| Description |
This dissertation is focused on the radiolysis of plutonium tetrafluoride under long-term storage conditions. Amorphous plutonium tetrafluoride samples were subjected to thermogravimetric/differential thermal analyses, X-ray diffraction analyses, and muffle furnace annealing experiments in argon gas to investigate the totality of this radiolysis, and the effect that thermal annealing has on its reordering. There are three main areas of focus presented in this work that were used to investigate these phenomena. First, thermogravimetric/differential thermal analyses and X-ray diffraction analyses were used to uncover the possible mechanisms responsible for the amorphization in plutonium tetrafluoride through pre-annealing and post-annealing analyses on milligram samples. Second, gram samples of the plutonium tetrafluoride were annealed within flowing argon gas for short time durations. These samples were analyzed with X-ray diffraction to determine the rapidity of recrystallization in plutonium tetrafluoride. Third, gram samples of the plutonium tetrafluoride were annealed within flowing argon gas for long time durations. These samples were analyzed with X-ray diffraction to determine the effect of time at temperature on the recrystallization in plutonium tetrafluoride. The results of these three investigations are that plutonium tetrafluoride that has been stored near 50 years is amorphous. Its amorphization appears to be a result of self-induced alpha radiolysis from the decay of the plutonium isotopes. The alpha particle and the recoil nucleus of this decay look to be the primary driver of this radiolysis through Frenkel type defects and F-center formation. Radiolysis in plutonium tetrafluoride does not follow the crystal lattice parameter expansion as seen in plutonium dioxide. The crystallite size in amorphous plutonium tetrafluoride has been shown to increase under annealing conditions, and this recrystallization begins near 400°C under short and long time scales (minutes to hours) in argon gas. |
