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Includes bibliographical references. / Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1980. / by Richard Keith Lester. / Ph.D.

Mass spectrometers are analytical instruments that convert neutral atoms and molecules into gaseous ions and separate those ions according to the ratio of their mass to charge, m/z. The measurement is reported as a mass spectrum: a plot of relative intensity vs. m/z that can be used to deduce the chemical structure and composition of materials and compounds. Initially, the use of mass spectrometers was restricted to the analysis of volatile compounds. Recent advances in the development of ionisation techniques to produce intact molecules directly from samples in the liquid or solid phase, has extended the powerful use of mass spectrometry to compounds of increasingly higher molecular mass. The aim of this study was twofold: develop diagnostic techniques for the in-situ measurement of isotope ratios in laser isotope separation experiments; and to correlate it with the measured isotope ratios on the collected product. The outcome is a thesis that can be divided into two distinct fields of application: Firstly; the Atomic Vapour Laser Isotope Separation (AVLIS) of lithium, and secondly the Molecular Laser Isotope Separation (MLIS) of uranium, In both AVLIS and MLIS pulsed laser systems were used to ionise and/or dissociate atomic or molecular beams. The pulsed nature of the lasers is ideally suited to in-situ time-of-flight detection of the produced ions. Different types of inter-changeable ion sources are common to the same TOF mass spectrometer. Each of these sources is selected according to its application. For instance, applications vary from photo- and multiphoton ionisation (laser ionisation) to surface analysis (laser desorption or particle bombardment) to chromatography (electron impact ionisation). Four different source configurations were considered in this study: (i) Atomic Laser Isotope Separation (AVLIS) of lithium; (ii) Multiphoton Ionisation (MPl) of UF6 gas; (iii) Non-resonant ionisation during Laser Desorption (LDI) of solids; and (iv) Matrix-Assisted Laser Desorption (MALD) of biopolymers. The design of each of these sources will be discussed in detail in chapters to follow. Bulk analysis of harvested laser-produced products needs to be in correlation with in-situ analysis. Three different characterisation methods were used in this study: (i) Laser Desorption Time-of-Flight Mass Spectrometry (LD-TOF-MS) (ii) Quadrupole-based Secondary Ion Mass Spectrometry (SIMS); and (iii) TOF-MS-based Secondary Ion Mass Spectrometry (TOF-SIMS). Chapter I describes the principles of time-of-flight mass spectrometry, design parameters, as well as the instrumentation that were designed and constructed for the purposes of this study. Chapter II describes the principles of Secondary Ion Mass Spectrometry (SIMS). In particular, research done on the establishment of tools to the non-expert user of SIMS to select analyses conditions, is described. Chapter III reports on the application of TOF-MS and SIMS during the AVLIS of lithium. Chapter IV reports on the application of the different combinations of TOF-MS, LD-TOF-MS, SIMS, and TOF-SIMS during the MLIS of uranium. / Thesis (Ph.D.)-University of Natal, Durban, 1999.

D.Ing. / An optimal laser pulser topology for employment in a future commercial molecular laser isotope separation (MLIS) plant is proposed by this thesis. It is pointed out in the introduction that power modulator research and development were performed without much regard to economic constraints in the past. These conditions were mainly caused by international strategic initiatives and spawned a wealth of different circuit topologies and techniques. Many more can be devised by using the various subsystems of these topologies and techniques in different combinations. However, under the paradigm of a modern day commercial application, the luxury of trying yet another new topology, merely on the merits of personal preference, does not exist. Therefore, it is proposed that a laser pulser topology be formally selected by using suitable criteria derived from the application. Formal definitions are provided for the general subsystems found in all laser excitation systems, as a foundation for the selection process. The available options for each subsystem type, as well as the options for combining them into various topologies are described. Many examples are quoted from the literature to corroborate the basic descriptions. Practical circuit issues are dealt with in an appendix. Selection criteria are determined by contemplating the theory and practical issues of pulse power technology, transversely excited atmospheric carbon dioxide lasers as well as molecular laser isotope separation. It is argued that all of these criteria can be combined into a single economic criterion, namely life cycle cost. This argument is supported by the commercial requirement of economic viability of the future plant. The author formulates a life cycle cost calculation model (LCCCM) from all the technical and economic issues previously mentioned. It includes a flexible design section that can accommodate any of the possible topology options. Cost functions, which include reliability analysis, are used to calculate capital and operating costs from the design parameters, throughout the life cycle of the plant. Probability theory is used to model parameters with indeterminate values. The use of the LCCCM and its subtleties are demonstrated by comparing two basic options in a case study. It is finally used in a reasoned process of elimination to find the best topology option for the application.