The UCNA Experiment at the Los Alamos Neutron Science Center (LANSCE) uses an electron spectrometer to observe angular correlations between the neutron spin and the momenta of β particles emitted during the process of β decay. These angular correlations give rise to an asymmetry determined by the ratio of two coupling constants, gA and gV . Combined with neutron lifetime measurements, these observations probe physics beyond the standard model through unitarity tests of the Cabbibo-Kobayashi-Maskawa Matrix. UCNA’s current spectrometer uses a multi-wire proportional chamber and a plastic scintillator coupled to four photomultiplier tubes (PMTs) by 2 meters of light guides to record energy, position, and time data. The UCNA Collaboration is exploring ways to modernize the detector package using silicon photomultipliers (SiPMs) to increase the sensitivity of the experiment. The new configuration of the spectrometer is expected to improve systematic uncertainties; namely the 2 meter path the produced light must travel to reach the PMTs and the SiPMs’ quantum efficiency being a factor of 2 greater than the prior PMTs’. The subject of this paper is a prototype detector for evaluating the SiPMs as the only detectors present, the goal being to compare the position and energy resolution with that of the current spectrometer in use at UCNA.

The primary goal of this research was to investigate the effects associated with the application of magnetic fields to single electrodes.

<p> Compositionally asymmetric multiple quantum well (AMQW) lasers are used for the demonstration of the gain flattening coating functionality. The gain spectra of the lasers are extracted using a non-linear least square fitting method. An optimum facet reflectance spectrum is calculated for a chosen current. For manufacturability, a modified reflectance spectrum of the gain flattening coating is proposed, in order to achieve operation over a wider spectral range without the 'difficult' gap which was a region where lasing was difficult or impossible to achieve due to insufficient gains at these wavelengths. </p> <p> Silicon oxides films with high, medium, and low refractive indices fabricated in an inductively coupled plasma (ICP) enhanced chemical vapor deposition (CVD) system are chosen as the building blocks of the gain flattening coating. An 18-layer coating is designed by the insertion of needle-like refractive index variation with a few optimization methods applied to minimize the merit function. A laser bar holder is custom designed and fabricated. Experiments and modification on the laser bar holder are carried out for better performance. The 18-layer gain flattening coating is then fabricated in the ICPCVD system with an in-situ spectroscopic ellipsometric measurement. It is observed that the non-lasing gap has disappeared after the coating is applied. Without external feedback, the coated laser shows tuning over 85 nm with the central wavelength of 1593 nm, while the uncoated laser has a non-lasing gap of about 25 nm in the central region of the tuning range of 70 nm. </p> <p> Finally, the coherence length of a low coherent source synthesized from the gain flattening coated AMQW laser is measured by using Michelson interferometer. The highest depth resolution that can be achieved is measured as 40 μm. The power intensity of the synthesized low coherence light source from the gain flattening coated AMQW laser is rendered from the interferogram using fast Fourier transform (FFT). </p> / Thesis / Doctor of Philosophy (PhD)

<p> Various areas of studies on the natural and the prosthetic aortic valves are reviewed. </p> <p> A microtensile technique devised to investigate the inhomogeneous and anisotropic material properties of a porcine aortic valve's leaflets is described. Also, the theory and apparatus of a new stereophotogrammetric technique to define points in space by their Cartesian coordinates is introduced. The technique is used to investigate the local surface strains and curvatures of a porcine aortic valve's leaflets from 0 to 120 mm. Hg. in-vitro. </p> <p> It is found that the valve leaflets display marked inhomogeneity and anisotropy (orthotropy is assumed) in the elastic moduli and transition strains. For the non-coronary leaflet, the radial post-transition moduli vary from 42 to 215 gm/mm² with a mean of 111 gm/mm² (s.d. = 43 gm/mm²); and the radial transition strains vary from 30% to 70% with a mean of 58% (s.d. = 7%). Areas nearer the leaflet's coaptation edge tend to exhibit lower radial transition strains than the annulus edge. The central region of the leaflet is found to be the stiffest. For the same non-coronary leaflet, the circumferential post-transition moduli vary from 220 to 590 gm/mm² with a mean of 342 gm/mm² (s.d. = 118 gm/mm²); and the circumferential transition strains vary from 22% to 47% with a mean of 33% (s.d. = 3%). </p> <p> Inhomogeneity between leaflets is also observed; preliminary results seem to suggest that the non-coronary leaflet is the stiffest in the radial direction and the least stiff in the circumferential direction. In comparison, the right coronary leaflet exhibits the largest radial transition strains (~80% ) and the smallest circumferential transition strains (~25%). </p> <p> For the diastolic valve in-vitro, the circumferential strains are less than 10% at all pressures; therefore , this suggests pre-transition behaviour during diastole which is contrary to the general belief. Radial strains at diastole vary from 10% to well over 100% and show a definite tendency to increase from the sinus-annulus edge to the coaptation edge. The non-coronary leaflet is the least strained of the leaflets (10% to 60% at diastole). </p> <p> The determination of pre-or post-transition state at diastole is discussed and the implications of the results on stress analyses and trileaflet valve designs are noted. </p> / Thesis / Master of Engineering (ME)

