RADIATION INDUCED SOFTENING OF CRYSTALS

Under irradiation of crystals, atomic vibrations of the lattice that are large enough in amplitude so that the linear approximation and therefore the conventional phonon description of the lattice is not enough. At the same time, these vibrations are localized and can travel long distances in a crystal lattice [1, 2]. In metals and other crystals, they are called discrete breathers (DBs), which are the secondary products of irradiation damage, the primary one being the creations of defects that involve atom displacements to produce point and extended defects, which results in radiation induced hardening (RIH). A part of the remaining energy transforms in DBs before decaying into pho-nons. Thus, while a material is being irradiated in operational conditions, as in a reactor, a considerable amount of DBs with energies of the order of one eV is produced, which helps dislocations to unpin from pinning centers, pro-ducing Radiation Induced Softening (RIS), which opposes RIH [3, 4]. This effect is investigated under (in-situ) im-pulse and steady-state electron irradiation.