GB1425051A - X-ray image intensifier tube and input screen therefor - Google Patents

Abstract

1425051 Luminescent screens GENERAL ELECTRIC CO 30 May 1973 [30 May 1972] 25772/73 Heading C4 [Also in Division H1] An X-ray image intensifier input screen comprises a substrate 13, X-ray sensitive phosphor 11, photo-cathode 12 (e.g. GaAs : Cs; S11 or S20 type, barrier layer 60 (e.g. In 2 O 3 , slightly chemically reduced TiO 2 , CuI or ZnO) chemically compatible with the phosphor and p/c material and providing chemical isolation between the two, the barrier thickness being 0À5 to 3À0 microns so as to provide smoothing of surface irregularities on the phosphor layer and permitting a more uniform thickness of p/c film. The barrier layer has a resistance of 10 to 10<SP>6</SP> #/ sq. (e.g. 10<SP>3</SP> #/sq.) to provide sufficient conductance to electron replenish the p/c film and so reduces electron optic image distortion caused by the high potential drops laterally across the p/c. The phosphor may be granular ZnCdS or transparent CsI, the thickness of the layer or multi-layers being 5 to 15 mms., or thicker with a barrier layer. P/c film 12 may be 50 to 520 Š thick and of multi-alkali type, ring (14) (Fig. 1, not shown) supplying the potential and supporting the assembly. The assembly may be directly on the faceplate, an Al electrode may be peripheral and a continuous Al film may reflect backward phosphor emissions. Substrate (13) may be glass or low At. No. metal, e.g. Al. The first embodiment, Fig. 7, may optionally include electrically non-conductive barrier layer 30. Fig. 8 (not shown) is as the prior art screen of Fig. 4 (not shown), but with a 1 to 3 Á barrier layer. If the cracks extend to the Al substrate, it may not be necessary to electrically connect layer 60 edges and the ring electrode. Alternatively, the substrate may be glass and also insulating barrier (30) may be provided. Fig. 9 (not shown) includes columnar, honeycomb or other symmetrical phosphor structures providing light pipe effects. Structures may be square hexagonal or circular cross-section with a 2 : 1 to 10 : 1 height : width ratio. The p/c layer bridges narrow but not wider gaps. Layer 60 may be 1 to 3 Á. Fig. 10 (not shown) utilizes granular phosphors with no or only limited binder. Fig. 2 (not shown) is a known screen with >0À3 mm. phosphor grains (e.g. ZnCdS: Ag or Gd oxysulphide : Tb), silicone resin coated, p/c layer thicknesses being exemplified, Fig. 3 (not shown) includes conventional 0À1 to 1 Á aluminium oxide or silicon oxide layer (30). The silicone resin of the phosphor layer being in larger quantities than the Fig. 2 screen, Fig. 4 (not shown) a known evaporated CsI : Tl phosphor (11) with undesired cracks. The In 2 O 3 may be evaporated at low O pressure (e.g. 10 Á), then fully oxidized in air at 200‹ C. or may be evaporated on to a 200‹ to 300‹ C. substrate in 50 to 150 microns of oxygen. Fig. 5 (not shown) illustrates wavelength responses. In Fig. 6 (not shown), layer 60 slightly overlaps substrate 13 edges to contact electrode (14), or an edge conductive film may be provided. Examination of body organs is exemplified.