Patent GB-675042-A (GB)
Title: Thermal radiography
IPC: G02B23/12
Filed: 1950-02-13
Abstract: 675,042. Photographic processes; photometers. EASTMAN KODAK CO. Feb. 13, 1950 [Feb. 11, 1949], No. 3624/50. Classes 97 (i) and 98 (ii). [Also in Group XL (a)] An image formed by heat-producing radiation is rendered visible by uniformly illuminating with exciting radiation a layer of a phosphor whose brightness is a maximum at some particular temperature, maintaining the phosphor at a temperature at which its brightness is above nil but substantially below said maximum, and focusing the heat-producing radiation thereon. Fluorescence or phosphorescence phenomena, e.g. spontaneous afterglow, stimulation quenching or exhaustion may be used. In Fig. 1, the heat from a kettle 10 is imaged by a rock salt lens 12 on to a phosphor layer 13 which is uniformly illuminated by an ultraviolet lamp 17, the heat radiation causing variation in luminescence which is detected by the eye 18 or a camera 22. A screen 16 protects the phosphor from other heat radiations, e.g. the hot plate 11. In a modification, the heat radiation is focused by means of an apertured concave mirror, and the distance of the U.V. source from the phosphor layer is made adjustable. In this case a mask may be made by photographing the phosphor layer when not subjected to imaged heat radiation but under normal conditions of illumination, the developed negative being a representation of unevenness in the phosphor or in the ultra-violet illumination. This compensating mask is thereafter used in front of the image of the phosphor layer. In another modification, the phosphor image is scanned by a photo-electric device and its brightness recorded on a rotating drum. Alternatively the heated object moves relative to a fixed photo-electric cell. Fig. 7 shows an arrangement for operation at low or constant temperatures, the radiation unit being surrounded by a cooling system 90. The phosphor screen 71 is supported on springs 73 in a chamber enclosed by the rock salt plates and provided with valves 95, 97 so that the gas therein can be evacuated and replaced with cooled dry gas which removes any residual heat image. The heat image is focused on to the phosphor 71 by the aspheric plate 78 and reflector 79, the visible image being viewed by a telescopic system 84 and mirror 85. The screen, Fig. 9, may comprise phosphor tips 103 mounted on the ends of closely-spaced nylon bristles 104, giving high individual heat insulation. Curves are included showing the relative brightness variation with temperature of zinc cadmium sulphide activated by silver, copper or manganese, plus four parts in a million of nickel, cadmium borate activated by manganese and cadmium and lead molybdates or mixtures thereof. Zinc and cadmium selenides and mixtures thereof and with the sulphides of these metals, cadmium silicate activated by manganese, and calcium lead and strontium tungstates either alone or in combination are also referred to as suitable phosphors with negative or positive temperature coefficients. Mixtures of phosphors with different temperature ranges may be employed. A minimum amount of binder is used in the screen construction. Specification 675,043, [Group XL (a)], is referred to as describing other suitable phosphors.