Patent Application
20140034836
1. Field of the Invention
The present invention relates to a radiation detection apparatus, a manufacturing method thereof, and a radiation detection system.
2. Description of the Related Art
Methods of manufacturing a radiation detection apparatus that includes a sensor panel for detecting light and a scintillator layer for converting radiation into light are divided into two main types. One type is a manufacturing method called “direct type”, in which the scintillator layer is formed directly on the sensor panel by vapor deposition, coating, or the like. The other type is a manufacturing method called “indirect type”, in which a scintillator panel obtained by forming a scintillator layer on a substrate is bonded to the sensor panel with an adhesive or the like. In the direct manufacturing method described in Japanese Patent Laid-Open No. 2002-286846, a sensor panel is coated with a paste obtained by mixing an organic resin and a scintillator into an organic solvent, and a scintillator layer is formed by then drying the paste. This scintillator layer adheres to the sensor panel due to the adhesive force of the organic resin.
According to a first aspect, a radiation detection apparatus includes a sensor panel configured to detect light, and a scintillator layer arranged on the sensor panel. The scintillator layer has a scintillator configured to convert radiation into light of a wavelength that is detectable by the sensor panel, particles that have a property of generating a bubble and expanding so as to weaken adhesive force between the sensor panel and the scintillator layer, and a resin that holds the scintillator and the particles so as to be mixed together. The scintillator layer is adhered to the sensor panel with use of the resin.
According to a second aspect, a method of manufacturing a radiation detection apparatus includes preparing a sensor panel configured to detect light, and forming a scintillator layer directly on the sensor panel. The scintillator layer has a scintillator configured to convert radiation into light of a wavelength that is detectable by the sensor panel, particles that have a property of generating bubbles and expanding so as to weaken adhesive force between the sensor panel and the scintillator layer, and a resin that holds the scintillator and the particles so as to be mixed together. In the forming, the scintillator layer is adhered to the sensor panel with use of the resin.
According to a third aspect, a radiation detection system includes the radiation detection apparatus described above, and a processing unit configured to process a signal from the radiation detection apparatus.
Further features of the present disclosure will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the description, serve to explain the principles of the embodiments.
While the present invention will now be 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.
When forming a scintillator layer on a sensor panel, there are cases in which the scintillator layer includes foreign material, air bubbles, or the like. Thus, if a defect occurs in only the scintillator layer, the scintillator layer is separated from the sensor panel and the sensor panel is re-used. However, since the resin included in the scintillator layer has a strong adhesive force, there are cases in which the sensor panel is damaged if the scintillator layer is separated from the sensor panel. In view of this, some embodiments provide a technique for enabling easy separation of a scintillator layer formed directly on a sensor panel.
Embodiments of the present invention will be described below with reference to the accompanying drawings. Elements that are similar in various embodiments have identical reference numerals, and a description thereof will not be repeated. Also, the embodiments can be changed or combined as appropriate. Some embodiments of the present invention relate to a radiation detection apparatus that includes a sensor panel that detects light, and a scintillator layer that is formed on the sensor panel, and that converts radiation into light of a wavelength that is detectable by the sensor panel.
A structure of a radiation detection apparatus 100 of some embodiments of the present invention will be described below with reference to
The sensor panel 110 may have any kind of configuration, as long as it can detect light. Here, examples of structures of the sensor panel 110 will be described with reference to
A configuration of the scintillator layer 120 will be described in detail below with reference to
The scintillator 121 converts radiation into light of a wavelength that is detectable by the photoelectric converter 204. In some embodiments of the present invention, the scintillator 121 is in particle form, and the particle size thereof is 1 to 30 μm. Here, “particle size” is a convenient value corresponding to the diameter when the particle is assumed to be a perfect sphere. The particle size may be measured using a Coulter counter method, or a laser diffraction/dispersion method (micro-track method).
The particle size of the particles 122 below is measured similarly. Materials such as a material obtained by doping gadolinium oxysulfide (Gd2O2S) with terbium (Tb) can be used as the material for the scintillator 121. Also, an alkali halide material typified by a material obtained by doping cesium iodide (CsI) with thallium (Tl) may be used as the scintillator 121.