Second project report of two. Part A is available at http://hdl.handle.net/11375/17551 / <p> The design, construction, and initial operation of an ultra high vacuum testing system was undertaken. The final UHV system is equipped with a residual gas analyser (RGA). </p> <p> The system was used to test a National Research Council of Canada magnetron pump-gauge. The pumping action of the device was adequate with speeds of litres/second for hydrogen and other chemically active species. A speed of ≃0.3 L/S was measured for methane (CH₄). The pressure measuring capabilities of this particular pump may be in question due to the presence of surface leakage currents. </p> / Thesis / Master of Engineering (ME)

One of two Project Reports / <p> This report describes the basic physical properties of surface wave devices and design procedures necessary to realize filter functions from such devices. The mathematical form of the surface wave is presented. Filter models based on this wave are reviewed and the strong relationship between device geometry and resultant transfer functions is developed. </p> <p> Design and experimental procedures adopted for the synthesis of a surface-wave filter used for colour T.V. I.F. strips are given. Two such filters are actually made in the laboratory and experimental-theoretical results are compared. Results obtained indicate good agreement between theory and experiment, and clearly demonstrate the superiority of surface wave filters over conventional L-C filters in high frequency applications. </p> / Thesis / Master of Engineering (ME)

One of two project reports. Part B can be found at: / No abstract was provided. / Thesis / Master of Engineering (ME)

One of two project reports. Part A can be found at: http://hdl.handle.net/11375/17866 / <p> It was observed that the spontaneous carrier lifetimes of GaAlAs injection lasers, as measured by the time delay method, exhibit a strong dependence on the DC bias current flowing through the laser. As the DC bias current is increased, the measured lifetimes decrease, passing through a minimum at bias currents less than 0.1 mA, and then rise again to an intermediate value at high bias currents. It was also found that the impedance of these lasers to fast current pulses drops sharply at the same DC bias currents as the minimum measured lifetime mentioned above. Evidence is presented to suggest that both of these effects are due to an electrical resonance between the stray drive circuit inductance and the DC bias dependent capacitance of the laser's junction under forward bias. </p> <p> In addition, two methods of determining the spontaneous carrier lifetime by other than the time delay method are described. One method involves measurement of the vector impedance of lasers to sinusoidal drive currents at frequencies less than 100 MHz, as a function of DC bias. The second method is based upon the frequency dependence of the phase shift between a sinusoidal drive current and the resulting spontaneous light. </p> / Thesis / Master of Engineering (ME)

One of two project reports. Part B can be found at: / Track-etch imaging is investigated as a recording method for neutron radiographic purposes. A theoretical model is formulated and evaluated together with experimental data which is analyzed in an attempt to explore the possibility of maximizing optical contrast. A central converter system with Lithium-6 as the converter and cellulose-nitrate as the recorders is used. It is found that the maximum contrast is achieved by using a clear cellulose-nitrate recorder at least 10 µm thick and a Lithium-6 converter of approximately 140 µm thickness. / Thesis / Master of Engineering (ME)

One of two project reports. Part B can be found at: / No abstract was provided. / Thesis / Master of Engineering (ME)