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Finite difference solution of the time dependent neutron group diffusion equations

Description: In this thesis two unrelated topics of reactor physics are examined: the prompt jump approximation and alternating direction checkerboard methods. In the prompt jump approximation it is assumed that the prompt and delayed neutrons in a nuclear reactor may be described mathematically as being instantaneously in equilibrium with each other. This approximation is applied to the spatially dependent neutron diffusion theory reactor kinetics model. Alternating direction checkerboard methods are a family of finite difference alternating direction methods which may be used to solve the multigroup, multidimension, time-dependent neutron diffusion equations. The reactor mesh grid is not swept line by line or point by point as in implicit or explicit alternating direction methods; instead, the reactor mesh grid may be thought of as a checkerboard in which all the ''red squares'' and '' black squares'' are treated successively. Two members of this family of methods, the ADC and NSADC methods, are at least as good as other alternating direction methods. It has been found that the accuracy of implicit and explicit alternating direction methods can be greatly improved by the application of an exponential transformation. This transformation is incompatible with checkerboard methods. Therefore, a new formulation of the exponential transformation has been developed which is compatible with checkerboard methods and at least as good as the former transformation for other alternating direction methods. (auth)
Date: August 1, 1975
Creator: Hendricks, J.S. & Henry, A.F.
Partner: UNT Libraries Government Documents Department

High statistics study of omega$sup 0$ production at 6 GeV/c

Description: The spin-projected cross sections for $omega$$sup 0$ production at 6 GeV/ c were measured in a counter-spark chamber experiment at the Zero Gradient Synchrotron of Argonne National Laboratory. Results are presented for a sample of 25,000 $omega$$sup 0$ events, and critical tests are shown for any residual background. The reaction is dominated by the s-channel natural-parity helicity one projection (rho$sub 11$ + rho/sub 1-1) dsigma/dt which shows a turnover in the forward direction and no strong dip at t = 0.6 (GeV/c)$sup 2$. The unnatural- parity helicity-zero cross section rho$sub 00$ dsigma/dt shows no forward turnover suggesting a sizeable helicity-nonflip contribution. Comparisons are made with the predictions of a Regge exchange model with absorptive corrections. (auth)
Date: January 1, 1975
Creator: Shaevitz, M.H.
Partner: UNT Libraries Government Documents Department

Finite element method for neutron diffusion problems in hexagonal geometry

Description: The use of the finite element method for solving two-dimensional static neutron diffusion problems in hexagonal reactor configurations is considered. It is investigated as a possible alternative to the low-order finite difference method. Various piecewise polynomial spaces are examined for their use in hexagonal problems. The central questions which arise in the design of these spaces are the degree of incompleteness permissible and the advantages of using a low-order space fine-mesh approach over that of a high-order space coarse-mesh one. There is also the question of the degree of smoothness required. Two schemes for the construction of spaces are described and a number of specific spaces, constructed with the questions outlined above in mind, are presented. They range from a complete non-Lagrangian, non-Hermite quadratic space to an incomplete ninth order space. Results are presented for two-dimensional problems typical of a small high temperature gas-cooled reactor. From the results it is concluded that the space used should at least include the complete linear one. Complete spaces are to be preferred to totally incomplete ones. Once function continuity is imposed any additional degree of smoothness is of secondary importance. For flux shapes typical of the small high temperature gas-cooled reactor the linear space fine-mesh alternative is to be preferred to the perturbation quadratic space coarse-mesh one and the low-order finite difference method is to be preferred over both finite element schemes. (auth)
Date: June 1, 1975
Creator: Wei, T.Y.C. & Hansen, K.F.
Partner: UNT Libraries Government Documents Department

Nucleus--nucleus total cross sections for light nuclei at 1.55 and 2.89 GeV/ C/nucleon

Description: Total cross sections have been measured for protons, deuterons, alphas, and $sup 12$C on hydrogen, deuterium, helium, and carbon targets at 1.55 and 2.89 GeV/c/nucleon using the ''good geometry'' transmission method. In addition, the inelastic cross sections and elastic slope parameters were measured for reactions initiated by deuterons, alphas, and $sup 12$C. The factorization relation sigma/ sub T/(AA) = sigma/sub T/(AB)$sup 2$/sigma/sub T/(BB) is violated for some of these reactions. The results generally agree with Glauber theory predictions except in their detailed energy behavior. It is found that sigma/sub T/ approximately equal to 144 (A/sub T//sup $sup 1$/$sub 3$/ + A/sub P//sup $sup 1$/ $sub 3$/ - 1.48)$sup 2$ and sigma/sub IN/ approximately equal to 78 (A/sub T//sup $sup 1$/$sub 3$/ + A/sub P//sup $sup 1$/$sub 3$/ - 1.25)$sup 2$, where A/sub T/(A/ sub P/) is the atomic mass number of the target (projectile) and the cross sections are given in mb. (auth)
Date: November 1, 1975
Creator: Jaros, J.A.
Partner: UNT Libraries Government Documents Department

