Ceramic scintillator array, radiation detector, and radiation detection device

Abstract

A ceramic scintillator array 1 according to an embodiment of the present invention is provided with a plurality of scintillator segments 2 and a reflection layer. The amount of chlorine contained in the reflection layer is 3000 µg / g or less.

Description

Ceramic scintillator array, radiation detector, and radiation detection device

[0001] SUMMARY OF THE INVENTION Embodiments according to the present invention relate to ceramic scintillator arrays, radiation detectors, and radiation detection devices.

[0002] In the fields of medical diagnosis and industrial non-destructive testing, inspections are performed using radiation detection devices such as X-ray computed tomography (hereinafter referred to as "X-ray CT devices"). X-ray detectors in X-ray CT devices often use a detector that uses a solid scintillator, which emits visible light or the like when excited by X-rays, together with a photoelectric conversion element. X-ray detectors that use a solid scintillator can easily reduce the size of the photoelectric conversion element and increase the number of channels, thereby further improving the resolution of the X-ray CT device.

[0003] Radiation inspection devices such as X-ray CT scanners are used in a variety of fields, including medical and industrial applications. The X-ray detectors installed in X-ray CT scanners have photoelectric conversion elements arranged two-dimensionally, vertically and horizontally, with one or more scintillator segments, which are solid-state scintillators, provided for each photoelectric conversion element. X-rays incident on the scintillator segments are converted into visible light, which is then converted into electrical signals by the photoelectric conversion elements, and the electrical signals are analyzed by a computer to create an image. In recent years, photoelectric conversion elements have been made smaller and the pitch between adjacent photoelectric conversion elements has been narrowed to obtain high-resolution images. Accordingly, the size of the scintillator segments has also been reduced.

[0004] A reflective layer is provided between adjacent scintillator segments or on the X-ray irradiated surface of the scintillator segment. The reflective layer reflects visible light generated by X-ray irradiation and confines it within the scintillator segment, allowing the visible light to be efficiently guided to the photoelectric conversion element side. Various studies have also been conducted on the reflective layer used together with the scintillator segments. For example, Patent Document 1 discloses a ceramic scintillator array having a reflective layer with a glass transition point of 50° C. or higher and a thermal expansion coefficient of 3.5×10 at temperatures higher than the glass transition point. －５It is described that a transparent resin having a temperature of not higher than 100° C. is used, which makes it possible to suppress dimensional changes during the manufacture, use, and storage of the ceramic scintillator array.

[0005] International Publication No. 2017 / 082337 Japanese Patent Application Laid-Open No. 2020-173226 International Publication No. 2022 / 191214

[0006] When a ceramic scintillator array is irradiated with X-rays for a long period of time, the reflective layer tends to become colored. The colored reflective layer absorbs a portion of the visible light generated by the scintillator segments, resulting in a decrease in light output and a decrease in the sensitivity of the X-ray detector. Various studies have been conducted to solve this problem. For example, Patent Document 2 describes a scintillator array in which the reflective layer uses a cured product obtained by using a cationic polymerization initiator or an acid anhydride curing agent. The scintillator array described in Patent Document 2 reduces the decrease in reflectance of the reflective layer due to X-ray irradiation. Furthermore, Patent Document 3 describes a scintillator array in which a resin having a C═O bond is used for the reflective layer. The scintillator array described in Patent Document 3 can reduce the coloration of the reflective layer due to X-ray irradiation. However, even the scintillator arrays described in Patent Documents 2 and 3 still have room for improvement in suppressing the decrease in light output due to long-term X-ray irradiation, and a ceramic scintillator array that can further suppress the decrease in light output even when irradiated with X-rays for a long period of time has been desired.

[0007] Embodiments according to the present invention provide ceramic scintillator arrays that exhibit reduced degradation in light output after prolonged exposure to X-rays.

