Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/02—Dosimeters
  • G01T1/08—Photographic dosimeters
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
  • Y10S430/167—X-ray

Definitions

• Hart 1 ABSTRACT A layer comprising particles of a low melting point metal alloy of lead, bismuth, tin and cadmium and a binder is provided as an intensification screen. Good intensification without fog is obtained using particles of alloys, such as Wood metal, which melt lower than 80C.
• the present invention relates to intensification screens for radiographic films. More particularly, the invention relates to coated layers as intensification screens for radiographic films and to radiographic films including such layers, and i to a method for making such layers.
• an intensifying screen of the type we are dealing with absorbs high energy X-rays which causes secondary electron emission to which the emulsion is highly sensitive.
• Variousintensification screens of this type are known, employing heavy metals such as lead, usually in the form ofa metal plate or foil.
• This and other objects are achieved according to the invention by providing an intensification screen for radiography and the like comprising a layer with particles of a low melting point alloy which comprises a heavy metal that emits secondary electrons when exposed to X or y radiation, dispersed in a film-forming binder.
• a preferred alloy has a low melting point, below 95 C. and preferably less than 80 C.
• the major ingredient is bismuth, which generally constitutes about one-half of the weight ofthe alloy.
• Lead makes up about one-fourth and cadmium and tin about one-eighth each.
• melting points of less than about 95C. are preferred since a pressurized process would berequired to reduce water losses to a controllable degree. Still more preferably, the melting point is below 80C.
• the alloy is incorporated in an intensification screen layer by simply heating a mixture of the alloy and a suitable binder to melt the alloy, and dispersing the molten alloy in the binder and forming the dispersion into a layer or film.
• the layer can be self-supporting and applied as such to a radiographic film or it can be coated on a support which is applied to a radio graphic film or it can be coated directly on a radiographic film all as will become more apparent in light of the following detailed description which includes a preferred embodiment of the invention. 7
• a radiographic film for use withan intensification screen according to the invention can be any film plate or the like containing-one-or more silver halide or other radiation sensb tive layers provided on a support.
• the silver content of such radiation-sensitive silver halide emulsions is generally higher than for other light-sensitive emulsions, reaching up to 3.6 grams per square foot.
• the iodide content is relatively high and the binder content is generally low.
• Gelatin is a preferred binder and hardened gelatin is preferred. It is quite'important that the film be resistant to chemical fog.
• An intensifying screen composition is prepared by heating a mixture of 300 grams of Wood alloy and 30milliliters of dibutyl phthalate, which is used to stabilize the final dispersion, to C. to melt the alloy. The molten alloy is then added to 200 grams of a l0 percent gelatin solution maintained at a temperature of 80 C. and vigorously mixed for 2 minutes to disperse the molten alloy at that temperature. The mixture is then cooled, with continued stirring, below the melting point of the alloy to 40 C. which causes the alloy to form small solid spherical particles having a diameter ofabout 6 to 7 microns.
• the resultant dispersion is coated. directly on a polyester (polyethylene terephthalate) support 0.06-millimeters thick at a coverage of 3 grams alloy per square decimeter.
• the gelatin binder sets on cooling. Examination of the dried layers shows that the alloy beads have settled by gravity and are concentrated mostly at the polyester support interface leaving mostly gelatin binder at the outer surface. This settling effect is helpful to improve resolution by bringing the alloy-rich side of the layer into contact with the silver emulsion.
• the coated layer can be wet-transferred from a temporary support on which it has been coated to a permanent receiving supporting sheet, with the alloy-rich side outward.
• the layer can be coated and settled directly on the surface ofa radiographic recording element, or a layer can be wet-transferred from a temporary coating support, on which the layer has been coated and settled, to the surface having a substratum, after stripping off the temporary support, the resulting material is applied onto the radiographic element, with the alloy-rich face inward against the recording element.
