Date of Award

3-24-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Engineering Physics

First Advisor

Larry W. Burggraf, PhD.

Abstract

The three-dimensional positron annihilation spectroscopy system (3D-PASS) at the Air Force Institute of Technology (AFIT) correlates coincidence Doppler broadening of annihilation radiation with two-dimensional angular correlation of annihilation radiation measurements using two position-sensitive, high-purity germanium (HPGe) detectors. The low photoelectric cross section of germanium, combined with the limited output of the radioisotope-based positron beam, produced sparse data necessitating careful data extraction. Processing techniques employed to increase 3D-PASS spectra quality include an improved algorithm for determining radiation-interaction position on HPGe double-sided strip detectors, a momentum sampling function based correction scheme and spectra folding informed by crystal symmetries. The 3D nature of the correlated data allowed for leveraging multiple axes of crystal symmetry and producing 2D momentum plots along different projection directions. Integration of the 3D-PASS with a low-energy positron beam enables future studies of enhanced annihilation as well as nondestructive characterization of material surfaces.

AFIT Designator

AFIT-ENP-DS-16-M-056

DTIC Accession Number

Pending

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