[0008] The above-described problems are solved by the following embodiments. <1> A ceramic scintillator array including a plurality of scintillator segments and a reflective layer, wherein the reflective layer has a chlorine content of 3000 μg / g or less. <2> The ceramic scintillator array according to <1>, wherein the reflective layer contains at least one selected from the group consisting of epoxy resin, silicone resin, phenolic resin, urea resin, melamine resin, unsaturated polyester, polyurethane, acrylic resin, polyethylene terephthalate, epoxy-modified silicone, and glycidyl ether. <3> The ceramic scintillator array according to <1> or <2>, wherein the reflective layer contains at least one selected from the group consisting of titanium oxide, aluminum oxide, barium sulfate, zinc oxide, zirconium oxide, and silicon oxide. <4> The ceramic scintillator array according to any one of <1> to <3>, wherein the scintillator segments contain a rare earth oxysulfide phosphor or a garnet-structure oxide phosphor. <5> The ceramic scintillator array according to any one of <1> to <4>, wherein the reflective layer is a first reflective layer provided so as to surround the side surfaces of the scintillator segments. <6> The ceramic scintillator array according to any one of <1> to <5>, wherein the reflective layer is a second reflective layer provided so as to cover the X-ray irradiated surfaces of the scintillator segments. <7> A radiation detector comprising the ceramic scintillator array according to any one of <1> to <6>. <8> A radiation inspection device comprising the radiation detector according to <7>.

[0009] Fig. 1 is a cross-sectional view showing an example of a ceramic scintillator array according to an embodiment. Fig. 2 is a plan view showing an example of a ceramic scintillator array according to an embodiment. Fig. 3 is a cross-sectional view showing another example of a ceramic scintillator array according to an embodiment. Fig. 4 is a cross-sectional view showing an X-ray detector which is an example of a radiation detector according to an embodiment. Fig. 5 is a schematic configuration diagram showing an X-ray CT device which is an example of a radiation inspection device according to an embodiment.

[0010] Various embodiments will be described below with reference to the drawings. Each figure is a schematic diagram for facilitating understanding of the embodiment, and the shapes, dimensions, ratios, etc. may differ from the actual ones in some places. However, these can be appropriately modified in design by taking into consideration the following explanation and known technologies.

[0011] <Ceramic scintillator array> Fig. 1 is a cross-sectional view showing an example of a ceramic scintillator array according to an embodiment, and Fig. 2 is a plan view showing an example of a ceramic scintillator array according to an embodiment. The ceramic scintillator array 1 includes a plurality of scintillator segments 2 and a reflective layer. A first reflective layer 3 is interposed between adjacent scintillator segments 2 as a reflective layer. The first reflective layer 3 is bonded to each adjacent scintillator segment 2. The plurality of scintillator segments 2 are bonded and integrated by the first reflective layer 3. In other words, the ceramic scintillator array 1 has a structure in which the plurality of scintillator segments 2 are integrated by the first reflective layer 3. Furthermore, a second reflective layer 4 is provided as a reflective layer on the X-ray irradiated surfaces of the plurality of scintillator segments 2. Note that the second reflective layer 4 is not shown in Fig. 2.

[0012] In the ceramic scintillator array 1 of the embodiment, focusing on one scintillator segment 2, a first reflective layer 3 is provided so as to surround the side surface of the scintillator segment 2, and a second reflective layer 4 is provided so as to cover the X-ray irradiated surface of the scintillator segment 2. In this embodiment, the scintillator segment 2 is covered with a reflective layer except for one surface. The first reflective layer 3 and the second reflective layer 4 may be made of the same material or different materials.

[0013] A photodiode that detects visible light converted from X-rays by the scintillator segment 2 is directly or indirectly attached to the surface of the scintillator segment 2 that is not covered with the reflective layer (the surface opposite to the X-ray irradiated surface), thereby forming a radiation detector.

[0014] The ceramic scintillator array 1 may have a structure in which a plurality of scintillator segments 2 are arranged in a line, or as shown in Fig. 2, a plurality of scintillator segments 2 are arranged two-dimensionally, with a predetermined number of the scintillator segments 2 arranged vertically and horizontally. When a plurality of scintillator segments 2 are arranged two-dimensionally, a first reflective layer 3 is provided between each of the scintillator segments 2 in the vertical and horizontal directions. Furthermore, a second reflective layer 4 is provided on the X-ray irradiated surfaces of the plurality of scintillator segments 2 integrated together via the first reflective layer 3. The second reflective layer 4 is bonded to the scintillator segments 2 and the first reflective layer 3 so as to cover the X-ray irradiated surfaces of the plurality of scintillator segments 2. The number of scintillator segments 2 is set appropriately depending on the structure and resolution of the X-ray detector.

[0015] Fig. 3 is a cross-sectional view showing another example of a ceramic scintillator array according to an embodiment. The ceramic scintillator array 1 shown in Fig. 3 differs from the ceramic scintillator array 1 shown in Fig. 1 in that it does not include a second reflective layer 4. That is, the ceramic scintillator array according to an embodiment may include a plurality of scintillator segments 2 and a first reflective layer 3, but may not include a second reflective layer 4.

