| 摘要 |
898,433. Electron multipliers. WESTING- HOUSE ELECTRIC CORPORATION. Sept. 15, 1960 [Sept. 30, 1959], No. 31814/60. Class 39(1). In an electron multiplier comprising a plurality of transmissive dynodes 13, Fig. 1, between cathode 12 and anode 20, each dynode is secured to a peripheral metallic support, and each support is spaced from adjacent supports by insulating members 14 defining isolated compartments between successive dynodes. At least the first dynode comprises a continuous, electron-transmissive, secondaryemissive, insulating layer so that cathode material is confined to the compartment defined between the cathode and first dynode and ion feedback to the cathode from other parts of the multiplier is prevented. As shown, the ceramic members 14 are coated internally with resistive chromic oxide, and externally with platinum or silver to minimise charging. They are formed with holes 16 for electrical connections and for evacuating the spaces between the dynodes, and are held together by insulating rods 15. A coaxial line connection is made to the anode 20 and the last dynode, which is connected to metal envelope portion 19. During processing of the caesiated antimony photo-cathode 12, the pumping hole 23 in shield 22 may be closed by a ball manipulated through a side-arm at 33, or hole 23 may be omitted, the cathode compartment being evacuated separately. The last dynode may be replaced by an accelerating grid which electrostatically shields the anode. The dynodes may be made by settling a solution of nitrocellulose lacquer from water on to a nickel mesh and forming a film of aluminium or carbon with or without a thin film of gold on the organic film which is subsequently baked away. The secondary-emissive layer of potassium chloride, 200-2000A thick, is then formed by evaporation. Alternatively, the secondary-emissive layer and conductive scattering layer may be formed on a permanent film of SiO, Al or Al 2 O 3 on a grid, or on a self-supporting film of metal or aluminium or magnesim oxides. In a further embodiment, the dynodes are supported by non-magnetic spacers 63, Fig. 5, and rings 61 of a magnetic alloy which are sealed, by heliarc wetting, between glass or ceramic envelope portions 62, e.g. of alumina. The photo-emissive cathode 64, which may be of gold, may be evaporated on to the surface of a movable glass plate facing away from the dynodes, a wire spring mechanism being provided to flip over the glass to place the cathode in the operating position. The anode 69 may be replaced by a layer of aluminized phosphor, the device being disposed in a uniform magnetic focusing field. For use in photographing rapidly moving objects, the image intensifier may be provided with a fine mesh control grid between its first and second dynodes. In a further image intensifier, Fig. 7 (not shown), the cathode and phosphor are disposed on part-spherical ends of a frusto-conically shaped envelope, the dynodes also being part-spherical, to obtain image magnification. Specifications 792,507 and 862,211 are referred to.
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