Ceramic scintillator array, radiation detector, and radiation inspection device

Abstract

The present invention provides a ceramic scintillator array that can suppress the decrease in optical output after prolonged X-ray irradiation. [Solution] The ceramic scintillator array 1 of the embodiment comprises a plurality of scintillator segments 2 and a reflective layer. The reflective layer contains a resin composition. The resin composition contains a transparent resin and an additive. The additive is a dibasic acid ester.

Description

Technical Field

[0001] Embodiments according to the present invention relate to a ceramic scintillator array, a radiation detector, and a radiation inspection apparatus.

Background Art

[0002] In fields such as medical diagnosis or industrial non-destructive inspection, inspections using radiation inspection apparatuses such as X-ray computed tomography apparatuses (hereinafter referred to as "X-ray CT apparatuses") are being performed. For the X-ray detector of an X-ray CT apparatus, a detector using a solid scintillator that emits visible light or the like by excitation with X-rays together with a photoelectric conversion element is frequently used. In an X-ray detector using a solid scintillator, it is easy to miniaturize the photoelectric conversion element and increase the number of channels, so that the resolution of the X-ray CT apparatus can be further enhanced.

[0003] Radiation inspection apparatuses such as X-ray CT apparatuses are used in various fields such as medical use and industrial use. The X-ray detector mounted on an X-ray CT apparatus includes photoelectric conversion elements arranged two-dimensionally in the vertical and horizontal directions, and one or more scintillator segments, which are solid scintillators, are provided for each photoelectric conversion element. The X-ray incident on the scintillator segment is converted into visible light, the visible light is converted into an electrical signal by the photoelectric conversion element, and the electrical signal is analyzed by a computer to form an image.

[0004] A reflective layer is provided between adjacent scintillator segments or on the X-ray irradiation surface of the scintillator segment. The reflective layer reflects the visible light generated by the irradiation with X-rays and confines it within the scintillator segment so that the visible light can be efficiently guided to the photoelectric conversion element side.

[0005] When the ceramic scintillator array is irradiated with X-rays for a long time, the reflective layer tends to be colored. The colored reflective layer absorbs a part of the visible light generated from the scintillator segment, resulting in a problem that the light output decreases and the sensitivity of the X-ray detector decreases. Various studies have been conducted to address these problems. For example, Patent Document 1 describes a scintillator array in which a cured product of a cationic polymerization initiator or an acid anhydride curing agent is used for the reflective layer. In the scintillator array described in Patent Document 1, the decrease in reflectivity of the reflective layer due to X-ray irradiation is reduced. Furthermore, Patent Document 2 describes a scintillator array that uses a resin having a C=O bond as the reflective layer. The scintillator array described in Patent Document 2 can reduce the discoloration of the reflective layer due to X-ray irradiation. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-173226 [Patent Document 2] International Publication No. 2022 / 191214 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, even with the scintillator arrays described in Patent Documents 1 and 2, there is room for improvement in suppressing the decrease in optical output due to prolonged X-ray irradiation, and there has been a need for a ceramic scintillator array that can further suppress the decrease in optical output even when irradiated with X-rays for a long time.

[0008] Embodiments of the present invention provide a ceramic scintillator array that can suppress the decrease in optical output after prolonged X-ray irradiation. [Means for solving the problem]

[0009] The above problems are solved by the following embodiment. <1> A ceramic scintillator array comprising multiple scintillator segments and a reflective layer, The reflective layer comprises a resin composition, The resin composition comprises a transparent resin and an additive. A ceramic scintillator array in which the aforementioned additive is a dibasic acid ester. <2> The content of the additive in the resin composition is 1 to 20% by mass. <1> The ceramic scintillator array described above. <3> The transparent resin is 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. <1> or <2> The ceramic scintillator array described above. <4> The transparent resin is a bisphenol A type epoxy resin or an alicyclic polyfunctional epoxy resin. <1> ~ <3> A ceramic scintillator array as described in one of the following. <5> The reflective layer includes reflective particles, The reflective particles are at least one selected from the group consisting of titanium oxide, aluminum oxide, barium sulfate, zinc oxide, zirconium oxide, and silicon oxide. <1> ~ <4> A ceramic scintillator array as described in one of the following. <6> The scintillator segment comprises a rare earth acid sulfide phosphor or a garnet structure oxide phosphor. <1> ~ <5> A ceramic scintillator array as described in one of the following. <7> The reflective layer is a first reflective layer provided so as to surround the side surface of the scintillator segment. <1> ~ <6> A ceramic scintillator array as described in one of the following. <8> The reflective layer is a second reflective layer provided so as to cover the X-ray irradiation surface of the scintillator segment. <1> ~ <7> A ceramic scintillator array as described in one of the following. <9> <1> ~ <8> A radiation detector comprising a ceramic scintillator array as described in any one of the following. <10> <9>The radiation inspection apparatus comprising the radiation detector according to <9>.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a ceramic scintillator array of an embodiment. [Figure 2] FIG. 2 is a plan view showing an example of a ceramic scintillator array of an embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing another example of a ceramic scintillator array of an embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing an X-ray detector which is an example of a radiation detector of an embodiment. [Figure 5] FIG. 5 is a schematic configuration diagram showing an X-ray CT apparatus which is an example of a radiation inspection apparatus of an embodiment.

