1. Field of the Invention
The present invention relates to a scintillator panel, method of manufacturing the same, and radiation detection apparatus.
2. Description of the Related Art
Recently, digital radiation detection apparatuses in which scintillator layers for converting a radiation such as an X-ray into light such as visible light are stacked on a sensor panel having a plurality of photoelectric converters have been commercially available. Scintillator materials are mainly an alkali halide-based material typified by a material prepared by doping Tl in CsI, and a material prepared by doping Tb in GdOS. Especially, an alkali halide-based scintillator material typified by CsI can form and grow columnar crystals by a vapor deposition method. The columnar crystal scintillator exhibits a light guiding effect when converting a radiation into visible light, and contributes to sharpness.
Various methods have been tried to control the columnar crystal shape of a scintillator and improve sharpness. For example, Japanese Patent No. 04345460 discloses a method for improving sharpness by gradually increasing the columnar crystal formation rate in vapor deposition to control the columnar crystal shape. Japanese Patent Laid-Open No. 2005-337724 discloses a method of improving sharpness by controlling the partial pressure of an evaporation source in vapor deposition.
To improve the luminance and DQE (Detective Quantum Efficiency) of a scintillator, the scintillator film needs to be made thick. In general, as a scintillator film having columnar crystals becomes thicker, the columnar crystal diameter becomes larger. As a result of increasing the scintillator film thickness, sharpness tends to drop. Even in the methods disclosed in Japanese Patent No. 04345460 and Japanese Patent Laid-Open No. 2005-337724, when the scintillator film is made thick for high scintillator luminance and high DQE, the columnar crystal diameter increases and no satisfactorily sharpness can be expected.
The present invention provides a technique advantageous for preventing a decrease in sharpness while increasing the scintillator film thickness.
The first aspect of the present invention provides a scintillator comprising a scintillator layer having a first surface and second surface which are surfaces opposite to each other, wherein the scintillator layer includes a plurality of columnar portions, each columnar portion including a columnar crystal for converting a radiation into light, and the columnar crystal of each columnar portion having a diameter which increases from an intermediate portion between the first surface and the second surface toward the first surface and the second surface.
The second aspect of the present invention provides a radiation detection apparatus comprising: a scintillator defined as the first aspect; and a sensor panel including a photoelectric converter which detects light converted by a scintillator layer of the scintillator.
The third aspect of the present invention provides a method for manufacturing a scintillator, the method comprising: a first growing step of growing a plurality of first columnar crystals on a first substrate to form a first scintillator layer including the plurality of first columnar crystals; a separation step of separating the first substrate from the first scintillator layer; and a second growing step of growing, in a direction opposite to a direction of growing the plurality of first columnar crystals in the first growing step, a plurality of second columnar crystals from portions of the plurality of first columnar crystals, which are exposed after the separation step, thereby forming a second scintillator layer including the plurality of second columnar crystals.
The fourth aspect of the present invention provides a method for manufacturing a scintillator, the method comprising: a growing step of growing columnar crystals from a plurality of protrusive portions of a substrate to form a scintillator layer including the plurality of columnar crystals; and a separation step of separating the substrate from the scintillator layer.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
A scintillator according to a preferred embodiment of the present invention includes a scintillator layer having the first and second surfaces which are surfaces opposite to each other. The scintillator may be formed from only the scintillator layer, or may further include another element such as a protection film and/or protection substrate. The scintillator layer includes a plurality of columnar portions, and each columnar portion includes a columnar crystal for converting a radiation into light. The diameter of the columnar crystal increases from an intermediate portion between the first and second surfaces toward the first and second surfaces. The columnar crystal of each columnar portion can have a structure in which the first and second columnar crystals are bonded so that the bonding portion between the first and second columnar crystals is positioned at the intermediate portion. Each columnar portion may have a structure in which the first and second columnar crystals are bonded by an adhesive material, or a structure in which they are directly bonded (that is, without the mediacy of another material or member).
The diameters of the columnar crystals a and b increase from an intermediate portion between the first and second surfaces toward the first and second surfaces. The columnar crystal of each columnar portion can have a structure in which the first columnar crystal a and second columnar crystal b are bonded so that the bonding portion between the first columnar crystal a and the second columnar crystal b is positioned at the intermediate portion. The columnar crystal includes the growth start portion in structure examples 1 and 2, and the growth start portion is removed in structure examples 3 and 4. The growth start portion is a portion where crystals vary greatly, and may decrease sharpness because it scatters light propagating through the columnar crystal. Structure examples 3 and 4 are advantageous to sharpness, but require processing for removing the growth start portion. In contrast, structure examples 1 and 2 are disadvantageous to sharpness, but advantageous to easy manufacture.
