Dissertation discussing the results of experiments to study the behavior of superconductors under light illumination.

In Chapter I we present the results on a study of cross polarization dynamics, between protons and carbon-13 in adamantane, by the direct observation of the dilute, carbon-13, spins. These dynamics are an important consideration in the efficiency of proton enhancement double-resonance techniques and they also provide good experimental models for statistical theories of cross relaxation. In order to test these theories we present a comparison of the experimental and theoretical proton dipolar fluctuation correlation time {tau}{sub c}, which is experimentally 110 {+-} 15 {micro}sec and theoretically 122 {micro}sec for adamantane. These double resonance considerations provide the background for extensions to deuterium and double quantum effects discussed in Chapter II. In Chapter II an approach to high resolution nmr of deuterium in solids is described. The m = 1 {yields} -1 transition is excited by a double quantum process and the decay of coherence Q({tau}) is monitored. Fourier transformation yields a deuterium spectrum devoid of quadrupole splittings and broadening. If the deuterium nuclei are dilute and the protons are spin decoupled, the double-quantum spectrum is a high resolution one and yields information on the deuterium chemical shifts {Delta}{omega}. The relationship Q({tau}) {approx} cos 2{Delta}{omega}{tau} is checked and the technique is …

Experimental studies have been carried out in which the A15 phase of the Nb-Al-Ge system has been synthesized in the form of thin filaments contained in form rolled wires. A powder metallurgy approach has been used to achieve controlled porosity in compacts of sintered niobium powder. Infiltration with an aluminum-germanium eutectic alloy followed by mechanical deformation has produced small interconnected filaments embedded in the Nb matrix. Diffusion heat treatment for a short time transforms them into the A15 superconducting compound with a size range of 1-5 microns at 1300/sup 0/C and 1-9 microns at 1750/sup 0/C. The superconducting properties T/sub c/ and J/sub c/ were evaluated for samples subjected to different condition of time and temperature. The influence of certain parameters involved in the process has been investigated. The microstructure and microhardness of the Al-Ge eutectic alloy cooled at high and low cooling rates from temperatures between 900-400/sup 0/C have been evaluated. Optical and electron beam metallographic results are presented for the analysis of the different phases and relative compositions. The critical temperature measured inductively is between 16.4/sup 0/K and 18.1/sup 0/K depending on the heat treatment. The critical current density as a function of the applied magnetic field is …

The investigation of two poorly understood but technologically important physical properties of silicate glasses and related materials is described. The use of Electron Paramagnetic Resonance to investigate the nature of radiation-induced damage in glasses exposed to a variety of high-energy radiation sources is discussed first. Second, the measurement of the nonlinear index of refraction coefficient in a variety of optical materials related to the design of high-power laser systems is described. The radiation damage investigations rely heavily on the comparison of experimental results for different experimental situations. The comparison of EPR lineshapes, absolute spin densities and power saturation behavior is used to probe a variety of microscopic and macroscopic aspects of radiation damage in glasses. Comparison of radiation damage associated with exposure to gamma rays and fast neutrons (and combinations thereof) are interpreted in terms of the microscopic damage mechanisms which are expected to be associated with the specific radiations. Comparison of radiation damage behavior in different types of glasses is also interpreted in terms of the behavior expected for the specific materials. The body of data which is generated is found to be internally self-consistent and is also generally consistent with the radiation damage behavior expected for specific situations. …

A method is developed to optimize the separated-pair independent particle (SPIP) wave function; it is a special case of the separated-pair theory obtained by using two-term natural expansions of the geminals. The orbitals are optimized by a theory based on the generalized Brillouin theorem and iterative configuration interaction (CI) calculations in the space of the SPIP function and its single excitations. The geminal expansion coefficients are optimized by serial 2 x 2 CI calculations. Formulas are derived for the matrix elements. An algorithm to implement the method is presented, and the work needed to evaluate the molecular integrals is discussed. (auth)

