GB677856A - Improvements in and relating to cathodes for ionization detection devices - Google Patents

Abstract

677,856. Discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. July 10, 1950 [July 22, 1949], No. 17213/50. Class 39 (i). A method of producing a cathode for an ionization detection device comprises applying a metal halide to the inner surface of an envelope of vitreous or ceramic material which is heated so as to form thereon an electrically conductive coating. As shown, the tube 1, of glass or ceramic material, is flared outwardly at 2 to receive a thin mica sheet or window 3 which is sealed to the tube 1 by means of a low melting-point glass 4. The end of the tube opposite the window 3 is sealed and a wire anode 5 of chromium-iron alloy, tungsten, or other suitable metal, is mounted within the tube and passes through the tube wall, a glass bead 6 being fused to the inner end of the anode to prevent leakage of the discharge from the sharp point. An electrically conductive coating produced by treatment with tin chloride covers the inner surface of the tube 1, electrical contact being provided by a split ring or band 8 of metal connected to a wire 9 and fitting tightly on the coating 7, the metal parts being polished and oxidized to prevent corrosion or absorption of the halogen gas. The atmosphere of the tube consists of a halogen and other inert gas or gases, a typical composition being 1 part by volume of halogen to 760 parts by volume of neon and 4 parts by volume of argon. The non - corroding and non - halogen absorbing cathode is produced by treating the inner surface of the envelope with a metal halide which should preferably have a boiling point below the temperature at which the coating is formed, tin chloride being preferred, but other halides such as those of iron, titanium, columbium, aluminium, and tantalum may be used. Preferably the tin chloride is dissolved in a solution of alcohol and sprayed into the envelope, which is maintained at a temperature of 400‹ to 700‹ C., a preferred solution consisting of 50 parts by weight of tin chloride dissolved in 45 parts by weight of ethyl alcohol. In a modification, Fig. 2 (not shown), the tube has no mica window, the radiation to be measured passing directly through the thin side walls, which are coated on their inner surface with a conductive film as described.