[0016] Next, the scintillator segments 2 and reflective layers constituting the ceramic scintillator array of the embodiment will be described. Note that the characteristics of the reflective layers described below may apply to the first reflective layer, the second reflective layer, or both the first reflective layer and the second reflective layer.

[0017] <Scintillator Segments> The type of scintillator segment 2 in the ceramic scintillator array 1 of the embodiment is not particularly limited, and may be composed of, for example, a rare earth oxysulfide phosphor or a garnet-structure oxide phosphor. The scintillator segment 2 is composed of, for example, one type of phosphor or two or more types of phosphors. Examples of rare earth oxysulfide phosphors include rare earth oxysulfide phosphors containing praseodymium (Pr) as the luminescent center. Examples of rare earth oxysulfides constituting rare earth oxysulfide phosphors include oxysulfides of rare earth elements such as yttrium (Y), gadolinium (Gd), lanthanum (La), and lutetium (Lu). Examples of garnet-structure oxide phosphors include gadolinium gallium aluminum garnet (GGAG), lutetium aluminum garnet (LuAG), lutetium gallium aluminum garnet (LuGAG), and gadolinium aluminum garnet (GdAG).

[0018] The scintillator segment 2 has the general formula: RE ２ O ２ It is preferable that the phosphor be made of a rare earth oxysulfide phosphor having a composition represented by the formula: S:Pr (1) (wherein RE represents at least one element selected from the group consisting of Y, Gd, La and Lu).

[0019] Among the rare earth elements mentioned above, Gd has a large X-ray absorption coefficient and contributes to improving the light output of the ceramic scintillator array 1. Therefore, in the ceramic scintillator array 1 of the embodiment, the scintillator segments 2 are made of Gd ２ O ２ It is more preferable to use an S:Pr phosphor. Note that a part of Gd may be replaced with another rare earth element. In this case, the amount of Gd replaced by the other rare earth element is preferably 10 mol % or less.

[0020] That is, in the ceramic scintillator array 1 of the embodiment, １－Ｘ , R.E. Ｘ ) ２ O ２It is preferable to use a rare earth oxysulfide phosphor represented by the formula: S:Pr ... (2) (wherein RE represents at least one element selected from the group consisting of Y, La, and Lu, and X is a number (atomic ratio) satisfying 0≦X≦0.1) for the scintillator segment 2.

[0021] The ceramic scintillator array 1 of the embodiment contains praseodymium (Pr) as the luminescent center of the rare earth oxysulfide phosphor. Pr can reduce afterglow compared to other rare earth elements. Therefore, a rare earth oxysulfide phosphor containing Pr as the luminescent center is effective as a material for a solid-state scintillator that constitutes a radiation detector.

[0022] The content of Pr in the rare earth oxysulfide phosphor is determined by the phosphor matrix (RE in formula (1)). ２ O ２ The Pr content is preferably in the range of 0.001 to 10 mol %, more preferably 0.01 to 1 mol %, relative to the Pr content (compounds represented as PrS). This allows the phosphor to exhibit high luminous efficiency. Caution is required, as a Pr content exceeding 10 mol % may result in a decrease in light output. Furthermore, if the Pr content is less than 0.001 mol %, the Pr effect as a luminescent center cannot be fully achieved.

[0023] The rare earth oxysulfide phosphor used in the embodiment may contain a small amount of cerium (Ce) as an activator in addition to Pr as the luminescent center. Ce is effective in suppressing afterglow. The Ce content is preferably in the range of 0.00001 to 0.1 mol% relative to the phosphor host.

[0024] Furthermore, in the ceramic scintillator array 1 of the embodiment, the scintillator segments 2 are preferably made of a high-purity rare earth oxysulfide phosphor. Since impurities cause a decrease in the sensitivity of the scintillator segments 2, it is preferable to reduce the amount of impurities contained in the scintillator segments 2 as much as possible. In particular, phosphate radicals (PO ４) causes a decrease in sensitivity, so it is preferable to set the content of phosphate radicals in the scintillator segments 2 to 100 ppm or less. When the scintillator segments 2 are densified using a fluoride or the like as a sintering aid, the sintering aid remains in the scintillator segments 2 as an impurity, resulting in a decrease in sensitivity.

[0025] The scintillator segment 2 is preferably a solid scintillator having a cubic or rectangular parallelepiped shape. The volume of the scintillator segment 2 is 1 mm ３ By miniaturizing the scintillator segments 2, the detected image can be made higher in definition.

