Scintillator unit and radiation detector

Abstract

The present invention relates to a scintillator unit and a radiation detector. When the scintillator unit includes a plurality of scintillators and a radiation detector, the scintillator unit can reduce cross talk. More specifically, the scintillator unit includes a reflection layer between the plurality of scintillators and the plurality of scintillators, wherein a low-refractive layer having a lower refractive index than an adhesive layer is sequentially provided on the scintillator between the scintillator and the reflection layer.

Description

Technical Field

[0001] This invention relates to a scintillator unit and a radiation detector. Background Technology

[0002] Radiation detectors are used to image subjects using radiation in medical settings and other environments. Specifically, a radiation detector for computed tomography (CT) mainly consists of a scintillator and a detection unit. The scintillator generates light using radiation (e.g., X-rays), and the detection unit includes light-receiving devices arranged in a two-dimensional pattern. When a subject is irradiated by X-rays, the X-rays passing through the subject generate light from the scintillator, and the light-receiving device corresponding to each scintillator detects the light and forms a two-dimensional image of the transmitted X-rays.

[0003] However, the light generated from the scintillator is emitted in all directions. To guide most of the light generated from the scintillator to the detection unit, a reflective layer can be provided on the surface of the scintillator opposite the detection unit via an adhesive layer. For example, Patent Document 1 describes a flat panel detector (FPD) that sequentially includes an air layer, a dielectric multilayer reflective film, an adhesive layer, a phosphor layer, and a photodetector along the incident direction of radiation. Patent Document 2 discloses a structure that sequentially includes an adhesive layer and a refractive coating with a refractive index of less than 1.3 between the scintillator and a silver coating to improve the light collection efficiency of the detector.

[0004] Citation List

[0005] Patent documents

[0006] PTL 1: International Open WO 2016 / 167334

[0007] PTL 2: PCT Japanese Translation Patent Publication No. 2001-516888 Summary of the Invention

[0008] Technical issues

[0009] The inventors of this invention have studied the structure of the FPD described in Patent Document 1 by applying it to a detector used in CT scans, which includes multiple scintillators and corresponding light receiving devices for each scintillator. The study found that light generated from the scintillator does not enter the corresponding light receiving device, but instead enters an adjacent light receiving device, causing crosstalk.

[0010] Patent document 2 does not apply the structure of including an adhesive layer and a refractive coating sequentially between the scintillator and the silver coating, and on the scintillator, to a detector that includes multiple scintillators and a light receiving device corresponding to each scintillator.

[0011] Therefore, one object of the present invention is to provide a scintillator unit that can reduce crosstalk when comprising a plurality of scintillators. Another object of the present invention is to provide a radiation detector comprising a scintillator unit.

[0012] Problem Solution

[0013] The present invention relates to a scintillator unit, wherein the scintillator unit includes a reflective layer between a plurality of scintillators, wherein an adhesive layer and a low refractive index layer with a refractive index lower than that of the adhesive layer are sequentially provided between the scintillators and the reflective layer and on the scintillators.

[0014] The present invention also relates to a radiation detector comprising: a scintillator unit including a reflective layer between a plurality of scintillators; and a detection unit configured to detect light generated from the scintillators, wherein the scintillator unit includes, in sequence, an adhesive layer and a low refractive index layer with a refractive index lower than that of the adhesive layer between the scintillators and the reflective layer.

[0015] The present invention can provide a scintillator unit that can reduce crosstalk when including multiple scintillators, and the present invention can also provide a radiation detector. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of an example of a low refractive index layer according to an embodiment of the present invention.

[0017] Figure 2 This is a schematic bird's-eye view of an example of a radiation detector according to an embodiment of the present invention.

[0018] Figure 3 This is a schematic bird's-eye view of a reflectance measurement sample according to an embodiment of the present invention.

[0019] Figure 4A This is a schematic cross-sectional view of a reflectance measurement sample according to an exemplary embodiment of the present invention, and is a schematic cross-sectional view of Exemplary Embodiment 1.

[0020] Figure 4B This is a schematic cross-sectional view of a reflectance measurement sample according to an exemplary embodiment of the present invention, and is a schematic cross-sectional view of a scintillator / air layer / reflective layer.

[0021] Figure 4C This is a schematic cross-sectional view of a reflectance measurement sample according to an exemplary embodiment of the present invention, and is also a schematic cross-sectional view of Comparative Example 1.

[0022] Figure 5AThis is an example of the measurement results of the reflectance spectrum in the description of exemplary embodiments of the present invention, and is the measurement result of the reflectance spectrum of Exemplary Embodiment 1 and Comparative Example 1 at an incident angle of 70 degrees.

[0023] Figure 5B This is an example of the measurement results of the reflectance spectrum in the description of exemplary embodiments of the present invention, and is the measurement result of the reflectance spectrum of Exemplary Embodiment 1 and Comparative Example 1 at an incident angle of 74 degrees. Detailed Implementation

[0024] The scintillator unit according to the present invention includes a reflective layer between a plurality of scintillators. Furthermore, an adhesive layer and a low-refractive-index layer with a refractive index lower than that of the adhesive layer are sequentially provided between the scintillator and the reflective layer, and on the scintillator. Because the low-refractive-index layer is located between the scintillator and the reflective layer, a portion of the light generated by one scintillator and guided to an adjacent scintillator is reflected by the interface between the adhesive layer and the low-refractive-index layer, as well as by the reflective layer. This phenomenon is caused by the physical phenomenon of "total internal reflection" resulting from the refractive index difference between the two media. Therefore, this reduces crosstalk caused by light generated from a scintillator entering an adjacent optical receiving device instead of its corresponding optical receiving device.

[0025] Embodiments of the present invention will now be described in detail. Unless otherwise stated, physical properties were measured at 25°C.