Modes for Carrying Out the Invention

[0011] Hereinafter, various embodiments will be described with reference to the drawings. Each figure is a schematic diagram for facilitating understanding of the embodiment, and there are parts where its shape, dimensions, ratio, etc. are different from the actual ones, but these can be appropriately designed and changed in consideration of the following description and known techniques.

[0012] <Ceramic Scintillator Array> Figure 1 is a cross-sectional view showing an example of a ceramic scintillator array according to an embodiment, and Figure 2 is a plan view showing an example of a ceramic scintillator array according to an embodiment. The ceramic scintillator array 1 comprises 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. That is, 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 irradiation surface of the plurality of scintillator segments 2. Note that the second reflective layer 4 is not shown in Figure 2.

[0013] In the ceramic scintillator array 1 of this embodiment, focusing on a single 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 irradiation surface of the scintillator segment 2. In this embodiment, the scintillator segment 2 is covered with reflective layers on all sides except one. The first reflective layer 3 and the second reflective layer 4 may be made of the same material or different materials.

[0014] In scintillator segment 2, a photodiode for detecting visible light converted from X-rays by scintillator segment 2 is directly or indirectly attached to the surface not covered by the reflective layer (the surface opposite to the X-ray irradiation surface), thereby serving as a radiation detector.

[0015] The ceramic scintillator array 1 may have a structure in which multiple scintillator segments 2 are arranged in a row, or, as shown in Figure 2, may have a structure in which multiple scintillator segments 2 are arranged two-dimensionally in predetermined numbers in the vertical and horizontal directions. When multiple scintillator segments 2 are arranged two-dimensionally, a first reflective layer 3 is provided between the scintillator segments 2 in the vertical and horizontal directions, respectively. Furthermore, a second reflective layer 4 is provided on the X-ray irradiation surface of the multiple scintillator segments 2 integrated 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 irradiation surface of the multiple scintillator segments 2. The number of scintillator segments 2 is appropriately set according to the structure and resolution of the X-ray detector.

[0016] Figure 3 is a cross-sectional view showing another example of the ceramic scintillator array of the embodiment. The ceramic scintillator array 1 shown in Figure 3 differs from the ceramic scintillator array 1 shown in Figure 1 in that it does not have a second reflective layer 4. That is, the ceramic scintillator array of the embodiment may include a plurality of scintillator segments 2 and a first reflective layer 3, but may not include a second reflective layer 4.

[0017] Next, the scintillator segment 2 and reflective layer constituting the ceramic scintillator array of the embodiment will be described. Note that the characteristics of the reflective layer described below may apply to the first reflective layer, the second reflective layer, or both the first and second reflective layers.

[0018] <Scintillator segment> The type of scintillator segment 2 in the ceramic scintillator array 1 of the embodiment is not particularly limited and may consist of, for example, a rare earth oxysulfide phosphor or a garnet structure oxide phosphor. The scintillator segment 2 may consist of, for example, one type of phosphor or two or more types of phosphors. Examples of rare earth oxysulfide phosphors include those containing praseodymium (Pr) as the luminescent center. Examples of rare earth oxysulfides that make up rare earth oxysulfides include oxysulfides of rare earth elements such as yttrium (Y), gadolinium (Gd), lanthanum (La), and lutetium (Lu). Examples of garnet-structured oxide phosphors include gadolinium-gallium-aluminum garnet (GGAG), lutetium-aluminum garnet (LuAG), lutetium-gallium-aluminum garnet (LuGAG), and gadolinium-aluminum garnet (GdAG).

[0019] Scintillator segment 2 is General formula: RE2O2S:Pr…(1) (In the formula, RE represents at least one element selected from the group consisting of Y, Gd, La, and Lu.) It is preferable that the phosphor is composed of a rare earth acid sulfide having the composition represented by [formula].

