X-RAY IMAGE INTENSIFIER INPUT

• US 3,838,273 A
• Filed: 05/30/1972
• Issued: 09/24/1974
• Est. Priority Date: 05/30/1972
• Status: Expired due to Term

• Current Assignee: Dominic A. Cusano
• Original Assignee: Dominic A. Cusano
• Inventors: Cusano, Dominic A.
• Primary Examiner(s): Borchelt, Archie R.
• Application Number:
  US05/257,538
• Time in Patent Office: 847 Days
• Field of Search: 250/213VT,483,486,487,488
• US Class Current: 250/214.0VT
• CPC Class Codes: G21K 4/00 Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens photographic processes using X-ray intensifiers G03C5/17; discharge tubes comprising luminescent screens H01J1/62; cathode ray tubes for X-ray conversion with optical output H01J31/50
• CPC Class Codes: H01J 29/385 Photocathodes comprising a layer which modified the wave length of impinging radiation

Abstract

A barrier layer of an electrically conductive material such as indium oxide (In2O3), optically transparent to x-ray phosphor luminescence, is disposed between the phosphor layer and photocathode film of an x-ray image intensifier tube to provide sufficient electrical sheet conductance relative to the photocathode film. The barrier layer provides electron replenishment to the photocathode at all points of electron emission therefrom to thereby reduce potential drop laterally across the photocathode from the ring electrode to the center of the photocathode, and also minimizes surface irregularities on the phosphor layer to thereby significantly reduce electron-optic image distortion in the image intensifier tube.

Claims

2. The improved input screen set forth in claim 1 wherein said nonconductive barrier layer is of thickness in the range of 0.1 to 1.0 micron.

3. The improved input screen set forth in claim 1 wherein said relatively electrically nonconductive material is aluminum oxide.

4. An improved x-ray image intensifier tube input screen comprising a substrate member for supporting an x-ray sensitive phosphor layer thereon, an x-ray sensitive phosphor layer disposed along a major surface of said substrate member, and a photocathode film in optical communication with said phosphor layer for producing emission of photoelectrons therefrom in response to x-ray photons being converted to light photons by luminescence in said phosphor layer, the improvement consisting of said phosphor layer being a single layer of a plurality of slightly spaced apart relatively thick phosphor structures providing a light piping effect to the phosphor luminescence and having base portions disposed on said substrate member along a major surface thereof opposite from a source of the x-ray photons, and a relatively thick barrier layer of a relatively electrically conductive material, optically transparent to the phosphor luminescence, chemically compatible with at least the photocathode film material, and disposed between said phosphor layer and said photocathode film, the thickness of said barrier layer being sufficient to provide substantial smoothing of surface irregularities on the phosphor layer, the barrier layer material having an electrical resistance in the range of 10 to 106 ohms per square to provide sufficient electrical sheet conductance relative to said photocathode film so that said barrier layer upon being connected to a source of electric potential provides electron replenishment to said photocathode film to thereby significantly reduce elctron-optic image distortion due to undesired relatively high potential drops across said photocathode film laterally thereof.

5. The improved input screen set forth in claim 4 wherein said barrier layer deposited along the nonbase portions of the phosphor structures to thereby coat at least the surface portion of the phosphor structures opposite the base portion thereof, and said photocathode film disposed along the barrier layer deposited on the surface portions of the phosphor structures opposite the base portions thereof.

6. The improved screen set forth in claim 5 wherein said relatively thick phosphor structures are of columnar shape and the axes thereof are substantially normal to said substrate member, said barrier layer being of thickness in the range of 1 to 3 microns.