Date of Award

Spring 2002

Document Type

Restricted Thesis

Terms of Use

© 2002 Lisa M. Larrimore. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Physics & Astronomy Department

First Advisor

Amy Lisa Graves

Abstract

Positronium (Ps) is modeled inside a solid Argon lattice using the path integral Monte Carlo (PIMC) technique. Statistics on site occupancy, Ps structure, and energies are collected for argon both with and without a monovacancy. The Ps atom is found to avoid the monovacancy and to have only modest increases in lifetime when the vacancy is available. Although the calculated lifetimes are somewhat different from experimental measurements, this model correctly predicts a longer lifetime for triplet state o-Ps (700 ± 15 ps) than for a bare positron (510 ± 5 ps) inside a defect-free Ar lattice. The p-Ps lifetime in Ar is predicted to be under 90 ps. The calculated wave function for isolated Ps is exactly fit to theory, and the internal contact density of Ps in Ar, which describes the ratio of electron-positron overlap at the origin compared to that of free Ps, is determined from the modified Ps wave functions. The internal contact density is κ, = 1.25 ± 0.02 in Ar with or without a monovacancy. This result contrasts with the measurements of κ, < 1 in many solids, for instead of being polarized by the surrounding atoms, Ps is compressed by the potential model used.

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