[0020] Among the rare earth elements mentioned above, Gd has a large X-ray absorption coefficient and contributes to improving the optical output of the ceramic scintillator array 1. Therefore, in the ceramic scintillator array 1 of the embodiment, it is even more preferable to use a Gd2O2S:Pr phosphor for the scintillator segment 2. Note that a portion of the Gd may be substituted with other rare earth elements. In this case, it is preferable that the amount of Gd substituted with other rare earth elements be 10 mol% or less.

[0021] That is, in the ceramic scintillator array 1 of the embodiment, General formula: (Gd 1-X ,RE X )2O2S:Pr …(2) (In the formula, RE represents at least one element selected from the group consisting of Y, La, and Lu, and X is a number (atomic ratio) that satisfies 0 ≤ X ≤ 0.1.) It is preferable to use a rare earth oxysulfide phosphor represented by in the scintillator segment 2.

[0022] In the ceramic scintillator array 1 of this embodiment, praseodymium (Pr) is included as the luminescence center of the rare earth sulfide phosphor. Compared to other rare earth elements, Pr can reduce afterglow. Therefore, rare earth sulfide phosphors containing Pr as the luminescence center are effective as materials for solid scintillators that constitute radiation detectors.

[0023] The Pr content in the rare earth acid sulfide phosphor is preferably in the range of 0.001 to 10 mol%, and more preferably in the range of 0.01 to 1 mol%, relative to the phosphor matrix (the compound represented as RE2O2S in formula (1)). This allows the phosphor to exhibit high luminescence efficiency. It is important to note that a Pr content exceeding 10 mol% may lead to a decrease in light output. Furthermore, a Pr content of less than 0.001 mol% will not provide sufficient effectiveness as a light-emitting center.

[0024] In the rare earth sulfide phosphor used in the embodiment, in addition to Pr as the luminescence center, a small amount of cerium (Ce) may be included as an activator. 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 matrix.

[0025] Furthermore, in the ceramic scintillator array 1 of the embodiment, the scintillator segment 2 is preferably made of a high-purity rare-earth acid sulfide phosphor. Since impurities are a factor in reducing the sensitivity of the scintillator segment 2, it is preferable to reduce the amount of impurities contained in the scintillator segment 2 as much as possible. In particular, since phosphate (PO4) is a cause of reduced sensitivity, it is preferable to keep the phosphate content in the scintillator segment 2 to 100 ppm or less. When fluoride or the like is used as a sintering aid to increase the density of the scintillator segment 2, the sintering aid remains in the scintillator segment 2 as an impurity, which leads to a decrease in sensitivity.

[0026] The scintillator segment 2 is preferably a solid scintillator in the shape of a cube or rectangular parallelepiped. The volume of the scintillator segment 2 is 1 mm³. 3 The following is preferable: By miniaturizing the scintillator segment 2, the detected image can be made higher resolution.

[0027] The dimensions of the scintillator segment 2 in length, width, and thickness are not necessarily limited, but are preferably 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 segment 2. The visible light travels through the inside of the scintillator segment 2, but if the optical path length of the visible light is large, the visible light is scattered and attenuated. By keeping the dimensions of the scintillator segment 2 below a certain level, the optical path length of the visible light is reduced, and the visible light can be efficiently delivered to the photoelectric conversion element.

[0028] <Reflection layer> The reflective layer includes a resin composition. For example, the reflective layer includes a resin composition and reflective particles, and is composed of reflective particles and a resin composition that embeds the reflective particles. By including reflective particles in the reflective layer, the reflective layer can reflect visible light and confine it within the scintillator segment 2, efficiently guiding the visible light to the photoelectric conversion element. Furthermore, it is preferable that the resin composition constituting the reflective layer has high transparency. High transparency of the resin composition suppresses the absorption of visible light generated in the scintillator segment 2 into the reflective layer, allowing it to reach the photoelectric conversion element efficiently.

[0029] Examples of reflective particles include white pigments such as titanium dioxide, aluminum oxide, barium sulfate, zinc oxide, zirconium oxide, and silicon oxide. 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.

[0030] From the viewpoint of efficiently guiding visible light from the scintillator segment 2 to the photoelectric conversion element, it is preferable that the reflective layer has a high reflectivity, for example, it is preferable that it has a reflectivity of 80% or more for visible light with a wavelength of 500 to 800 nm. From the viewpoint of achieving high reflectivity, when reflective particles are used, the content of the resin composition in the reflective layer is preferably 40 to 60% by mass, and the content of reflective particles in the reflective layer is preferably 40 to 60% by mass. The median particle size of the reflective particles is preferably 0.2 to 0.4 μm.

