Relativistic and electron correlation effects in neon and argon

The differential cross sections for electrons scattered from atoms are determined in the first Born approximation by the Fourier transform of the sum of the first- (times $2Z$) and the second-order density matrix elements. When scattered intensities are measured with high accuracy, features such as electron correlation and relativistic effects can be studied. In the present experiment using 40-keV electrons, a precision of 0.1% in the count rates and 2 arc sec in the scattered angle has been achieved in the angular range of 7 to 200 mrad. The experimental data are matched at large scattering angles to theoretical cross sections based on Hartree-Fock potentials. The deviations between theory and experiment at small angles are discussed with respect to changes in the first- and second-order densities based on configuration-interaction wave functions.