Influence of microstructure on stress corrosion cracking of mild steel in synthetic caustic-nitrate nuclear waste solution

Description: The influence of alloy microstructure on stress corrosion cracking of mild steel in caustic-nitrate synthetic nuclear waste solutions was studied. An evaluation was made of the effect of heat treatment on a representative material (ASTM A 516 Grade 70) used in the construction of high activity radioactive waste storage tanks at Savannah River Plant. Several different microstructures were tested for susceptibility to stress corrosion cracking. Precracked fracture specimens loaded in either constant load or constant crack opening displacement were exposed to a variety of caustic-nitrate and nitrate solutions. Results were correlated with the mechanical and corrosion properties of the microstructures. Crack velocity and crack arrest stress intensity were found to be related to the yield strength of the steel microstructures. Fractographic evidence indicated pH depletion and corrosive crack tip chemistry conditions even in highly caustic solutions. Experimental results were compatible with crack growth by a strain- assisted anodic dissolution mechanism; however, hydrogen embrittlement also was considered possible. (auth)
Date: December 1, 1975
Creator: Sarafian, P.G.
Partner: UNT Libraries Government Documents Department

Oxygen potential of uranium--plutonium oxide as determined by controlled- atmosphere thermogravimetry

Description: The oxygen-to-metal atom ratio, or O/M, of solid solution uranium- plutonium oxide reactor fuel is a measure of the concentration of crystal defects in the oxide which affect many fuel properties, particularly, fuel oxygen potential. Fabrication of a high-temperature oxygen electrode, employing an electro-active tip of oxygen-deficient solid-state electrolyte, intended to confirm gaseous oxygen potentials is described. Uranium oxide and plutonium oxide O/M reference materials were prepared by in situ oxidation of high purity metals in the thermobalance. A solid solution uranium-plutonium oxide O/M reference material was prepared by alloying the uranium and plutonium metals in a yttrium oxide crucible at 1200$sup 0$C and oxidizing with moist He at 250$sup 0$C. The individual and solid solution oxides were isothermally equilibrated with controlled oxygen potentials between 800 and 1300$sup 0$C and the equilibrated O/ M ratios calculated with corrections for impurities and buoyancy effects. Use of a reference oxygen potential of -100 kcal/mol to produce an O/M of 2.000 is confirmed by these results. However, because of the lengthy equilibration times required for all oxides, use of the O/M reference materials rather than a reference oxygen potential is recommended for O/M analysis methods calibrations. (auth)
Date: October 1, 1975
Creator: Swanson, G.C.
Partner: UNT Libraries Government Documents Department

CARBON-13 NMR STUDIES OF LIQUID CRYSTALS

Description: High resolution, proton decoupled {sup 13}C nmr are observed for a series of neat nematic liquid crystals, the p-alkoxyazoxybenzenes, and a smectic-A liquid crystal, diethylazoxydibenzoate in a magnetic field of 23 kG. The (uniaxial) order parameters S = <P{sub 2}(cos{theta})> are found to be about 0.4 and 0.9 for the nematic and smectic-A phase respectively at the clearing points. The order parameter increases with decreasing temperature in the nematic phase but is constant, or nearly so, with temperature in the smectic-A phase. In the nematic series studied, the ordering exhibits an even-odd alternation along the series and qualitative agreement with a recent theory due to Marcelja is found. In both phases, the spectra show that the molecule rotates rapidly about its long axis. Tentative conclusions about molecular conformational motion and {sup 14}N spin relaxation are presented for both nematic and smectic-A phases. In the smectic-A phase, the sample is rotated about an axis perpendicular to H{sub 0} and the resulting spectra are discussed. The theory of observed chemical shifts in liquid crystals is treated in an appendix. Equations are derived which relate the nmr spectra of liquid-crystals to the order parameters. A model for the smectic-C phase due to Luz and Meiboom and Doane is described and lineshapes are determined on the basis of this model for special cases. Experiments on smectic-C liquid crystals are currently underway for comparison with the theory. Also treated in an appendix is the dependence of the order parameters on the molecular potential which give rise to the various degrees of order in the different liquid crystalline phases. To a good approximation the functional dependence of the order parameters on the molecular potential is shown to be a simple one in the limit of small tilt angle in the smectic-C phase.
Date: June 1, 1975
Creator: Allison, Stuart
Partner: UNT Libraries Government Documents Department