[0031] The resin composition includes a transparent resin and additives. The transparent resin will be described below, in order.

[0032] Examples of transparent resins include epoxy resin, silicone resin, phenolic resin, urea resin, melamine resin, unsaturated polyester, polyurethane, acrylic resin, polyethylene terephthalate, epoxy-modified silicone, and glycidyl ether. For example, in the case of ceramic scintillators used in X-ray CT scanners, the operating temperature is known to reach 50-60°C. Therefore, it is preferable that the transparent resin used in the reflective layer has heat resistance, 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 shift during use. Therefore, the reflective layer in the embodiment preferably 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, and among these, it is preferable to include epoxy resin from the viewpoint of handling properties, transparency, and storage stability required during the manufacture of the reflective layer.

[0033] Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol B type epoxy resin, bisphenol AP type epoxy resin, diphenolic acid type epoxy resin, or structures obtained by adding hydrogen to the alicyclic structure thereof, novolac type epoxy resin, glycidylamine type epoxy resin, aliphatic type epoxy resin, alicyclic polyfunctional epoxy resin, alicyclic epoxy resin having a biphenyl skeleton, etc. It is preferable to use one or a mixture of two or more of these epoxy resins. Among these, bisphenol A type epoxy resin or alicyclic polyfunctional epoxy resin is preferred, bisphenol A type epoxy resin is more preferred, and bisphenol A diglycidyl ether is even more preferred.

[0034] When curing epoxy resins, it is common to use a curing agent. Examples of curing agents include aliphatic polyamines, aromatic polyamines, acid anhydrides, imidazole compounds, and dicyandiamides. Among these, at least one selected from the group consisting of aliphatic polyamines and aromatic polyamines is preferred because of its suitable pot life and glass transition temperature.

[0035] When curing a transparent resin using a curing agent, curing is completed when the transparent resin and the curing agent undergo a polymerization reaction to form macromolecules. Therefore, it is preferable to mix in an amount of curing agent sufficient to cause the entire amount of transparent resin to undergo the polymerization reaction. Furthermore, if the amount of curing agent mixed in is too much relative to the transparent resin, unreacted curing agent may remain in the cured product, which may alter the properties of the cured product. For this reason, it is preferable to adjust the curing agent content appropriately depending on the type of transparent resin and curing agent used. For example, the curing agent content is preferably 10 parts by weight or more, and more preferably 20 parts by weight or more, per 100 parts by weight of the resin composition. Also, the curing agent content is preferably 30 parts by weight or less, and more preferably 25 parts by weight or less, per 100 parts by weight of the resin composition.

[0036] The viscosity of the transparent resin before curing is preferably 300 to 600 mPa·s. Having a viscosity within a certain range allows the transparent resin to have appropriate fluidity, making it easy to uniformly mix the reflective particles with the transparent resin when forming the reflective layer. As a result, a reflective layer can be formed in which the reflective particles are uniformly distributed within the transparent resin. Furthermore, the appropriate fluidity of the transparent resin improves workability when forming the reflective layer between the scintillator segments 2.

[0037] If the fluidity of the transparent resin is low, the fluidity can be improved by adding an appropriate additive (also called a functionalizing agent) to the resin composition. Additives that enhance the fluidity of transparent resins, that is, additives that have the function of reducing the viscosity of transparent resins, include lubricants, thixotropic agents, and plasticizers. Among these, plasticizers that have good compatibility with transparent resins and do not degrade over time are preferred. Plasticizers are additives that penetrate between the molecules of transparent resins, weakening the intermolecular forces and thereby imparting flexibility and fluidity to the resin.

[0038] Typical plasticizers include epoxidized vegetable oils and phthalates. Among these, phthalates are highly versatile plasticizers and are widely used as additives in flexible polyvinyl chloride and other materials. However, in recent years, the harmful effects of phthalates have been questioned, and some phthalates are considered to potentially be carcinogenic. Therefore, dibasic acid esters are sometimes used as plasticizers instead of phthalate esters.

[0039] Dibasic acid esters are esters composed of a dibasic acid and an alcohol. Dibasic acid esters have excellent storage stability, low volatility, non-migratory properties, and heat resistance, and as mentioned above, they are sometimes used as plasticizers.

[0040] Examples of dibasic acids that make up dibasic acid esters include adipic acid, azelaic acid, sebacic acid, cyclohexanedicarboxylic acid, cyclohexenedicarboxylic acid, maleic acid, fumaric acid, terephthalic acid, isophthalic acid, and pyromellitic acid. Alternatively, acid anhydrides obtained by dehydration condensation of dibasic acids may also be used.

