In metals, the contribution of the interstitialcy mechanism to thermal diffusion is insignificant. This is due to the relatively high formation enthalpies of self-interstitials when compared to vacancies. However, the interstitialcy mechanism plays a crucial role in radiationinduced diffusion. When a crystal is subjected to energetic particles such as protons, neutrons, or electrons, the atoms within the lattice are displaced from their original positions, resulting in vacancies. Simultaneously, the displaced atom becomes a self-interstitial as it is embedded back into the lattice. Consequently, pairs of vacancies and self-interstitials, known as Frenkel pairs, are created without thermal activation. Once these defects gain mobility, they facilitate diffusion and contribute to radiation-induced diffusion, which pertains to the study of crystal damage caused by radiation.