[0026] The length, width, and thickness dimensions of the scintillator segments 2 are not necessarily limited, but are preferably each 2 mm or less, and more preferably 1.5 mm or less. When X-rays are irradiated onto the ceramic scintillator array 1, the X-rays are converted into visible light in the scintillator segments 2. The visible light travels inside the scintillator segments 2, but as the optical path length of the visible light increases, the visible light is scattered and attenuated. By setting the length, width, and thickness dimensions of the scintillator segments 2 to a certain value or less, the optical path length of the visible light is shortened, allowing the visible light to efficiently reach the photoelectric conversion elements.

[0027] <Reflective Layer> The reflective layer is composed of, for example, reflective particles and a transparent resin in which the reflective particles are embedded. When the reflective layer contains reflective particles, the reflective layer reflects visible light and confines it within the scintillator segments 2, allowing the visible light to be efficiently guided to the photoelectric conversion elements. Furthermore, the high transparency of the resin that constitutes the reflective layer makes it possible to suppress absorption of visible light by the reflective layer and suppress a decrease in the light output of the ceramic scintillator array 1.

[0028] Examples of reflective particles include white pigments such as titanium oxide, aluminum oxide, barium sulfate, zinc oxide, zirconium oxide, silicon oxide, etc. Therefore, the reflective layer in the embodiment preferably contains at least one selected from the group consisting of titanium oxide, aluminum oxide, barium sulfate, zinc oxide, zirconium oxide, and silicon oxide.

[0029] From the viewpoint of efficiently guiding visible light from the scintillator segments 2 to the photoelectric conversion elements, the reflective layer preferably has a high reflectance, for example, a reflectance of 80% or more for visible light with a wavelength of 500 to 800 nm. From the viewpoint of achieving a high reflectance, when reflective particles are used, the content of the transparent resin in the reflective layer is preferably 40 to 60 mass %, and the content of the reflective particles in the reflective layer is preferably 40 to 60 mass %. The median particle size (median diameter) of the reflective particles is preferably 0.2 to 0.4 μm.

[0030] Examples of transparent resins include epoxy resins, silicone resins, phenolic resins, urea resins, melamine resins, unsaturated polyesters, polyurethanes, acrylic resins, polyethylene terephthalate, epoxy-modified silicones, and glycidyl ethers. For example, it is known that ceramic scintillators used in X-ray CT scanners reach temperatures of 50 to 60°C during use. Therefore, it is preferable that the transparent resin used in the reflective layer be heat-resistant, and it is particularly preferable to use a thermosetting resin with excellent heat resistance. If a transparent resin with low heat resistance is used, there is a risk of deformation or pitch deviation during use. Therefore, the reflective layer in the embodiment preferably contains at least one selected from the group consisting of epoxy resins, silicone resins, phenolic resins, urea resins, melamine resins, unsaturated polyesters, polyurethanes, acrylic resins, polyethylene terephthalate, epoxy-modified silicones, and glycidyl ethers. Among these, it is preferable that the reflective layer contain an epoxy resin from the viewpoints of handleability, transparency, storage stability, and the like required during the production of the reflective layer.

[0031] When curing an epoxy resin, a curing agent is generally used. Examples of the curing agent include aliphatic polyamines, aromatic polyamines, acid anhydrides, imidazole compounds, and dicyandiamide. Among them, at least one selected from the group consisting of aliphatic polyamines and aromatic polyamines is preferred because of its favorable pot life and glass transition temperature.

[0032] When a transparent resin is cured using a curing agent, the transparent resin and the curing agent undergo a polymerization reaction to form macromolecules, completing the curing process. Therefore, it is preferable to mix a sufficient amount of curing agent to polymerize the entire amount of transparent resin. Furthermore, if the amount of curing agent mixed is too large relative to the transparent resin, unreacted curing agent may remain in the cured product, changing the properties of the cured product. Therefore, it is preferable to appropriately adjust the content of the curing agent depending on the type of transparent resin and curing agent used. For example, the content of the curing agent is preferably 10 parts by weight or more, more preferably 20 parts by weight or more, per 100 parts by weight of transparent resin. Furthermore, the content of the curing agent is preferably 30 parts by weight or less, more preferably 25 parts by weight or less, per 100 parts by weight of transparent resin.