The particles 122 are heat-expandable particles, and have a property of generating bubbles and expanding upon being heated. The adhesive force between the sensor panel 110 and the scintillator layer 120 is weakened by expansion of the particles 122, and thus the scintillator layer 120 can be easily separated from the sensor panel 110. For example, the particles 122 are micro-encapsulated bubble-generating agents whose volume expands by a factor of 5 to 10 if heated to a prescribed temperature or above. As this type of bubble-generating agent, it is possible to use microspheres, which are obtained by a substance that is gasified and expands easily upon being heated, such as isobutene, pentane, propane, or the like, being included inside elastic capsules. Capsules of the particles 122 can be formed by a thermo-plastic substance, a thermo-fusible substance, a substance that bursts due to thermal expansion, or the like. For example, vinylidene chloride acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfone, or the like may be used as the substance that forms the capsule of each of the particles 122. The particles 122 can be manufactured using coacervation, interfacial polymerization, or the like.
An inorganic bubble-generating agent may be used as the material of the particle 122. Ammonium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, an azide, or the like may be used as the inorganic bubble-generating agent.
Commercial products may be used as the particles 122. “Matsumoto Microsphere F-30”, “Matsumoto Microsphere F-50”, “Matsumoto Microsphere F-80S”, or “Matsumoto Microsphere F-85” (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.) may be used for example. Also, the product named “Expancel Du” (manufactured by Akzo Nobel Surface Chemistry AB) or the like may be used.
Alternatively, in some other embodiments, water-absorbing particles that generate a bubble or that swell due to water absorption may be used as the particles 122. For example, the particles 122 are micro-encapsulated bubble-generating agents whose volume swells by a factor of 5 to 10 if water is absorbed. As this type of bubble-generating agent, it is possible to use microspheres obtained by enclosing a substance that generates gas by absorbing water in an elastic capsule. The capsules of the particles 122 can be formed by a material that transmits water, or a water-soluble material, such as a so-called “water-soluble resin”. For example, the material forming the capsules of the particles 122 may be a water-soluble acrylic-based polymer such as sodium polyacrylate or polyacrylamide, polyvinyl alcohol, polyethyleneimine, polyethylene oxide, or polyvinyl pyrrolidone. The particles 122 can be manufactured using coacervation, interfacial polymerization, in-site polymerization, a spray-drying method, a dry-mixing method, or the like.
The material for the particles 122 may be a material that gasifies using water as a solvent, for example, a mixture of sodium hydrogen carbonate (or sodium carbonate) and citric acid, or a mixture of sodium hydrogen carbonate (or sodium carbonate) and fumaric acid.
Alternatively, in another embodiment, the particles 122 are made up of a substance whose volume swells by a factor of 5 to 100 if water is absorbed, for example. For example, such particles may be microspheres that are particles formed from a substance that swells upon absorbing water. The material for the particles 122 may be a so-called water-absorbing polymer such as a starch-based polymer, a cellulose-based polymer, a polyacrylate-based polymer, a polyvinyl alcohol-based polymer, or a polyacrylamide-based polymer, which are obtained by graft polymerization or carboxymethylation. The particles 122 may be a sodium polyacrylate-based polymer having a property of being unlikely to release absorbed water even if pressure is applied.
Alternatively, commercial products may be used as the particles 122. For example, Arasorb (manufactured by Arakawa Chemical Industries, Ltd.), Wondergel (manufactured by Kao Corporation), KI Gel (manufactured by Kuraray Isoprene), Sanwet (manufactured by Sanyo Chemical Industries, Ltd.), Sumika Gel (manufactured by Sumitomo Chemical Co., Ltd.), Lanseal (manufactured by Japan Exlan Co., Ltd.), Aquareserve GP (manufactured by Nippon Shokubai Co., Ltd.), Diawet (manufactured by Mitsubishi Chemical Corporation), Water Lock (manufactured by Grain Processing Corporation), or Aqualon (manufactured by Hercules Incorporated) may be used. Also, Vargas 700 (manufactured by Lion Corporation), Aqua Keep TM (a polyacrylate-based super-absorbent resin) (manufactured by Sumitomo Seika Chemicals Co., Ltd.), or the like may be used.
The particle size of the particles 122 may be 1 to 80 μm, and in particular may be 3 to 50 μm. The amount of bubble generation to be performed by the particles 122 can be set by adjusting the type and amount of the material enclosed in the capsules. Also, the particles 122 may have an appropriate degree of strength such that they not rupture until the volume expansion coefficient reaches 5 or above, and in particular 10 or above. Due to having such a strength, the adhesive force between the sensor panel 110 and the scintillator layer 120 can be efficiently weakened if the particles 122 expand by being heated or by absorbing water.