Commercial secondary hardening steel, VASCO MA, has been subjected to modified heat treatments to introduce mixed microstructures of martensite and lower bainite. Dilatometry, tensile testing, hardness measurements and slow-bend testing have been carried out and the mechanical properties obtained have been correlated to microstructure using scanning electron microscopy and metallography. Duplex microstructures containing small amounts of lower bainite are found to show an increased toughness (at similar strength levels) on tempering in the secondary hardening range, as compared to initially fully martensitic microstructures. As the percentage of lower bainite in the duplex microstructures is increased, the secondary hardening peak is found to attenuate. The effect of different austenitization treatments on the secondary hardening behavior, has also been studied. Thermal cycling (for grain refinement) at lower austenitization temperatures is found to reprecipitate out carbon, which has been taken into solution in earlier high temperature austenitization, thereby leading to a significant depletion in the strength of this secondary hardening steel. Alloy carbides, in the secondary hardening stage, have also been analyzed using energy dispersive analysis of x-rays.

The (/sup 6/Li,/sup 8/B) reaction has been investigated on targets of /sup 26/Mg, /sup 24/Mg, /sup 16/O, /sup 13/C, /sup 12/C, /sup 11/B, /sup 10/B, and /sup 9/Be at a bombarding energy of 80.0 MeV, and on targets of /sup 16/O, /sup 12/C, /sup 9/Be, /sup 7/Li, and /sup 6/Li at a bombarding energy of 93.3 MeV. Only levels consistent with direct, single-step two-proton pickup reaction mechanisms were observed to be strongly populated. On T/sub z/ = 0 targets, the spectroscopic selectivity of this reaction resembles that of the analogous (p,t) reaction. Additionally, these data demonstrate the dominance of spatially symmetric transfer of the two protons. On T/sub z/ greater than 0 targets the (/sup 6/Li,/sup 8/B) reaction was employed to locate two previously unreported levels (at 7.47 +- 0.05 MeV and 8.86 +- 0.07 MeV) in the T/sub z/ = 2 nuclide /sup 24/Ne and to establish the low-lying 1p-shell states in the T/sub z/ = /sup 3///sub 2/ nuclei /sup 11/Be, /sup 9/Li, and /sup 7/He. However, no evidence was seen for any narrow levels in the T/sub z/ = /sup 3///sub 2/ nuclide /sup 5/H nor for any narrow excited states in /sup 7/He. The angular distributions …

Tracer self-diffusion coefficients were measured as functions of temperature and deviations from stoichiometry. The arc-transfer technique of crystal growth was found to produce crystal of Co/sub 1-x/O of essentially the same purity as the starting Co rod, and the quality was comparable to commercially available crystals grown by Verneuil process. Measurements at x = 0.005 in Co/sub 1-x/O showed the Co tracer self-diffusion coefficient to be D = 3.88 x 10$sup -4$ exp (--31600 +- 2400/RT) cm$sup 2$/s between 1037 and 1350$sup 0$C. This activation energy is in agreement with measurements made in air, if proper compensation is made for the effect of variation in stoichiometry. Measurements on crystals having deviations between 0.002 and 0.008 at 1150$sup 0$C showed the diffusion coefficient to depend on p/sub O$sub 2$/ as D = 9.74 x 10$sup -9$ p/sub O$sub 2$//sup 1/(3.59)/ cm$sup 2$/s, where p/sub O$sub 2$/ varied between 10$sup -2$.$sup 5$ and 10$sup -0$.$sup 25$ atm. Comparison with thermogravimetric and electrical conductivity measurements confirms that the defects responsible for Co diffusion in the range of temperature and p/sub O$sub 2$/ of this investigation are singly ionized cobalt vacancies. The Co tracer self-diffusion coefficients in single crystals are nearly identical to those …

