X- and gamma-ray sensitive image intensification tube

Abstract

The invention relates to an X- and Gamma-ray sensitive image intensification tube for use in a so-called gamma camera or the like, which tube preferably has a single crystal input phosphor.

I claim: 
     
       1. In an image-forming device including an image intensification tube, .Iadd.said tube including an evacuated envelope, .Iaddend.and .Iadd.said device further including .Iaddend.means to reproduce an image output from said tube, an improved image tube input phosphor layer comprising: a. a single crystalline sheet .Iadd.of cesium iodide, said sheet being .Iaddend.of substantially uniform thickness .Iadd.and being located within said evacuated envelope; .Iaddend.   b. said sheet having the following physical properties: i. photoluminescent and transparent to its own light;   ii. efficient in absorption of ray energy;   iii. of sufficient thickness and absorption to convert to light energy substantial percentages of gamma energy emanating from a source of energy of 250 kev. or less;   iv. of high resolution characteristics; and   v. dish-shaped in configuration and focused to an accelerating electron field in said tube. .[.2. The image device of claim 1 wherein said sheet     
     
     
        is cesium iodide..].3. The image device of claim 1 wherein said sheet is a 
     
     
        single crystal. .[.4.  The image device of claim 1 wherein said sheet is a 
     
     
        single crystal of cesium iodide..]. 5. An image intensification tube responsive to stimulation by gamma energy or the like comprising: a. an evacuated envelope having an input end and an output phosphor spaced therefrom;   b. a dish-shaped light-emissive layer near said input end and composed of a single crystalline sheet of photoluminescent material;   c. an electron-emissive layer deposited near an inner surface of said light-emissive layer such that light photons emitted by said light-emissive layer stimulate said electron-emissive layer and cause the latter layer to emit electrons;   d. means for accelerating electrons from said electron-emissive layer against said output phosphor;   e. said dish shape of said light-emissive layer and said electron layer being substantially contoured to the shape of an accelerating electron field produced by said acceleration means so as to be focused therewith, and   f. a mounting means supporting said light-emissive layer and   
     
     
        electron-emissive layer near said input end. 6. The tube of claim 5 wherein said photoluminescent material is a single crystal of cesium 
     
     
        iodide. 7. The tube of claim 5 wherein said photoluminescent material is a 
     
     
        single crystal. 8. The tube of claim 5 wherein said photoluminescent 
     
     
        material is cesium iodide. 9. The tube of claim 5 wherein said photoluminescent material is of sufficient thickness to absorb about 30 percent of source energy of 150 kev. or less and is transparent to its own 
     
     
        light. 10. The tube of claim 5 wherein said photoluminescent material can withstand temperatures of 300° F. without distortion or other 
     
     
        degradation. 11. The tube of claim 5 wherein said mounting means is open at a central portion whereby entering energy passing through said central portion is not filtered or otherwise obstructed by said mounting means. 
     
     
            The method of forming an input gamma ray sensitive structure for an image intensification tube comprising the steps of: a. heat softening a single crystal of cesium iodide;   b. molding the single crystal of cesium iodide while heat softened to a dish-shaped configuration having a concave output surface to form a photoemissive layer;   c. depositing an electron-emissive layer on the output dish of said formed dish-shaped cesium iodide crystal with the electron layer and crystal in sufficiently close juxtaposition that light energy emitted by the crystal stimulates said electron-emissive layer and causes the emission of electrons when in use; and   d. securing a mounting means to the periphery of said photoemissive layer and mounting said layers in an envelope with the convex surface of the   
     
     
        photoemissive layer oriented toward an input end of said envelope. 13. The method of claim 12 wherein the depositing steps is on a barrier layer and including the step of providing a barrier layer between the electron-emissive layer and the crystal. .Iadd. 14. The image-forming device of claim 1 wherein said sheet is of sufficient thickness to absorb approximately thirty percent of source energy at 150 kev. or less. .Iaddend.