[0026] Figure 2 This is a schematic bird's-eye view of an embodiment of a radiation detector according to the present invention. Figure 2 In the scintillator unit 205, there are two-dimensionally arranged scintillators 201 and a reflective layer 204 between the two scintillators 201. An adhesive layer 202 and a low refractive index layer 104 are sequentially provided between the scintillators 201 and the reflective layer 204, and on the scintillators 201, and the components are in close contact with each other.

[0027] Furthermore, if an adhesive layer, a low-refractive-index layer with a refractive index lower than that of the adhesive layer, and a reflective layer are sequentially arranged between and on the scintillators, the scintillators may come into contact with the reflective layer.

[0028] If the advantages of the present invention can be achieved, other layers may be provided between the scintillator and each layer.

[0029] Examples of layers constituting a scintillator unit include structures comprising a scintillator, an adhesive layer, a low-refractive-index layer, and a reflective layer in sequence, as well as structures comprising a scintillator, an adhesive layer, a low-refractive-index layer, a reflective layer, a low-refractive-index layer, an adhesive layer, and a scintillator in sequence.

[0030] Examples also include structures comprising, in sequence, a scintillator, an adhesive layer, a low-refractive-index layer, a substrate, a low-refractive-index layer, an adhesive layer, and a scintillator, and structures comprising, in sequence, a scintillator, a reflective layer, a low-refractive-index layer, an adhesive layer, a low-refractive-index layer, a reflective layer, and a scintillator. The substrate may be a material described below.

[0031] The scintillator unit 205 includes a reflective layer 204 between two low-refractive-index layers 104, and the low-refractive-index layers 104 may be located on both sides of the reflective layer 204. Therefore, from a scintillator (e.g., Figure 2 The upper part) travels to another scintillator (e.g., Figure 2 The light from the lower part (of the layer) is likely to be reflected by the reflective layer 204 and the low refractive index layer 104 (of the layer). Figure 2 The interface between the lower part of the scintillator and the upper part of the other scintillators (the other side) reflects light. Therefore, even a small number of reflective layers can reduce crosstalk. This allows for the arrangement of multiple scintillators at high density and improves sensitivity to radiation and the resolution of the resulting image.

[0032] In the FPD structure described in Patent Document 1, an air layer is formed by an inhomogeneous prism sheet and a dielectric multilayer reflective film. With such an inhomogeneous prism sheet between multiple scintillators, the scintillator unit cannot have sufficient strength. Furthermore, the air layer is formed only on one side of the dielectric multilayer reflective film, and multiple dielectric multilayer reflective films are required to reduce crosstalk. Therefore, it is difficult to arrange multiple scintillators at a high density.

[0033] Therefore, the scintillator unit according to this embodiment is particularly useful for applications using radiation detectors comprising multiple scintillators arranged in a two-dimensional configuration (such as CT). Furthermore, the low-refractive-index layer 104 and adjacent components ( Figure 2 The reflective layer 204 and the adhesive layer 202 are in surface contact. Therefore, the scintillator unit according to this embodiment has sufficient strength when used as a device.

[0034] [Scintillator 201]

[0035] According to this embodiment, the scintillator 201 in the scintillator unit 205 preferably contains a material that emits light through radiation (X-rays, gamma rays, charged particles, etc.).

[0036] Examples of materials suitable for scintillator 201 include halides of alkali metals, alkaline earth metals, transition metals, typical elements, and rare earth metals. Additional examples include oxides, nitrides, chalcogenides, and Group 13 and 14 compounds. Specific examples include Tl-doped NaI, Tl-doped CsI, Na-doped CsI, Ce-doped Lu₂SiO₅ (LSO), Ce-doped Lu₂Y₂SiO₅ (LYSO), Gd₂SiO₅, and Bi₄Ge₃O₅. 12ZnWO4, CdWO4, PbWO4, LuAlO3, and Ce-doped Y3Al5O 12 Ce-doped YAlO3 (YAP), Ce-doped GdAlO3 (GAP), Ce-doped LuAlO3 (LuAP), Ce-doped Lu3Al5O 12 Lu3Al5O doped with Pr 12 And CeF3. Specifically, the scintillator 201 preferably comprises at least one of Ce-doped Lu2Y2SiO5 and Ce-doped Lu2SiO5.

[0037]

Adhesive Layer 202

[0038] The adhesive layer 202 may be formed from at least one optical adhesive selected from epoxy resin, acrylic resin or vinyl resin.

[0039] For example, the refractive index of the adhesive layer 202 is preferably greater than 1.30 and less than 1.70, more preferably greater than 1.30 and less than 1.50. When the refractive index of the adhesive layer 202 is less than 1.70, this reduces the likelihood that light reflected at the interface between the reflective layer 204 and the low-refractive-index layer 104 will be reflected at the interface between the low-refractive-index layer 104 and the adhesive layer 202 and guided to the adjacent scintillator. Therefore, the light can return to the initial scintillator 201.

[0040] The thickness of the adhesive layer 202 is preferably 5 μm or less, more preferably 1 to 5 μm, and even more preferably 2 to 5 μm. An adhesive layer 202 with a thickness of 5 μm or less has a smaller thickness variation and can reduce manufacturing errors in the scintillator unit. An adhesive layer 202 with a thickness of 2 μm or greater has sufficient adhesive strength.

[0041]

Reflective Layer 204

[0042] For example, the reflective layer 204 can be formed of a metallic material such as aluminum or silver. The reflective layer can also be formed of a polyethylene terephthalate (PET) film (Alpet (registered trademark)) on which aluminum is vapor-deposited in the vapor phase.

[0043] The reflective layer formed of metallic material has a light reflectivity ranging from 80% to 100% in the wavelength range of 400 nm to 700 nm. The light reflectivity is measured in air.

[0044] Dielectric multilayer film

[0045] The reflective layer 204 can be a dielectric multilayer film with high reflectivity. The reflective layer formed by the dielectric multilayer film has a light reflectivity in the range of 95% to 100% within the wavelength range of 400 nm to 700 nm. The light reflectivity is measured in air. The dielectric multilayer film only needs to have high reflectivity within the emission wavelength range of the scintillator to be used, and does not need to have high reflectivity in wavelength ranges outside the emission wavelength. The light reflectivity of the dielectric multilayer film is higher than that of metallic materials such as aluminum or silver. This can further reduce crosstalk caused by light generated from the scintillator and leaking into adjacent scintillators.