[0041] Examples of alcohols that make up dibasic acid esters include butanol, decanol, nonanol, octanol, 4-butoxyethanol, isononyl alcohol, 2-ethylhexanol, isobutyl alcohol, and isodecyl alcohol.

[0042] Dibasic acid esters are synthesized by the esterification reaction of the above-mentioned dibasic acids with the above-mentioned alcohols. Examples of such dibasic acid esters include diisodecyl adipate, diisononyl adipate, dibutyl azelaate, dibutyl sebacate, dinonyl sebacate, diethylhexyl cyclohexanedicarboxylate, diethylhexyl cyclohexenedicarboxylate, dibutyl maleate, dinonyl maleate, diisobutyl maleate, dibutyl fumarate, dinonyl fumarate, diethylhexyl terephthalate, diethylhexyl isophthalate, and diethylhexyl pyromellitic acid.

[0043] By adding dibasic acid esters to a transparent resin such as epoxy resin, discoloration of the resin composition due to prolonged X-ray irradiation can be suppressed. By using such a resin composition as the reflective layer, a ceramic scintillator array can be fabricated that suppresses the decrease in optical output even when irradiated with X-rays for a long time.

[0044] The reason why dibasic acid esters can suppress the discoloration of resin compositions is presumed to be as follows: Transparent resins are generally known to discolor when exposed to X-rays for extended periods. One possible reason for this is that small amounts of metal or halogen elements present in the transparent resin become radicalized by X-ray irradiation, causing discoloration. Dibasic acid esters are presumed to have the effect of inactivating these radicals. Therefore, it is thought that adding dibasic acid esters to a resin composition can suppress discoloration of both the resin composition and the reflective layer.

[0045] The content of additives in the resin composition is preferably 3 to 15% by mass, and more preferably 5 to 10% by mass, with a lower limit of 1% by mass and an upper limit of 20% by mass. When the additive is a dibasic acid ester, increasing the content of the additive in the resin composition above the lower limit can further suppress discoloration of the resin composition due to prolonged X-ray irradiation. When the additive is a dibasic acid ester, decreasing the content of the additive in the resin composition below the upper limit allows the resin composition to have an appropriate viscosity, facilitating the formation of a reflective layer.

[0046] The additive content in the resin composition refers to the content before the resin composition is cured with a hardening agent. Mass of additive / (Mass of transparent resin + Mass of additive) × 100 …(3) It can be calculated using this method.

[0047] <Method for forming a reflective layer> The reflective layer is formed, for example, as follows: Multiple scintillator segments, processed to a predetermined shape, are arranged at regular intervals. A reflective layer composition is prepared by mixing a resin composition, reflective particles, and a curing agent, and this is applied or filled between adjacent scintillator segments. The first reflective layer can be formed by curing the reflective layer composition with heat. Next, a reflective layer composition is applied to the X-ray irradiation surface of a ceramic scintillator array consisting of scintillator segments and a first reflective layer. A second reflective layer can be formed by curing the newly applied reflective layer composition with heat.

[0048] Furthermore, a second reflective layer can be formed by bonding a predetermined film to the X-ray irradiation surface of a ceramic scintillator array using an adhesive. Examples of films that serve as the second reflective layer include films obtained by processing a reflective layer composition containing a resin composition and reflective particles into a sheet using a doctor blade or the like and then curing it. However, the film that serves as the second reflective layer is not limited to this, and commercially available white films can also be used, for example.

[0049] <Radiation detectors and radiation inspection equipment> Next, the radiation detector and radiation inspection apparatus of the embodiment will be described.

[0050] The radiation detector of this embodiment comprises the ceramic scintillator array 1 of the embodiment described above as a solid scintillator that emits visible light according to the amount of incident radiation, and further comprises a photoelectric conversion element that receives visible light from the solid scintillator and converts the visible light into an electrical signal. Figure 4 shows an X-ray detector, which is an example of the radiation detector of this embodiment. The X-ray detector 6 shown in Figure 4 comprises a ceramic scintillator array 1 which is a solid scintillator, and a photodiode 7 which is a photoelectric conversion element.

[0051] 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 photodiode 7 is arranged to correspond to each scintillator segment 2 that makes up the ceramic scintillator array 1. In this way, the X-ray detector 6 is constructed.

