This thesis concerns the investigation of radioisotopes as indicators for precipitation reactions. As a precipitate forms in the presence of a radioisotope, adsorption may take place on its surface. If this adsorption changes markedly at the stoichiometric point it will be possible to use this variation as an indicator for the reaction.

The purpose of this investigation is to reveal the effects of certain factors affecting adsorption on some specific precipitates. It is hoped that the choice of precipitate types will enable extension of the information gained here to other precipitates similar to those investigated.

The Palm Valley oasis in arid central Australia is characterised by stands of palm trees (Livistona mariae). How these unique plants, separated by nearly a 1000 kilometres of arid country from their nearest relatives persist, has long fascinated visitors. Defining the hydrogeology of the Hermannsburg Sandstone, a regionally extensive and thick Devonian sequence of the Amadeus Basin that underlies Palm Valley, is the major thrust of investigation. Appraisal of drilling data shows this aquifer to be a dual porosity fractured rock aquifer which, on a regional scale, behaves as a low permeability, hydraulically continuous resource. Groundwater is low salinity (TDS &lt1000 mg/L) and bicarbonate rich. Slight variations in cation chemistry indicate different flow paths with separate geochemical histories have been sampled. Stable isotope (????H, ???????O) results from Palm Valley show groundwater to have a uniform composition that plots on or near a local meteoric water line. Radiocarbon results are observed to vary from effectively dead (&lt 4%) to 87 % modern carbon. To resolve groundwater age beyond the radiocarbon window the long lived radioisotope 36Cl was also used. Ratios of 36Cl/Cl range from 130 to 290 x 10-15. In this region atmospheric 36Cl/Cl ratio is around 300 x 10-15. Thus an age range of around 300 ka is indicated if, as is apparent, radioactive decay is the only significant cause of 36Cl/Cl variation within the aquifer. A review of previous, often controversial, 36Cl decay studies shows results are usually ambiguous due to lack of certainty when factoring subsurface Cl- addition into decay calculations. Apparently, due to the thickness of the Hermannsburg Sandstone, no subsurface sources of Cl- such as aquitards or halites, are encountered along groundwater flow paths, hence the clear 36Cl decay trend seen. The classic homogenous aquifer with varying surface topography, the &quotToth&quot flow model, is the simplest conceptual model that need be invoked to explain these isotope data. Complexities, associated with local topography flow cells superimposed on the regional gradient, signify groundwater with markedly different flow path lengths has been sampled. The long travel times (&gt 100 ka) indicate groundwater discharge would endure through arid phases associated with Quaternary climate oscillations. Such a flow system can explain the persistence of this arid zone groundwater-dependent ecosystem and highlight the possibility that Palm Valley has acted as a flora refuge since at least the mid- Pleistocene.

Thesis (Ph.D.) in Physics--University of Maine, 2006. / Includes vita. Includes bibliographical references (leaves 94-99).

Graduation date: 1963

Currently the Food and Drug Administration publishes radiopharmaceutical information for physicians to choose appropriate medical diagnosis and therapy for their patients. The primary functions of these radiopharmaceuticals are diagnosis and delivering doses to a patient with appropriate energy, biological half life, chemical behavior, and radiological half life. These radiopharmaceuticals preferentially react with certain type of cells. Diagnosis or therapy must be accurately prepared for and planned by medical professionals. The fast access to the internet has become a key tool for medical professionals to obtain this type of information. A web page has been developed that links nuclear and biological data to radiopharmaceutical information. Queries can be performed on this database to sort the radiopharmaceuticals by radiological half life, gamma energy, biological half life, medical application, chemical information or other parameters. This capability allows medical professionals and scientists to select radiopharmaceuticals by their characteristics. There are approximately 100 medical isotopes in the database. / Graduation date: 2000

With the advent of more powerful, less expensive computing resources, more and more attention is being given to Monte Carlo techniques in design application. In many circles, stochastic solutions are considered the next best thing to experimental data. Statistical uncertainties in Monte Carlo calculations are typically determined by the first and second moments of the tally. For certain types of calculations, there is concern that the uncertainty estimate is significantly non-conservative. This is typically seen in reactor eigenvalue problems where the uncertainty estimate is aggravated by the generation-to-generation fission source. It has been speculated that optimization of the random walk, through biasing techniques, may increase the non-conservative nature of the uncertainty estimate. A series of calculations are documented here which quantify the reliability of the Monte Carlo Neutron and Photon (MCNP) mean and uncertainty estimates by comparing these estimates to the true mean. These calculations were made with a liquid metal fast reactor model, but every effort was made to isolate the statistical nature of the uncertainty estimates so that the analysis of the reliability of the MCNP estimates should be relevant for small thermal reactors as well. Also, preliminary reactor physics calculations for two different special isotope production test assemblies for irradiation in the Fast Flux Test Facility (FFTF) were performed using MCNP and are documented here. The effect of an yttrium-hydride moderator to tailor the neutron flux incident on the targets to maximize isotope production for different designs in different locations within the reactor is discussed. These calculations also demonstrate the useful application of MCNP in design iterations by utilizing many of the codes features. / Graduation date: 1992

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and the Woods Hole Oceanographic Institution), September 2003. / Includes bibliographical references.

published_or_final_version / abstract / toc / Physics / Doctoral / Doctor of Philosophy

MSc. (ARST) North-West University, Mafikeng Campus, 2003