[0046] The dielectric material constituting the dielectric multilayer film can be an inorganic material, an organic material, or a combination thereof. Organic materials are preferred because they are lightweight and flexible. Examples of organic materials include polyester resins, polyurethane resins, and acrylic resins.

[0047] The dielectric multilayer film is preferably in contact with a low-refractive-index layer. This increases the refractive index difference between the dielectric multilayer film and adjacent layers, and improves the light reflectivity in the wavelength range of 400 nm to 700 nm. When the dielectric multilayer film is in contact with the low-refractive-index layer, the refractive index range of the low-refractive-index layer is preferably 1.05 to 1.30, more preferably 1.10 to 1.20, and particularly preferably 1.15 or less.

[0048] (Low-refractive-index layer)

[0049] <Composition and Structure>

[0050] exist Figure 1 In this process, the strength of the low refractive index layer 104 can be improved by using a solid material with a refractive index of 1.65 or lower as a framework and appropriately setting the porosity for the lower refractive index.

[0051] Solid materials can be crystalline or amorphous. Solid materials can be particles. The particles can be, but are not limited to, spherical particles, irregularly shaped particles, spherical or irregularly shaped particles connected in a bead-like or branched manner, hollow particles with cavities, or hollow particles connected in a bead-like or branched manner.

[0052] Examples of solid materials include resins such as fluorinated polymers and acrylic resins, fluorides such as magnesium fluoride and calcium fluoride, carbonates such as calcium carbonate and potassium carbonate, sulfates such as barium sulfate, and oxides such as silicon dioxide (hereinafter also referred to as silica) and aluminum oxide.

[0053] Examples of solid materials with low refractive indices include organic materials such as fluorinated polymers and inorganic materials such as magnesium fluoride and silicon dioxide.

[0054] However, even fluorinated polymers with low refractive indices have a refractive index of about 1.30, while magnesium fluoride and silicon dioxide (quartz) have refractive indices of 1.38 and 1.46, respectively. Simple materials with refractive indices far below 1.30 are mainly gases such as nitrogen or oxygen.

[0055] In terms of refractive index, cost, and chemical stability, solid materials preferably contain silicon dioxide. More specifically, solid materials are preferably composed primarily of silicon dioxide. The phrase "solid materials are composed primarily of silicon dioxide" as used herein means that the silicon dioxide content of the solid material is 50% (by mass) or more. The silicon dioxide content of solid materials is typically 90% (by mass) or more.

[0056] Specific examples of silica particles include the Snowtex series manufactured by Nissan Chemical Industries, Ltd., the silica sol and Thrulya series manufactured by JGC Catalysts and Chemicals Ltd., and the Aerosil series manufactured by Evonik Industries AG. and sold by Nippon Aerosil Co., Ltd.

[0057] Given a refractive index of n a Material A and refractive index n b The composite material C composed of material B typically has a refractive index n approximately expressed by equation (1). c :

[0058] Equation (1)

[0059] n c =[n a ×v a / 100]+[n b ×v b / 100] (1)

[0060] Among them, v a and v b The volume fractions (v) of materials A and B constituting the composite material are indicated respectively. a +v b =100).

[0061] According to equation (1), a composite material of solid material and air (i.e., a porous membrane with a solid material framework serving as the low-refractive-index layer 104) can have a lower refractive index than the initial solid material. In such a structure, a solid material framework with a lower refractive index or a low-refractive-index layer 104 with higher porosity results in a low-refractive-index layer 104 with a lower refractive index. To increase the porosity of the low-refractive-index layer 104, the low-refractive-index layer 104 can have a porous structure. In this respect, the low-refractive-index layer 104 can be referred to as a porous membrane.

[0062] In equation (1), when material A is air and material B is silicon dioxide, the refractive index n of air is... a The refractive index n of silicon dioxide is 1.00. b The value is 1.46, while the volume fraction v of silica is... b 100-V a Therefore, v can be... a The refractive index n of the low-refractive-index layer 104 was determined. c The function. v a This refers to porosity.

[0063] When the low refractive index layer 104 has voids, the porosity of the low refractive index layer is preferably in the range of 60.0% to 95.0%, more preferably 65.0% to 90.0%.

[0064] For example, according to equation (1), when the porosity of the low refractive index layer 104 with a silica (refractive index 1.46) framework is less than 60.0%, the refractive index may exceed 1.15.

[0065] On the other hand, a porosity greater than 95.0% may result in the low refractive index layer 104 having an excessively low refractive index of less than 1.05, and low strength due to the small amount of skeleton constituting the low refractive index layer 104.

[0066] Silica preferably has at least one of organic groups and hydroxyl groups on its surface. Silica with hydroxyl groups on its surface has high hydrophilicity. Therefore, the low refractive index layer 104 having such a silica particle framework can have high hydrophilicity.

[0067] For example, the surface of silica can be modified with silane coupling agents to impart functionality to the low-refractive-index layer 104. For silica with hydroxyl groups on its surface, the dehydration condensation reaction between the hydroxyl groups of the silane coupling agent and the hydrolysate can be utilized.

[0068] Examples of organic groups include alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, propyl and butyl; hydrocarbon groups having a polymerizable moiety, such as vinyl, acrylic and methacrylate; and aromatic hydrocarbon groups, such as phenyl.

[0069] Silicon dioxide with organic groups on its surface can impart various functions to the low refractive index layer 104, such as water repellency, oil repellency, biocompatibility, electron transport properties, and polymerizability.

[0070] Not all functional groups on the surface of silica are necessarily replaced by organic groups, and organic groups and hydroxyl groups can exist in any proportion.

