From cascade to spike a fractal-geometry approach

The fractal nature of collisional cascades in solids is investigated by means of a model of "idealized" collisional cascade and the Winterbon-Sigmund-Sanders theory of atomic collisions. It is shown that the fractal dimensionality increases as the cascade evolves because of the change of the effective interaction potential. The condition of a spike is shown to arise naturally from the concept of "space-filling" fractals. The characteristic kinetic energy per particle in a spike is estimated to be on the order of a few electronvolts.