  We introduce a method for calculating the probability with which a low-energy
electron hitting the wall of a plasma gets stuck in it and apply the method to
a dielectric wall with positive electron affinity smaller than the bandgap
using MgO as an example. In accordance with electron beam scattering data we
obtain energy-dependent sticking probabilities significantly less than unity
and question thereby for electrons the perfect absorber assumption unisono used
in plasma modeling.