[0071] Hollow particles

[0072] The low-refractive-index layer 104 containing hollow particles will be further described below. However, the invention is not limited thereto. The hollow particles have a shell formed of solid material and cavities (voids) inside the shell.

[0073] The low-refractive-index layer 104 preferably contains a plurality of hollow particles. In addition to hollow particles, the low-refractive-index layer 104 containing a plurality of hollow particles may also contain solid particles or a binder.

[0074] Figure 1 An example of a structure containing a low-refractive-index layer 104 with hollow particles (as primary particles composed of solid material) is shown.

[0075] The low-refractive-index layer 104 comprises multiple hollow particles 301 and voids 302 between the hollow particles 301. The hollow particles also include voids 304. Figure 1 In the figure, reference numeral 303 indicates the housing, while reference numeral 305 indicates the substrate.

[0076] Porosity X (%) and porosity Y (%) preferably satisfy the relationship X < Y, wherein porosity X (%) is the ratio of the total volume of voids in the hollow particles to the unit volume of the low refractive index layer 104, and porosity Y (%) is the ratio of the total volume of voids between the hollow particles to the unit volume of the low refractive index layer 104, and (X+Y) represents the porosity of the low refractive index layer 104.

[0077] The refractive index n of the low refractive index layer 104 is expressed by the following equation (2):

[0078] Equation (2)

[0079] n = [n a [×(X+Y) / 100]+[n s [×(100-XY) / 100] (2)

[0080] Where n a Indicator of the refractive index of air (n) a =1), while n s The refractive index (n) of the shell of the hollow particle indicates the refractive index of the particle. s >1). According to equation (2), n increases with X+Y or ns decreases as it decreases.

[0081] The refractive index n of the low refractive index layer 104 is also represented by the following equation (3):

[0082] Equation (3)

[0083] n = [n a × Y / 100] + [n p × (100 - Y) / 100] (3)

[0084] where n p indicates the refractive index of a hollow particle (n p > 1). The refractive index n p is an apparent refractive index calculated based on the ratio of the volume and refractive index of the outer shell to the volume and refractive index of the voids in a hollow particle. Therefore, if n a = 1, n b = n s , in Equation (1), v a indicates the void volume of the hollow particle, and v b indicates the volume of the outer shell, then n c = n p . According to Equation (3), n decreases as Y increases or n p decreases.

[0085] It is also possible to calculate X and Y by measuring the refractive index n of the low refractive index layer 104 via optical measurement and substituting the known n a , n s and n <e000046>into Equations (2) and (3).

[0086] The dense arrangement of the hollow particles reduces the volume fraction of the voids between the hollow particles and increases the volume fraction of the outer shell formed by the component with a refractive index higher than air, thereby increasing the refractive index of the low refractive index layer 104. In contrast, the sparse arrangement of the hollow particles increases the volume fraction of the voids between the hollow particles and reduces the volume fraction of the outer shell, thereby reducing the refractive index of the low refractive index layer 104. Therefore, to further reduce the refractive index of the low refractive index layer 104, it is preferable to increase Y / X. More specifically, it is preferable to satisfy the relationship Y / X > 1, that is, X < Y. [[ID=B]]

[0087] X and Y preferably satisfy the relationship X < (100 - X - Y) < Y. ;

[0088] The low-refractive-index layer 104 may contain particles composed of a solid material and a binder that binds the particles together to increase strength. When a binder is used, the solid in the low-refractive-index layer 104 serves as both the shell of the hollow particles and the binder, and the volume fraction of the solid relative to the unit volume of the low-refractive-index layer 104 is represented by (100-X-Y)(%).

[0089] Satisfying the relationship X < (100 - XY) further increases the intensity of the low refractive index layer 104. Satisfying the relationship (100 - XY) < Y further decreases the refractive index of the low refractive index layer 104.

[0090] The sum of X and Y (X+Y) is preferably in the range of 60.0% to 95.0%, more preferably 65.0% to 90.0%. These ranges of (X+Y) make it easy to adjust the intensity and refractive index of the low-refractive-index layer 104 within the desired range.

[0091] In the low refractive index layer 104, the range of X is preferably 8.0% to 32.0%, more preferably 10.0% to 28.0%, and even more preferably 12.0% to 24.0%.

[0092] On the other hand, the range of Y is preferably 30.0% to 80.0%, more preferably 35.0% to 75.0%, and even more preferably 40.0% to 70.0%.

[0093] The range of X and Y makes it easy to adjust the intensity and refractive index of the low-refractive-index layer 104 within the desired range.

[0094] Although Figure 1 In the example shown, the hollow particle is essentially spherical, but a hollow particle can have any shape. The hollow particle has a shell 303 and voids 304 surrounded by the shell and formed inside the hollow particle. In this case, the hollow particle can be considered a core-shell particle containing air (as a nucleus).

[0095] The refractive index n of a hollow particle p Equation (4) represents:

[0096] Equation (4)

[0097] n p =[n s ×(100-V a ) / 100]+[n a ×V a / 100] (4)

[0098] Among them, V aThe refractive index n indicates the volume fraction of internal voids relative to the total volume of the hollow particle. Therefore, the refractive index n of a hollow particle... p The refractive index n of the outer shell material s Porosity V of hollow particles a Sure.

[0099] Porosity V of a hollow particle a The preferred range is 30.0% to 70.0%, more preferably 35.0% to 65.0%.

[0100] Porosity V within these ranges a This allows the low-refractive-index layer 104 to have a refractive index that can be easily reduced, giving the hollow particles a shell of constant strength, and giving the low-refractive-index layer 104 a constant strength.

[0101] Similar to the refractive index of solid materials, the refractive index n of the outer shell of hollow particles is... s Preferably, the refractive index n is 1.10 or more, 1.20 or more, 1.25 or more, 1.30 or more, or 1.35 or more, and preferably 1.65 or less or 1.60 or less. These ranges can be freely combined. The refractive index n of the hollow particle shell... s More preferably, it is in the range of 1.35 to 1.60.

