Abstract: Disclosed is a method for the fabrication of an X-ray image intensifier tube. Before being introduced into the X-ray image intensifier, one of all the electrodes are entirely or partially covered with a layer of an orgainc polymer which is an electronic conductor of electricity and which has the property of reacting chemically with the alkaline metals deposited on the electrodes. Thus, the spurious illumination of the observation screen, due to the alkaline metals deposited on the electrodes during the preparation of the photocathode, is eliminated.

Abstract: Before being introduced within the intensifier, the grid which is nearest the anode is coated with a layer of electrically conductive material having the property of oxidizing alkali metals. This has the effect of elininating any parasitic illumination of the viewing screen caused by alkali metals unintentionally deposited on the grid at the time of formation of the photocathode.

Abstract: A polyurethane topcoat composition is provided comprising a water-free organic solvent solution containing from 0.5-2.6 isocyanate equivalents of the biuret of 1,6-hexamethylene diisocyanate per hydroxy equivalent of the polyesterification reaction product of the components set forth below having an acid number of less than 7:______________________________________ Parts by Permitted Component Weight Variation ______________________________________ 1,6-hexanediol 11.63 .+-. 1.0 di-(2-hydroxyethyl) dimethylhydantoin 20.92 .+-. 1.0 trimethylol propane 17.75 .+-. 1.0 dimethyl terephthalate 28.10 .+-. 1.0 adipic acid 21.15 .+-. 1.