Thesis (Ph. D.)--University of Wisconsin--Madison, 1921. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis--Catholic University of America. / Bibliography: p. 14-15.

The luminescent decay of pure potassium iodide has been measured under various conditions of temperature, annealing and x-irradiation time. The decay curves are found to be approximately of the form I(t) = [formula omitted] where I(t) is the luminescent intensity at the time t. Using a method that has been developed for the analysis of decay curves, numerical values for the decay constants, λi , and the trap populations Pi, have been estimated. The decay constants are found to be simple temperature functions of the form λi = [formula omitted] with the activation energies, Ei, lying between 0.4 and 0.8 ev and escape probabilities, Si, between 10⁴ and 10⁸ sec.⁻¹. The temperature dependence of the Pi is complicated and indicates that radiationless transitions strongly contribute to the emptying of traps at high temperatures. An irreversible increase in luminescent output produced by repeated x-irradiation without intermediate annealing is discovered; it points to considerable deviation from a first order decay mechanism in the case of slowly decaying traps. The mechanism of the irreversible effect is discussed on a semi-quantitative basis. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The reflectivity at room temperature and the absorption coefficient at room temperature, 77°K and 12°K have been measured for CsI. These and the results of a Kramers-Kronig analysis of the reflectivity by Vergnat et al. (1969) have been compared to the calculated optical constants (complex dielectric constant and complex refractive index), reflectivity and absorption coefficient. The calculation, using the lattice dynamical data of Karo and Hardy (1963), is based on the work of Wallis and Maradudin (1962) and Cowley (1963). The cubic coupling coefficient has been evaluated for nearest neighbors with a correction due to Eldridge (1973) for long-range Coulombic forces. The predicted features in the imaginary part of the complex phase shift, gamma, are all assigned to specific two-phonon processes except for a small feature at 91 cm⁻¹. The agreement between theory and experiment is very poor at room temperature but improves significantly in all cases at low temperatures. The discrepancies between theory and experiment give evidence of the fundamental importance of third and higher-order processes in the CsI lattice and suggest that next-nearest neighbor repulsive forces need to be included in the calculation of the cubic coupling coefficient. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

Thesis (Ph. D.)--Columbia University, 1938. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1956. / Typescript. Abstracted in Dissertation abstracts, v. 16 (1956) no. 11, p. 2042. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 64-65).

Dortmund, Universiẗat, Diss., 2001.

Iodine-129 is a high-yield fission product of 235U and 239Pu; is produced in nuclear power plants and is therefore present in substantial quantities in radioactive wastes. In the environment, iodine exists as a range of species: iodate (IO3-), iodide (I-), elemental iodine (I2), HOI and organic species are the most common. The behaviour of iodine in the environment is linked to its speciation which can be affected by different factors such as pH, redox potential and enzymatic reduction. Previous research has shown that iodine speciation can determine its fate in the environment; however the mechanisms of redox cycling amongst the different species are not yet fully understood. This research project has focused on improving the understanding of the changes on speciation of iodine in sediment and mineral systems undergoing redox cycling reactions. The fate and changes in iodine speciation were studied under reducing and oxidising conditions, with all experiments conducted under circumneutral pH conditions. Overall the results showed that when microbial activity is promoted in a sediment system, iodate is reduced to iodide with the reduction occurring during manganese reduction. Further, when nitrate is present at high concentrations the reduction of iodate is retarded. A net release of native iodine from sediments was observed in all experiments conducted with sediments; confirming previous observations that sediment bound iodine is released from sediments under reducing conditions. Modest abiotic reduction of iodate was observed under manganese and iron reduction; and iodate reduction happened faster in a mixed system with iron and pure culture bacteria than solely by the pure culture alone or via abiotic reduction with Fe(II). When reduced experiments were exposed to air, concentrations of iodide decreased with no iodate ingrowth or losses in total iodine in solution. This suggested that iodide had been oxidised to intermediate species (I2, HOI) that were not detected, although this reaction has been described in past research. Finally, when no microbial activity is promoted, iodine remains as iodate which showed modest sorption onto sediment systems and Fe(III) oxide. Overall, these results highlight the important role that bacteria play in the reduction of iodate. This research also confirms that iodine speciation impacts on the fate of 129I throughout the environment, where it may be less mobile in an oxic environment than under reducing conditions. Moreover, some techniques of bioremediation (e.g. promoting metal reducing conditions) may cause the release of radioactive iodine to solution.

The mechanism of oxidation of Potassium iodide by Chlorine and Fluorine gas has been studied using powdered KI, pressed pellets and single crystals (pressed pellets only in the case of Fluorine). The electrical conductivity of a KI pellet has also been determined as a function of temperature. The major part of the experimental work concerns changes in D.C. electrical conductivity during reaction. The main conclusions are as follows: (a) The room temperature conductivity of KI is always higher than that obtained by extrapolating the impurity-range, and the activation energy below about 92° C. is very small; this is tentatively attributed to a space-charge effect. (b) In the KI/CI₂ reaction, the products are invariably KCl and I₂ in various forms (including V-Centres), although poly-halides are thermodynamically more stable. Thus the reduction of Chlorine occurs in a manner which does not allow reorganization to ICI₂-. (c) In pressed pellets, the conductivity always increases at the start of oxidation, but the enhanced conductivity may be ionic or electronic in different circumstances, and the initial increase may be followed by several alternative processes which are structure-sensitive. There is an inverse correlation between initial conductance and reactivity which is interpreted in terms of competition between (i) trapping of positive holes at isolated cation vacancies and (ii) nucleation of solid Iodine at grain boundaries. (d) Unpressed powders show no increase in conductance during reaction; this is attributed to preferential oxidation of bound surface states. / Science, Faculty of / Chemistry, Department of / Graduate