Theory of the late stage of radiolysis of alkali halides

Abstract

Recent results on heavily irradiated natural and synthetic NaCl crystals give evidence for the formation of large vacancy voids, which were not addressed by the conventional Jain±Lidiard model of radiation damage in alkali halides. This model was constructed to describe metal colloids and dislocation loops formed in alkali halides during earlier stages of irradiation. We present a theory based on a new mechanism of dislocation climb, which involves the production of V F centers (self-trapped hole neighboring a cation vacancy) as a result of the absorption of excess H centers. Voids are shown to arise due to the reaction between F and V F centers at the surface of halogen bubbles. Critical parameters associated with the bubble-to-void transition are evaluated. Voids can grow to sizes exceeding the mean distance between colloids and bubbles, eventually absorbing them, and, hence, igniting a back reaction between the halogen gas and metal. The amount of radiation damage in alkali halides should be evaluated with account of void formation, which strongly aects the radiation stability of material.

Systematic UHV‐AFM experiments on Na nano‐particles and nano‐structures in NaCl

“…Therefore, it is likely that sodium colloids nucleate and grow along dislocations by absorption of F-centers. This explanation is in contrast with the existing models of radiolysis in NaCl [7,8], which are based on the postulate that dislocations are biased toward absorption of H-centers compared to F centers, or more correctly, the dislocation bias for H centers is larger than the mean bias of the system. The discrepancy can be explained by the fact that the dislocation bias depends on arrangement of the dislocations and total sink strength.…”

“…The mechanism of dislocation patterning is related to the mechanism of gas bubble growth. According to our model [8] the process of growth of Cl 2 gas bubbles is accompanied by punching dislocation loops. These loops are assumed to grow and form dislocation pile-ups.…”

New mechanism for radiation defect production and aggregation in crystalline ceramics

“…The dislocation bias is determined by the ratio of relaxation volumes associated with H and F centers, X H =X F , and is given by [8] …”

A model for void-induced back reaction between radiolytic products in NaCl

“…We explain this by a back reaction between radiolytic products. Indeed, according to our model of void formation [5,6], fast growing voids bring chlorine bubbles and Na colloids into contact, which results in the instantaneous back reaction between the radiolytic Na and Cl. In our previous paper [7] the kinetics of the exothermic back reaction was considered assuming that after colloid-void collision the colloid instantaneously evaporates into the void.…”