A vector meson dominance model of the electromagnetic form factors of hadrons is developed which is based on the use of unstable particle propagators. Least-square fits are made to the proton, neutron, pion and kaon form factor data in both the space and time-like regions. A good fit to the low-energy nucleon form factor data is obtained using only rho, $omega$, and phi dominance, and leads to a determination of the vector meson resonance parameters in good agreement with experiment. The nucleon-vector meson coupling constants obey simple sum rules indicating that there exists no hard core contribution to the form factors within theoretical uncertainties. The prediction for the electromagnetic radii of the proton is in reasonable agreement with recent experiments. The pion and kaon charge form factors as deduced from the nucleon form factors assuming vector meson universality are compared to the data. The pion form factor agrees with the data in both the space and time-like regions. The pion charge radius is in agreement with the recent Dubna result, but the isovector P-wave pion-pion phase shift calculated from the theory disagrees with experiment. A possible contribution to the form factors from a heavy rho meson is also evaluated. (auth)

The neutron detection efficiency is a parameter required in the measurement of reactivity by the modified source technique. The direct solution of the detection efficiency at a perturbed state is costly. To solve for this, a particular variational functional, the Lewins' type variational functional, is presented. The functional is a ratio of two other functionals, each dealing with a reaction rate. The evaluation of this particular functional was done by treating the numerator and the denominator functionals separately. This leads to three flux equations, one for forward flux, and two for adjoint fluxes. The advantages of this formulation over, and the equivalence of this formulation to, the conventional functional presented in the literature are described in detail. The flexibility of the proposed functional is demonstrated by using it to estimate the detection efficiency with four different methods: variational interpolation, conventional variational, variational extrapolation, and multi- reference-state variational. Results are presented for one-dimensional and two- dimensional problems. All results are compared with direct calculations. In all cases, the results show that the variational interpolational method and the multi- reference-state variational method are efficient and practically acceptable.

A method for obtaining solutions to the time-independent Boltzmann neutron transport equation on triangular grids with nonorthogonal boundaries and anisotropic scattering is developed. A functional is obtained from the canonical form of the multigroup transport equation. The angular variable is then removed by expanding the functional in spherical harmonics, retaining only the first two moments and limiting the anisotropic scattering to be linear. The finite element method is then implemented by using quadratic Lagrange-type interpolating polynomials to span the spatial domain. The resultant set of coupled linear equations is then solved iteratively. The applicability of convergence acceleration techniques developed for the finite difference method is tested and implemented where appropriate. Finally, a number of numerical experiments are performed to evaluate the performance of the proposed method. The results are compared to results obtained by various established methods. In all cases, agreement is excellent. 16 figures, 7 tables. (auth)

Results of studies on the stoichiometry, structure, vaporization behavior, and thermodynamic properties of the Sc--S system are reported. The thermodynamic results for the stability of ScS(s) are compared with reported results for other transition-metal and rare-earth monosulfides. Various models are discussed in regard to their ability to describe the bonding in these refractory solids. (JRD)

The reactions pp $Yields$ pp $pi$$sup +$pi$sup -$ and pp $Yields$ pp$pi$$sup +$$pi$$sup -$$pi$$sup +$$pi$$sup -$ at 200 and 300 GeV/c were investigated using the Fermilab 30-inch hydrogen bubble chamber and downstream wide-gap spark chambers. This analysis is based upon approximately 9500 4- pronged and 6-pronged events. The cross sections were consistent with pomeron dominance for these reactions. The final state pp $pi$$sup +$$pi$$sup -$ is dominated by single diffractive dissociation, whose features are quite similar to those observed at low energy. A strong signal for double excitation was seen in the pp $pi$$sup +$$pi$$sup -$$pi$$sup +$$pi$$sup -$ final state and pomeron factorization was found to be satisfied. In the pp $pi$$sup +$$pi$$sup -$ final state, 66 events passed the criterion of double pomeron exchange defined by D. M. Chew. However, these events were found to be severely contaminated by diffractive events. The two-particle exclusive azimuthal correlations agreed well with the prediction of a photostatistical model. (auth)

