Dawson, Bruce RobertSimpson, Kenneth Mark2007-09-052007-09-052001adt-SUA20011218.143923http://hdl.handle.net/2440/37751This thesis describes several aspects of cosmic ray composition studies using the Utah Fly's Eye and High Resolution Fly's Eye (HiRes) detectors. The Fly's Eye detector utilises the atmospheric fluorescence technique to measure the development of cosmic ray cascades as they pass through the atmosphere. This is complementary to the surface array technique, as used by the Akeno experiment in Japan, which measures the electromagnetic and muon content of air showers at a single observation level. For some time it was thought that Fly's Eye and Akeno gave inconsistent composition results. In Chapter 4 I show that the inconsistency is due, for the most part, to a difference in the assumptions made about hadronic interactions. In Chapter 5 I present analysis of the composition between 10^17 and 10^18 eV using the prototype High Resolution Fly's Eye (HiRes) detector in coincidence with the Michigan Muon Array (MIA). The hybrid nature of these measurements gives us more information about cosmic ray showers than either technique on its own. The consistency or otherwise of the composition measured by the two detectors is discussed. Finally, in Chapter 6, I discuss a method of extracting the total proton-proton cross section from the cosmic ray data. This information is of interest because it is derived at centre of mass energies much higher (by at least an order of magnitude) than those currently accessible by collider experiments. I present a preliminary calculation of the cross section using the HiRes/MIA hybrid data set.4228470 bytes119287 bytesapplication/pdfapplication/pdfencosmic rays, cosmic radiation, fluorimetry, fluorescence detectorThesis