[0033] In an embodiment, the chlorine content in the reflective layer is 3000 μg / g or less, preferably 2000 μg / g or less, more preferably 1300 μg / g or less, and even more preferably 1000 μg / g or less. When the chlorine content in the reflective layer is a certain level or less, the reflective layer is less likely to be colored even when irradiated with X-rays for a long period of time, and a decrease in the light output of the ceramic scintillator array can be suppressed even after long-term irradiation with X-rays.

[0034] The reason why the light output of a ceramic scintillator array is likely to decrease with prolonged X-ray irradiation when the reflective layer contains chlorine is thought to be as follows: The chlorine present in the reflective layer generates chlorine radicals when exposed to X-rays for a long period of time. The generated chlorine radicals react with metal elements contained in the reflective particles to produce metal radicals, which are generally colored. Alternatively, the generated chlorine radicals react with the transparent resin that makes up the reflective layer to produce organic radicals such as alkyl radicals, alkoxy radicals, and nitroxyl radicals. Organic radicals are generally unstable, and once generated, radical substitution reactions occur sequentially. As the radical substitution reaction progresses, the molecular structure of the transparent resin is destroyed, causing the resin to become colored. It is thought that the colored metal radicals and the colored resin absorb visible light without reflecting it, resulting in a decrease in the light output of the ceramic scintillator array.

[0035] Among the metal elements that react with chlorine radicals to generate metal radicals, some easily return to their state before reacting with chlorine radicals. Therefore, even after prolonged X-ray irradiation, the colored metal radicals may decrease over time. On the other hand, transparent resins whose molecular structure has been destroyed are difficult to return to their original state once destroyed, and the coloration of the resin is unlikely to decrease over time after prolonged X-ray irradiation. Therefore, it is believed that colored resins have a greater impact on the reduction in light output of ceramic scintillator arrays than colored metal radicals.

[0036] It is most preferable that the reflective layer does not contain chlorine. That is, it is most preferable that the chlorine content in the reflective layer is 0 μg / g. However, since the transparent resin constituting the reflective layer may contain chlorine as an impurity due to the manufacturing method, the chlorine content in the reflective layer is practically 300 μg / g or more, more practically 400 μg / g or more, and even more practically 500 μg / g or more. In general, even if the chlorine content in the reflective layer is 1000 μg / g or more, the effect of suppressing a decrease in the light output of the ceramic scintillator array even after long-term irradiation with X-rays is fully exhibited.

[0037] The reason why transparent resins may contain chlorine as an impurity will be explained using epoxy resin as an example. The main methods for producing epoxy resins include the epichlorohydrin method and the oxidation method. The epichlorohydrin method is a conventional method for producing epoxy resins, synthesizing epoxy resins using a condensation reaction between raw material monomers and epichlorohydrin. For example, bisphenol A epoxy resin, a typical epoxy resin, is obtained by condensation reaction of bisphenol A monomer with epichlorohydrin. When producing epoxy resins using the epichlorohydrin method, in addition to the main product, epoxy resin, chlorine-containing components, hydrolyzable chlorine (unreacted products), and bound chlorine (excess adducts), are generated as by-products. To remove these by-products from the epoxy resin, the epoxy resin is repeatedly washed with alkali. However, it is difficult to completely remove the by-products even with alkali washing, and some of the by-products remain in the epoxy resin. Therefore, epoxy resins produced by the epichlorohydrin method contain chlorine as an impurity. Since the epichlorohydrin method is easier to use to produce epoxy resins than the oxidation method, most of the epoxy resins on the market are produced by the epichlorohydrin method, and therefore most of the epoxy resins on the market contain chlorine as an impurity.

[0038] The chlorine content in the reflective layer is measured, for example, by combustion ion chromatography, specifically by the method described in the examples below.

[0039] <Method of forming reflective layer> The reflective layer is formed, for example, as follows: A plurality of scintillator segments processed into a predetermined shape are arranged at regular intervals. A composition made by mixing a transparent resin, reflective particles, and a curing agent is applied or filled between adjacent scintillator segments. A first reflective layer can be formed by curing the composition with heat. Next, a composition made by mixing a transparent resin, reflective particles, and a curing agent is applied to the X-ray irradiated surface of the ceramic scintillator array consisting of the scintillator segments and the first reflective layer. A second reflective layer can be formed by curing the newly applied composition with heat.

[0040] Alternatively, a second reflective layer can be formed by adhering a predetermined film to the X-ray irradiated surface of the ceramic scintillator array using an adhesive. An example of a film that can be used as the second reflective layer is a film obtained by processing a composition containing a transparent resin and reflective particles into a sheet using a doctor blade or the like and then curing the composition. However, the film that can be used as the second reflective layer is not limited to this, and a commercially available white film can also be used, for example.

