GB527353A - Improvements in photoelectric cells and methods and means for making, sensitizing, and stabilizing the same - Google Patents

Abstract

527,353. Photo-electric cells cathode-ray tubes. ILLINOIS, BOARD OF TRUSTEES OF THE UNIVERSITY OF. Dec. 30, 1938, No. 37927. Convention date, Jan. 5, 1938. [Class 39 (i)] The cathode of a photo-electric cell or an iconoscope screen is rendered more sensitive and stabilized by bombarding the alkali-metal forming the photosensitive layer with atomic hydrogen and with electrons from a thermionic cathode. The metal may be located on the screen or before or during deposition; the latter may be effected by passing molecular hydrogen through boiling alkali metal, when it is deposited. Fig. 1 shows an arrangement in which molecular hydrogen is supplied from a tank 1, through pressure reduction valve 2, cut off valve 3, water trap 4 whose temperature is adjustable, valve 5, actuating bulb 6 and velocity selector 20 to the tube 11. The bulb 6 contains a filament or spherical spaced electrodes, or may be of quartz and be irradiated with ultra-violet light, in which case a trace of mercury is present in the hydrogen. After the tube has been evacuated through 10 the valve 5 is closed, and the bulb 6 operated for five seconds. After evacuation the sensitivity may be tested the process repeated if necessary. Finally the cathode is bombarded with electrons from the gun 18, for a time depending on the potential used. This stabilizing operation and the sensitizing operation may be carried on alternately or simultaneously until the desired sensitivity is obtained. In an automatic apparatus (Fig. 1) a Pirani or other pressure gauge 32 is mounted in the atmosphere of the tube and connected through the balance bridge 42 to a relay controlling the valve 5. The valve 10 and a series of contact 40 ... 52 are controlled by cams so that the various operations are performed. In this case a filament 8 acts as anode, and remains cold while the sensitivity of the tube is measured, is heated by a small current to dissociate the hydrogen (contact 46 open), and by a large current to bombard the cathode with electrons (contact 46 closed). An iconoscope, Fig. 7 may be provided with four filaments, 33, 34, 35, 36, of which 33 is of tantalum loaded with hydrogen, 34 of tungsten, 35 of an alloy of tantalum and barium and 36 of platinum coated with emulsive material. Filament 33 is heated first to release hydrogen, which is then dissociated by 34 ; 35 is then heated to absorb the hydrogen and any free gas in the tube, and 36 to bombard the cathode surface with thermions, and 35 again to complete the gettering. A filament loaded with alkali metal may be provided to restore the photosensitive surface. Alternatively three of the filaments may have appropriate heatable capsules. The Specification as open to inspection under Sect. 91 describes the use of dissociated water vapour to provide the atomic hydrogen, as described in Specification 527,484 ; this subject-matter does not appear in the Specification as accepted.