Patent GB-1308672-A (GB)
Title: Radiographic intensifying screens
IPC: G21K4/00
Filed: 1970-03-05
Abstract: 1308672 Luminescent screens FUJI SHASHIN FILM KK 5 March 1970 [7 March 1969 18 Oct 1969] 10733/70 Heading C4S [Also in Divisions B3 and H5] A radiographic intensifying screen comprises a carrier 3 and a luminescent material, 2, the latter being in a layer containing regularly arranged zones 1 of a non-luminescent material capable of absorbing secondary radiation produced by the impact of X-rays on the luminescent material, the carrier surface including no recesses containing luminescent material. The structure reduces granularity and loss of sharpness in a photographic film comprising a support coated on both sides with emulsion and held so that one or both emulsions are exposed in contact with one or two intensifying screens and reduces the agglomeration of phosphorgrains, or "mottles", into small sections not offensive to the eye in examining X-ray photographs, e.g. 20 lines/mms. for a fiber. A metal layer (e.g. Cu) may be electro plated on the carrier surface and striped or chequered pattern, (e.g. Figs. 1 and 2, not shown) formed by photoetching with or without electro plating, by chemical etching, electrical discharge or electrochemical machining, spark erosion, or liquid machining, a liquid containing phosphor then being applied. The pattern may be formed by printing or xeroprinting. The screen may also be formed by embedding in a luminescent layer, a metal mesh or perforated metal foil as used in spectrophotometry, and the mesh may be produced by reprica method or etching. Fig. 3 (not shown), illustrates the response against spatial frequency of the screen structure for varying X-ray source focus dimensions. Fig. 4 (not shown) illustrates sensitivities for the Figs. 1 and 2 stripe and chequer pattern for varying metal widths, W M , and patterns, N/mm. e.g. for S = 0À5, W M  is 25 and 10Á and N is 19 and 28 lines/mm. Reduced sensitivity may be compensated by higher sensitivity phosphors which normally exhibit high "mottling". In Fig. 5, phosphor 2 is moulded between metal strips 1 laid on carrier 3, and includes protective layer 4. Figs. 6 and 7 (not shown) include trapezoid-section and parabolic metal strips generally of dimensions T:10-300Á; W 1 : 10- 200Á; W M : 5-100Á, the light emitted increasing with T to reach a constant value at the proper phosphor thickness. Support 3 may be cellulose triacetate, polyethylene terephthalate, phenol resins or acrylic resins, metal 1 of high A. No., a coating 4 light transparent and mechanically strong, e.g. gelatine, P.V.A., or cellulose triacetate, preferably 1 to 10Á thick. In Figs. 8 to 17 (not shown), the metal reaches short of the upper or lower surface of the phosphor moulding. Fig. 9 includes light reflecting or absorbing layer 5, Fig. 10 including metal coating 5 of higher A. No. than the metal strip to further absorb scattered X-rays. In Figs. 11 to 13 the metal strips are partly embedded in the support to increase absorbtion of the X-rays. The strips may be flush with the moulding (Fig. 14) or at the middle level (Fig. 15). Generally T I : 10-300Á; T M : 10-300Á; W I : 10-200 Á; W M  = S-200 Á. The light reflecting or absorbing layer 5 may be titanium white pigment or evaporated Al or Ag as reflector in a low sensitivity screen or an absorber such as C for a high sensitivity screen in a similar manner to a halation protecting layer on radiographic films. Figs. 16 and 17 use two different phosphors in different layers to improve granularity, e.g. low sensitivity phosphor 2 on coarsely granulated highly sensitive phosphor 2<SP>1</SP>, layer 2 being thinner, preferably by at least 3 times, than layer 2<SP>1</SP>. A tricomposite layer or a mixture of different phosphor materials may be used.