During penetration of the matter by energetic ions, they transfer a part of their energy to atoms of the target by collisions. In this way a collision cascade is created. The tree-like structured collision cascade can be described with the help of fractal calculations. Describing the collisions in a cascade by the power-inverse potential V~r^-1/m it can be shown that the fractal dimension D of the cascade equals 1/2 m. When D reaches 3 it means that nonlinear processes begin in the cascade. Cascade evolves into a spike. In this paper a dependence of fractal dimension of collision cascade on ion energy is presented. The examplary calculations of cascade fractal dimensions from the total path length and the vacancies distribution are presented too.