The present invention is directed to a device and system for verifying the electron beam kinetic energy spectrum and determining changes in kinetic electron beam energy spectrum that comprises a radiation-absorbing mass defined by a top surface, a bottom surface, and side walls, said mass having at least four separate slots containing one or more of dosimeter strips, wherein said slots are located at different depths within the mass as measured from the top surface of the mass, and said slots are positioned substantially parallel to the top surface of the mass. The present invention also relates to a method of determining and comparing changes in a kinetic electron energy spectrum.