GB736227A - An electronic x-ray image converter - Google Patents

Abstract

736,227. Cathode-ray tubes. LICENTIA PATENT - VERWALTUNGS - GES. Oct. 10,. 1952 [Oct. 19, 1951], No. 25456/52. Class 39 (1). An image intensifier tube for X-ray pictures comprises a semi-conductive layer 2 on a metal backing of which the conductivity varies according to the incident X-ray intensity or according to light intensity from an X-ray image on a luminescent screen, and the metal backing is held at the potential of cathode 4 so that electrons. therefrom are variably reflected by the semi-conductive layer and form an intensified image on luminescent screen 3. The first luminescent screen referred to may also be inside the tube envelope. It is stated that the semi-conductive layer may be of selenium, or the oxides, sulphides, selenides, tellurides, carbonates, sulphates and chlorides of Zn, Cd, Hg, Pb, Sb, Bi, Tl, Cu, Ag, Mn, or conventional fluorescent materials such as the above-mentioned sulphides and is formed by evaporation or deposition from suspensions. They are given a high transverse resistance, e.g. by forming them as a mosaic of electricallyinsulated elements. The layer thickness is 10<SP>-3</SP>-1 mm. CdS, CdSe and CdTI are stated to be most suitable for excitation by light from the intermediate fluorescent screen. In the form shown. the electrons pass through a small hole 5 in luminescent screen 3 and are accelerated by anode 6 to 2000 volts before being reduced to cathode potential at layer 2. The electron paths to the layer may be made curved by magnetic or electric deflecting fields. A second anode 7 has a variable voltage of 10-100 volts to enable the final image size to be enlarged or reduced. It is stated that due to the velocity distribution in the beam some electrons will always strike layer 2. A prior art image transformer using a semi-. conductive layer for forming an image of an object. illuminated by or emitting infra-red rays, is referred to.