[0102] The refractive index n of the hollow particle shell s Within these ranges, the low refractive index layer 104 can be easily prepared, producing high-strength hollow particles, high-strength low refractive index layer 104, and low refractive index layer 104.

[0103] The outer shell of hollow particles can be formed from the same material as the solid material.

[0104] The outer shell of hollow particles can have micropores. These micropores can further reduce the refractive index of the outer shell.

[0105] The number-average particle size of the primary particles of the hollow particles is preferably in the range of 1 nm to 200 nm, more preferably 5 nm to 100 nm, further preferably 10 nm to 100 nm, and particularly preferably 20 nm to 100 nm.

[0106] Number-average particle sizes within these ranges facilitate the fabrication of hollow particles, reduce light scattering, and further enhance the transmittance of the low-refractive-index layer 104.

[0107] Fumed silica particles and chain-like silica particles

[0108] The low-refractive-index layer 104 preferably contains at least one type of particles selected from the group consisting of: secondary particles forming a three-dimensional structure from primary particles composed of solid material, chain-like secondary particles composed of primary particles composed of solid material connected in a chain-like manner, and branched secondary particles composed of primary particles composed of solid material connected in a branched manner. When particles composed of solid material form an aggregate, the aggregate is also included in the secondary particles forming a three-dimensional structure from primary particles composed of solid material.

[0109] The formation of secondary particles from primary particles composed of solid material into a three-dimensional structure, the chain-like secondary particles formed by primary particles of solid material connected in a chain-like manner, and the branched secondary particles formed by primary particles of solid material connected in a branched manner reduce the volume fraction of solid material in the low-refractive-index layer 104. This increases the volume fraction of voids. Therefore, the refractive index of the low-refractive-index layer 104 can be reduced.

[0110] The number-average particle size range of the primary particles composed of solid materials is preferably from 1 nm to 200 nm, more preferably from 5 nm to 100 nm. The number-average particle size range of the primary particles composed of solid materials is more preferably from 10 nm to 100 nm, and particularly preferably from 20 nm to 100 nm.

[0111] When the number-average particle size of the primary particles is within these ranges, particle aggregation can be appropriately controlled and dispersibility in the coating solution can be improved. Furthermore, it is possible to potentially prevent the primary particles from becoming light scatterers in the 400 nm to 700 nm wavelength range and further improve the transmittance of the low-refractive-index layer 104.

[0112] The following description of fumed silica particles will take as an example the formation of a three-dimensional structure from primary particles made of solid materials. However, the present invention is not limited thereto.

[0113] Fumed silica particles can be prepared by high-temperature hydrolysis of silicon tetrachloride in an oxygen and hydrogen flame. In the fumed silica particles prepared by this method, primary particles of tens of nanometers fuse to form secondary particles with a three-dimensional structure. The secondary particles can aggregate and possess complex higher-order structures.

[0114] Due to their characteristic structure, fumed silica particles are extremely large particles, with an apparent specific gravity ranging from 0.01 g / cm³. 3 Up to 0.1 g / cm 3 Therefore, the low-refractive-index layer 104 containing fumed silica particles has high porosity and can significantly reduce the refractive index.

[0115] The number-average particle size range of the secondary particles is preferably 10 nm to 1000 nm, more preferably 50 nm to 500 nm.

[0116] When the number-average particle size of the secondary particles is within these ranges, for example, primary particles of silica form a three-dimensional structure, and the secondary particles do not have the simple structure of aggregated primary particles.

[0117] The secondary particles with the above-described structure make it easy to control the porosity and refractive index of the low-refractive-index layer 104 within the aforementioned range. Furthermore, this makes it difficult to form large gaps between the secondary particles, which can be light scatterers with wavelengths ranging from 400 nm to 700 nm, and makes it easy to control the light transmittance of the low-refractive-index layer 104.

[0118] The number-average particle size of primary and secondary particles can be determined using transmission electron microscopy (TEM) (calculated as the arithmetic mean of the maximum diameters). The number-average particle size of primary and secondary particles can be controlled, for example, by adjusting the conditions of high-temperature hydrolysis of silicon tetrachloride in an oxygen and hydrogen flame as described above.

[0119] <Membrane Formation Methods>

[0120] [Methods for preparing coating solutions]

[0121] The method for preparing the coating liquid for forming the low refractive index layer 104 will be described below. Although the formation of three-dimensional structures from primary silica particles by fumed silica particles will be described below, the present invention is not limited thereto.

[0122] Fumed silica particles are dispersed in a solvent. The solvent used for dispersing the fumed silica particles is preferably a solvent with a high affinity for the fumed silica particles. Depending on the type of functional groups on the surface of the fumed silica particles, one solvent or a mixture of two or more solvents can be used.

[0123] The solvent is preferably an organic solvent, and may be: alcohol solvents, such as methanol, ethanol, propanol or isopropanol; glycol solvents, such as ethylene glycol or propylene glycol; ether solvents, such as dimethyl ether, diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether or propylene glycol monoethyl ether; acetate solvents, such as ethyl acetate, propyl acetate, propylene glycol monomethyl ether acetate or propylene glycol monoethyl ether acetate; or ketone solvents, such as acetone or methyl ethyl ketone.

[0124] Although water can be used as a solvent, its high surface tension generates significant capillary forces during drying, sometimes causing the voids between fumed silica particles to shrink. This could reduce the porosity of the low-refractive-index layer 104 and potentially increase its refractive index.

[0125] When alkali metals, especially CsI, are used as the material for scintillator 105, water is unsuitable as a solvent due to its strong deliquescence. Particles composed of solid materials can be used alone or in combination of two or more types.

[0126] The mass content of particles composed of solid materials in the coating solution is preferably 1.0% or more, more preferably 2.0% or more, further preferably 3.0% or more, and particularly preferably 7.0% or more. The mass content of silica particles in the coating solution is preferably 50.0% or less, more preferably 30.0% or less, and further preferably 20.0% or less. These ranges can be freely combined.