In structure examples 1 and 3, the first columnar crystal a and second columnar crystal b are bonded by an adhesive material c. In structure examples 2 and 4, the first columnar crystal a and second columnar crystal b are directly bonded. The structure in which the first columnar crystal a and second columnar crystal b are bonded can advantageously decrease the maximum diameter of the columnar crystal. When the total thickness of the first columnar crystal a and second columnar crystal b is formed by one continuous growing process, unlike the present invention, the diameter of the columnar crystal increases in correspondence with the growing process.
As a material for forming a columnar crystal, a material mainly containing an alkali halide is available. Preferable examples are CsI:Tl, CsI:Na, CsBr:Tl, NaI:Tl, LiI:Eu, and KI:Tl. When CsI:Tl is adopted, a columnar crystal can be formed by simultaneously depositing CsI and TlI.
The structure of a radiation detection apparatus according to the first embodiment will be described with reference to
As exemplified in
Examples of the material of the protection layer 501 are general organic sealing materials (for example, a silicone resin, acrylic resin, and epoxy resin), and polyester-, polyolefin-, and polyamide-based hot-melt resins. In particular, a resin having low moisture permeability is desirable. As the protection layer 501, an organic film made of polyparaxylylene, polyurea, polyurethane, or the like is preferably used. A hot-melt resin is also preferably used as long as it can resist a heating process during the manufacture.
The hot-melt resin melts as the resin temperature rises, and hardens as the resin temperature drops. The hot-melt resin exhibits adhesion to other organic and inorganic materials in a heating melting state, and becomes solid and does not exhibit adhesion at room temperature. The hot-melt resin contains none of a polar solvent, solvent, and moisture, and does not dissolve the scintillator layer 230 (for example, a scintillator layer having an alkali halide columnar crystal structure) even if it contacts the scintillator layer. Thus, the hot-melt resin is preferably used for the protection layer 501. The hot-melt resin differs from a solvent evaporation setting adhesive resin prepared by a solvent application method using a thermoplastic resin-dissolved solvent. The hot-melt resin also differs from a chemical reaction adhesive resin prepared by a chemical reaction, typified by an epoxy resin.
Hot-melt resin materials are classified by the type of base polymer (base material) serving as a main component, and polyolefin-, polyester-, and polyamid-based materials and the like are available. For the protection layer 501, high moisture resistance, and high light transparency of transmitting a visible ray generated by a scintillator are important. Hot-melt resins which satisfy moisture resistance requested of the protection layer 501 are preferably a polyolefin-based resin and polyester-based resin. A polyolefin-based resin having low moisture absorptivity is preferably used. As a resin having high light transparency, a polyolefin-based resin is preferable. From this, a polyolefin resin-based hot-melt resin is more preferable for the protection layer 501.
A polyolefin resin preferably mainly contains at least one material selected from an ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, and ionomer resin.
A hot-melt resin mainly containing an ethylene-vinyl acetate copolymer can be Hirodine 7544 (available from Hirodine Kogyo).
A hot-melt resin mainly containing an ethylene-acrylic acid ester copolymer can be O-4121 (available from Kurabo Industries).
A hot-melt resin mainly containing an ethylene-methacrylic acid ester copolymer can be W-4210 (available from Kurabo Industries).
A hot-melt resin mainly containing an ethylene-acrylic acid ester copolymer can be H-2500 (available from Kurabo Industries).
A hot-melt resin mainly containing an ethylene-acrylic acid copolymer can be P-2200 (available from Kurabo Industries).
A hot-melt resin mainly containing an ethylene-acrylic acid ester copolymer can be Z-2 (available from Kurabo Industries).
The support substrate 210 supports the scintillator layer 230, and when a reflecting layer is formed, functions as even the reflecting layer. The reflecting layer has a function of increasing the light use efficiency by reflecting light traveling in a direction opposite to the photoelectric converter 213 out of light converted by the scintillator layer 230 and guiding the light to the photoelectric converter 213. The reflecting layer prevents light (external ray) other than one generated by the scintillator layer 230 from entering the photoelectric converter 213, and prevents noise arising from an external ray from entering the photoelectric converter 213. The support substrate 210 can be, for example, a metal substrate or a substrate having a metal film on the surface of a base material. A thick support substrate 210 has a large radiological dose, and may lead to a large radiation dose by which a subject is exposed. When the support substrate 210 is formed from a metal thin plate, its material is preferably aluminum or the like. When a reflecting layer is formed on a support substrate having no reflecting layer, the support substrate is preferably a carbon- or resin-based substrate which resists heat and hardly absorbs X-rays. The reflecting layer can be made of a metal material such as aluminum, gold, or silver. In particular, aluminum and gold are preferable as high-reflectivity materials.
