a portion of an x - ray image intensifier is shown in fig1 identifying the components thereof necessary for explaining the principles of the present invention . the x - ray image intensifier has a substantially cylindrical outer jacket or housing 1 . a first electrode 2 , a second electrode 3 and a third electrode 4 , forming the electrode system for the x - ray image intensifier , are situated within the jacket 1 . a mounting element 5 for the first electrode 2 is provided . the output luminescent screen ( not shown ) follows to the left of the mount element 5 , and the input luminescent screen ( not shown ) of the x - ray image intensifier follows to the right of the third electrode 4 . the first electrode 2 has a region 6 which overlaps a region 8 of the second electrode 3 , with an insulating member 7 disposed therebetween . the regions 6 and 8 are cylindrical , with the region 6 having a channel 9 therein and the region 8 having a channel 10 therein , which are disposed opposite each other when the electrodes 2 and 3 are fitted together . the insulating member 7 is a shaped ceramic member situated in the channels 9 and 10 , and having a thickness sufficient to maintain a spacing between the electrodes 2 and 3 . the insulating member 7 may be , for example , a plurality of ceramic spheres , a ceramic ring , or segments of a ceramic ring . for assembling the electrode system , a region 11 of the first electrode 2 can be shrunken onto the mount 5 . the insulating member 7 is then arranged in the channel 9 . the region 8 of the second electrode 3 is warmed , thereby causing that region to expand , and it is slipped over the region 6 of the first electrode 2 and over the insulating member 7 . when the region 8 cools , it will shrink onto the region 6 and onto the insulating member 7 . the spacing of the regions 6 and 8 from each other is prescribed by the insulating member 7 , and is has a dimension so that no voltage arcing will occur between the electrodes 2 and 3 , particularly between the regions 6 and 8 , during operation of the x - ray image intensifier . the same procedure is undertaken for fastening the third electrode 4 to the second electrode 3 . an electrode system for an x - ray image intensifier which is fast and simple to assemble is thus obtained , wherein mounts for the electrodes which are in communication with the jacket 1 of the x - ray image intensifier can be eliminated . the mounting of the electrodes is so stable at the cylindrical regions 6 and 8 that an impact to the x - ray image intensifier does not cause any of the electrodes to move out of adjustment . adjustment of the electrodes can even be omitted , because the channels 9 and 10 and the insulating member 7 will correctly position the adjoining electrodes in an optimum arrangement . contact pins 12 , 13 , and 14 respectively connected to the electrodes 2 , 3 , and 4 are provided which extend through the jacket 1 in a known manner in vacuum - tight fashion to supply voltage to the electrodes 2 , 3 , and 4 . because additional mounting components for the electrodes are omitted , fewer parts are situated in the vacuum vessel of the x - ray image intensifier , so that the stability of the vacuum is improved . although a plurality of electrodes are shown in the embodiment of fig1 the mounting structure disclosed herein can be used for only a single electrode which is shrunken onto a mounting element . in the embodiment of fig1 the mounting element is another electrode , however , that need not necessarily be so . a further embodiment is shown in fig2 wherein a cylindrical portion 15 of a mounting element has a channel 17 for retaining an electrode 16 . this channel 17 is disposed in the inner surface 18 of the cylindrical part 15 of the mounting element , and extends transversely relative to the longitudinal axis 19 of the cylindrical portion 15 . it is also possible to provide a plurality of channels 17 , spaced from each other , in the surface 18 . the outer surface 20 , i . e ., the surface facing the interior of the cylindrical portion 15 , the electrode 16 has resilient springs or clips 22 formed by slots 23 in the surface of the electrode 16 . in the assembled condition of the electrode with the mounting element , a bead or projection 21 on the clips 22 engages the channel 17 . for assembly , the electrode 16 is introduced into the cylindrical portion 15 of the mounting element , for example from the left , so that the clips 22 are pressed resiliently inwardly by the bead 21 . when the electrode 16 reaches its predetermined position , which is defined by the channel 17 , the bead 21 snaps into the channel 17 , so that the electrode 16 is positioned and held in the cylindrical portion 15 of the mounting element . it is also possible , however , to provide the electrode 16 with a channel , instead of a bead , and to provide a bead , instead of a channel , on the surface 18 . the arrangement shown in fig2 is suitable if the cylindrical portion 15 of the mounting element is not electrically conductive . if the cylindrical portion 15 of the mounting element is to be electrically conductive , such as when the mounting element is another electrode , an insulating member must be provided between the cylindrical portion 15 and the clip 22 . such an insulating member may be received in the channel 17 of the cylindrical portion 15 or in a recess in the clip 22 , so that the insulating member is held clamped between the cylindrical portion 15 and the electrode 16 when the components are in the position shown in fig2 . although modifications and changes may be suggested by those skilled in the art , it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art .