New insight on the high radiation resistance of UO2 against fission fragments

- Uniform features of track formation are demonstrated.
- Semiconductors are more stable than insulators against fission fragments.
- Melting point and width of the thermal spike control the track size.
- High threshold for tracks Set = 20 keV/nm for fission fragments in semiconducting UO2.
- An Arrhenius equation describes the inelastic sputtering in UO2 and other solids.

Track radii are derived for semiconductors from a temperature distribution Θ(r) in which the width of the distribution is the only materials parameter. Analysis of track data for GeS, InP, GaAs and GaN show that the projectile velocity has no effect on track radii in semiconductors. Due to the missing velocity effect, the threshold for track formation, Set = 20 keV/nm is high in semiconducting UO2 in the whole range of projectile velocities. This is the origin of the high radiation resistance for fission fragments. Consequences for the simulation experiments with insulating CeO2 are discussed. It is verified that sputtering is described accurately by the Arrhenius equation for various materials including UO2. The ion-induced surface potential has a strong effect on the activation energy.