Date of Award

12-2019

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Dr. John A. Tanis

Second Advisor

Dr. Thomas Gorczyca

Third Advisor

Dr. Asghar Kayani

Fourth Advisor

Dr. Anna Simon

Keywords

Electron capture, x-ray omission, RDEL

Abstract

The collision between a charged ion and an atom resulting in the capture of two electrons, simultaneous with the emission of a single photon is referred to as radiative double electron capture (RDEC). For ion-atom collisions, this process can be considered the inverse of double photoionization. The study of either process, where just two electrons are involved without influence from neighboring electrons, promises new insight into electron correlation and the role it plays in quantum mechanics. Such a study for photoionization has not yet been done experimentally for two-electron ions because the only target system for which two electrons are available is atomic helium. The ability to gain information on pure correlation will thus be important to fundamental studies of RDEC and double photoionization and to applications in astrophysics and in plasma physics. RDEC is related to the well-known process of radiative electron capture (REC), in which a single electron is captured to a bound state with the simultaneous emission of a photon, considered the ion-atom analog of radiative recombination.

Several attempts have been made to observe RDEC experimentally but without definitive results using mid- to high-Z, high-energy projectiles on thin-foil and gaseous targets. Several theoretical studies have been performed over the last 25 years, with recent results suggesting that mid-Z, lower-energy projectiles would yield better results by giving larger cross sections. The first successful observation of RDEC was performed at Western Michigan University using 2.38 MeV/u O8+ projectiles incident on thin-foil carbon targets. This result was followed by measurements for 2.21 MeV/u F9+ also on carbon foils, which however suffered from contaminants in the target. Multiple-collision effects were present as expected for thin-foil targets, causing the RDEC events to be distributed over the double and single capture channels. These previous measurements provide the motivation for the present RDEC work with gaseous targets.

Presented in this study are the results for RDEC by 2.11 MeV/u fully-stripped, and also one-electron fluorine ions colliding with N2 and Ne. Cross sections for both projectiles are determined and compared with theoretical calculations to the extent possible, as well as with each other. The measurements were done under single-collision conditions to prevent complication from multiple collision events. High purity target gases were used to minimize the effects of contaminants.

Comments

Fifth Advisor: Andrzej Warczak

Access Setting

Dissertation-Open Access

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