Ceramic scintillator array, radiation detector, and radiation inspection 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 reflective layer. The reflective layer contains a resin composition. The resin composition contains a transparent resin and an additive. Dibasic acid esters serve as the additive.

Description

Ceramic scintillator array, radiation detector, and radiation inspection device

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

[0002] In fields such as medical diagnosis and industrial non-destructive testing, inspections are performed using radiation inspection equipment such as X-ray tomography (hereinafter referred to as "X-ray CT scanners"). X-ray detectors in X-ray CT scanners frequently use detectors that utilize a solid scintillator, which emits visible light when excited by X-rays, together with a photoelectric conversion element. With X-ray detectors using solid scintillators, it is easy to increase the number of channels by miniaturizing the photoelectric conversion element, thereby further improving the resolution of the X-ray CT scanner.

[0003] Radiation inspection equipment such as X-ray CT scanners are used in various fields, including medical and industrial applications. The X-ray detector mounted on an X-ray CT scanner is equipped with photoelectric conversion elements arranged in two dimensions, and one or more scintillator segments, which are solid scintillators, are provided for each photoelectric conversion element. X-rays incident on the scintillator segments are converted into visible light, the visible light is converted into electrical signals by the photoelectric conversion elements, and an image is created by analyzing the electrical signals with a computer.

[0004] A reflective layer is provided between adjacent scintillator segments or on the X-ray irradiation surface of a scintillator segment. The reflective layer reflects the visible light generated by the X-ray irradiation, trapping it within the scintillator segment and efficiently guiding it towards the photoelectric conversion element.

[0005] When ceramic scintillator arrays are irradiated with X-rays for extended periods, the reflective layer tends to become discolored. This discolored reflective layer absorbs some of the visible light emitted from the scintillator segments, leading to a decrease in light output and a reduction in the sensitivity of the X-ray detector. Various studies have been conducted to address this problem. For example, Patent Document 1 describes a scintillator array in which the reflective layer is cured using a cationic polymerization initiator or an acid anhydride curing agent. 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 in which a resin having a C=O bond is used for the reflective layer. The scintillator array described in Patent Document 2 can reduce the discoloration of the reflective layer due to X-ray irradiation.

[0006] Japanese Patent Publication No. 2020-173226, International Publication No. 2022 / 191214

[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 irradiation with X-rays.

[0009] The above problems are solved by the following embodiments. <1> A ceramic scintillator array comprising a plurality of scintillator segments and a reflective layer, wherein the reflective layer comprises a resin composition, the resin composition comprises a transparent resin and an additive, and the additive is a dibasic acid ester. <2> The ceramic scintillator array according to <1>, wherein the content of the additive in the resin composition is 1 to 20% by mass. <3> The ceramic scintillator array according to <1> or <2>, wherein the transparent resin is at least one selected from the group consisting of epoxy resin, silicone resin, phenol 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 any one of <1> to <3>, wherein the transparent resin is a bisphenol A type epoxy resin or an alicyclic polyfunctional epoxy resin. <5> A ceramic scintillator array according to any one of <1> to <4>, wherein the reflective layer comprises reflective particles, and 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> A ceramic scintillator array according to any one of <1> to <5>, wherein the scintillator segment comprises a rare earth oxysulfide phosphor or a garnet structure oxide phosphor. <7> A ceramic scintillator array according to any one of <1> to <6>, wherein the reflective layer is a first reflective layer provided so as to surround the side surface of the scintillator segment. <8> A ceramic scintillator array according to any one of <1> to <7>, 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 according to any one of <1> to <8>. <10> A radiation inspection device comprising the radiation detector according to <9>.

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

[0011] Various embodiments will be described below with reference to the drawings. Each drawing is a schematic representation of the embodiment to facilitate understanding, and its shape, dimensions, ratios, etc., may differ from the actual product. These can be modified as appropriate in the following description and in reference to known technology.

[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 the scintillator segment 2, a photodiode for detecting visible light converted from X-rays by the 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 becoming a radiation detector.

[0015] The ceramic scintillator array 1 may have a structure in which a plurality of scintillator segments 2 are arranged in a row, or, as shown in Figure 2, may have a structure in which a predetermined number of scintillator segments 2 are arranged two-dimensionally in the vertical and horizontal directions. When a plurality of 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 plurality of 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 plurality of 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 is 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 luminescence center. Examples of rare earth oxysulfides constituting the rare earth oxysulfide phosphor 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).