[0052] In the X-ray detector 6 described above, when X-rays are irradiated from the second reflection layer 4 side, the X-rays enter each scintillator segment 2, and visible light is emitted from the scintillator segment 2 according to the amount of incident X-rays. The visible light emitted from the scintillator segment 2 is detected by the photodiode 7. The visible light emitted based on the amount of incident X-rays is converted into an electrical signal by the photodiode 7 and then sent to a computer from the output terminal 8.

[0053] The radiation inspection apparatus of this embodiment comprises a radiation source that irradiates radiation toward a subject and a radiation detector that detects radiation that has passed through the subject. The radiation detector used is the radiation detector of the embodiment described above. Figure 5 shows an X-ray CT apparatus 10, which is an example of the radiation inspection apparatus of this embodiment. The X-ray detector 6 is attached, for example, to the inner wall surface of an arc on which the subject 11 is placed. An X-ray tube 12 that emits X-rays is installed at the center of the arc on which the X-ray detector 6 is attached. The subject 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.

[0054] The X-ray detector 6 and X-ray tube 12 are configured to rotate around the subject 11 and image the subject 11. Image information of the subject 11 is collected three-dimensionally from different angles. The signal obtained by X-ray imaging (electrical signal converted by a photoelectric conversion element) is processed by a computer 13 and displayed on a display 14 as a subject image 15. The subject image 15 is, for example, a tomographic image of the subject 11. As shown in Figure 2, it is also possible to configure a multi-tomographic type X-ray CT apparatus 10 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 acquired simultaneously, and for example, the imaging results can be depicted three-dimensionally.

[0055] This technology allows the radiation inspection device of the embodiment to contribute to improving inspection accuracy, among other things. Furthermore, the radiation inspection device of the embodiment is applicable not only to X-ray inspection for medical diagnosis of the human body, but also to X-ray inspection of animals or X-ray inspection for industrial purposes, etc. Furthermore, the radiation inspection apparatus of the embodiment comprises a radiation detector having the ceramic scintillator array of the embodiment. As described above, the ceramic scintillator array of the embodiment contains dibasic acid esters in the resin composition of at least one selected from the group consisting of a first reflective layer and a second reflective layer, so that the decrease in optical output after prolonged irradiation with X-rays can be suppressed. [Examples]

[0056] Next, we will describe specific examples of the embodiments and their evaluation results.

[0057] The epoxy resins, curing agents, and additives used in the following Reference Examples 1-9, Examples 1 and 2, and Comparative Example 1 are as follows: Epoxy resin A Hydrogenated bisphenol A diglycidyl ether, product name: EP-4080E, manufactured by ADEKA Corporation. Epoxy resin B Hydrogenated bisphenol A diglycidyl ether, trade name: Epolite 4000, manufactured by Kyoeisha Chemical Co., Ltd. • Epoxy resin C Alicyclic polyfunctional epoxy resin, product name: TETRAD-C, manufactured by Mitsubishi Gas Chemical Company, Inc. • Hardener Alicyclic polyamine-based curing agent, product name: NBDA, manufactured by Mitsui Chemicals Fine, Inc. • Additives Dibasic acid esters in which the dibasic acid is cyclohexenedicarboxylic acid and the alcohol is 2-ethylhexanol.

[0058] [Reference example 1] As a resin composition, a 5% by mass additive was added to epoxy resin A. A mixture of 90% by mass titanium oxide powder and 10% by mass aluminum oxide powder was prepared as the reflective particles. A reflective layer composition was prepared by mixing a resin composition, a curing agent, and reflective particles in a mass ratio of 100:20:120. The reflective layer composition was poured into a silicone mold and heat-cured at 70°C for 5 hours. The resulting cured material was cut into an appropriate shape and ground to a thickness of 1.0 (±0.2) mm using a surface grinder to form a thin plate, thereby creating a reflective layer structure for Reference Example 1 that mimics the second reflective layer.

[0059] [Reference example 2] The reflective layer structure of Reference Example 2 was fabricated in the same manner as in Reference Example 1, except that the resin composition used was epoxy resin A with 10% by mass of an additive added.

[0060] [Reference example 3] The reflective layer structure of Reference Example 3 was fabricated in the same manner as in Reference Example 1, except that the resin composition used was epoxy resin B with 5% by mass of an additive added.

[0061] [Reference example 4] The reflective layer structure of Reference Example 4 was fabricated in the same manner as in Reference Example 1, except that the resin composition used was epoxy resin B with 10% by mass of an additive added.

[0062] [Reference example 5] A reflective layer structure for Reference Example 5 was fabricated in the same manner as in Reference Example 1, except that the resin composition used was epoxy resin C with 5% by mass of an additive added, and the resin composition, curing agent, and reflective particles were mixed in a mass ratio of 100:40:120.

