Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis--University of California, Berkeley, 1961. / "UC-4 Physics" -t.p. "TID-4500 (16th Ed.)" -t.p. Includes bibliographical references (p. 88-91).

Thesis (M.S. in Physics)--United States Naval Postgraduate School, California. / "Unclassified Physics." Includes bibliographical references (p. 36). 14

Thesis (Master's)--University of California, Berkeley. / Includes bibliographical references (p. 33-35). 54

Foi desenvolvido, implementado e testado um formalismo que permite descrever propriedades nucleares em regimes de deformação fora do equilíbrio, utilizando o método Macroscópico-Microscópico em associação com o Método Semimicroscópico Combinado. Esse formalismo foi utilizado para a interpretação e elucidação de alguns problemas abertos como as estruturas na seção de choque de fotofissão do 237.ANTPOT Np, distribuições angulares de fotofissão do 239.ANTPOT. Pu, e a concentração de transições M1 no 237.ANTPOT Np e 239.ANTPOT. Pu em baixas energias. Também, foram interpretadas informações experimentais referentes aos estados isoméricos do 237.ANTPOT Pu e 239.ANTPOT. Pu. Com relação ao potencial preditivo do formalismo, foram identificados os possíveis candidatos (spin e paridade) a estados isoméricos no 241.ANTPOT Np, bem como foi calculada também pela primeira vez a distribuição de momentos de nêutrons para o 239.ANTPOT Np fora da deformação de equilíbrio. / It was developed, implemented and tested a formalism suitable to the description of nuclear properties at non equilibrium deformations regime, by using the Macroscopic-Microscopic method in association with the Combined Semimicroscopic Method. This formalism was used for the interpretation and elucidation of some open problems, as the structures in the 237Np photofission cross section, photofission angular distributions of 239Pu, and the concentrations of low-energy Ml transitions in 237Np and 239Pu. Also, experimental information on 237Pu and 239Pu isomeric states was interpreted. Concerning the prediction potentialities of the formalism, were identified possible candidates (spin and parity) for the 241Pu isomeric states, as well as the 239Pu neutron momentum distributions, at non equilibrium deformation, was also calculated for the first time.

In this project, we have successfully joined MA956 Oxide Dispersion-Strengthened (ODS) steel plates using Friction Stir Welding (FSW). ODS steels are prime candidate materials for the fuel cladding in Generation IV nuclear fission reactors and as first wall components in nuclear fusion reactors. This is due to their exhibiting excellent high temperature strength and creep behaviour, together with enhanced resistance to radiationinduced void swelling. ODS steels are heavily reliant on a fine dispersion of (Y-Al-O) nanooxide particles to provide the aforementioned properties. This, however, makes ODS steels particularly problematic to join. Most joining techniques melt the material along the joint line, but this would severely alter or deplete the nano-oxide dispersion and hence be highly detrimental to the material’s performance in a nuclear environment. FSW is a solid-state joining technique, and therefore can join ODS steel without melting the material. Although FSW can potentially alter the microstructure of the base material and affect the distribution of nano-oxide particles, if a sufficient number of nano-sized particles and a sufficiently homogeneous dispersion remain after the welding process, then a major roadblock for the implementation of ODS steels will have been removed. The research of this thesis focused on the impact of FSW on: i) the microstructure, ii) the mechanical properties, iii) the residual stresses, and iv) the abnormal grain growth behaviour of ODS steels; utilizing a wide array of techniques to assess the micro-to-nano scale structure and the properties of the base material and welds, including optical, scanning and transmission and electron microscopy, X-ray and neutron diffraction, small-angle neutron scattering, tensile testing and micro-hardness measurements. We also produced welds with systematic changes to the tool traverse speed and rotation speed to investigate the impact of changing the welding parameters on the weld microstructure, and therefore optimise the process parameters for enhanced radiation and mechanical performance of the ODS steel welds.

A hybrid Quasi-diffusion/Monte Carlo Method for solving multigroup criticality problems in slab geometry was investigated. Analog Monte Carlo was used to calculate functionals (Eddington Factors) that were then used in solution of the quasi-diffusion equations. The hybrid method was shown to accurately and precisely predict the k-eigenvalue and fission source distribution for loosely coupled problems with high dominance ratios and significant spatial gradients. The hybrid method was also shown to be computationally more efficient than analog Monte Carlo. / Graduation date: 2012

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1998. / Vita. Abstract. Author's abstract: Adapting Thomas P. Hughes's "large technological systems" thesis, I focus on the technical, social, political, and human problems that nuclear weapons scientists faced while pursuing the thermonuclear project, demonstrating why the early American thermonuclear bomb project was an immensely complicated scientific and technological undertaking. I concentrate mainly on Los Alamos Scientific Laboratory's Theoretical, or T, Division, and its members' attempts to complete an accurate mathematical treatment of the "Super"--The most difficult problem in physics in the postwar period -- and other fusion weapon theories. Although tackling a theoretical problem, theoreticians had to address technical and engineering issues as well. I demonstrate the relative value and importance of H-bomb research over time in the postwar era to scientific, politician, and military participants in this project. I analyze how and when participants in the H-bomb project recognized both blatant and subtle problems facing the project, how scientists solved them, and the relationship this process had to official nuclear weapons policies. Consequently, I show how the practice of nuclear weapons science in the postwar period became an extremely complex, technologically-based endeavor. "LA-13577-T thesis, issued July 1999." Includes bibliographical references. Also available online via Internet.

In the past decade, research in the field of singlet fission, the process in which one high energy singlet fission exciton forms two lower energy triplet excitons, has seen a resurgence as a process that has the potential to improve solar energy conversion efficiency and contribute to a push for renewable energy. While an impressive motivation, there is still much progress in terms of understanding the physics of the process as well as improving molecular design for actual applications that needs to be made before this motivation can be fully realized. Two significant current hurdles in this field are the extraction of the newly formed triplet excitons from their entangled triplet pair state before recombination, and the lack of stable chromophores with viable energetics for singlet fission and high triplet energies for application purposes. Over the past five years, we have addressed these issues with targeted molecular design. Only a couple of studies have successfully separated the triplet pair state in intramolecular singlet fission systems. We create an intramolecular singlet fission system, a PDI-pentacene-pentacene-PDI tetramer, in which a charge transfer state is utilized to separate an electronically entangled triplet pair. We have also shown that singlet fission can be controlled as well as actually induced in chromophores by employing molecular contortion to tune the energetics. With this work, we have contributed to the motivation of using singlet fission in real-life applications.

Approved for public release, distribution is unlimited / Thermophotovoltaic energy conversion offers a means of efficiently converting heat into electrical power. This has potential benefits for space nuclear reactor power systems currently in development. The primary obstacle to space operation of thermophotovoltaic devices appears to be the low heat rejection temperatures which necessitate large radiator areas. A study of the tradespace between efficiency and radiator size indicates that feasible multi-junction TPV efficiencies result in substantial overall system mass reduction with manageable radiator area. The appendices introduce the endothermodynamic model of a TPV cell and briefly assess the utility of advanced carbon-carbon heat pipe radiator concepts. / Lieutenant, United States Navy