[0041] <Radiation Detector and Radiation Inspection Apparatus> Next, a radiation detector and a radiation inspection apparatus according to an embodiment will be described.

[0042] The radiation detector of the embodiment includes the ceramic scintillator array 1 of the above-described embodiment as a solid scintillator that emits visible light in response to the amount of incident radiation, and further includes a photoelectric conversion element that receives the visible light from the solid scintillator and converts the visible light into an electrical signal. Fig. 4 shows an X-ray detector, which is an example of the radiation detector of the embodiment. The X-ray detector 6 shown in Fig. 4 includes the ceramic scintillator array 1, which is a solid scintillator, and a photodiode 7, which is a photoelectric conversion element.

[0043] Each scintillator segment 2 has an X-ray irradiation surface, and a photodiode 7 is attached to the surface opposite to the X-ray irradiation surface. The photodiodes 7 are arranged to correspond to the respective scintillator segments 2 that make up the ceramic scintillator array 1. In this manner, the X-ray detector 6 is constructed.

[0044] In the above-described X-ray detector 6, when X-rays are irradiated from the second reflective layer 4 side, the X-rays are incident on each scintillator segment 2, and visible light is emitted from the scintillator segments 2 in accordance with the amount of incident X-rays. The visible light emitted from the scintillator segments 2 is detected by the photodiodes 7. The visible light emitted based on the amount of incident X-rays is converted into an electrical signal by the photodiodes 7 and then sent from the output terminal 8 to a computer.

[0045] The radiation inspection apparatus of the embodiment includes a radiation source that irradiates radiation toward an object to be inspected, and a radiation detector that detects radiation that has passed through the object to be inspected. The radiation detector of the above-described embodiment is used as the radiation detector. FIG. 5 shows an X-ray CT apparatus 10, which is an example of the radiation inspection apparatus of the embodiment. The X-ray detector 6 is attached to, for example, the inner wall surface of an arc on which the object to be inspected 11 is placed. An X-ray tube 12 that emits X-rays is installed at the center of the arc to which the X-ray detector 6 is attached. The object to be inspected 11 is placed between the X-ray detector 6 and the X-ray tube 12. A collimator (not shown) is provided on the X-ray irradiation surface side of the X-ray detector 6.

[0046] The X-ray detector 6 and the X-ray tube 12 are configured to image the subject 11 while rotating around the subject 11. Image information of the subject 11 is collected three-dimensionally from different angles. Signals obtained by X-ray imaging (electrical signals converted by photoelectric conversion elements) are processed by a computer 13 and displayed as a subject image 15 on a display 14. The subject image 15 is, for example, a tomographic image of the subject 11. As shown in FIG. 2, a multi-tomographic image type X-ray CT device 10 can be configured by using a ceramic scintillator array 1 in which scintillator segments 2 are arranged two-dimensionally. In this case, multiple tomographic images of the subject 11 are simultaneously captured, and the imaging results can be depicted three-dimensionally, for example.

[0047] With this technology, the radiological inspection device of the embodiment also contributes to improving inspection accuracy, etc. Furthermore, the radiological inspection device of the embodiment is not limited to X-ray inspection for medical diagnosis of the human body, and is also applicable to X-ray inspection of animals or X-ray inspection for industrial purposes, etc. Furthermore, the radiological inspection device of the embodiment includes a radiation detector having the ceramic scintillator array of the embodiment. As described above, the ceramic scintillator array of the embodiment has a reduced chlorine content in at least one selected from the group consisting of the first reflective layer and the second reflective layer, and therefore, a decrease in light output after long-term irradiation with X-rays can be suppressed.

[0048] Next, specific examples of the embodiment and their evaluation results will be described.

[0049] The epoxy resins and curing agents used in the ceramic scintillator arrays of Examples 1 to 5 and Comparative Examples 1 to 5 below are as follows: Epoxy resin A: Hydrogenated bisphenol A diglycidyl ether, trade name: jER (registered trademark) YX-8000, manufactured by Mitsubishi Chemical Corporation; Epoxy resin B: Hydrogenated bisphenol A diglycidyl ether, trade name: jER (registered trademark) YX-8000D, manufactured by Mitsubishi Chemical Corporation; Epoxy resin C: Hydrogenated bisphenol A diglycidyl ether, trade name: EP-4080E, manufactured by ADEKA Corporation; Curing agent: Alicyclic polyamine-based curing agent, trade name: NBDA, manufactured by Mitsui Chemicals Fine, Inc.