Theoretical studies of some nonlinear laser-plasma interactions

Description: The nonlinear coupling of intense, monochromatic, electromagnetic radiation with plasma is considered in a number of special cases. The first part of the thesis serves as an introduction to three-wave interactions. A general formulation of the stimulated scattering of transverse waves by longitudinal modes in a warm, unmagnetized, uniform plasma is constructed. A general dispersion relation is derived that describes Raman and Brillouin scattering, modulational instability, and induced Thomson scattering. Raman scattering (the scattering of a photon into another photon and an electron plasma wave) is investigated as a possible plasma heating scheme. Analytic theory complemented by computer simulation is presented describing the nonlinear mode coupling of laser light with small and large amplitude, resonantly excited electron plasma waves. The simulated scattering of a coherent electromagnetic wave by low frequency density perturbations in homogeneous plasma is discussed. A composite picture of the linear dispersion relations for filamentation and Brillouin scattering is constructed. The absolute instability of Brillouin weak and strong coupling by analytic and numerical means is described. (auth)
Date: August 15, 1975
Creator: Cohen, B.I.
Partner: UNT Libraries Government Documents Department

Thermodynamic and kinetic studies of some Group III and Group V elements and alloys by solid state electrochemical techniques

Description: The Gibbs free energy of forming gallium sesquioxide and indium sesquioxide are measured using a CO$sub 2$--CO--O$sub 2$ gas reference electrode and calcia stabilized zirconia as the solid electrolyte. The free energies are: $delta$G$sup 0$/sub f/($beta$-Ga$sub 2$O$sub 3$(c)) equals -(265,309 +- 152) + (82.47 +- 0.16) (T/K) cal mol$sup -1$ and $delta$G$sup 0$/sub f/(In$sub 2$O$sub 3$ (c)) equals -(223,160 +- 137) + (79.47 +- 0.12) (T/K) cal mol$sup -$.$sup 1$ A solid state galvanic cell is employed to measure gallium activities in Ga--Sb liquid alloys. Results show moderate negative deviations from ideality in the composition range 0.039 less than x/sub Ga/ less than 0.833. Partial molar enthalpies and entropies are calculated, and agree wih calorimetric data. Results are combined with calorimetric data to calculate the liquidus temperatures of the Ga--Sb system, which are in excellent agreement with measurements. Effect of short-range ordering is also investigated. Coulometric titration techniques are used to investigate the solubility and diffusivity of oxygen in liquid indium. Dissolved atomic oxygen is found to follow Henry's law and a saturation solubility of x$sub 0$/sup sat/ equals 3.3 x 10$sup -3$ is determined at 908$sup 0$K. From a galvanostatic response of an indium electrode, an oxygen diffusivity of 2.2 x 10$sup -6$ cm$sup 2$ s$sup -1$ is found, in good agreement with other available data. (LK)
Date: October 1, 1975
Creator: Anderson, T.J.
Partner: UNT Libraries Government Documents Department

Strong turbulence and the anomalous length of stored particle beams

Description: A theoretical analysis is made of the longitudinal stability of intense beams of charged particles in high energy storage rings. The effect of externally applied radiofrequency fields, i.e., synchrotron oscillations, is included. For electron and positron beams, the damping and quantum excitation due to particle radiation are also included. A criterion for the stability of small longitudinal plasma oscillations is derived and used to obtain the stable size of intense stored beams of electrons and positrons. (auth)
Date: November 1, 1975
Creator: Channell, P.J.
Partner: UNT Libraries Government Documents Department