[0127] For example, the mass concentration of fumed silica particles (solid component) in the coating solution is preferably in the range of 1.0% to 30.0%, more preferably 2.0% to 20.0%.

[0128] When the amount (concentration) of particles composed of solid materials in the coating solution, such as fumed silica particles, is within the above-mentioned range, it is easy to adjust the thickness of the low refractive index layer 104 to 500 nm or more. This also improves the uniform dispersion of fumed silica particles in the solvent and makes it easier to adjust the transmittance of the low refractive index layer 104 within the above-mentioned range.

[0129] Vaporized silica particles are added to a solvent and dispersed. When forming a coating film with a complex, high-order structure while dispersing the fumed silica particles, the gaps between the fumed silica particles have a size that allows visible light to scatter, thus potentially reducing the transmittance of the low-refractive-index layer 104. When the fumed silica particles are dispersed, the transparency of the coating solution increases with increasing dispersion time.

[0130] When a coating liquid containing appropriately dispersed fumed silica particles is formed into a film, the framework of the fumed silica particles and the voids between the particles have a size that does not become visible light scatterers. Therefore, the low refractive index layer 104 has high transmittance.

[0131] Further dispersion processing may disrupt the large, high-order structure of fumed silica particles into primary particles, potentially reducing porosity and tending to increase the refractive index of the low-refractive-index layer 104.

[0132] Furthermore, excessive dispersion treatment can lead to so-called over-dispersion, which can easily cause the fumed silica particles to re-aggregate and may reduce the transmittance of the low-refractive-index layer 104 after film formation.

[0133] Therefore, a suitable dispersion state is preferred. Dispersion can be performed using agitators, ultrasonic mixers, planetary mixers, ball mills, bead mills, homogenizers, etc.

[0134] Although hollow particles with a silica shell are used as solid materials in the following embodiments, the invention is not limited to this example.

[0135] Hollow particle dispersions can be used. A hollow particle dispersion can be any hollow particle dispersion that satisfies the porosity of the hollow particles, the refractive index of the hollow particle shell, the number-average particle size of the primary particles, etc.

[0136] For example, the Thrulya series manufactured by JGC Catalysts and Chemicals Ltd. is preferably used. The Thrulya series is an isopropanol (hereinafter also referred to as IPA) dispersion of hollow particles (hereinafter also referred to as hollow silica particles) having a silica shell. In addition to commercial products such as the Thrulya series, hollow silica particles dispersed in a solvent by the same method as solvent dispersion of fumed silica particles can also be used.

[0137] The concentration of hollow particles in the solvent can be within the same range as the concentration of fumed silica particles (solid component) in the coating solution.

[0138] Hollow silica particles have hydroxyl groups on their surface and are hydrophilic. Therefore, highly hydrophobic solvents are unsuitable. More specifically, an octanol / water partition coefficient log P is preferred. ow The solvent is 2 or less. Organic solvents can be: alcohols, such as methanol, ethanol, propanol, or isopropanol; glycols, such as ethylene glycol or propylene glycol; ethers, such as dimethyl ether, diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, or propylene glycol monoethyl ether; acetates, such as ethyl acetate, propyl acetate, propylene glycol monomethyl ether acetate, or propylene glycol monoethyl ether acetate; or ketones, such as acetone or methyl ethyl ketone.

[0139] As mentioned above, to reduce the refractive index of the film, it is necessary to increase Y and X+Y. One approach is to randomly arrange hollow silica particles.

[0140] The following describes a method for randomly arranging hollow silica particles. Hollow silica particles can be randomly arranged by forming loose aggregates of them in a dispersion.

[0141] The polymer also contains secondary particles that form a three-dimensional structure from primary particles composed of solid materials.

[0142] One method for polymerizing well-dispersed hollow silica particles in a dispersion is to add log P. ow A method using a solvent (hereinafter referred to as an agglomerator) with a higher concentration than the dispersion medium. The agglomeration method is not limited to this method, but is preferably a method capable of controlling the aggregation state of the hollow silica particles.

[0143] Hollow silica particles have hydroxyl groups on their surface and are hydrophilic. Therefore, adding log P... ow Aggregators that are more hydrophobic than the dispersion medium will cause hollow silica particles to aggregate.

[0144] The following describes the logP of the agglomerant used to aggregate hollow silica particles that are well dispersed in a dispersion. ow And the amount added. The log P between the dispersion medium and the agglomerant. ow A difference that is too small will cause the hollow silica particles to fail to aggregate. The log P value between the dispersion medium and the aggregator... ow Excessive differences can cause hollow silica particles to aggregate strongly, even with the addition of small amounts of agglomerating agents. When hollow silica particles form large aggregates, the aggregates themselves may become light scatterers.

[0145] On the other hand, the large gaps formed between the large aggregates of hollow silica particles tend to become light scatterers, which may make the coated low refractive index layer 104 cloudy and may reduce the transmittance.

[0146] Furthermore, excessive aggregation tends to reduce the storage stability of the coating solution. Therefore, in order to form a low-refractive-index layer 104 with low refractive index and high transmittance, it is preferable to control the aggregation state of the hollow silica particles by the type and amount of agglomerating agent. The refractive index of the low-refractive-index layer 104 can be controlled by utilizing these characteristics and by controlling the aggregation state of the hollow silica particles by the type and amount of agglomerating agent.

[0147] Furthermore, filling the voids between the hollow silica particles with certain materials can reduce Y and X+Y and increase the refractive index of the low-refractive-index layer 104. Therefore, the agglomerant can preferably be removed, and more preferably volatilized by heating during downstream processes.

[0148] The agglomerating agent may be, but is not limited to, silicone oils such as X-22-164 (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0149] The method for forming the low-refractive-index layer 104 will be described below.

[0150] The coating solution is used to form the film. The film can be formed by rod coating, doctor blade coating, squeegee method, spray coating, spin coating, dip coating, or screen printing. Among these methods, spin coating is preferred to ensure uniform thickness of the low refractive index layer 104. When forming the film on a large-area sensor panel with a scintillator, spray coating is preferred.