[0050] [Example 1] <Preparation of scintillator segments> A scintillator segment having a median particle size of 5 to 10 μm (Gd ０．９９９２８ , Pr ０．０００７ , Ce ０．００００２ ) ２ O ２Gadolinium oxysulfide phosphor powder having a composition of S was molded by wet cold isostatic pressing (wet-CIP). The molded body was processed to fit a cylindrical capsule made of tantalum (Ta) with an outer diameter of 90 mm and a height of 150 mm. The molded body was then wrapped around the periphery of the capsule with molybdenum (Mo) foil, and then placed in the capsule and vacuum-sealed. The Ta capsule was then placed in a hot isostatic pressing (HIP) processor. Argon gas was sealed in the HIP processor as a pressure medium, and a sintered body was produced by processing the HIP processor at a pressure of 180 MPa and a temperature of 1300-1500°C for 3 hours. After cooling, the sintered body was removed and cut into a 2.0 mm thick plate along the height direction of the cylinder using a wire saw. Grooves were machined into the surface of this plate at intervals of 1.39 mm vertically and 1.18 mm horizontally using a blade to produce multiple scintillator segments. The groove width was 0.10 mm vertically and 0.27 mm horizontally. <Preparation of Reflective Layer Composition> Epoxy resin A was prepared as a transparent resin. A mixture of 90% by mass of titanium oxide powder and 10% by mass of aluminum oxide powder was prepared as a white pigment. The transparent resin, curing agent, and white pigment were mixed in a mass ratio of 100:20:120. In this manner, a reflective layer composition was prepared. <Preparation of Ceramic Scintillator Array> The reflective layer composition was filled into the grooves between the scintillator segments. The reflective layer composition was thermally cured to form a first reflective layer, and adjacent scintillator segments were bonded together via the first reflective layer to prepare a ceramic scintillator array as shown in Figures 2 and 3. One side of this ceramic scintillator array was polished to a desired surface, and then the other side was covered with a reflective layer composition and thermally cured to form a second reflective layer. Finally, both sides were polished to a total thickness of 1.0 mm and a second reflective layer thickness of 0.17 mm. Using the above method, a ceramic scintillator array of Example 1 was prepared, comprising scintillator segments, a first reflective layer, and a second reflective layer.

[0051] [Example 2] A ceramic scintillator array of Example 2 was produced in the same manner as Example 1, except that epoxy resin B was used as the transparent resin and the transparent resin, curing agent, and white pigment were mixed in a mass ratio of 100:25:120.

[0052] Example 3 A ceramic scintillator array of Example 3 was produced in the same manner as in Example 2, except that a mixture of 97 mass % of epoxy resin A and 3 mass % of epoxy resin C was used as the transparent resin.

[0053] Example 4 A ceramic scintillator array of Example 4 was produced in the same manner as in Example 2, except that a mixture of 95 mass % of epoxy resin A and 5 mass % of epoxy resin C was used as the transparent resin.

[0054] Example 5 A ceramic scintillator array of Example 5 was produced in the same manner as in Example 2, except that a mixture of 92 mass % of epoxy resin A and 8 mass % of epoxy resin C was used as the transparent resin.

[0055] Comparative Example 1 A ceramic scintillator array of Comparative Example 1 was produced in the same manner as in Example 2, except that a mixture of 80% by mass of epoxy resin A and 20% by mass of epoxy resin C was used as the transparent resin.

[0056] Comparative Example 2 A ceramic scintillator array of Comparative Example 2 was produced in the same manner as in Example 1, except that a mixture of 80 mass % of epoxy resin A and 20 mass % of epoxy resin C was used as the transparent resin.

[0057] Comparative Example 3 A ceramic scintillator array of Comparative Example 3 was produced in the same manner as in Example 2, except that a mixture of 50% by mass of epoxy resin A and 50% by mass of epoxy resin C was used as the transparent resin.

[0058] Comparative Example 4 A ceramic scintillator array of Comparative Example 4 was produced in the same manner as in Example 1, except that a mixture of 50% by mass of epoxy resin A and 50% by mass of epoxy resin C was used as the transparent resin.

[0059] Comparative Example 5 A ceramic scintillator array of Comparative Example 5 was produced in the same manner as in Example 2, except that epoxy resin C was used as the transparent resin.