Using new experimental techniques, the spectra of $gamma$-rays from the capture of neutrons by $sup 181$Ta were measured at the Livermore 100-MeV linac for neutrons from 2 eV to 9 x 10$sup 4$ eV with a (Ge(Li)-NaI) three-crystal spectrometer. Individual primary $gamma$-ray lines were resolved to 1778-keV excitation in $sup 182$Ta. Neutron resonances were resolved to 200-eV neutron energy. Data analysis techniques and codes were developed to extract positions and intensities of resolved transitions from the large data matrices accumulated in this experiment. Techniques were developed to unfold the unresolved $gamma$- ray spectra using the simple response of the three-crystal spectrometer. The resolved transition data were used to place 110 states with spin and parity assignments in the $sup 182$Ta level diagram below 1780-keV excitation. A set of 1240 E1 transition strengths were analyzed to extract 1.38 +- 0.11 degrees of freedom for the most likely chisquared fit to the distribution of widths. The E1 strength function was extracted for E/sub gamma/ = 4 to 6 MeV and compared with previous results. The $gamma$-ray spectra for E/sub gamma/ = 1.5 to 6.1 MeV were unfolded for neutron energy groups between 20 and 9 x 10$sup 4$ eV. Below 5-MeV $gamma$-ray …

A study of the gamma-ray de-excitation following the beta decays of $sup 93$Kr, $sup 93$Rb, and $sup 93$Sr using the TRISTAN on-line separator facility is reported. Gamma-ray singles and gamma-gamma coincidence measurements were made using Ge(Li) detectors. Of the 162 gamma rays observed in the decay of $sup 93$Sr, 143, representing more than 99 percent of the total gamma-ray intensity observed, were placed in a level scheme containing 36 levels. For the decay of $sup 93$Rb, 243 gamma rays were observed, of which 231 are placed in a level scheme consisting of 74 levels. This again represents a placement of over 99 percent of the total gamma-ray intensity measured. In the case of the $sup 93$Kr decay approximately 98.5 percent of the observed gamma-ray intensity has been accounted for by the proposed level scheme. This results from the placement of 203 of the 217 gamma rays assigned to this decay in a level scheme comprising 56 levels. Beta-branching for these decays were determined from transition intensity balances. Spin and parity assignments were proposed, whenever possible, on the basis of gamma-ray transition probabilities and deduced log ft values. A comparison is made with the available reaction data for the $sup 93$Y …

A high-pressure liquid-phase microreactor was developed to determine the kinetics and reaction networks of catalytic hydrodesulfurization and hydrodenitrogenation of polynuclear aromatic compounds found in coal-derived liquids. This reactor permits the use of small quantities of reactants and catalyst. This reactor design is expected to be useful generally and is not limited to hydroprocessing. The microreactor was designed to operate entirely in the liquid phase. The hydrogen required for the hydrogenation reactions is dissolved into the liquid phase before entering the reactor. A high total pressure is kept on the system, and no gas phase is ever permitted. Further, the system was designed to allow either the pulse or steady-state mode of operation. The specific design criteria were: hydrogen saturation pressure 0-61 atm, total pressure 0-272 atm, reactor temperatures up to 450/sup 0/C and space velocities between 1 and 10 (1/hr). The equipment has been operated at 21 atm hydrogen pressure and 104 atm total pressure over a range of temperatures and flow rates. A four-day test was conducted at steady-state conditions. The results indicate a significant break-in period for fresh catalyst.

The primary emphasis of this thesis involves an investigation of techniques for the control and modulation of x-ray radiation through acoustic perturbation of solids. The use of x-ray diffraction and x-ray optical techniques for the study of acoustic fields and atomic motion was also investigated. Analysis of the basic properties of x-ray propagation in solids reveals that practical methods for x-ray control or modulation must involve changes in the spatial configuration of x-ray scatterers. Numerical methods for the study of x-ray propagation in acoustically perturbated crystals are formulated. In developing these methods special emphasis has been placed on Borrmann transmission in thick crystals. Modulation and shuttering (on a micro-second timescale) of x-rays are experimentally demonstrated. A quantitative investigation of the basic interactions used to produce modulation and shuttering is presented. Agreement between the experimental observations and the theoretical predictions is within experimental error. An analytical investigation of the basic potential and limitations of x-ray modulation shuttering and control devices is presented. Basic design criteria for x-ray modulation devices is formulated and applied to practical configurations.