Observation of the submillimeter cosmic background spectrum

Description: An experimental measurement of the spectrum of the submillimeter cosmic background radiation is described. The experiment consists of measuring the night sky emission at an altitude of 39 km, correcting for the atmospheric molecular line emission, and placing limits on the contamination from sources of continuum radiation such as the apparatus itself and the earth. The observations were made on 24 July 1974 using a fully calibrated liquid-helium-cooled balloon- borne spectrophotometer. Important features of the apparatus include a cooled antenna, a polarizing interferometer, and a germanium bolometric detector. The characterization of the spectrophotometer includes the large angle response and emission of the antenna. The calibration of the instrument and corrections to the observed sky spectrum are based on measurements made during the flight. A simple model of the molecular line emission is used to determine the atmospheric contribution. The resulting spectrum covers the frequency range from 4 to 17 cm$sup -1$ and establishes that the cosmic background radiation follows the high frequency quantum cutoff for a 3K blackbody. A blackbody temperature of 2.99/sub -.$sub 14$/$sup +$.$sup 07$/K is deduced from our data. The present status of the cosmic background observations, which span more than three decades in frequency, is analyzed and it is concluded that they are all consistent with a blackbody temperature of 2.90 +- .04K (+- 1 SIGMA). This firmly supports the Big Bang cosmological model of the universe. (auth)
Date: November 13, 1975
Creator: Woody, D.P.
Partner: UNT Libraries Government Documents Department

Quantum electrodynamics with the spear magnetic detector

Description: One makes a study of quantum electrodynamic processes which are present at the SPEAR colliding beam magnetic detector. We begin by describing the experiment performed by the SLAC-LBL collaboration and the results concerning the strong interaction. Then the interactions e$sup +$e$sup -$ $Yields$ e$sup +$e$sup -$ and e$sup +$e$sup -$ $Yields$ $mu$$sup +$$mu$$sup -$ are considered along with their third-order radiative corrections. These events, previously used to determine new limits for cutoff parameters in QED breakdown models, are further studied to show that the full distribution in coplanarity angle fits the theoretical prediction well. The major focus is on the fourth order two-photon process, e$sup +$e$sup -$ $Yields$ e$sup +$e$sup -$A$sup +$A$sup -$, which only recently has been realized to be significant in such experiments. Cross sections are derived and calculated exactly for this process and the results compared to a Weizacker-Williams equivalent photon calculation. The two-photon data are then isolated and fit to the calculation. A special experiment was done where the small-angle scattered electron or positron is ''tagged'' along with particles in the main detector. Cross sections and coplanarity distributions are measured and compared to calculation. Through these studies, one feels confident that one understand the nature of the two-photon process in the detector. One further explores the hadronic physics of the two-photon process, e$sup +$e$sup -$ $Yields$ e$sup +$e$sup -$ hadrons, measuring pion cross sections, searching for resonances, and discussing future experiments. (auth)
Date: September 1, 1975
Creator: Zipse, J.E.
Partner: UNT Libraries Government Documents Department

Vibrational inelasticity in H$sub 2$ collisions with He and Li$sup +$

Description: The partially averaged version of classical S-matrix theory was applied to three-dimensional collisions of H$sub 2$ with He and Li$sup +$. For H$sub 2$- Li$sup +$, cross-sections for the de-excitation of H$sub 2$ from (n$sub 1$,j$sub 1$) = (1,0) to the ground vibrational manifold were computed at a total energy of 1.2 eV and compared to previously done coupled channel calculations of Schaefer and Lester. The agreement is very good. For H$sub 2$-He, the Kutzelnigg- Tsapline interaction potential was extended to small atom-diatom separations, the ab initio points were then fit to an analytic form, and cross sections for the de- excitation of H$sub 2$ from the states (n$sub 1$,j$sub 1$), n$sub 1$ = 1, j$sub 1$ = 0,2,4 to the ground vibrational manifold were computed at total energies of .9, 1.1, 1.3 and 1.5 eV. For comparison, coupled channel calculations were also performed on the system at the same energies. The agreement was poorer than in the H$sub 2$-Li$sup +$ case, for identifiable reasons. The cross sections were used to compute rate constants and relaxation times for the H$sub 2$-He system. Comparison of these results with the results of experiment and of other calculations shows good agreement, certainly within the expected errors. (7 figs., 30 refs., 3 tables) (auth)
Date: September 1, 1975
Creator: Raczkowski, A.W.
Partner: UNT Libraries Government Documents Department

