22,073 Matching Results

Search Results

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

Diffusion Compton profondement virtuelle dans le Hall A au Jefferson Laboratory

Description: Generalized Parton Distributions (GPDs), introduced in the late 90s, provide a universal description of hadrons in terms of the underlying degrees of freedom of Quantum Chromodynamics: quarks and gluons. GPDs appear in a wide variety of hard exclusive reactions and the advent of high luminosity accelerator facilities has made the study of GPDs accessible to experiment. Deeply Virtual Compton Scattering (DVCS) is the golden process involving GPDs. The first dedicated DVCS experiment ran in the Hall A of Jefferson Lab in Fall 2004. An electromagnetic calorimeter and a plastic scintillator detector were constructed for this experiment, together with specific electronics and acquisition system. The experiment preparation, data taking and analysis are described in this document. Results on the absolute cross section difference for opposite beam helicities provide the first measurement of a linear combination of GPDs as a function of the momentum transfer to the nucleon.
Date: December 1, 2005
Creator: Camacho, Carlos Munoz
Partner: UNT Libraries Government Documents Department

Measurement of the Electric and Magnetic Elastic Structure Functions of the Deuteron at Large Momentum Transfers

Description: The deuteron elastic structure functions, A(Q{sup 2}) and B(Q{sup 2}), have been extracted from cross section measurements of elastic electron-deuteron scattering in coincidence using the Continuous Electron Beam Accelerator and Hall A Facilities of Jefferson Laboratory. Incident electrons were scattered off a high-power cryogenic deuterium target. Scattered electrons and recoil deuterons were detected in the two High Resolution Spectrometers of Hall A. A(Q{sup 2}) was extracted from forward angle cross section measurements in the squared four-momentum transfer range 0.684 ≤ Q{sup 2} ≤ 5.90 (GeV/c){sup 2}. B(Q{sup 2}) was determined by means of a Rosenbluth separation in the range 0.684 ≤ Q{sup 2} ≤ 1.325 (GeV/c){sup 2}. The data are compared to theoretical models based on the impulse approximation with the inclusion of meson-exchange currents and to predictions of quark dimensional scaling and perturbative quantum chromodynamics. The results are expected to provide insights into the transition from meson-nucleon to quark-gluon descriptions of the nuclear two-body system.
Date: October 1, 1999
Creator: Suleiman, Riad
Partner: UNT Libraries Government Documents Department

Measurement of the deuteron elastic structure functions at large momentum transfers

Description: The cross section for elastic electron-deuteron scattering has been measured using the Hall A Facility of Jefferson Laboratory. Scattered electrons and recoiling deuterons were detected in coincidence in the two 4 GeV/c High Resolution Spectrometers (HRS) of Hall A. The deuteron elastic structure functions A(Q{sup 2}) and B(Q{sup 2}) have been extracted from these data. Results for the measurement of A(Q{sup 2}) in the range of 0.7 ≤ Q{sup 2} ≤ 6.0 (GeV/c){sup 2} are reported. Results for the magnetic structure function, B(Q{sup 2}), are presented in the range of 0.7 ≤ Q{sup 2} ≤ 1.35 (GeV/c){sup 2}. The results for both structure functions are compared to predictions of meson-nucleon based models, both with and without the inclusion of meson-exchange currents. The A(Q{sup 2}) results are compared to predictions of the dimensional scaling quark model and perturbative quantum chromodynamics. The results can provide insights into the transition from meson-nucleon to quark-gluon descriptions of the nuclear two-body system.
Date: August 1, 1999
Creator: McCormick, Kathy
Partner: UNT Libraries Government Documents Department