Thermal annealing and simulation of fission fragment self-irradiation of baddeleyite

Abstract

The discovery of loop type defects along straight lines originating from uranium inclusions in natural zirconia (baddeleyite) was the first evidence for radiation tracks in this material. The tracks were assumed to be a result of U fission fragments. The physical processes such as change in pressure and temperature before and after the volcanic emplacement process was unknown. However, the crystalline transition from tetragonal to monoclinic in the range 700 -1100 C is well known. It was therefore necessary to use the same material and expose it to 167Mev Xe ions to simulate the U fission fragment tracks. The as-irradiated bulk material was subsequently annealed at 800 C and thin sections were vacuum heated in-situ up to 500C. The microstructure of the material, before and after annealing was investigated by transmission electron microscopy (TEM). The results showed that the loop like structures along the fission tracks could be produced after annealing. The application of high resolution TEM demonstrated the presence of a localized tetragonal phase transformation, which was quenched into the ion track material being surrounded by monoclinic bulk material (the stable isomorph at room temperature)