Skip to Main Content. A not-for-profit organization, IEEE is the world's largest technical professional organization dedicated to advancing technology for the benefit of humanity. Use of this web site signifies your agreement to the terms and conditions. Average depths of electron penetration: use as characteristic depths of exposure Abstract: The average depth of electron penetration is introduced as the physical quantity useful in electron beam irradiation. It is defined as the average of the maximum depths on the trajectories of electrons passing through finite, semi-infinite or infinite medium. The relation between the transmission coefficient as a function of slab thickness and the distribution of the maximum depths is analyzed, and a semiempirical equation to calculate the average depth of electron penetration is given for 0.