GB814625A - Improvements in or relating to radiation detectors - Google Patents

Abstract

814,625. Photo-conductive devices. PHILIPS ELECTRICAL INDUSTRIES Ltd. Sept. 5, 1956 [Sept. 8, 1955], No. 27174/56. Class 37. [Also in Group XL (a)] A device for the detection of radiation comprising a photo-sensitive part and a luminescent part connected together in an electric circuit, the emission of the luminescent part being controlled under the action of variations in the electrical properties of the photo-sensitive part produced by the radiation to be detected, is characterized in that the luminescent part comprises a luminescent substance exhibiting field quenching, means being provided for causing the luminescent part to luminesce by irradiation. Fig. 1 shows an arrangement for producing a positive image of a photographic negative. The image screen 1 comprises a photo-sensitive layer 6 of cadmium sulphide and a luminescent layer 8 of zinc sulphide activated with silver separated by an opaque layer 7 of black lacquer. Electrodes 5 and 9 in the form of transparent layers of conductive stannic oxide or other metal or in the form of metal grids are connected to an alternating voltage supply 12. The layers are held between glass plates 2 and 3 in a frame 4. A projection device 20 comprising a light source 23, a diffusion screen 24, a half condenser 25 and a movable projection lens 26 attached to a housing 21 by a bellows 27, projects an image of a photographic negative 22 on the photo-sensitive layer 6 of the image screen 1. An auxiliary light source 13 comprising an ultra-violet lamp 14, a filter 15 and a lens 16 produces ultra-violet radiation U which causes the layer 8 to luminesce. Since the material of the layer 8 exhibits field quenching, an increase in the voltage across the layer 8 due to irradiation of the photo-sensitive layer 6 will produce a decrease in the luminescence of the layer 8 produced by the auxiliary radiation U. A positive image of the negative 22 is thus produced on the layer 8, and by using subdivided colour filters, together with a corresponding subdivision of the photo-sensitive and/or luminescent layer, positive reproductions of colour negatives may be obtained. Fig. 2 shows an arrangement for use as a night viewer or as an intensifying screen in the projection of cinematograph film and photographic images. The image screen 40 differs from the screen 1 of Fig. 1 in that there is only one glass plate 41 on which the various layers are coated in contact with one another, and the photo-sensitive layer 45 consists of zinc sulphide activated by silver and gallium which exhibits infra-red quenching of the photo-conductivity. The electrode 46 can be replaced by a fabric of thin glass filaments made conductive by means of stannic oxide. A light source 51 comprising a filter 53 which filters out infra-red and a lens 54 throws on to the photo-sensitive layer 45 a beam L, comprising for example, ultra-violet rays, such that the photo-conductivity caused by it in the layer 45 is decreased in accordance with the intensity of simultaneous irradiation by infra-red rays from a filter 57. The luminescent layer 43 is irradiated by ultra-violet rays U from a source 13. The layer 43 exhibits field quenching so the visible image on the luminescent layer 43 shows the same contrast between light and dark as the image produced by the lens 56 on the photo-sensitive layer 45.