Positron annihilation lifetime spectroscopy (PALS) has been used to characterize as extruded and aged LEXAN polycarbonate. The long-lived component of the PALS analysis is attributed to orthoPositronium (oPs) pick off annihilations. The oPs pickoff component lifetime and intensity decrease as the result of the aging heat treatment, and this decrease is associated with a decrease in the free volume site size and concentration in glassy polycarbonate due to aging. Isothermal relaxation experiments performed over the range 12 C to 30 C performed on as-extruded and aged polycarbonate indicate that the relaxation kinetics are significantly different, and are consistent with a decrease in molecular mobility as the result of aging. An activation energy for structural relaxation of 8.2 kcal/mole for aged polycarbonate versus 3.0 kcal/ mole for unaged polycarbonate was determined. The relaxation kinetics observed using PALS is related to the structural state and molecular mobility of the polymer.

Positrons provide a non-destructive technique for probing the nature and size of defects in materials with atomic-scale sensitivity. This work will focus on the powerful capabilities of positron annihilation spectroscopy (PAS) to study the evolution of defects and defect structures. This invaluable tool can aid in developing and characterizing advanced materials, with diverse applications such as nuclear reactors, optoelectronics, nanotechnology, polymers, medical sciences, and more. The work presented in this thesis aims to gain a fundamental understanding of the formation and evolution of defect structures of various metals and alloys under irradiation by applying the techniques and concepts of PAS. Various other characterization techniques are also utilized simultaneously to interpret the positron data better and further enhance our understanding of these materials. Depth-resolved PAS was used to identify vacancy clusters and measure their density as a function of depth in three samples (HfMoTiVZr, HfNbTiZr, and HfNbTaTiZr bulk alloys), performed at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Dresden, Germany. The samples were studied before and after irradiation from 10 MeV Si ions. The behavior of these alloys under irradiation is discussed and quantified in this work. A single branch of samples from the multi-principal element alloy (MPEA) HfNbTaTiZr (Nb, HfNb, HfNbZr, HfNbTiZr, HfNbTaTiZr) was synthesized into thin films on MgO substrate at the Center of Integrated Nanotechnologies (CINT) at the Los Alamos National Laboratory (LANL), to study the role of chemical complexity in an alloy's response to irradiation. There are four sets of these MPEA-based thin film samples, where one will be kept as a reference, and one will be studied with in situ PAS (iPAS), and two sets will be studied with ex situ PAS. The synthesis of these MPEA-based thin films and the design of the PAS experiment for each set is described in this work, along with other characterization techniques used together with this work. This work was made possible through the support of the National Science Foundation (NSF) under grant number DMR-2005064 and by the Fundamental Understanding of Transport Under Reactor Extremes (FUTURE), an Energy Frontier Research Center funded by the DOE, Office of Science, Basic Energy Sciences.

An insightful exploration of cutting-edge spectroscopic techniques in polymer characterization In Spectroscopic Techniques for Polymer Characterization: Methods, Instrumentation, Applications, a team of distinguished chemists delivers a comprehensive exploration of the vast potential of spectroscopic characterization techniques in polymer research. The book offers a concise outline of the principles, advantages, instrumentation, experimental techniques, and noteworthy applications of cutting-edge spectroscopy. Covering a wide range of polymers, from nylon to complex polymeric nanocomposites, the author presents recent developments in polymer science to polymer, analytical, and material chemists, assisting them in keeping track of the progress in modern spectroscopy. Spectroscopic Techniques for Polymer Characterization contains contributions from pioneers in modern spectroscopic techniques from around the world. The included materials bridge the gap between spectroscopists, polymer scientists, and engineers in academia and industry. The book also offers: A thorough introduction to the progress in spectroscopic techniques, including polymer spectroscopy and near-infrared spectroscopy Comprehensive explorations of topical polymers studied by spectroscopy, including polymer thin films, fluoropolymers, polymer solutions, conductive polymers Practical discussions of infrared imaging, near-infrared imaging, two-dimensional correlation spectroscopy, and far-ultraviolet spectroscopy In-depth examinations of spectroscopic studies of weak hydrogen bonding in polymers Spectroscopic Techniques for Polymer Characterization: Methods, Instrumentation, Applications is a must-read reference for polymer, analytical, and physical chemists, as well as materials scientists and spectroscopists seeking a one-stop resource for polymer characterization using spectroscopic analyses.

This comprehensive book reports on recent investigations of lattice imperfections in semiconductors by means of positron annihilation. It reviews positron techniques, and describes the application of these techniques to various kinds of defects, such as vacancies, impurity vacancy complexes and dislocations.