The elastic small-angle scattering of 15- to 25-keV electrons by He, Ne, and Ar shows a rapid increase towards decreasing scattering angles superimposed with a diffraction pattern. The observed excess of the elastic differential cross section as compared with the Born cross section is due to the coupling to the inelastic channels. It may be also explained as a diffraction into the shadow of the inelastic scattering which dominates the forward direction.

• Received 26 February 1979

DOI:https://doi.org/10.1103/PhysRevLett.42.1336