[0063] [Reference example 6] The reflective layer structure of Reference Example 6 was fabricated in the same manner as in Reference Example 5, except that the resin composition used was epoxy resin C with 10% by mass of an additive added.

[0064] [Reference example 7] The reflective layer structure of Reference Example 7 was fabricated in the same manner as in Reference Example 1, except that 100% by mass of epoxy resin A was used instead of a resin composition of 95% by mass of epoxy resin A and 5% by mass of additives.

[0065] [Reference example 8] The reflective layer structure of Reference Example 8 was fabricated in the same manner as in Reference Example 3, except that 100% by mass of epoxy resin B was used instead of the resin composition of 95% by mass of epoxy resin B and 5% by mass of additives.

[0066] [Reference example 9] The reflective layer structure of Reference Example 9 was fabricated in the same manner as in Reference Example 5, except that 100% by mass of epoxy resin C was used instead of a resin composition of 95% by mass of epoxy resin C and 5% by mass of additives.

[0067] [Evaluation of reflectance] Using a UV-Vis spectrophotometer (product name: UV-2700i, manufactured by Shimadzu Corporation), the reflectance R0 of the reflective layer structures of Reference Examples 1 to 9 was measured by irradiating them with visible light at a wavelength of 510 nm. Next, the reflective layer structure was irradiated with 4.2 kGy of X-rays. This X-ray dose of 4.2 kGy is equivalent to the amount of X-rays used by a medical X-ray CT scanner over approximately 10 years. The reflectance R1 of the reflective layer structure was measured after 4.2 kGy of X-ray irradiation, in the same manner as before the 4.2 kGy X-ray irradiation. The value of R1 relative to R0 (R1 / R0) was defined as the reflectivity maintenance rate. A higher reflectivity maintenance rate for the reflective layer structure corresponds to better suppression of the decrease in reflectivity even after prolonged X-ray irradiation, and thus to better suppression of the decrease in the optical output of the ceramic scintillator array. Furthermore, since the trivalent Pr in the rare earth oxysulfide phosphor shown in general formula (2) has the maximum peak in its emission spectrum at 510 nm, the reflective layer in the ceramic scintillator is required to reflect visible light at 510 nm well. For this reason, visible light with a wavelength of 510 nm was used to measure the reflectance of the reflective layer structure. The results are shown in Table 1.

[0068] [Table 1]

[0069] As is clear from Table 1, the reflective layer structures of Reference Examples 1-6, in which dibasic acid esters were added to the transparent resin, showed a greater reflectivity retention rate and suppressed the decrease in reflectivity after irradiation with 4.2 kGy of X-rays, compared to the reflective layer structures of Reference Examples 7-9, in which dibasic acid esters were not added to the transparent resin. Furthermore, the reflective layer structures of Reference Examples 2 and 6, in which 10% by mass of dibasic acid esters were added to the transparent resin, showed a greater retention rate of reflectivity and a greater suppression of the decrease in reflectivity compared to the reflective layer structures of Reference Examples 1 and 5, in which 5% by mass of dibasic acid esters were added to the transparent resin.

[0070] [Example 1] <Fabrication of scintillator segments> The median particle size is 5-10 μm, (Gd 0.99928 ,Pr 0.0007 Ce 0.00002 Gadolinium oxysulfide phosphor powder having the composition 2O2S was molded by wet cold isostatic pressing (wet-CIP) treatment. 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 covered with molybdenum (Mo) foil and placed in the capsule, which was then degassed and sealed. Next, the Ta capsule was set in a hot isostatic pressing (HIP) treatment device. Argon gas was sealed in the HIP treatment device as a pressurizing medium, and a sintered body was produced by processing at a pressure of 180 MPa and a temperature of 1300-1500°C for 3 hours. After cooling, the sintered body was removed, and a 2.0 mm thick flat plate was cut along the height direction of the cylinder using a wire saw. Grooves were then machined into the surface of this flat plate at intervals of 1.39 mm vertically and 1.18 mm horizontally using a blade, creating multiple scintillator segments. The width of the grooves was 0.10 mm vertically and 0.27 mm horizontally. <Fabrication of reflective layer composition> As a resin composition, a 5% by mass additive was added to epoxy resin A. A mixture of 90% by mass titanium oxide powder and 10% by mass aluminum oxide powder was prepared as the reflective particles. The resin composition, curing agent, and reflective particles were mixed in a mass ratio of 100:20:120. A reflective layer composition was thus prepared. <Fabrication of ceramic scintillator arrays> A reflective layer composition was filled into the grooves between the scintillator segments described above. The reflective layer composition was heat-cured to form a first reflective layer, and adjacent scintillator segments were bonded together via the first reflective layer to fabricate a ceramic scintillator array as shown in Figures 2 and 3. After polishing one side of the ceramic scintillator array to create a smooth surface, the other side was covered with a reflective layer composition and heat-cured to form a second reflective layer. Finally, both sides were polished to an overall 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 fabricated, comprising a scintillator segment, a first reflective layer, and a second reflective layer.

