Cascade fragmentation under ion beam irradiation: a fractal approach.

Based on the fractal nature of collisions, the fragmentation of displacement cascades is investigated. Introducing the caliper diameter to take into account large displacements of atoms in a collision cascade, it is possible to describe this fragmentation in terms of a threshold energy Ec. From the knowledge of Ec, the number and the volume fraction of subcascades produced is then derived. This last information allows us to classify the efficiency of impinging particles to induce structural changes of solids.