The invariant embedding principle was applied to obtain closed analyti
cal expressions of several magnitudes of interest in electron probe mi
croanalysis [ionization distribution function, Phi(rho z) backscatteri
ng probability, etc.], This approach permits one easily to obtain solu
tions for a model which explicitly considers the mean free path betwee
n effective electron collisions, (C) 1998 John Wiley & Sons, Ltd.