[0019] Scintillator segment 2 has the general formula: RE ２ O ２ It is preferable that the rare earth oxysulfide phosphor has a composition represented by S:Pr …(1) (wherein RE represents at least one element selected from the group consisting of Y, Gd, La, and Lu).

[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 this embodiment, the scintillator segment 2 is Gd ２ O ２ S: It is even more preferable to use a Pr phosphor. 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, the general formula is: (Gd １－Ｘ RE Ｘ ) ２ O ２S: 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) satisfying 0 ≦ X ≦ 0.1.) It is preferable to use the rare earth oxysulfide phosphor represented by this as the scintillator segment 2.

[0022] In the ceramic scintillator array 1 of the embodiment, it contains praseodymium (Pr) as the emission center of the rare earth oxysulfide phosphor. Pr can reduce afterglow compared to other rare earth elements. Therefore, the rare earth oxysulfide phosphor containing Pr as the emission center is effective as a material for the solid scintillator constituting the radiation detector.

[0023] The content of Pr in the rare earth oxysulfide phosphor is preferably in the range of 0.001 to 10 mol% with respect to the phosphor matrix (the compound represented by RE ２ O ２ S), and more preferably in the range of 0.01 to 1 mol%. Thereby, the phosphor comes to exhibit high luminous efficiency. If the content of Pr exceeds 10 mol%, it may cause a decrease in light output, so care is required. Also, if the content of Pr is less than 0.001 mol%, the effect as an emission center cannot be sufficiently obtained.

[0024] In the rare earth oxysulfide phosphor used in the embodiment, in addition to Pr as the emission center, a trace amount of cerium (Ce) may be contained as an activator. Ce shows an effect on suppressing afterglow. The content of Ce is preferably in the range of 0.00001 to 0.1 mol% with respect to the phosphor matrix.

[0025] Further, in the ceramic scintillator array 1 of the embodiment, it is preferable that the scintillator segment 2 is made of a high purity rare earth oxysulfide 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, phosphate radical (PO ４Therefore, since it causes a decrease in sensitivity, it is preferable that the content of phosphate radicals in the scintillator segment 2 be 100 ppm or less. When a fluoride or the like is used as a sintering aid to densify the scintillator segment 2, the sintering aid remains in the scintillator segment 2 as an impurity, resulting in a decrease in sensitivity.

[0026] The scintillator segment 2 is preferably a solid scintillator having a cubic shape or a rectangular parallelepiped shape. The volume of the scintillator segment 2 is preferably 1 mm ３ or less. By miniaturizing the scintillator segment 2, the detected image can be made high-definition.

[0027] The dimensions of the length, width, and thickness of the scintillator segment 2 are not necessarily limited, but are preferably 2 mm or less, and more preferably 1.5 mm or less for each. When X-rays are irradiated on the ceramic scintillator array 1, the X-rays are converted into visible light in the scintillator segment 2. The visible light travels inside the scintillator segment 2, but when the optical path length of the visible light becomes large, the visible light is scattered and attenuated. By making the dimensions of the length, width, and thickness of the scintillator segment 2 below a certain level, the optical path length of the visible light becomes small, and the visible light can reach the photoelectric conversion element efficiently.

[0028] <Reflection layer> The reflection layer contains a resin composition. The reflection layer includes, for example, a resin composition and reflection particles, and is composed of reflection particles and a resin composition embedding the reflection particles. Since the reflection layer contains reflection particles, the reflection layer can reflect visible light and confine it within the scintillator segment 2, and can efficiently guide the visible light to the photoelectric conversion element. Also, it is preferable that the transparency of the resin composition constituting the reflection layer is high. Since the transparency of the resin composition is high, it is possible to suppress the visible light generated in the scintillator segment 2 from being absorbed by the reflection layer, and it can reach the photoelectric conversion element efficiently.

