Using the Monte carlo technique, we have developed a model for the Ato
mic Scale Simulation of the formation of dislocation loops in material
s under irradiation. We assume that vacancy interstitial pairs are cre
ated by particle impact and diffuse through the solid. Three types of
reaction are considered : vacancy interstitial recombination, intersti
tial association to form a nucleus for a new dislocation loop and inco
rporation of interstitials into already existing dislocation loops lea
ding to their growth. We have determined the concentration of intersti
tials, vacancies and dislocation loops, together with the average radi
us of the latter. Our results are compared with those obtained by usin
g the chemical rate theory and with experimental data on CdTe. Moreove
r, Atomic Scale Simulations lead to the spatial distribution of disloc
ation loops, in agreement with TEM experimental observations, and to i
ndications about the distribution of vacancies around these loops. Thi
s kind of information is totally missing in the chemical rate theory.