current work, x rays associated with projectile charge-changing by single and double electron capture and no charge change by F9+ ions are observed and compared with recent work for O8+ ions and with theory. Both the F9+ and O8+ ions have energies in the ~MeV/u range. REC, in turn, is investigated as a means to compare with the theoretical predictions of the RDEC/REC cross section ratio. The most significant background processes including various mechanisms of x-ray emission that may interfere with the energy region of interest are addressed in detail. This enables isolation of the contributions of REC and RDEC from the entire continuous spectrum of x-ray emission or at least ensures that the background processes have negligible contribution to the energy range of interest. Special emphasis is given to showing how the data analysis was carried out by the subtraction of the x-rays due to contamination lines.