[0029] Examples of the reflective particles include white pigments such as titanium oxide, 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, the reflective layer preferably has a high reflectivity. For example, it preferably has a reflectivity of 80% or more with respect to visible light having a wavelength of 500 to 800 nm. From the viewpoint of realizing a high reflectivity, when using reflective particles, the content of the resin composition in the reflective layer is preferably 40 to 60% by mass, and the content of the reflective particles in the reflective layer is preferably 40 to 60% by mass. In addition, the median diameter of the reflective particles is preferably 0.2 to 0.4 μm.

[0031] The resin composition includes a transparent resin and an additive. Hereinafter, the transparent resin will be described in order.

[0032] Examples of the transparent resin include epoxy resin, silicone resin, phenol resin, urea resin, melamine resin, unsaturated polyester, polyurethane, acrylic resin, polyethylene terephthalate, epoxy-modified silicone, and glycidyl ether. For example, in the case of a ceramic scintillator used as an X-ray CT device, it is known that the temperature during use reaches 50 to 60°C. Therefore, the transparent resin used for the reflective layer preferably has heat resistance, and it is particularly preferable to use a thermosetting resin having excellent heat resistance. When using a transparent resin with low heat resistance, 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 resin, silicone resin, phenol resin, urea resin, melamine resin, unsaturated polyester, polyurethane, acrylic resin, polyethylene terephthalate, epoxy-modified silicone, and glycidyl ether. Among them, from the viewpoints of handling properties, transparency, storage stability, etc. required during the production of the reflective layer, it is preferable to contain epoxy resin.

[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, and so on. 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. Furthermore, 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 a transparent resin is low, the fluidity can be increased by adding appropriate additives (also called functional additives) to the resin composition. Additives that increase the fluidity of a transparent resin, that is, additives that have the function of reducing the viscosity of the transparent resin, include lubricants, thixotropic agents, and plasticizers. Among these, plasticizers that have good compatibility with the transparent resin and do not degrade over time are preferred. Plasticizers are additives that impart flexibility and fluidity to the transparent resin by penetrating between the molecules of the transparent resin and weakening the intermolecular forces.

[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 be potentially carcinogenic. Therefore, dibasic acid esters are sometimes used as plasticizers instead of phthalates.

[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 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 by adding dibasic acid esters to a resin composition, discoloration of both the resin composition and the reflective layer can be suppressed.

[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 hardener, and can be calculated as follows: Mass of additive / (Mass of transparent resin + Mass of additive) × 100 …(3).

[0047] <Method for forming the reflective layer> The reflective layer is formed, for example, as follows: Multiple scintillator segments processed into 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 applied or filled between adjacent scintillator segments. The first reflective layer can be formed by curing the reflective layer composition with heat. Next, the reflective layer composition is applied to the X-ray irradiation surface of the ceramic scintillator array, which consists of scintillator segments and the first reflective layer. The 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 Detector and Radiation Inspection Device> Next, the radiation detector and radiation inspection device 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, X-rays are incident on 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 while imaging 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] Through this technology, the radiation inspection apparatus of the embodiment contributes to improving inspection accuracy, etc. Furthermore, the radiation inspection apparatus 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 applications, etc. Moreover, the radiation inspection apparatus of the embodiment is equipped with a radiation detector having the ceramic scintillator array of the embodiment. As described above, the ceramic scintillator array of the embodiment has 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.

[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, trade 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, trade name: TETRAD-C, manufactured by Mitsubishi Gas Chemical Co., Ltd. • Curing Agent: Alicyclic polyamine-based curing agent, trade 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] A resin composition was prepared by adding 5% by mass of an additive to epoxy resin A. A mixture of 90% by mass of titanium oxide powder and 10% by mass of aluminum oxide powder was prepared as reflective particles. The resin composition, curing agent, and reflective particles were mixed in a mass ratio of 100:20:120 to prepare a reflective layer composition. 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 producing a reflective layer structure of 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 of Reference Example 5 was fabricated in the same manner as in Reference Example 1, except that a resin composition of epoxy resin C with 5% by mass of an additive was used, 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 the 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 the 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), visible light with a wavelength of 510 nm was irradiated onto the reflective layer structures of Reference Examples 1 to 9, and the reflectance R of the reflective layer structure was evaluated. ０ The reflectance R of the reflective layer structure was measured. Next, the reflective layer structure was irradiated with 4.2 kGy of X-rays. The X-ray irradiation 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 reflectance R of the reflective layer structure was measured in the same manner as before irradiation with 4.2 kGy of X-rays. １ R was measured. ０ R for １ value (R １ / R ０The reflectance retention rate was defined as follows: The higher the reflectance retention rate of the reflective layer structure, the more effectively the decrease in reflectance can be suppressed even after prolonged irradiation with X-rays, and thus the more effectively the decrease in the optical output of the ceramic scintillator array can be suppressed. Since the trivalent Pr in the rare earth sulfide 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. Therefore, visible light at a wavelength of 510 nm was used to measure the reflectance of the reflective layer structure. The results are shown in Table 1.

