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Thesis. Recent theoretical developments have led to evermore refined theories for the Josephson effects in a variety of superconducting weak link'' structures. One of the major refinements has been the inclusion of the effects of intrinsic thermal fluctuations upon Josephson-like behavior. Some other developments include the investigation of mechanisms for the origin of the Josephson effects in non-tunneling structures, and equivalent circuit representations. Experimental investigations were made which encompass both of these areas; with special emphaais placed upon fluctuation effects; in pariicular, the effect of fluctuations upon the driven dc Josephson effect has been studied in considerable detail. The weak links studied included niobium point contacts, tin whisker'' crystals, and tin thin film bridges, the latter fabricated via an optical photoresist technique. The experiments were conducted in a temperature regime which extended to within a few mK of T/sub c/, the regime in which fluctuation effects are enhanced (and thus tnore experimentally accessible). The data consisted of relatively high resolution (ln V) low noise 1- -V characteristics obtained with an apparatus which incorporated ( plus or minus 10 mu K) temperature control with wide-band rf transmission, in a highly shielded environment. Experiniental rf-induced step pi-ofiles (the driven ac Josephsorin effect) …

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A numerical method is presented which is designed to solve the Navier- Stokes equations for two-dimensional, incompressible flow. The method is intended for use on problems with high Reynolds numbers for which calculations via finite difference methods have been unattainable or unreliable. The proposed scheme is a hybrid utilizing a time-splitting finite difference method in areas away from the boundaries. In areas neighboring the boundaries, the equations of motion are solved by the newly proposed vortex method by Chorin. The major accomplishment of the new scheme is that it contains a simple way for merging the two methods at the interface of the two subdomains. The proposed algorithm is designed for use on the time-dependent equations but can be used on steady state problems as well. The method is tested on the popular, time-independent, square cavity problem, an example of a separated flow with closed streamlines. Numerical results are presented for a Reynolds number of 10$sup 3$. (auth)

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Thesis. The heat capacity of the system (La,Ce)Al//sub 2/ for 0.0, 0.193, 0.64, and 0.906 at.% Ce has been measured between approximately 0.06 and 22 K and in magnetic fields up to 38 kOe. In the normal state, there is R1n2 entropy associated wtih the Ce spin system and this entropy is removed in the formation of the spin-compensated state. The nonmal state Kondo temperature is 0.42 K. The three more-dilute samples exhibit supenconductivity but cannot be described by the Bardeen - Cooper -- Schrieffer on Abrlkosov -Gor'kov theories. Significant low-energy excitations are evident in the superconducting state and they may be associated with quasibound states deep in the energy gap of the pure superconductor. Fon the 0.193 at.% Ce alloy in the superconducting state the characteristic temperature associated with Ce-spin ordering in the nonmal state is reduced by an estimated order of magnitude. For the 0.64 at.% Ce alloy a small, broadened superconducting anomaly appears in the heat capacity above 1 K, however, no anomaly that could be interpreted as a broadened discontinuity was found at the magnetically-detected transition back into the normal state at lower temperatures. The heat capacities of five samples of alpha -U have been measured …

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Thesis. Delayed neutron characteristics of six fission product nuclides were determined using a mass separator operated on-line with a nuclear reactor. Beta-decay half-lives were- measured using neutron multiscaling techniques for the precursors /sup 88/Br, /sup 89/Br, /sup 98/Kr, /sup 93/Kr, /sup 137/I, and / sup 138/I. The observed half-lives were 16.52 plus or minus .17 seconds, respectively.. Energy spectra were measured for delayed neutrons emitted in the beta-decays of /sup 17/N, /sup 137/I, /sup 93/Kr , and /sup 93/Rb. The spectra of neutron emissions in the mass 93 parentdaughter decay chain were observed using a moving tape collector to effect isobaric separation. Two different types of /sup 3/He- filled neutron spectrometer were used to determine the spectra; a proportional counter with risetime discrimination electronics, and a high resolution ionization chamber. The measured delayed, neutron spectra using both detector types are presented, and the results compared, where possible, with other reported measurements. (auth)

Thesis. The development of a directional high energy (20 to 160 MeV) neutron detector which was flown to satellite altitudes (500 km; circular equatorial orbit) in the NASA Orbiting Solar Observatory (OSO-6) in August 1969 is described. Both the angle of incidence and the energy of the neutron are determined by a proton-recoil telescope (Pilot B scintillation plastic) which provides the source for proton-recoils and defines the dE/dX versus E method for particle identification and energy determination. The telescope is embedded in a scintillation plastic guard counter envelope which eliminates the unwanted charged particle background as well as recoil protons (electrons) whose energies and direction do not satisfy neutron (gamma-ray) detection requirements, respectively. Results from a Monte Carlo calculation indicate that the overall average efficiency within an average angular acceptance of about 29 deg (FWHM) is approximately (2.25 plus or minus 0.113) x 10/sup -4/. The inflight calibration procedure, the main frame data bit error analysis, and the method for determining the orientation of the detector axis in the spacecraft spin plane are described. Results indicate a discrepancy in the measured (0.461 x 10/sup -2/ plus or minus 0.254 x 10/sup -2/ n/cm/sup 2/sec) and theoretical (2 to 70 n/cm/ …

The high-temperature internal friction of germanium and silicon, intrinsic and highly n-type, was measured as a function of temperature, frequency, dislocation density, and dopant concentration. Two features found in the internal-friction spectrum were investigated. At moderate temperatures in both materials, when not too highly doped, there appears a peak, the features of which are independent of dislocation density, due to the acousto-electric effect. The high-temperature dislocation-dependent damping in intrinsic and intrinsic- behaving germanium and silicon was found to agree well with most previous studies. If deformed at high temperature and allowed to anneal, highly doped, n-type material behaved intrinsically due to preferential precipitation at dislocations. if deformed at minimum temperatures and not allowed to anneal, a greatly enhanced dislocation-dependent internal friction was found that depended upon the extrinsic carrier concentration. (23 figures, 93 references) (DLC)

Thesis. Lithium fluoride crystals, with TlF added to the charge, were prepared by the Bridgman- Stockbarger method. The scintillation response to photon energies between 25 and 1250 keV for these crystals and a commercially prepared LiF (Ti) crystal was studied. The response of the LiF (Ti) crystal was compared to the response of an NE109 scintillator at 1250 keV. The dose response of the LiF (Ti) crystal was evaluated over the energy range 25 to 1250 keV. The absorption and emission spectra of the LiF (Ti) crystal are discussed. A historical review precedes the discussion. (auth)

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