When a reflecting layer is formed on the support substrate 210, the adhesion layer 209 can preferably use a material which has high transmittance in the emission wavelength region of the scintillator, in order to effectively use light generated from the scintillator layer 230. Further, when a metal reflecting layer is formed on the support substrate 210, a material excellent in corrosion resistance is preferably used. Also, a material excellent in X-ray durability is preferable. A thinner adhesion layer 209 is preferable because sharpness less decreases. However, an excessively thin adhesion layer 209 decreases the adhesion force of the adhesive material itself, and the adhesion layer 209 may peel from the interface between the adhesion layer 209 and the protection layer or that between the adhesion layer 209 and the support substrate. In contrast, when the adhesion layer thickness exceeds 200 μm, the resolution and MTF may drop, similar to the case of the scintillator protection layer.
The sensor panel 203 includes a photoelectric conversion portion (image sensing region) 216 in which the photoelectric converters 213 and TFTs (not shown) are arrayed two-dimensionally on an insulating substrate 204 made of glass or the like. Each signal wiring line 214 is connected to the photoelectric converter 213 or TFT. A connection lead portion 205 is used to connect an external wiring line 207 and the sensor panel 203. The connection lead portion 205 is electrically connected to the external wiring line 207 such as a flexible wiring board via a wiring connection portion 206 such as a solder or anisotropic conductive film (ACF), thereby connecting the sensor panel 203 to an external electric circuit. The sensor panel 203 can include a protection layer 217 made of silicon nitride or the like. The photoelectric converter 213 converts, into charges, light converted from a radiation by the scintillator layer 230. The photoelectric converter 213 can use a material such as amorphous silicon. The structure of the photoelectric converter 213 is not particularly limited, and a MIS sensor, PIN sensor, TFT sensor, or the like is appropriately usable. The signal wiring line 214 is part of a signal wiring line for reading out, via the TFT, a signal photoelectrically converted by the photoelectric converter 213, a bias wiring line for applying a voltage Vs to the photoelectric converter 213, or a driving wiring line for driving the TFT. A signal photoelectrically converted by the photoelectric converter 213 is read out via the TFT, and output to an external signal processing circuit via a peripheral circuit (not shown) and the signal wiring line 214. The gates of TFTs arranged in the row direction are connected to a driving wiring line for each row, and a TFT driving circuit selects a TFT from each row.
Examples of the material of the protection layer 217 are SiN, TiO2, LiF, Al2O3, and MgO. Other examples of the material of the protection layer 217 are a polyphenylene sulfide resin, fluoroplastic, polyether ether ketone resin, and liquid crystal polymer. Still other examples of the material of the protection layer 217 are a polyether nitrile resin, polysulfone resin, polyether sulfone resin, polyallylate resin, polyamide-imide resin, polyetherimide resin, polyimide resin, epoxy resin, and silicone resin. The protection layer desirably has high transmittance at the wavelength of light radiated by the scintillator layer 230 because light converted by the scintillator layer 230 passes through the protection layer upon radiation irradiation. A sealing material 212 which seals the scintillator layer 230 has a moisture-resistant function of preventing moisture from entering the photoelectric conversion portion 216, similar to a scintillator protection layer to be described later. The sealing material 212 is preferably a material having high moisture resistance or a material having low moisture permeability. A preferable example is a resin material such as an epoxy resin or acrylic resin. A silicone-based resin, polyester-based resin, polyolefin-based resin, and polyamide-based resin are also available.
A method of manufacturing a scintillator and radiation detection apparatus according to the first embodiment will be explained with reference to
In a support process shown in
In the second growing process shown in
In an assembly process shown in
A method of manufacturing a scintillator and radiation detection apparatus according to the second embodiment will be explained with reference to
In an assembly process shown in
A method of manufacturing a scintillator and radiation detection apparatus according to the third embodiment will be explained with reference to
A method of manufacturing a scintillator and radiation detection apparatus according to the seventh embodiment will be explained with reference to
In a separation process shown in
In a bonding process shown in
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2011-014382, filed Jan. 26, 2011, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2011-014382 | Jan 2011 | JP | national |