Radiation-enhanced diffusion of oxygen-18 in uranium dioxide thin films

Radiation-enhanced diffusion (RED);UO2;Anion Diffusion;Uranium dioxide thin films

Bernhardt, Joseph ; Heuser ; Brent J.

关键词: Radiation-enhanced diffusion (RED);    UO2;    Anion Diffusion;    Uranium dioxide thin films;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/45289/Joseph_Bernhardt.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Anion radiation enhanced diffusion (RED) and thermal diffusion of a buried 18O tracer layer in thin film UO2 was measured using Secondary-Ion Mass Spectroscopy (SIMS). Thin films were grown using a dedicated magnetron sputtering chamber. Samples were irradiated with 1.8 MeV Kr+ over a temperature range from 295 K to 623 K. Measurements have been made for both single crystal and textured films. This difference in crystal structure led to significantly different results. Thin film stoichiometry was also shown to have an effect on RED and thermal diffusion. For RED, activation energies found from best fit analysis were Ea = 0.83 and Ea = 0.37, for single crystal and textured samples, respectively. RED for single crystal UO2 thin films can be represented by,D_RED=8.7×〖10〗^(-14)exp⁡((-0.83)/kT)〖cm〗^2/secRED for textured UO2 thin films can be represented by,D_RED=2.0×〖10〗^(-15)exp⁡((-0.37)/kT)〖cm〗^2/secThermal diffusion measurements resulted, from best fit analysis, in similar activation energies for single crystal and textured thin films, Ea = 0.46 and Ea = 0.53, respectively. This was shown to agree well with published experimental and calculated values for UO2-x for anion vacancies. Thin films used in this work were thought to be substoichiometric and thermal diffusion is thought to be controlled by anion vacancies. Mixing parameter measurements found ξ = 2.1 ± 0.2〖 Å〗^5 〖eV〗^(-1) on the anion sublattice, which indicated that ballistic mixing was the dominant mechanism of ion-mixing and that thermal spike activity is negligible.