[0060] [Measurement of Chlorine Content in Reflective Layer] The reflective layer compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were thermally cured to form reflective layers, and then combusted under an oxygen inflow using an automatic sample combustion apparatus (product name: AQF-2100H, electric furnace HF-210, absorption unit GA-210, solid auto sample changer ACS-240S, manufactured by Mitsubishi Chemical Analytech Corporation). The generated gas was collected with an absorption liquid (hydrogen peroxide solution). The absorption liquid was analyzed with an ion chromatography analyzer (product name: ICS-1600, manufactured by Thermo Fisher Scientific Co., Ltd.) to measure the chlorine content in the reflective layer. The measurement results are shown in Table 1.

[0061] [Evaluation of Light Output] For each of the ceramic scintillator arrays of Examples 1 to 5 and Comparative Examples 1 to 5, a photodiode was attached to the surface opposite to the X-ray irradiated surface to construct an X-ray detector as shown in Figure 4. The light emission energy E detected by the photodiode when the X-ray detector was irradiated with X-rays of 120 kV and 60 to 80 mA was measured so that the detected light emission energy was the same each time. ０ Next, the X-ray detector was irradiated with 4.2 kGy of X-rays. The X-ray exposure dose of 4.2 kGy corresponds to the amount of X-rays used in a medical X-ray CT scanner for approximately 10 years. Even after the 4.2 kGy X-ray exposure, the luminous energy E detected by the photodiode when the X-ray detector was irradiated with 120 kV, 60 to 80 mA X-rays in the same manner as before the 4.2 kGy X-ray exposure was １ was measured. ０ E for １ The value of (E １ / E ０ ) was defined as the light output maintenance rate. A higher light output maintenance rate indicates that the decrease in light output can be suppressed even when irradiated with X-rays for a long period of time. Table 1 shows the relative values ​​of the light output maintenance rates in Examples 1 to 5 and Comparative Examples 1 to 5, where the light output maintenance rate in Example 1 is set to 100%.

[0062]

[0063] As is clear from Table 1, the ceramic scintillator arrays of Comparative Examples 1 to 5, in which the chlorine content in the reflective layer exceeded 3000 μg / g, had a relative light output maintenance rate of 92.75% or less, while the ceramic scintillator arrays of Examples 1 to 5, in which the chlorine content in the reflective layer was 3000 μg / g or less, were able to maintain a relative light output maintenance rate of 94.04% or more. This demonstrates that the ceramic scintillator arrays of Examples 1 to 5, in which the chlorine content in the reflective layer was 3000 μg / g or less, were able to suppress a decrease in light output after irradiation with 4.2 kGy of X-rays. Furthermore, the ceramic scintillator arrays of Examples 1 to 4, in which the chlorine content in the reflective layer was 940 μg / g or less, were able to maintain a relative light output maintenance rate of 97.67% or more, further demonstrating that a decrease in light output after irradiation with 4.2 kGy of X-rays was suppressed.

[0064] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0065] REFERENCE SIGNS LIST 1 ceramic scintillator array 2 scintillator segment 3 first reflective layer 4 second reflective layer 6 X-ray detector 7 photodiode 8 output terminal 10 X-ray CT device 11 subject 12 X-ray tube 13 computer 14 display 15 subject image

Claims

1. A ceramic scintillator array comprising a plurality of scintillator segments and a reflective layer, wherein the chlorine content in the reflective layer is 3000 μg / g or less.

2. The ceramic scintillator array of claim 1, wherein the reflective layer comprises at least one selected from the group consisting of epoxy resin, silicone resin, phenolic resin, urea resin, melamine resin, unsaturated polyester, polyurethane, acrylic resin, polyethylene terephthalate, epoxy-modified silicone, and glycidyl ether.

3. The ceramic scintillator array according to claim 1 or 2, wherein the reflective layer comprises at least one selected from the group consisting of titanium oxide, aluminum oxide, barium sulfate, zinc oxide, zirconium oxide and silicon oxide.

4. The ceramic scintillator array according to claim 1 or 2, wherein the scintillator segments contain a rare earth oxysulfide phosphor or a garnet-structure oxide phosphor.

5. A ceramic scintillator array according to claim 1 or 2, wherein the reflective layer is a first reflective layer provided so as to surround the side surfaces of the scintillator segments.

6. The ceramic scintillator array according to claim 1 or 2, wherein the reflective layer is a second reflective layer provided so as to cover the X-ray irradiated surface of the scintillator segment.

7. A radiation detector comprising the ceramic scintillator array according to claim 1 or 2.

8. A radiation inspection device comprising the radiation detector according to claim 7.

Images