GB975554A - Improvements in or relating to devices for detecting radio-active radiation - Google Patents

Abstract

975,554. Radiation detectors. ELECTRIC & MUSICAL INDUSTRIES Ltd. March 10, 1961 [March 10, 1960], No. 8418/60. Heading G1A. A device for detecting radio-active radiation comprises a light-tight casing including a fluorescent screen 4 sensitive to said radiation and having at least one rectilinear edge (the lefthand vertical edge as illustrated), a light reflecting surface 3 on said casing facing said screen and a photo-sensitive device 8 having a photosensitive target 9, 10 disposed in said casing to receive light from the screen and reflecting surface, the target being so shaped so as to receive light from directions parallel to and perpendicular to said rectilinear edge and being of such extent and position that the response of the device to radiation incident near the extremeties of said edge of the screen is substantially the same as the response of the device to radiation incident near the centre of the screen. Preferably the screen 4 is square so that the device is suitable for detecting radiation at the corners of benches or the like. The photo-sensitive device is of the photo-multiplier type and is housed in a tubular extension 7 of the casing with the target end projecting into the casing. If the target extends into the casing about one-third of the distance along screen 4 to the rectilinear edge, the response to radiation at the extreme corners of the edge is about 90% of that to radiation at the screen centre. If the target extends half the distance, the response at the edge is more nearly equal to that at the screen centre, but the response to radiation at the other two corners, i.e., the right-hand corners, is reduced. The appropriate shape of the photo-sensitive target is obtained by arranging the target to extend not only over the end wall of the device as shown at 9, but also for a similar distance over the side wall, as shown at 10. If desired, the end wall, when viewed from the exterior, may be slightly convex. Where it is desired to detect a radiation, the screen 4 may comprise a zinc sulphide phosphor deposited on a methyl methacrylate support. Where it is desired to detect both α and # radiation, the screen comprises zinc sulphide and a fluorescent plastic phosphor. Over the screen is provided a light opaque screen of beryllium, aluminium or the material known under the Registered Trade Mark "Melinex" suitably aluminised. The assembly is completed by a protection grille 6 which is positioned over the screen as described in Specification 975,555.