Tem Study of Radiation Damage and Annealing of Neutron Irradiated Zirconolite

Abstract

AbstractNeutron irradiation was used to simulate alpha-decay damage in zirconolite, resulting in a transformation from the crystalline to the amorphous state at doses of 4–25 × 1019 n/cm2 (E ≥ 1 MeV). With increasing dose, the radiation damage microstructures resemble damage caused by: 1) alpha-decay of 232Th and 238U in natural zirconolites, 2) alpha-decay of 238Pu or 244Cm in synthetic samples, and 3) collision cascades in samples irradiated with heavy ions. Heavily damaged zirconolite recovers to a defect fluorite phase on annealing at temperatures up to 1000 °C. The main stage of structural recovery was found to occur at temperatures of 600–800 °C. The microstructures after heating depend on the initial level of damage: zirconolite grains with low to moderate levels of damage anneal to imperfect single crystals, whereas heavily damaged grains recrystallize to a polycrystalline microstructure. Complications encountered in this work include the production of fission tracks (due to trace amounts of U) and a non-uniform distribution of damage at higher dose levels (possibly due to electron beam heating).