Abstract
A set of coupled linear integral equations for the energy distributions of energetic atoms in an irradiated polyatomic medium is further investigated. It is found that the asymptotic collision density, the number of collisions per unit volume per unit time per unit energy between energetic atoms with kinetic energy E and thermal atoms, is proportional to 1/E β for a wide class of energy change probability functions. For elastic collisions, the exponent β equals 2, and the constant of proportionality is determined from the energy current. The results are used to calculate the number of displaced and replaced atoms produced by primary energetic atoms in a polyatomic medium.