The temperature at which the particles 122, which can expand due to heating, start bubble generation can be set by adjusting the type of substance included in the capsules. The temperature at which the particles 122 included in the scintillator layer 120 of the radiation detection apparatus 100 start bubble generation may be set to 60 to 170° C., and in particular it may be set to 100 to 170° C. for example. Also, the color of the particles 122 may be colorless and transparent so as not to influence the detection of light by the sensor panel 110.
The degree to which the adhesive force between the sensor panel 110 and the scintillator layer 120 weakens in the case where the particles 122 expand depends on the amount of particles 122 included in the scintillator layer 120. The amount of particles 122 can be defined by the volume density of the particles 122 in the scintillator layer 120 for example. Below, let β be the expansion coefficient of the particles 122. If the volume density of the particles 122 is less than (400π)/(3β3) %, there will be cases where the adhesive force between the sensor panel 110 and the scintillator layer 120 cannot be sufficiently weakened, even if the particles 122 expand. If the volume density of the particles 122 is greater than or equal to (400π)/(3β3) % and less than (2000π)/(3β3) %, the adhesive force between the sensor panel 110 and the scintillator layer 120 will weaken if the particles 122 expand. However, there are cases where foam spheres resulting from the particles 122 generating bubbles and expanding are not distributed on the entire adhesion surface, and after separating the scintillator layer 120 from the sensor panel 110, resin 123 remains on the sensor panel 110.
If the volume density of the particles 122 is greater than or equal to (2000π)/(3β3) %, the adhesive force between the sensor panel 110 and the scintillator layer 120 will weaken if the particles 122 expand. Furthermore, the foam spheres resulting from the particles 122 generating bubbles and expanding are distributed on the entire adhesion surface, the scintillator layer 120 can be separated easily from the sensor panel 110, and no resin 123 remains on the sensor panel 110.
Additionally, if the volume density of the particles 122 in the scintillator layer 120 exceeds 50%, a sufficient amount of light generated by the scintillator 121 may not arrive at the sensor panel 110 due to being obstructed by the particles 122. As a result of this, the resolution (MTF) of the radiation detection apparatus 100 decreases. In view of this, in order to be able to easily separate the scintillator layer 120 from the sensor panel 110, and in order to secure the resolution of the radiation detection apparatus 100, the volume density of the particles 122 may be set in the range of (2000π)/(3β3) % to 50% inclusive.
The resin 123 functions as a binder for holding the scintillator 121 and the particles 122, and has a function of adhering the scintillator layer 120 to the sensor panel 110. Polyvinyl acetal, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral, cellulosic resin, or acrylic resin, which are water- or alcohol-soluble organic resins, can be used as the resin 123. In particular, a polyvinyl acetal resin such as water-soluble S-LEC KW manufactured by Sekisui Chemical Co., ethanol-soluble S-LEC B manufactured by Sekisui Chemical Co., or the like may be used as the resin 123. The resin 123 may be any kind of resin as long as it is a resin that can be used when creating a fluorescent material coating paste, and for example, it possible to use a general-use organic vehicle (binder), examples of which include a cellulose-based resin such as ethylcellulose, nitrocellulose, cellulose acetate butyrate, or cellulose acetate propionate, an acrylic resin, a urethane resin, an epoxy resin, a polyimide resin, a vinyl chloride-vinyl acetate copolymer resin, a polyvinyl butyral resin, a polyvinyl acetal resin, an alkyd resin, a phenol resin, a melamine resin, a urea resin, a rosin resin, and a urea resin high-melting-point fatty acid. Furthermore, it is possible to use one or any combination of these types of resins as the resin 123.
The resin 123 can mitigate stress that occurs between the sensor panel 110 and the scintillator layer 120 in the heating process and the like. This stress can be caused by a difference in thermo-expansion coefficients between the sensor panel 110 and the scintillator layer 120. In the case where the modulus of elasticity in tensile of the resin 123 is less than 0.7 GPa, the adhesive force between the sensor panel 110 and the scintillator layer 120 is insufficient, and there are cases where layer separation occurs. Also, there are cases where the adhesive force of both the scintillator 121 and the particles 122 held by the resin 123 is insufficient and a breakdown in the adhesion between the scintillator 121 and the particles 122 occurs. On the other hand, if the modulus of elasticity in tensile of the resin 123 is 3.5 GPa or higher, there are cases where stress in the scintillator layer 120 cannot be sufficiently absorbed and layer separation occurs. In view of this, the scintillator layer 120 may be formed such that the modulus of elasticity in tensile of the resin 123 is included in the range of greater than or equal to 0.7 GPa to less than 3.5 GPa. Also, the modulus of elasticity in tensile of the resin 123 may be uniform in the entire scintillator layer 120, but it does not need to be uniform. For example, the most intense stress is applied to positions in the proximity of the sensor panel 110, and therefore the scintillator layer 120 may have a distribution such that the modulus of elasticity in tensile of the resin 123 is lowest at positions in the proximity of the sensor panel 110. Also, the density of the particles 122 (e.g., the volume density) in the scintillator layer 120 may also be uniform in the entire scintillator layer 120, but it does not need to be uniform. For example, in order to efficiently weaken the adhesive force between the sensor panel 110 and the scintillator layer 120, there may be a distribution such that the density of the particles 122 is highest in positions that are in the proximity of the sensor panel 110.
