GB726333A - Improvements in and relating to image intensification apparatus - Google Patents

Abstract

726,333. Cathode-ray tubes. GENERAL ELECTRIC CO. Feb. 16, 1953 [Feb. 16, 1952], No. 4253/53. Class 39 (1). An image intensifier comprises means for generating a defocused electron beam along an axis, an X-ray responsive phosphor for converting X-ray images into light images, a photo-conductor adjacent the phosphor for receiving electrons from the beam and transforming the light images into reversely corresponding charge images, and an electronpermeable element positioned between the source of the beam and the photo-conductor and having an electron responsive phosphor on the side opposite the source of the beam whereby electrons in the beam pass through the electron-permeable element and are reflected by the charged areas of the photoconductor on to the electron responsive phosphor to form intensified light images reversely corresponding to the X-ray images. In the arrangement, Fig. 1, the electron beam is generated by a gun, the cathode of which is about 10 volts negative to earth, and the electrons are accelerated and focused in a diffuse beam by a wall coating 19 connected to grid 4 and maintained at a potential of about 10 Kv.; the grid 4 is coated with luminescent material on the side opposite the electron gun. The target 3, shown in Fig. 2, comprises a phosphor 6 sensitive to X-rays and deposited on a support 2 which may be the end wall of the tube; the phosphor is covered with a transparent conducting layer 7 which in turn is covered with a photo-conductive layer 8. The conducting layer 7 is maintained at a potential up to about 25 volts. In operation parts of the photo-conductive layer 8 become conductive due to the light image generated by the fluorescent layer 6 and the parts are not charged by the electron beam; the remainder of the layer is charged by the beam and the beam is then repelled by the charges on to the fluorescent screen 4-to form an image which is the reverse of the image on the layer 6. The image on the screen 4 may be projected on to a viewing screen 29<SP>1</SP> by an optical system 28'. The -emission spectrum of the phosphor on the grid 4 should be selected in conjunction with the photosensitivity spectrum of photoconductor 8 so that light from the grid 4 does not modify the charge on the photoconductor 8. In a modification, Fig. 4 (not shown), the electron beam is generated by an extended photocathode energized by an electro-luminescent cell which may be secured to the envelope. The photocathode may be composed of antimony on which caesium is deposited by flashing in a vacuum, the cathode then being heated to a temperature between 150‹ and 210‹C. to form a caesium antimony compound. Other suitable photosensitive surfaces may be produced by flashing caesium on arsenic or bismuth or any mixture of arsenic, antimony or bismuth, or by flashing other alkali metals, such as rubidium, or mixtures of these metals on deposits of arsenic, antimony or bismuth or mixtures of these. Specification 716,159 is referred to.