[0151] In addition, in order to form a low-refractive-index layer 104 with a desired thickness and a flat upper surface, the rotation speed in the spin coating process can be appropriately adjusted.

[0152] The membrane formed by this method is preferably dried in a temperature range of 20°C to 100°C.

[0153] The film can be further subjected to heat treatment. The heat treatment is preferably carried out at a temperature range of 100°C to 200°C, and more preferably at a temperature range of 120°C to 180°C.

[0154] For example, at heating temperatures of 100°C or higher, solvent is unlikely to remain in the voids of the hollow particles. At heating temperatures of 200°C or lower, the performance of the sensor panel corresponding to the photodetector unit is unlikely to degrade.

[0155] When the film contains a binder and a polymerization initiator, a thermosetting or photocuring step is preferred. For thermosetting, the solvent can be evaporated simultaneously with the thermosetting of the binder during the drying or heating step.

[0156] Membranes formed from microparticles typically maintain their shape through intermolecular forces. Furthermore, hydrophobic interactions occur on the hydrophobic surfaces of the microparticles, while liquid crosslinking acts on their hydrophilic surfaces. These are physical interactions. For example, when the membrane is heat-treated, the hydroxyl groups on the surface of the fumed silica particles chemically bond to each other through dehydration reactions, potentially improving the membrane's strength.

[0157] When forming a film containing particles of solid material to reduce the refractive index, van der Waals forces and liquid crosslinking between the particles maintain the structure and film shape.

[0158] One method to improve the strength of a film with this structure is to use a binder to bind the particles together. From the perspective of improving film strength, the low-refractive-index layer 104 may also contain a binder.

[0159] The low-refractive-index layer 104 preferably comprises a bonding material formed by bonding a solid material with a binder. More specifically, the low-refractive-index layer 104 preferably comprises a bonding material formed by bonding particles composed of solid material with a binder. The bonding of the solid material with the binder includes any concept of bonding between primary particles composed of solid material, between secondary particles formed from primary particles composed of solid material, and between primary and secondary particles. The bonding can be chemical bonding, such as ionic or covalent bonds, or mechanical adhesion.

[0160] The binder can be a resin, such as acrylic resin, fluoropolymer resin, styrene resin, imide resin, polyurethane resin, or phenolic resin.

[0161] The binder can also be an organosilicon compound prepared by polymerizing silicone oil with polymerizable groups or by hydrolysis and condensation reaction of silanol salts.

[0162] In addition to these binders, any transparent and colorless binder with a low refractive index that can bind particles can also be used.

[0163] An exemplary method for preparing a membrane containing a binder includes the following steps: preparing a liquid mixture containing a solid material, a solvent and a binder; preparing a coating liquid by dispersing the liquid mixture; and forming a membrane by coating and drying the coating liquid, and if necessary by heating the coating liquid or by high-energy radiation of the coating liquid.

[0164] The binder preferably contains siloxane, more preferably silsesquioxane.

[0165] Silsesquioxanes are composed of molecules with the molecular formula [R 1 (SiO 1.5 ) n Compounds with a T3 unit structure (R) are represented by [ ]. 1 It indicates a reactive functional group, for example, selected from at least one of polymerizable groups, hydroxyl groups, chlorine atoms, alkyl groups of 1-6 carbon atoms and alkoxy groups of 1-6 carbon atoms, and is a hybrid material of silicon dioxide and organic matter.

[0166] Silsesquioxanes (hereinafter sometimes abbreviated as SQ) are siloxane compounds whose main chain backbone is composed of Si-O bonds, and whose constituent chemical formulas are [R... 1 (SiO 1.5 ) n ] indicates. R 1 Preferably, it indicates at least one polymerizable group selected from groups consisting of acryloyl, methacryloyl, oxetanyl group, and epoxy group.

[0167] When silsesquioxanes act as a binder for a large number of particles composed of solid materials, the membrane can have higher strength while maintaining high porosity.

[0168] Silsesquioxanes can take any polymer form, such as known linear polysiloxanes, cage-like polysiloxanes, or ladder-like polysiloxanes. A silsesquioxane structure is one in which each silicon atom is bonded to three oxygen atoms and each oxygen atom is bonded to two silicon atoms (the number of oxygen atoms is 1.5 relative to the number of silicon atoms). For cost reasons, linear polysiloxanes, cage-like polysiloxanes, and ladder-like polysiloxanes can be used in combination.

[0169] Silsesquioxanes are preferably polymerizable groups in the molecule (R in the above formula). 1 Compounds that can be cured by free radical polymerization or cationic polymerization.

[0170] Silsesquioxanes that can be cured by free radical polymerization can be silsesquioxanes having an acryloyl group or a methacryloyl group as R. Silsesquioxanes that can be cured by cationic polymerization can be silsesquioxanes having an oxetane butyl group or an epoxy group as R.

[0171] Specific examples include the SQ series (AC-SQ, MAC-SQ, and OX-SQ) of silsesquioxane derivatives manufactured by Toagosei Co., Ltd.

[0172] Silsesquioxanes are high-viscosity liquids and are preferably added to the coating solution. A polymerization initiator may be added if desired.

[0173] For every 100 parts by weight of particles composed of solid material, the binder content of the functional membrane preferably ranges from 3.0 parts by weight to 60.0 parts by weight, more preferably from 7.0 parts by weight to 30.0 parts by weight. For every 100 parts by weight of particles composed of solid material, the binder content of the functional membrane more preferably ranges from 7.0 parts by weight to 25.0 parts by weight, particularly preferably from 10.0 parts by weight to 25.0 parts by weight.

[0174] The coating liquid can be applied to the substrate, and the silsesquioxane can be cured by heating or light irradiation.

[0175] In this operation, a film containing a binding material is formed, wherein particles composed of solid material are bonded together with silsesquioxane. The silsesquioxane can be cured to increase the strength of the film.