Next, an example of a method of manufacturing the radiation detection apparatus 100 will be described with reference to
When coating with the paste 402 at a position that covers the pixel array of the sensor panel 110 is complete, the paste 402 is heated and dried, thus eliminating the organic solvent and curing the paste 402. If the particles 122 are composed of a substance that can expand upon being heated, this heating is performed using a temperature that is lower than the temperature at which the particles 122 start generating bubbles, such as a temperature of 80 to 150° C. Thus, as shown in
In the embodiment described above, the scintillator layer 120, which includes a mixture of the scintillator 121 and the particles 122, was formed by mixing the particles 122 into the paste 402, but such a scintillator layer 120 may be formed by other methods. For example, after the particles 122 are arranged on the sensor panel 110, a paste formed by mixing the scintillator 121 and the resin 123 into an organic solvent may be used to coat the particles 122 and the sensor panel 110. The scintillator layer 120 formed in such a manner includes a mixture of the scintillator 121 and the particles 122 only in portions that are in the proximity of the sensor panel 110, and the particles 122 are not included in portions that are away from the sensor panel 110. In this case as well, the adhesive force between the sensor panel 110 and the scintillator layer 120 can be weakened by causing the particles 122 to generate bubbles. Furthermore, a configuration is possible in which the step of applying paste is performed multiple times, and the type of paste is changed in any of these steps. For example, the type of paste may be changed by mixing the scintillator 121, the particles 122, and the resin 123 at a different ratio into the solvent, and the type of paste may be changed by changing the materials of the various elements of the paste. Thus, the scintillator layer 120 can be formed such that the modulus of elasticity in tensile of the resin 123 is not uniform. Also, in the aforementioned embodiment, the resin 123 was cured by drying, but if a light curable resin is used as the resin 123, the resin 123 may be cured by irradiating the applied paste 402 with light.
Next, another example of a method of manufacturing the radiation detection apparatus 100 will be described with reference to
In the case where the scintillator layer 120 is to be separated from the radiation detection apparatus 100 manufactured as described above, for example, the particles 122 are heated to a temperature that is higher than the temperature at which the particles 122 start generating bubbles, and the adhesive force between the sensor panel 110 and the scintillator layer 120 is weakened. Alternatively, by adding water to the fluorescent material containing the particles 122, the particles generate bubbles or swell, and the adhesive force between the sensor panel 110 and the scintillator layer 120 is weakened. Subsequently, the scintillator layer 120 may be removed from the sensor panel 110.
In the example described above, the scintillator 121 was in particle form, but the scintillator 121 may be in column form. In the case of the columnar scintillator 121, first, the scintillator 121 is formed on the sensor panel 110 by vapor deposition. Subsequently, a paste including the particles 122 and the resin 123 is poured between the columns of the scintillator 121, and the scintillator layer 120 is formed by drying the paste.
Next, a structure of a radiation detection apparatus 600 according to some other embodiments of the present invention will be described with reference to
Similarly to the scintillator layer 120, the scintillator layer 620 includes the scintillator 121, the particles 122, and the resin 123, but the arrangement of the particles 122 in the scintillator layer 620 is different from that in the scintillator layer 120. As shown in detail in the plan view in
Next, an example of a method of manufacturing the radiation detection apparatus 600 will be described with reference to
When coating with the paste 702 at a position that covers the pixel array of the sensor panel 110 is complete, the paste 702 is heated and dried, thus eliminating the organic solvent and curing the paste 702. This heating is performed at a temperature that is lower than the temperature at which the particles 122 start generating bubbles, such as a temperature of 80 to 150° C. Thus, as 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 Nos. 2012-170377 filed Jul. 31, 2012 and 2013-148831 filed Jul. 17, 2013, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-170377 | Jul 2012 | JP | national |
| 2013-148831 | Jul 2013 | JP | national |
