GB481170A - Improvements in or relating to electron discharge devices - Google Patents

Abstract

481,170. Electric discharge devices. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 7, 1936, Nos. 24404 and 24405. Convention dates, Sept. 6, 1935 and. April 30, 1936. [Class 39 (i)] A secondary-electron-emitting electrode consists of a thin substantially insulating film or coating on a conductive surface, the film &c. being sensitized to produce a high emission of secondary electrons. The film &c. may consist of (a) aluminium oxide on an aluminium surface, (b) beryllium oxide on beryllium, (c) magnesium oxide on magnesium, (d) silicon oxide on silicon, or (e) Willemite on a conducting material; in all of these examples the surface may be sensitized with an oxide of an alkali metal such as caesium. The film of aluminium oxide is formed electrolytically and only sufficient alkali metal is used to form a sub-microscopic coating. The coated electrode is baked at 200‹ C. for ten minutes and oxygen is admitted. It is stated that the baking of an oxidized aluminium electrode and the introduction of oxygen, without alkali metal, produces a surface giving a considerable emission of secondary electrons. It is suggested that the positive charge left on the surface of the insulating film owing to the emission of secondary electrons, causes an attraction of electrons *from the aluminium surface and from the aluminium oxide film which shoot through the positively-charged surface. The emission persists for an appreciable time after the primary electron beam is cut off ; energization of the surface by light as well as by a primary beam reduces the secondary emission. The ratio of secondary emission to primary emission is of the order 3000. In the multiplier shown in Fig. 1, the secondary-electron-emitting electrode 7 is mounted at the apex of a V- or Y-shaped envelope 1, a photo-electric cathode 3 and an output electrode 5 being mounted in the arms, and the electron streams focused magnetically by windings 15, 17 or electrostatically. The multiplier shown in Fig. 4 has, during manufacture, a thin glass diaphragm 77 dividing the envelope to form a compartment 73 containing a secondary-electron-emitting electrode 79 and an output electrode 81, and a compartment 75 containing a photo-electric electrode 83 and two focusing electrodes 85, 87. After the electrodes 79, 83 have been sensitized separately, the diaphragm is broken by a metal ball 97. British Specifications 460,356, 469,477, and U.S.A. Specification 1,450,265 are referred to. The Specification as open to inspection under Sect. 91 includes also the use of a mosaic target, in a cathode-ray tube, formed of aluminium particles sensitized in the manner already referred to and scanned by a fine point of light. This subject-matter does not appear in the Specification as accepted.