The present invention relates to an electron gun cathode mount adapted at one end to secure a thermionic cathode and at the other end to be connected to an attachment member, wherein the electron gun cathode mount is structured so as to be capable of, when in use, reducing heat transfer from the thermionic cathode to the attachment member, and the material forming the electron gun cathode mount has a thermal conductivity of less than 10 Wm−1K−1 at the operating temperature of the thermionic cathode in a direction from the thermionic cathode to the attachment member. The present invention also relates to an electron gun assembly having the electron gun cathode mount installed therein.