[0068]

[0069] As is clear from Table 1, the reflective layer structures of Reference Examples 1 to 6, in which dibasic acid esters were added to the transparent resin, showed a higher 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 to 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 higher reflectivity retention rate and suppressed the decrease in reflectivity even more effectively than 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] <Preparation of scintillator segments> The median particle size (median diameter) is 5 to 10 μm, (Gd ０．９９９２８ , Pr ０．０００７ Ce ０．００００２ ) ２ O ２Gadolinium oxysulfide phosphor powder having the composition of S 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 covered with molybdenum (Mo) foil and then placed in the capsule and 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 to 1500°C for 3 hours. After cooling, the sintered body was removed, and a flat plate with a thickness of 2.0 mm was cut along the height direction of the cylinder using a wire saw. Multiple scintillator segments were created on the surface of this flat plate by cutting grooves at intervals of 1.39 mm vertically and 1.18 mm horizontally using a blade. The width of the grooves was 0.10 mm vertically and 0.27 mm horizontally. <Preparation of Reflective Layer Composition> A resin composition was prepared by adding 5% by mass of an additive to epoxy resin A. A mixture of 90% by mass of titanium oxide powder and 10% by mass of aluminum oxide powder was prepared as reflective particles. The resin composition, curing agent, and reflective particles were mixed in a mass ratio of 100:20:120. In this way, the reflective layer composition was prepared. <Preparation of Ceramic Scintillator Array> The reflective layer composition was filled into the grooves between the scintillator segments. The first reflective layer was formed by heat curing the reflective layer composition, and adjacent scintillator segments were bonded together via the first reflective layer to produce a ceramic scintillator array as shown in Figures 2 and 3. After polishing one side of this ceramic scintillator array to a smooth surface, the other side was covered with the 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. A ceramic scintillator array of Example 1, comprising a scintillator segment, a first reflective layer, and a second reflective layer, was fabricated using the method described above.

[0071] [Example 2] A ceramic scintillator array of 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 of 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 X-ray detector was irradiated with 120 kV, 60-80 mA X-rays, and the emission energy E detected by the photodiode was measured. ０ The following was measured. Next, the X-ray detector was irradiated with 4.2 kGy of X-rays. The X-ray irradiation 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 E detected by the photodiode when the X-ray detector was irradiated with 120 kV, 60-80 mA of X-rays, in the same manner as before the 4.2 kGy irradiation, was measured. １ E was measured. ０ E for １ Value (E １ / E ０ The optical power maintenance rate was defined as ) . A higher optical power maintenance rate 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 reflectance R of the second reflective layer of each of the ceramic scintillator arrays of Examples 1 and 2 and Comparative Example 1 was evaluated. ０ and R １ Measure R ０ R for １ value (R １ / R ０ The reflectance maintenance rate was defined as ). The results are shown in Table 2.

[0075]

[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, showed higher optical output maintenance and reflectance maintenance compared to the ceramic scintillator of Comparative Example 1, in which dibasic acid esters were not added to the transparent resin. This indicates that the decrease in optical output and reflectance 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, showed higher optical 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 optical output and reflectance can be suppressed even more effectively.

[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 and their equivalents.

[0078] 1. Ceramic scintillator array 2. Scintillator segment 3. First reflection layer 4. Second reflection layer 6. X-ray detector 7. Photodiode 8. Output terminal 10. X-ray CT scanner 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 reflective layer comprises a resin composition, the resin composition comprises a transparent resin and an additive, and the 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 ceramic scintillator array according to claim 1 or 2, wherein the reflective layer comprises reflective particles, and 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 according to claim 1 or 2.

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

Images