[No abstract available] / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An investigation of minority carrier lifetimes in germanium and silicon semiconducting material has been undertaken. A comparison of optical and electrical injection methods, as reported in the literature is given. An optical arrangement, including a coaxiallized spark gap system, is described. Sample preparation is discussed with respect to surface treatments. A well etched surface (CP4 etched) reduces the surface effect to negligible proportions compared to the volume effect. However, a ground or sandblasted surface caused the surface term to be dominant. The effects of constant current, photovoltaic effect at contacts, response time, and electrical field sweep-out of carriers are discussed. A brief description of a suitable electrical injection circuit is given. Measured values of lifetime using this method are in good agreement with the optical measurements. The volume lifetimes of n-type germanium were obtained for resistivities of 0.01, 5, 19, and 50 Ω-cm material. The lifetimes found at room temperature were <2 μs, 45 μs, 200 μs, and 175 μs respectively. Both a 130 Ω-cm p-type silicon sample and an 8.2 Ω-cm n-type silicon sample displayed trapping effects at room temperature. A direct current light source, providing ambient background illumination, was found to eliminate the long decay component (>10⁻³ sec) for the p-type silicon only. Germanium at 78°K showed a trapping effect similar to the silicon at room temperature. A diffusion constant of 50 cm² /sec for holes in n-type material was used to establish a value for the surface recombination velocity of 2 x 10⁴ cm/sec for a ground surface. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (M.S. in environmental science)--Washington State University, December 2009. / Title from PDF title page (viewed on Jan. 4, 2010). "School of Earth and Environmental Science." Includes bibliographical references (p.59-67).

No description available.

Thesis-University of California, Berkeley, October 1956. / Bibliography references : p. 58.

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

In the context of the safety of nuclear installations, there is general concern over the release and dispersal of radioactive pollutants in particulate form into the atmosphere. Such a release may lead to radiation exposure to individuals under radioactive fall-out conditions in the form of direct gamma exposure, through inhalation or by the particulate material being deposited on internal and external surfaces of buildings. This project addresses the protection offered by buildings to the occupants, against such exposure pathways. A computer model (BHOUSE) has been developed to simulate the exchange and transport of pollution in aerosol form for a building. A particular aspect investigated, mainly through modelling, has been the protection afforded by buildings through the deposition indoors of aerosols which might infiltrate into the buildings in question. On the one hand this process is likely to reduce indoor air concentrations, thus reducing inhalation dose, on the other hand it may lead to the problem of long-term contamination inside buildings. A related consideration is the safety provided by the building, to the occupants inside, against the direct radiation emitted by the externally deposited activity. Various benchmarking exercises have been carried out to investigate the indoor air and contaminant dispersal. These exercises have included: pollution ingress rate to a building under a variety of conditions; effect of wet external deposition on mechanical transport rate; variation of indoor pollution level with and without vacuum cleaner operating and the calculation of inhalation dose rates. Measures to obtain higher protection factors against particulate inhalation have also been suggested. Predictions obtained with the model have been compared with an existing model. This comparison aimed to identify common features and significant differences between models. Such studies clearly relate to other non-nuclear aspects of indoor air quality research. A better understanding of the importance of individual parameters affecting indoor air quality has been achieved. The thesis also reports results obtained through participation in a joint experimental programme between Imperial College, the Danish Riso National Laboratory and the Building Research Establishment (BRE) which yielded measured indoor deposition velocities in an experimental terraced house using monodisperse aerosol labelled with a stable tracer. The deposition behaviour of particles with different sizes have also been studied. Neutron activation analysis was used to estimate aerosol concentration levels on air filters inside rooms, with the use of the Imperial College nuclear reactor. The resulting average deposition velocities were used in the model in order to illustrate the protection afforded by buildings against inhalation dose, for the aerosol sizes which were investigated. A critical review has also been conducted on aerosol test chamber studies.

No description available.

No description available.

No description available.