Levy flight of atoms in collision cascades

¹  CEA, DEN, SRMA, LAZM, Equipe Mixte MFE - F-91191 Gif-sur-Yvette, France, EU
²  CEA, DEN, SERMA, LLPR, Equipe Mixte MFE - F-91191 Gif-sur-Yvette, France, EU
³  CEA, LIST, SSTM, LPSS - F-91191 Gif-sur-Yvette, France, EU

Corresponding author: david.simeone@cea.fr

Received: 13 May 2008
Accepted: 11 July 2008

Abstract

In this work we analyze the ballistic phase of displacement cascades. Monte Carlo simulations performed with realistic cross-sections were used to calculate the probability density function, p_L(l), describing the length traveled by a particle between two successive collisions within the binary collision approximation framework. From the analysis of p_L(l), this work shows that the trajectories set displays a bifractal behavior. The comparison of different MC simulations clearly shows that this bifractality is only due to the long tail of p_L(l). The unusual form of p_L(l) implies that atoms displaced in the collision cascade during irradiation follow a Levy flight. Since the Levy law is scale invariant, an anomalous diffusion of atoms at large distances is then expected under irradiation and may explain experimental results.