Theory of ordering transformations in metals and minerals (open access)

Theory of ordering transformations in metals and minerals

This dissertation presents an investigation of ordering in FCC based systems using the pair potential approximation in the ground state and mean field limits. The theoretical approach is used to explain the occurrence of observed equilibrium phases and characteristics of thermodynamic instabilities, in particular, spinodal ordering and decomposition. It is shown that the stability of non-integer domain sizes in long period superstructures such as Al{sub 3}Ti and Ag{sub 3}Mg may result from the tendency of a system to reduce the number of non-dominant ordering waves, thus producing domain sizes that have rational fraction form n/m. This conclusion is used to explain the domain size stability with respect to variations in temperature and electron concentration. The cation ordering in the precipitate phases in calcite and dolomite is analyzed by analogy with ordering in FCC based metals. The ordered phases in calcite and dolomite are shown to be consistent with pair potential minima at {l brace}100{r brace} and {l brace}1/2, 1/2, 1/2{r brace} positions in reciprocal space respectively. 32 refs., 6 figs.
Date: July 1, 1991
Creator: Lindsey, Timothy Francis
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Method for the Routine Absolute Intensity and Energy Measurements of Beta Radiation; Application to Naturally Radioactive Potassium, Rubidium, Rhenium and Lutetium (open access)

Method for the Routine Absolute Intensity and Energy Measurements of Beta Radiation; Application to Naturally Radioactive Potassium, Rubidium, Rhenium and Lutetium

Photocopy of a dissertation discussing natural radioactivities and half life of potassium, Rubidium, Rhenium, and Lutetium.
Date: August 1952
Creator: Suttle, Andrew Dillard, Jr.
Object Type: Thesis or Dissertation
System: The UNT Digital Library
A Compton scatter camera for spectral imaging of 0.5 to 3.0 MeV gamma rays (open access)

A Compton scatter camera for spectral imaging of 0.5 to 3.0 MeV gamma rays

A prototype Compton scatter camera for imaging gamma rays has been built and tested. This camera addresses unique aspects of gamma-ray imaging at nuclear industrial sites, including gamma-ray energies in the 0.5 to 3.0 MeV range and polychromatic fields. Analytic models of camera efficiency, resolution and contaminating events are developed. The response of the camera bears strong similarity to emission computed tomography devices used in nuclear medicine. A direct Fourier based algorithm is developed to reconstruct two-dimensional images of measured gamma-ray fields. Iterative ART and MLE algorithms are also investigated. The point response of the camera to gamma rays of energies from 0.5 to 2.8 MeV is measured and compared to the analytic models. The direct reconstruction algorithm is at least ten times more efficient than the iterative algorithms are also investigated. The point response of the camera to gamma rays energies from 0.5 to 2.8 MeV is measured and compared to the analytic models. The direct reconstruction algorithm is at least ten times more efficient than the iterative algorithms and produces images that are, in general, of the same quality. Measured images of several phantoms are shown. Important results include angular resolutions as low as 4.4{degrees}, reproduction of phantom …
Date: December 31, 1994
Creator: Martin, J.B.
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Complex Ions of Lanthanum in Aqueous Solutions (open access)

Complex Ions of Lanthanum in Aqueous Solutions

The complexing of lanthanum by various anions and weak acids was investigated by observing the light absorption of the complex formed with thenoyltrifluoracetone (TTA). This species showed the properties needed for a satisfactory specgtrophotometric method of analysis.
Date: August 1, 1951
Creator: Mattern, Kenneth Lawrence
Object Type: Report
System: The UNT Digital Library