From the best fit of two adjustable parameters, B (escape probability) and ƛ (empirical escape depth of the secondary electrons, s.e.), the constant loss theory accounts fairly well for the s. e. emission from materials: δ (E0) = B [E0/E(e.h)] [ƛ/R] [1 - exp. -(R/ ƛ)] (1) (with E(e.h): energy required for generating a s.e. inside the specimen; R: range of the incident electron related to the primary beam energy, E0, via a power law of the form: R=C E0n). The influence of the angle of incidence, i, may also be estimated by changing R into R cos i (see fig la for the example of diamond with B/ E(e.h) = 22 keV-1; ƛ ≈ 10 nm). For insulators, δ is obtained from short pulse experiments (to prevent charging) and, in the 1-5 keV range, it is often one order of magnitude (or more) larger than that of metals via a larger ƛ value (also more sensitive to the temperature, to the crystalline state and resulting from a random walk involving many elastic and inelastic-phonon- scattering events).