Patent GB-1170074-A (GB)
Title: Radiation imaging systems and methods of operation therefor
IPC: G01T1/164
Filed: 1966-09-28
Abstract: 1,170,074. Television. WESTINGHOUSE ELECTRIC CORP. 28 Sept., 1966 [14 Oct., 1965], No.43285/66. Heading H4F. [Also in Divisions C7 and H1] A system for sensing radiation from an object comprises a plurality of optical elements 52 having laterally, spacially disposed axes, which can transmit radiation from the scene and spurous radiation, means 62 for collecting the radiation from the elements and converting it into an electron image, a target 68, means 74, 72, 70 for directing electrons from the electron image on to the target to form a charge pattern thereon, means for discharging the pattern and deriving an output signal in accordance with that pattern and means for discriminating against any portion of the output signal representing spurous radiation or extraneous signals developed within the system, the target comprising a conductive member and porous layer of dielectric storage material having a density less than 10% of the bulk density and storing more than 10 + electrons per element. A scintillation camera system 10 comprises a multi-aperture collimator 34, an image intensifier tube 12, a fibre optic member 52 and an electron image tube 14. The intensifier tube comprises an input screen 26 converting an incident X-ray or gamma ray image into an electron image, an electrostatic lens system 42 and a light emitting output target 36 disposed on the fibre member 52. The input screen comprises a glass plate 32 or the envelope end plate 22 coated with an X-ray sensitive layer of ZnCdS, CaF, Ca tungstate, ZnS or NaI and a photocathode layer of CeSb. The output target 36 includes a fluorescent layer of ZnCdS 40 on a tin oxide conductive layer 38. The light image from this is conveyed by the member 52 to a CeSb photocathode 60 of the camera tube 14. Electrons from the cathode 60 are focused and accelerated by electrodes 70, 72, 74 and a coil 97 on to a target 68 comprising layers of Al 2 O 3 , Al and a porous material, e.g. KC1, MgCl 2  or MgO capable of generating secondary electrons in response to electron bombardment, the porous material having a high resistivity and electron storage capacity. Pre-storage intensification may be provided by a number of dynodes between the photocathode 60 and the target 68 or between the photocathode layer 30 and target 36. A voltage source 98 is connected to the Al layer through an impedance 96 causing electrons to move towards the layer leaving a pattern of charges on the surface of the porous material. This surface is scanned periodically by a low velocity electron beam from a gun 66 consisting of a cathode 86, control and accelerating grids 88, 90, electrode 92 and deflecting coils 94, 97. The scanning beam at ground potential causes a series of capacitive discharges across the porous layer and voltage pulses across the impedance 96. This signal is passed through amplifiers 102, 128 to a C.R.T. directly or via image storage means 120 which may be a tube or magnetic recording disc or tape which permits continuous non-destructive read out as potential builds up on the porous layer. The amplifier may be replaced by a pulse height discriminator and to output connected either to the storage means or a pulse height sealer and a moving pen recorder. An equidensity plot of incident radiation may be obtained by applying to the Al plate successively lower voltages, each time scanning the target. Selected portions only of the target 68 may be scanned.