The invention relates to a device and a method for altering the characteristics of a three-dimensional article by means of electrons, including at least one electron accelerator for generating accelerated electrons and two electron exit windows, wherein the two electron exit windows are arranged opposite one another, wherein the two electron exit windows and at least one reflector delimit a process chamber in which the surface or surface layer of the article are bombarded with electrons, wherein an energy density distribution inside the process chamber can be detected at least over one spatial dimension by means of a sensor system.