• sedimentation of alloy particles can be inhibited by coating a more viscous dispersion or by rapidly settling the coated layer, as by rapid cooling, or both.
• Two screens are made: One by the settling technique described, followed by wet-transfer to a permanent support of 0.06-millimeter polyester film base, alloy side out; the second by coating the dispersion at a lower temperature and with rapid cooling to quickly set the gel and minimize settling. Both coatings contain 3 grams of alloy per square decimeter and 0.06-millimeter polyester film base.
• the screens are tested with a conventional silver halide radiographic film with exposure to X-rays at 240 KV, 3 ma. using a 6-millimeter copper filter, conventional processing. A control test is run with a conventional lead screen.- Results are tabulated showing density of the developed films after exposure with the respective screens.
• Wood Alloy Screen Concentrated at Wood Alloy Screen Lead Screen (dispersed through (Control) outer surface) layer
• 2.03 "1.9a 1.44 2.04 L89 L46 2.04 L89 1.46
• the nature of the binder of the screen can vary. Unhardened gelatin is a preferred binder, but others, including self-supporting resin sheets can be used depending primarily upon the manner in which the screen is utilized. Where the screen is provided in a layer distinct from the radiographic film and not integral therewith, the alloy can be provided in virtually any settable binder such as a thermoplastic natural or synthetic resin, gum or gel. The screen is merely placed next to the radiographic silver halide emulsion prior to exposure. In the event that long contact between some particular binder and the silver halide emulsion would cause some difficulty such as the formation of fog, the screen can be kept away until immediately before exposure.
• the screen in a layer integral with the film, it will usually be preferably that the screen be removed prior to developing and this can be accomplished by providing a screen layer which can be removable in any of several ways.
• the layer for example, can be melted and/or dissolved off, such as be treating in hot water.
• the layer can be applied over a water-soluble adhesive layer.
• Gelatin, polyvinyl alcohol, polyvinyl pyrrolidone and the like are watersoftenable and are suitable for such uses as binders and adhesive sublayers.
• the relative concentrations of alloy and binder in the intensification screen can vary quite widely.
• the layer is preferably richer in the alloy but can contain low amounts ifa low degree of intensification is desired. Generally, however, the layer will contain at least percent by weight of the alloy and up to 95 percent or more.
• the function of the screen is to provide the particles of intensifying material close to the silver halide emulsion during exposure thereofto X-rays and the amount of alloy in the layer is conveniently defined in terms of the amount of alloy provided per unit area since, when in operation, each unit area of the screen will'correspond to the same size unit area of the silver halide layer.
• the amount of alloy calculated in this manner will generally be between 0.l and I0 grams per square decimeter.
• a radiographic film comprising a support, at least one light-sensitive silver halide emulsion layer, and an intensification screen layer above said silver halide emulsion layer, said intensification screen layer comprising a binder and particles of an alloy of lead, bismuth, tin and cadmium having a melting point ofless than 95C.
• a radiographic film according to claim 2 wherein said intensification screen layer comprises from about 25 to about 95 percent by weight of said alloy particles based on the weight of the layer.
• a radiographic film according to claim 7 wherein the binder of said intensification layer comprises gelatin
• a radiographic film according to claim 9 wherein said alloy has the following composition:

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• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Physics & Mathematics (AREA)
• High Energy & Nuclear Physics (AREA)
• Molecular Biology (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Silver Salt Photography Or Processing Solution Therefor (AREA)
• Conversion Of X-Rays Into Visible Images (AREA)

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Family Applications (1)

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Cited By (5)

Citations (3)

• 1968
  • 1968-02-22 FR FR140896A patent/FR1564714A/fr not_active Expired
  • 1968-04-25 US US724256A patent/US3597610A/en not_active Expired - Lifetime
• 1969
  • 1969-02-20 BE BE728718D patent/BE728718A/xx unknown
  • 1969-02-20 GB GB9295/69A patent/GB1253446A/en not_active Expired

Patent Citations (3)

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