The spatial configuration of collision cascades induced by 10 and 15 keV per atom molecular ions in polycrystals

The simulation of collision cascades in solids induced by energetic clusters of atoms is made possible by a slight modification of the MARLOWE program. Cascades generated in polycrystalline tungsten by 10 and 15 keV per atom tungsten atoms and molecules are studied. The comparison suggests that no significant molecular non-linear effect starts during the cascade development. A detailed analysis reveals different types of individual cascade configurations when induced by W2 energetic molecules. About 15% of the incident molecules generate subcascades. Another 15% generate cascades with particularly extended elongations along the track of one or of the two atoms forming the primary molecule. The remaining two thirds of cascades have configurations comparable with those resulting from the slowing down of single atoms. Their volume is however systematically larger and consequently, average point defects and energy densities are not found to be additive quantities. It is suggested that non-linear molecular effects can only be generated when zones are created that are delimited by the overlap of the collision cascades induced by each atom forming the incident molecules. (orig.)