Electronic stopping power dependence of ion-track size in UO₂ irradiated with heavy ions in the energy range of ∼1 MeV/u

In order to investigate electronic stopping power dependence of ion-track size in UO₂, ion-tracks in UO₂ irradiated with various ions with the specific energy in the order of 1 MeV/u have been observed by a transmission electron microscope. The ion-track size shows monotonic increase as a function of the electronic stopping power. The ion-track size obtained for UO₂ is smaller than that obtained for CeO₂, although these two compounds have same crystallographic structure and similar thermal properties. The ion-track sizes for irradiations with ions having relatively low energy of about 1 MeV/u are smaller than those expected from the thermal spike models based on melting temperature criterion. The possible interpretations for the unusually small ion-tracks observed for UO₂ are discussed.