Formation of dislocations in LiF crystals under irradiation with energetic 209Bi, 58Ni and 36S ions

Full text: Formation of dislocations in LiF crystals irradiated with energetic (MeV-GeV) S, Ni, Bi and Pb ions has been investigated. Dislocation etching was performed on the irradiated surface and on the crystal cross-sections cleaved perpendicular to the irradiated surface. The irradiations with heavy (Bi, Pb) as well as with light (S, Ni) ion species leads to generation of mechanical stress between the irradiated layer and unirradiated part of crystal. At the vicinity of irradiated layer, the stresses can exceed the yield stress of LiF (∼20 MPa) and create dislocations in the non-irradiated part of the crystal. In case of Bi or Ni ions, new ion-induced dislocations are created on the irradiated surface. The light S ions do not produce dislocations neither on the irradiated surface, nor in the bulk of irradiated layer at fluences up to 1012 ions/cm2. The formation of dislocations is affected both by the ion fluence and the energy loss. The creation of dislocations in the irradiated area is related to accumulation of internal stress and collapse of vacancy disks formed by aggregation of vacancies. The ion irradiation produced dislocations modify the mechanical properties of the material and promote processes of crack generation and fracture