Damages in UO₂ and CeO₂ irradiated with high-energy heavy ions

Uranium Dioxide (UO₂) and Cerium Dioxide (CeO₂) both have a fluorite structure, and these materials do not undergo amorphization even when they are heavily irradiated with high-energy ions. Understanding the origin of such remarkable radiation resistance is important from the viewpoint of innovative nuclear fuel design and of novel ion-beam material modification technique. One of the intriguing characteristics of the radiation damages due to high-energy ion irradiation in these materials is the formation of ion-tracks along the ion-paths. It is well known that, if the electronic stopping power (Se) is sufficiently high, the ion-track in nanometer size is created. In order to characterize the radiation damage accompanied with ion-track formation in UO₂ and CeO₂, the consequence of single ion passage was first studied in terms of the ion-track size. The Se-dependence of the ion-track size is analyzed for these materials, and it is found that it exhibits somehow different behavior compared with that of amorphized ion-tracks. By means of X-ray diffraction (XRD), the crystal structure inside the ion-track is elucidated and the lattice parameter is found to be different from that of the matrix