An investigation was undertaken to compare airborne and ground-based radiometric survey techniques and to compare and contrast their relative merits and how they can be used in determining the environmental distribution of environmental radioisotopes, particularly those in the decay chains of 238U, 232Th and 40K. Before a detailed investigation was done of the survey techniques, it was necessary to look at the underlying physical principles of detection of ionizing radiation and the types of detector that are generally used in these different types of survey techniques. Having looked at the physics of detection, a detailed examination of the potential distribution of these environmental radioisotopes was undertaken. In these surveys, an assumption is often made, that the daughter isotopes in a decay chain are in secular equilibrium with one another. This assumption was examined and the various possible ways in which secular equilibrium could break down were considered, these included looking at biological, meteorological and chemical processes. Only after all the influences on assumptions used in these survey processes and the physical limitations on the measurements taken during surveys were considered, was a comparison made of a set of airborne and ground-based measurements taken at a chosen survey site compared. These measurements compared uranium, thorium and potassium activity concentrations, which had been determined by the two survey techniques, and a correlation was found particularly when the uranium measurements were examined.

Graduation date: 2004

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 2004. / Thesis advisor(s): Sherif Michael. Includes bibliographical references (p. 105-109). Also available online.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 174-186).

The purpose of this dissertation was to develop the C⁺⁺ program Emergency Dose to calculate transport of radionuclides through indoor spaces using intermediate fidelity physics that provides improved spatial heterogeneity over well-mixed models such as MELCOR[trademark] and much lower computation times than CFD codes such as FLUENT[trademark]. Modified potential flow theory, which is an original formulation of potential flow theory with additions of turbulent jet and natural convection approximations, calculates spatially heterogeneous velocity fields that well-mixed models cannot predict. Other original contributions of MPFT are: 1) generation of high fidelity boundary conditions relative to well-mixed-CFD coupling methods (conflation), 2) broadening of potential flow applications to arbitrary indoor spaces previously restricted to specific applications such as exhaust hood studies, and 3) great reduction of computation time relative to CFD codes without total loss of heterogeneity. Additionally, the Lagrangian transport module, which is discussed in Sections 1.3 and 2.4, showcases an ensemble-based formulation thought to be original to interior studies. Velocity and concentration transport benchmarks against analogous formulations in COMSOL[trademark] produced favorable results with discrepancies resulting from the tetrahedral meshing used in COMSOL[trademark] outperforming the Cartesian method used by Emergency Dose. A performance comparison of the concentration transport modules against MELCOR[trademark] showed that Emergency Dose held advantages over the well-mixed model especially in scenarios with many interior partitions and varied source positions. A performance comparison of velocity module against FLUENT[trademark] showed that viscous drag provided the largest error between Emergency Dose and CFD velocity calculations, but that Emergency Dose’s turbulent jets well approximated the corresponding CFD jets. Overall, Emergency Dose was found to provide a viable intermediate solution method for concentration transport with relatively low computation times. / text

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