[0071] [Example 2] A ceramic scintillator array for Example 2 was prepared in the same manner as in Example 1, except that the resin composition used was epoxy resin A with 15% by mass of an additive added.

[0072] [Comparative Example 1] A ceramic scintillator array of Comparative Example 1 was prepared in the same manner as in Example 1, except that 100% by mass of epoxy resin A was used instead of a resin composition of 95% by mass of epoxy resin A and 5% by mass of an additive.

[0073] [Evaluation of optical output] For each of the ceramic scintillator arrays in Examples 1 and 2 and Comparative Example 1, a photodiode was attached to the side opposite to the X-ray irradiation surface to construct an X-ray detector as shown in Figure 4. To ensure that the detected emission energy was the same each time, the emission energy E0 detected by the photodiode was measured when the X-ray detector was irradiated with 120kV, 60-80mA X-rays. Next, the X-ray detector was irradiated with 4.2 kGy of X-rays. This dose of 4.2 kGy is equivalent to the amount of X-rays used by a medical X-ray CT scanner over approximately 10 years. Even after irradiation with 4.2 kGy of X-rays, the luminescence energy E1 detected by the photodiode was measured when 120 kV, 60-80 mA X-rays were irradiated onto the X-ray detector, in the same manner as before the 4.2 kGy X-ray irradiation. The value of E1 relative to E0 (E1 / E0) was defined as the optical power maintenance ratio. A higher optical power maintenance ratio indicates that the decrease in optical power can be suppressed even with prolonged X-ray irradiation. The results are shown in Table 2.

[0074] [Evaluation of reflectance] Similar to the reflective layer structures of Reference Examples 1 to 9, the reflectances R0 and R1 were measured for the second reflective layer of each of the ceramic scintillator arrays in Examples 1 and 2 and Comparative Example 1, and the value of R1 relative to R0 (R1 / R0) was defined as the reflectance retention rate. The results are shown in Table 2.

[0075] [Table 2]

[0076] As is clear from Table 2, the ceramic scintillators of Examples 1 and 2, in which dibasic acid esters were added to the transparent resin, exhibited higher optical output maintenance and reflectivity maintenance compared to the ceramic scintillator of Comparative Example 1, in which dibasic acid esters were not added to the transparent resin. This demonstrates that the decrease in optical output and reflectivity after irradiation with 4.2 kGy of X-rays can be suppressed. Furthermore, the ceramic scintillator of Example 2, in which 15% by mass of dibasic acid esters were added to the transparent resin, exhibited significantly higher light output maintenance and reflectance maintenance compared to the ceramic scintillator of Example 1, in which 5% by mass of dibasic acid esters were added to the transparent resin. This indicates that the decrease in light output and reflectance was more effectively suppressed.

[0077] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0078] 1. Ceramic scintillator array 2. Scintillator segment 3 First reflective layer 4 Second reflective layer 6 X-ray detector 7 Photodiode 8 output terminals 10 X-ray CT device 11 Subjects 12 X-ray tube 13 Computers 14 displays 15. Subject images

Claims

1. A ceramic scintillator array comprising multiple scintillator segments and a reflective layer, The reflective layer comprises a resin composition, The resin composition comprises a transparent resin and an additive. A ceramic scintillator array in which the aforementioned additive is a dibasic acid ester.

2. The ceramic scintillator array according to claim 1, wherein the content of the additive in the resin composition is 1 to 20% by mass.

3. The ceramic scintillator array according to claim 1 or 2, wherein the transparent resin is 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.

4. The ceramic scintillator array according to claim 1 or 2, wherein the transparent resin is a bisphenol A type epoxy resin or an alicyclic polyfunctional epoxy resin.

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

6. The ceramic scintillator array according to claim 1 or 2, wherein the scintillator segment comprises a rare earth oxysulfide phosphor or a garnet-structured oxide phosphor.

7. The 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 surface of the scintillator segment.

8. 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 irradiation surface of the scintillator segment.

9. A radiation detector comprising the ceramic scintillator array described in claim 1 or 2.

10. A radiation inspection apparatus comprising the radiation detector described in claim 9.

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