Ballistic Deposition and Segregation of Polydisperse Spheres

A model for the random deposition of spherical particles under the influence of a strong external field has been investigated numerically. In this model particles fall, one at a time, along vertical trajectories until they reach the surface of the deposit. They then follow a path of steepest descent on the surface of the deposit until a local minimum is reached. For a binary mixture of particles with different radii the density is larger than that found for the monodisperse case. A segregation transition is found which occurs when the smaller spheres can penetrate into the random deposit of larger spheres. The exponent characterizing the divergence of the penetration length is estimated to have a value of 0.55.