"Considering processes of irradiation damage, different stages of effects should be distinguished. The primary effect of electron or gamma radiation penetrating into the alkali halide lattice is ioniza- tion, i.e. the formation of a free electron and an electron hole. In many cases they will quickly afterwards recombine leaving an undamaged lattice in which the energy will be released as heat. In other cases the ionization products will be trapped in the lattice. Due to this ionization the chlorine anions in sodium chloride may become positively charged and are then easily expelled from their lattice positions. This may give rise to two effects of irradiations. The anion vacancy will catch an electron thus forming an F-centre and the chlorine ion will occupy an interstitional position. Associating with another chlorine ion located at a lattice site it can form a pair of chlorine ions now located around the lattice position and aligning its molecular axis either along the direction [110] or [111]. Defects in the form of such molecular centres are generally characterized as H-centres [14]. Depending on temperature, impurities and dislocation density both the F-centres and the H-centres may become mobile and then give rise either to the formation of conglomerates or to annealing and restoring of the original lattice. Conglomeration of F-centres will lead to local regions with excess of sodium ions and if such regions become sufficiently large it is probable that due to gradually changed atom potentials the electron energy bands will be rearranged according to a scheme for sodium metal. In that case one may speak of particles of colloidal sodium. Similarly a mechanism of coagulation of chlorine molecular centres may be expected, giving rise to minor chlorine bubbles. Although the processes for the primary defect creation are now reasonably well understood, the complexity of secondary processes is still such that no unified description has been accomplished. " [14] P.W. Levy, Encyclopedic of Physics, R.G. Lerner and G.L. Trigg, editors (Addison-Wesley, Reading Mass., 1981) pp. 131-138. Source: J. BERGSMA , R.J. HEUBOER, RADIATION DOSE DEPOSITION AND ENERGY ACCUMULATION IN A ROCK SALT WASTE REPOSITORY, ECN-144, Nov. 1983 (in cache)
In other cases the ionization products will be trapped in the lattice. Due to this ionization the chlorine anions in sodium chloride may become positively charged and are then easily expelled from their lattice positions. This may give rise to two effects of irradiations.
Depending on temperature, impurities and dislocation density both the F-centres and the H-centres may become mobile and then give rise either to the formation of conglomerates or to annealing and restoring of the original lattice.
Although the processes for the primary defect creation are now reasonably well understood, the complexity of secondary processes is still such that no unified description has been accomplished. "
[14] P.W. Levy, Encyclopedic of Physics, R.G. Lerner and G.L. Trigg, editors (Addison-Wesley, Reading Mass., 1981) pp. 131-138.
Source: J. BERGSMA , R.J. HEUBOER, RADIATION DOSE DEPOSITION AND ENERGY ACCUMULATION IN A ROCK SALT WASTE REPOSITORY, ECN-144, Nov. 1983 (in cache)
