Improvements in or relating to secondary electron emissive electrodes

摘要

672,008. Cathode materials and processing. WESTERN ELECTRIC CO., Inc. Dec. 8, 1950 (Dec. 9, 1949], No. 30094/50. Class 39 (i). A secondary-electron-emitting electrode consists of a beryllium coating on an insulating layer on a metal base. Silica, 50-5000 A units thick, may be deposited on a tantalum or platinum base ; the thickness of the beryllium may be 50-500 A units or such that 10-90 per cent of light is absorbed. The electrode may be activated by heating to 750‹ C. for a period, which may be half-an-hour or two or three hours to produce a secondary emission ratio of over 14 when the primary voltage is 500. The insulating material may be zirconium oxide, aluminium oxide, manganese oxide, or beryllium oxide. It is stated that secondary emission is increased by traces of tin, palladium, copper, gold, iron manganese, nickel, lead, barium or silicon in chemically or commercially pure tantalum or platinum. The insulation or beryllium may be deposited on a plate 11, clamped on brackets 22 by spring clips 23 from a pure tungsten wire crucible 24 supported by the heater leads 25. To produce a silica layer 50-200 A units thick whilst the crucible is heated for 15 seconds, the crucible should contain 2 m.gms. of crushed silica. The container may be evacuated to a pressure of 10-5 mms. When beryllium is deposited from the crucible, light may be projected through an associated glass plate on to a photo-cell which can be used to record the reduced light intensity corresponding to the thickness of the beryllium. Alternatively, ethyl silicate is pumped into a cathode-ray tube, the target of which is heated to decompose the silicate to produce thereon a silica layer. Curves show the secondaryemitting ratio for various primary electron voltages at room temperatures and when the electrode is heated to 600‹ C.