Patent GB-792424-A (GB)
Title: A radiation indicator, particularly for radioactive radiation
IPC: G01T1/185
Filed: 1955-01-14
Abstract: 792,424. Radiation measuring instruments. FORSVARETS FORSKNINGSINSTITUTT. Jan. 14, 1955 [Jan. 18, 1954], No. 1240/55. Class 37. [Also in Group XL (b)] In a radiation indicator comprising a casing, an electrometer is included consisting of a vane with a filament passing through the centre of gravity and in the plane of the vane, the moving vane electrode or associated fixed electrode being connected to a supply while the other electrode receives charge as a result of the radiation causing ionization so that the moving vane rotates about the axis of the filament, approaching and touching the fixed electrode, whereupon it is discharged and repelled and the process of charging repeated. The frequency of oscillation is an indication of the strength of the radiation and the sensitivity of the instrument may be varied to allow use in different field strengths. The frame 17, Figs. 1 and 3, supports fixed electrodes 18, 20 connected to capacitor 7 which is charged over button 14 which may be connected to an external supply. The other pole of the capacitor 7 is connected to the conductive layer 5 of the ionisation chamber 4. The wire 30, due to ionization, tends to take up the potential of the layer 5, thereby causing the vane 24 to be attracted to the fixed electrode 18, 19, ultimately touching at the point 18<SP>1</SP> to discharge the vane and wire so that the vane is repelled and the process is repeated. The filament 22 is of tungsten or silver-coated quartz while the vane 24 is of mica coated with gold or silver. Rotation of the end support 26 allows the restoring force to be adjusted. For higher field strength the electrode system 20, 21, 25 is used, the wire 30 being dispensed with. In a modification, Figs. 4 and 5, a voltaic pile is mounted in container 34, a lead 58 being connected to the frame 45 supporting the fixed electrodes 40 ... 44, lead 57 being connected to the coating 33. The two vanes 39, 40 are mounted on filaments having springs 47, 49 at one end and screws 48, 50 at the other for adjustment. A wire 36 depends from the spring 47 to increase the sensitivity of vane 39. Windows 51, 52 are arranged in the graphite layer 33 with blocks 53, 54 of yellow fluorescent material, and phosphorescent strips 55, 56 to illuminate the vanes in low ambient light. A silica gel container 59 is provided to absorb the moisture. The light provided by the members 53, 54 and 55, 56 may be different to allow the reaction of the vanes 39, 40 to be more clearly differentiated. In a further modification, Figs. 7 and 8, a single electrometer system 65, 67 is mounted in a chamber 70 and may be associated through switch 89 with a Geiger-Muller tube 73. A tapped battery 76 is provided with one pole connected to the conductive layer 71, a further battery 82 energizing lamp 78. On depressing button 91 the spring 86 engages the outer surface of the lamp 78 to complete its circuit, the light shining through lens 79 and mirror 80 to illuminate the electrometer which is viewed through window 81. Button 91 may be used to rotate the switch spindle 89 into one of four positions, the light shining through disc 96 to show the position occupied. In position P1, P2 and P3 the Geiger-Muller tube is connected to the electrometer over switch 75 and the voltage applied to the tube is varied by the tappings on the battery 76. In position P4 the switch 75 is opened so that only the chamber 70 is effective as the instrument is in its least sensitive state. In a modification, Fig. 11 (not shown), the instrument is operated from an A.C. supply. A photo-cell device may be used as the detector, Fig. 12 (not shown).