Patent GB-492059-A (GB)
Title: Improvements in the manufacture of electric discharge devices employing secondary electron emission
IPC: H01J9/12
Filed: 1937-04-12
Abstract: 492,059. Electrode materials; electron multipliers. GENERAL ELECTRIC CO., Ltd., and SIMMS, C. H. April 12, 1937, No. 10384. [Class 39 (i)] In the manufacture of a multi-stage secondary emission electron multiplier in which an alkali metal such as caesium re-acts with superficially oxidized metal bodies to form the secondary electron emitting cathodes, the multiplier is maintained at a suitable temperature exceeding 100‹ C. while the metal vapour is admitted gradually, and the emission from the surface of one of the bodies to a neighbouring electrode is measured during the admission of the metal vapour. In the case of caesium coated silver oxide bodies the temperature should not differ greatly from 200‹ C. The invention is described in connection with the preparation of the multiplier shown in Fig. 1, comprising a lime-soda glass tube 1 and primary cathode 7<1> and secondary cathodes 7 of silver sheet À15 mm. thickness bent into channel form and attached to a mica plate 6 by tags 8. The potential plates 9 also of silver À15 mm. thick are attached to the mica sheet 6 by tags 11. Holes 10 are provided in the plates 9 to admit the caesium &c. vapour to the interior surfaces and are closed electrically by fine crossed wires. The potential plate 9<1> over the primary cathode 71 is a grid of fine molybdenum wires. The last potential plate is electrically connected to a metal gauze screen 12 in front of a silver collecting electrode 13. All the leads within the envelope are sheathed in glass, those connected to the cathodes being brought to a mica terminal plate 14 from which they pass through the ring seal 2. The tube 1 with the assembled electrodes is connected to a pump by means of a tube 21 and trap 22 as shown in Fig. 4, so that an electric oven 15 can be brought down over it. The upper end is connected to a tube 5 having a container 16 for caesium azide and including a capillary 17. The tube is evacuated while heated to 400‹ C. the trap 22 being cooled by liquid air. In the course of evacuation, the tube is flushed with oxygen at 1 mm. which is then pumped out. The oven is switched into a new circuit which will maintain it at 200Œ2‹ C. and raised, and the envelope filled with oxygen at À8ŒÀ05 mm. and the cathodes oxidized successively by electric discharge, until the colour is deep purple or blue. The oxygen is evacuated and the caesium azide in the container 16 decomposed and the nitrogen pumped away. Caesium is then distilled into the part 18 of the tube 5 which is now sealed off at 19. Before the entry of the caesium into the tube, the electrodes are brought to the temperature of 200‹ C. and for this purpose the end of the tube 18 is wrapped in wet cotton wool while the oven is brought down over the tube 1 for 15 minutes. This time may be reduced by filling the tube with argon which is subsequently pumped away. The wool is then removed and the distillation of the caesium into the tube allowed to take place until the emission at the cathode 7<1> farthest from the point of entry of the caesium reaches a maximum and begins to fall. The tube is sealed off at 20 and the heating continued to distribute the caesium and remove excess, after which it is finally sealed at 21. Specifications 345,375 and 469,477 are referred to.