Mass measurements of highly neutron-excess nuclei in the light elements

Description: The $sup 26$Mg($sup 7$Li,$sup 8$B)$sup 25$Ne reaction at 78.9 MeV was used to measure the mass-excess of $sup 25$Ne (-2.18 +- 0.10 MeV) and several low- lying excited states. Mass-excesses for $sup 43$Ar (-31.98 +- 0.07 MeV), $sup 45$Ar (-29.727 +- 0.06 MeV), and $sup 46$Ar (-29.732 +- 0.07 MeV) were determined from the $sup 48$Ca($alpha$,$sup 9$,$sup 7$Be)$sup 43$,$sup 45$Ar reactions at 77.7 MeV and the $sup 48$Ca($sup 6$Li,$sup 8$B)$sup 46$Ar reaction at 80.1 MeV. Several excited states of $sup 43$Ar and $sup 45$Ar were observed. These and the excited states of $sup 25$Ne are compared with theoretical predictions. Ground state differential cross sections are given for all reactions, ranging from 0.1 to 1 $mu$b/sr at forward angles. Upper limits of about 1 to 25 nb/sr were determined for the ground state cross sections of the reactions $sup 48$Ca($alpha$,$sup 8$,$sup 10$,$sup 11$B)$sup 44$,$sup 42$,$sup 41$Cl and $sup 48$Ca($alpha$,$sup 10$-$sup 13$C)$sup 42$-$sup 39$S at 110 MeV. Recoil coincidence techniques were used to measure the mass-excess of the particle- unbound nucleus $sup 10$Li(33.83 +- 0.25 MeV) by the $sup 9$Be($sup 9$Be,$sup 8$B)$sup 10$Li reaction at 121 MeV; the ground state cross section was 30 nb/sr. The $sup 14$C($sup 9$Be,$sup 8$B)$sup 15$B reaction at 120 MeV was also investigated using coincidence techniques. Contamination problems only permitted determining a ground state cross section upper limit of 50 nb/sr. A simple mass relation is derived, similar in approach to the Garvey-Kelson method but taking more explicit account of shell effects. Comparison is made with the Garvey- Kelson relation, and predictions of masses and of the stability of neutron-excess light nuclei are given for both methods. The modified mass relation is shown to offer better account for highly neutron-excess nuclei, including the values reported here for $sup 25$Ne and $sup 43$,$sup 45$,$sup 46$Ar. (26 figures, 2 ...
Date: May 1, 1975
Creator: Wilcox, K.H.
Partner: UNT Libraries Government Documents Department

Measurement of the $pi$$sup -$p $Yields$ $pi$$sup 0$n and $pi$$sup -$p $Yields$ eta n differential cross sections at beam momenta from 20 to 200 GeV/c

Description: The results of a measurement of the $pi$$sup -$p $Yields$ $pi$$sup 0$n and $pi$$sup -$p $Yields$ eta n differential cross sections at six pion beam momenta from 20 to 200 GeV/c are presented. The data for these cross sections were collected at the Fermi National Accelerator Laboratory in Batavia, Illinois. A 73.5 x 73.5 cm lead--scintillator hodoscope was used to detect the two photons from the decay of the $pi$$sup 0$ and the eta; all other reactions were eliminated by detection of their charged particles and additional photons in an array of veto counters. The zero-degree charge exchange cross sections determined from these measurements are shown to be consistent with the measured $pi$$sup +$p and $pi$$sup -$p total cross section differences. Effective Regge trajectories for the rho and the A$sub 2$ also extracted from the data. 34 figures, 9 tables. (auth)
Date: November 1, 1975
Creator: Johnson, R.A.
Partner: UNT Libraries Government Documents Department

Molecular beam kinetics

Description: The design of a crossed molecular beam ''supermachine'' for neutral-- neutral collisions is discussed. The universal electron bombardment ionizer, mass filter, and ion detection system of the detector, the supersonic nozzle sources, the differential pumping arrangement for the sources and detector, the time-of-flight detection of scattered products, and the overall configuration of the apparatus are described. The elastic scattering of two systems, CH$sub 4$ + Ar and NH$sub 3$ + Ar, has been measured using the supermachine with two supersonic nozzle sources. The rainbow structure and the interference oscillations are seen in each system. The best fit to the data was found using a Morse--Spline--Van der Waals (MSV) potential. The three potential parameters epsilon, r/sub m/, and $beta$ were found to be 2.20(+-0.04) x 10$sup -14$ ergs, 3.82(+-0.04)A, and 7.05 +- 0.20 for CH$sub 4$ + Ar, and 2.21(+-0.04) x 10$sup - 14$ ergs 3.93 (+-0.05)A, and 8.45 +- 0.30 for NH$sub 3$ + Ar. A new phenomenon in crossed molecular beams of condensation of a molecule on a cluster to form a complex was observed. A bromine molecule condensed on clusters of chlorine (Cl$sub 2$)/sub chi/ and ammonia (NH$sub 3$)/sub chi/. The value of chi for measurements in these experiments ranges from 7 to 40 for chlorine clusters and from 10 to 70 ammonia clusters. (auth)
Date: November 1, 1975
Creator: Behrens, R. Jr.
Partner: UNT Libraries Government Documents Department