Patent GB-671472-A (GB)
Title: Improvements in or relating to electron discharge tubes used in television or the like
IPC: H01J31/32
Filed: 1949-04-01
Abstract: 671,472. Cathode-ray tubes. COMPAGNIE POUR LA FABRICATION DES COMPTEURS ET MATERIEL D' USINES A GAZ. April 1, 1949 [April 13, 1948], No. 8899/49. Class 39 (i). An electron discharge tube comprises a storage electrode which includes a continuous conducting layer and a layer of material, the conductivity of elementary areas of which is proportional to the intensity of high velocity electrons of an electron image incident on one side of the storage electrode, the said conductivity being effective to control the emission of secondary electrons from the storage electrode when it is scanned on the other side by a cathode-ray beam. A thin electron permeable film 2 of aluminium, beryllium or magnesium supports three layers, one 7 of material fluorescing in the ultra-violet upon impact of electrons, e.g. calcium oxide activated by lead, calcium tungstate, zinc sulphide or an alkali halide activated by thallium; the second a thin layer 8 of cadmium iodide CdI 2  evaporated in vacuo, the conductivity of which is proportional to the intensity of the incident ultraviolet radiation; and a third layer 9 which is optional, comprising thin metallic particles insulated from each other and sensitized to give especially high secondary emission. Light from the object falls on the photo-cathode 4, the electrons are accelerated on to layer 7, producing ultra-violet radiation which gives a conductivity pattern in the cadmium iodide layer 8. The scanning beam 5 liberates secondary electrons which are collected by anode 6 and yield signals. Plate 2 may also act as the signal plate. The cadmium iodide may be replaced by an alkaline salt activated by a heavy metal. In a modification (Fig. 2, not shown), the layer 7 is emitted and a layer of cadmium selenide or sulphide is deposited on film 2, e.g. by sedimentation or electrophoresis, and covered by a secondary emissive mosaic 9 as before. The conductivity and/or dielectric constant of the deposited layer varies with the impact of the electron from the plate cathode, and sets up a conductivity pattern which determines the signals produced by the scanning. The layer of selenide must be thin, and an extremely thin layer of insulating material may be interpolated between film 2 and the conductive layer to stop slow electrons. The mosaic layer may be omitted, the cadmium selenide being secondary electron emitting. Specification 648,509 is referred to. The Specification as open to inspection under Sect. 91, also comprises the subject-matter of Fig. 3, (Cancelled), in which a modulated scanning beam falls on a target comprising a metal film 2<SP>1</SP>, a layer of cadmium selenide 10<SP>1</SP> covered by a photo-cathode layer 3<SP>1</SP> of silvered particles sensitized by oxygen and cµsium. The latter is flooded by light from a source 14. The scanning beam sets up a conductivity pattern which produces a control potential governing the emission from the photo-electric mosaic. The photo-electrons are accelerated by anode 13 on to a fluorescent layer 12. The induced conductivity is spontaneously alternated by means of a scanning period of the order of <SP>1</SP>/ 25  second. This subject-matter does not appear in the Specification as accepted.