On the relaxation of the energy distribution function of light particles in heavy gases

A stochastic approach to the thermalization problem of light particles in heavy gases is discussed which presents a number of advantages with respect to more conventional techniques. The procedure is used to study the relaxation of the distribution function in cold gases in two situations in which: i) only first order terms are retained and ii) second order terms are also included, with respect to the ratio m/M between light-particle mass m and atomic mass M. (orig.)