Abstract
Cross sections of double ionization of theK-shell by electron impact are calculated for Cr and Fe using Gryzinski's method and applying classical and quantum mechanical binary encounter approximations as developed by Gryzinski and Vriens. The average field of the nucleus is taken into account, and momentum transfer from impact electron to nucleus is found to decrease the cross sections near the threshold making them to agree better with measurements. It was found that the cross sections were not sensitive to momentum distributions of K-electrons, nor did the classical and quantum mechanical binary encounter approximations yield essentially different results. Within the present accuracy of measurements experiments and calculations are in good agreement.