A Study Of Positron Annihilation In Some Liquid Oxygen Systems

Author : Paul Richard Guagliardo
Publisher :
ISBN 13 :
Total Pages : 255 pages
Book Rating : 4.:/5 (816 download)

DOWNLOAD NOW!

Download or read book Positron Annihilation Studies of Solids and Surfaces written by Paul Richard Guagliardo and published by . This book was released on 2011 with total page 255 pages. Available in PDF, EPUB and Kindle. Book excerpt: [Truncated abstract] This thesis describes the first positron annihilation studies undertaken in the Atomic, Molecular and Surface Physics group in the School of Physics at the University of Western Australia (UWA). We have studied a range of systems with differing positron annihilation characteristics with the aim of characterising their defect properties, and in the process have gained insight into the interactions of positrons and positronium with materials. The project started with establishing a positron annihilation laboratory. This entailed developing procedures to produce and safely handle sealed 22Na sources, and testing positron annihilation instrumentation and experimental methods. The project evolved through collaboration with physicists, engineers, chemists, materials scientists, metallurgists and medical scientists and through a number of interesting experimental explorations of the physical phenomena affecting positron annihilation. An overview of these investigations and a thesis synopsis is given below. Chapter 1 is an introduction to positron annihilation techniques, concentrating on the interactions of positrons (and positronium) with materials, and on the spectroscopies that exploit the annihilation processes for the purpose of studying condensed matter systems. Chapter 2 describes the testing and optimisation of the positron annihilation lifetime spectrometer and Doppler broadening spectrometer. In Chapter 3, positron annihilation has been applied to study cation vacancies in oxides that exhibit ionic bonding. Such vacancies have a relative negative charge and so attract positrons, and the relatively low electron density at these sites causes enhanced positron lifetimes. Oxides considered in this work are (a) rutile, (Ti,Nb)O2, sintered in air and Ar; (b) tin oxide, (Sn,Nb)O2 sintered in air; (c) monoclinic zirconia, (Zr,Nb)O2; (d) pollucite, Cs(1-x)Al(1-x)Si(2+x)O6 and (e) Ta- and Ti-doped Zn2TiO4. All systems except (c) showed enhanced lifetimes when doping or off-stoichiometry was increased. In Chapter 4, positron annihilation has been used to study the nanoporosity of cementitious materials. The mechanical properties of these materials are heavily influenced by porosity, with the volume and size distribution of pores controlling both the strength and durability of the material...