Results of experimental and theoretical investigations are presented on hea
vily irradiated natural and synthetic NaCl crystals in the temperature rang
e where anion defects are mobile. They give a strong evidence for the forma
tion of vacancy voids, which cannot be explained by the Jain-Lidiard model
used up to date for description of metal colloids and dislocation loops for
med in ionic crystals during earlier stages of irradiation. We consider an
additional set of reactions between experimentally observed extended defect
s (metal colloids, gas bubbles and voids) and point defects. The latter inc
lude F and H centers that are the primary defects produced by irradiation,
and cation vacancies (with a trapped hole) that are secondary defects, prod
uced in the process of dislocation climb due to absorption of extra H cente
rs. We show that highly overpressurized bubbles of fluid halogen are strong
ly biased for absorption of H centers, which makes them grow via punching o
ut interstitial dislocation loops. The loops grow and produce cation vacanc
ies that are subsequently trapped at the incoherent colloids together with
extra F centers giving rise to the colloid-void transition. Elastic interac
tion between extended defects and point defects is shown to play a major ro
le, since it determines the bias factors of extended defects, which is a ma
jor driving force of the microstructural evolution under irradiation. A qua
ntitative comparison of the new model for radiation damage in NaCl with exp
erimental data is presented. Mean sizes and volume fractions of all types o
f observed defects are calculated. It is shown that voids formed due to agg
lomeration of F centers and cation vacancies can grow to the dimensions exc
eeding the mean distance between colloids and bubbles, eventually absorbing
them, hence, bringing the halogen gas and metal to a back reaction. Impuri
ties play a major role in the void development with increasing irradiation
dose, which strongly affects the radiation stability of NaCl. (C) 1999 Else
vier Science B.V. All rights reserved.