Graduate Thesis Or Dissertation
 

Microstructure of radiation damage in the uranium film and its backing materials irradiated with 136 MeV 136Xe+26

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Microstructure of radiation damage in the uranium film and its backing materials irradiated with 136 MeV ¹³⁶Xe⁺²⁶

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  • Microstructure changes in uranium and uranium/metal alloys due to radiation damage are of great interest in nuclear science and engineering. Titanium has attracted attention because of its similarity to Zr. It has been proposed for use in the second generation of fusion reactors due to its resistance to radiation-induced swelling. Aluminum can be regarded as a standard absorbing material or backing material for irradiation targets. Initial study of thin aluminum films irradiation by ²⁵²Cf fission fragments and alpha particles from source has been conducted in the Radiation Center, Oregon State University. Initial study of thin aluminum films irradiation by ²⁵²Cf fission fragments and alpha particles from source has been conducted in the Radiation Center, Oregon State University. Aluminum can be regarded as a standard absorbing material or backing material for irradiation targets. The AFM investigation of microstructure damages of thin aluminum surfaces revealed that the voids, dislocation loops and dislocation lines, formed in the thin aluminum films after bombardment by ²⁵²Cf fission fragments and alpha particles, depends on the irradiation dose. The void swelling and diameter and depth of voids increase linearly with the fluence of particles and dose; however, the areal density of voids decreased when formation of dislocation loops began. Study of deposition of uranium on titanium backing material by molecular plating and characterization of produced U/Ti film has been performed. The U/Ti film has smooth and uniform surfaces but the composition of the deposits is complex and does not include water molecules which probably involve the presence of U (VI). A possible structure for the deposits has been suggested. X-ray diffraction pattern of U/Ti films showed that The U/Ti film has an amorphous structure. Uranium films (0.500 mg/cm²) and stack of titanium foils (thickness 0.904 mg/cm²) were used to study the microstructural damage of the uranium film and its backing material. Irradiation of U/Ti film and Ti foils with 1 MeV/u (136 MeV) ¹³⁶Xe⁺²⁶ ions in was performed in the Positive Ion Injector (PII) unit at the Argonne Tandem Linear Accelerator System (ATLAS) Facility at Argonne National Laboratory, IL. Pre- and post- irradiation of samples was analyzed by X-ray diffraction, Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) and Atomic Force Microscopy (AFM). The irradiation of U/Ti films results in the formation of a crystalline U₄O₉ phase and polycrystalline Ti phase. Annealing of the thin uranium deposit on a titanium backing at 800°C in the air atmosphere condition for an hour produced a mixture of UO₃, U₃O₈, Ti, TiO and TiO₂ (rutile) phases; meanwhile, annealing at 800oC for an hour in the argon environment produced a mixture of β-U₃O₇, Ti and TiO₂ (rutile) phases. These phenomena indicate that the damage during irradiation was not due to foil heating. Microstructural damage of irradiated uranium film was dominated by void and bubble formation. The microstructure of irradiated titanium foils is characterized by hillocks, voids, polygonal ridge networks, dislocation lines and dislocation networks. Theory predicts that titanium undergoes an allotropic phase transformation at 882.5 °C, changing from a closed-packed hexagonal crystal structure (α-phase) into a body-centered cubic crystal structure (β- phase). When the titanium foils were irradiated with 136MeV ¹³⁶Xe⁺²⁶ at beam intensity of 3 pnA corresponding to 966°C, it was expected that its structure can change from hexagonal-close packed (hcp) to body-centered cubic (bcc). However, in contrast to the theory, transformation from α-Ti (hcp) phase to fcc-Ti phase was observed. This phenomenon indicates that during irradiation with high energy and elevated temperature, the fcc-Ti phase more stable than the hcp-Ti Phase.
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