[0176] Examples of polymerization initiators include free radical photopolymerization initiators, cationic photopolymerization initiators, thermal free radical polymerization initiators, and thermal cationic polymerization initiators. These polymerization initiators can be used alone or in combination.

[0177] Examples of free radical photopolymerization initiators include, but are not limited to: optionally substituted 2,4,5-triarylimidazolium dimers, such as 2-(o-chlorophenyl)-4,5-diphenylimidazolium dimer, 2-(o-chlorophenyl)-4,5-di(methoxyphenyl)imidazolium dimer, 2-(o-fluorophenyl)-4,5-diphenylimidazolium dimer, and 2-(o- or p-methoxyphenyl)-4,5-diphenylimidazolium dimer; benzophenone derivatives, such as benzophenone, N,N'-tetramethyl-4,4'-diaminobenzophenone (milchone), N,N'-tetraethyl-4,4'-diaminobenzophenone, 4-methoxy-4'-dimethylaminobenzophenone, 4-chlorophenyl... Benzyl, 4,4'-dimethoxybenzophenone, and 4,4'-diaminobenzophenone; α-amino aromatic ketone derivatives, such as 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-prop-1-one; quinones, such as 2-ethylanthraquinone, phenanthrenequinone, 2-tert-butylanthraquinone, octamethylanthraquinone, 1,2-benzanthraquinone, 2,3-benzanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone, 1-chloroanthraquinone, 2-methylanthraquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone, 2-methyl-1,4-naphthoquinone, and 2,3-dimethylanthraquinone; benzoin ether derivatives, such as Benzoin methyl ether, benzoin ethyl ether, and benzoin phenyl ether; benzoin derivatives, such as benzoin, methyl benzoin, ethyl benzoin, and propyl benzoin; benzyl derivatives, such as benzyl dimethyl ketal; acridine derivatives, such as 9-phenyl acridine and 1,7-bis(9,9'-acridyl)heptane; N-phenylglycine derivatives, such as N-phenylglycine; acetophenone derivatives, such as acetophenone, 3-methyl acetophenone, acetophenone benzoylacetyl ketal, 1-hydroxycyclohexylphenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone; thioxanthone derivatives, such as thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, and 2-chlorothioxanthone; acylphosphine oxide derivatives, such as 2, 4,6-Trimethylbenzoyl diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; oxime ester derivatives, such as 1,2-octanedione, 1-[4-(phenylthio)-,2-(O-benzoyl oxime)] and acetone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-,1-(O-acetyl oxime); xanthones, fluorenones, benzaldehyde, fluorene, anthraquinones, triphenylamine, carbazole, 1-(4-isopropylphenyl)-2-hydroxy-2-methyl-1-propanone and 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0178] Commercial examples of free radical photopolymerization initiators include, but are not limited to, Irgacure 184, 369, 651, 500, 819, 907, 784, 2959, CGI-1700, -1750 and -1850, CG24-61, Daro 1173, Lucirin TPO, LR8893 and LR8970 (manufactured by BASF, registered trademarks "Darocur" and "Lucirin") and Uvecryl P36 (manufactured by UCB).

[0179] The preferred cationic photopolymerization initiator is an onium salt, aromatic onium salt, aryl sulfonium salt, or aryl iodoonium salt. Specific examples of anions include tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroantimonate ion, perchlorate ion, trifluoromethanesulfonate ion, and fluorosulfonate ion.

[0180] Examples of commercially available cationic photopolymerization initiators include CPI-210S (manufactured by San-Apro Ltd.), UVI-6950 (manufactured by Union Carbide Corporation), and Adeka Optomer SP-150 (manufactured by San-Apro Ltd.) and Adeka Optomer SP-150 (manufactured by Adeka Corporation).

[0181] For every 100 parts by weight of sesquioxane solid, the polymerization initiator content in the coating liquid is preferably from 0.01 parts by weight to 1.5 parts by weight, more preferably from 0.03 parts by weight to 1.0 parts by weight.

[0182] The coating solution can be prepared by mixing particles consisting of a solid material, a solvent, a binder, and optionally a polymerization initiator. The solvent is preferably an organic solvent. The organic solvent can be, but is not limited to, alcohols, carboxylic acids, aliphatic or alicyclic hydrocarbons, aromatic hydrocarbons, esters, ketones, ethers, or mixtures of two or more of these.

[0183] Examples of alcohols include methanol, ethanol, 2-propanol, butanol, 2-methoxyethanol, 2-ethoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-propoxy-2-propanol, 4-methyl-2-pentanol, 2-ethylbutanol, 3-methoxy-3-methylbutanol, ethylene glycol, diethylene glycol, and glycerol.

[0184] Specific examples of carboxylic acids include n-butyric acid, α-methylbutyric acid, isovaleric acid, 2-ethylbutyric acid, 2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid, 2,3-dimethylbutyric acid, 3-methylvaleric acid, 4-methylvaleric acid, 2-ethylvaleric acid, 3-ethylvaleric acid, 2,2-dimethylvaleric acid, 3,3-dimethylvaleric acid, 2,3-dimethylvaleric acid, 2-ethylhexanoic acid, and 3-ethylhexanoic acid.

[0185] Specific examples of aliphatic or alicyclic hydrocarbons include n-hexane, n-octane, cyclohexane, cyclopentane, and cyclooctane.

[0186] The aromatic hydrocarbons are preferably toluene, xylene, or ethylbenzene.

[0187] Examples of esters include ethyl formate, ethyl acetate, n-butyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, and γ-butyrolactone.

[0188] Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone.

[0189] Examples of ethers include dimethoxyethane, tetrahydrofuran, dioxane, and diisopropyl ether.

[0190] To prepare the coating solution, alcohol is preferred among the solvents mentioned above, considering solution stability.

[0191] The coating liquid can be prepared by adding a predetermined amount of binder and optional polymerization initiator to a liquid containing particles composed of solid material dispersed in a solvent. The liquid containing particles dispersed in an organic solvent can be prepared by dispersing the particle powder in the solvent using the same method as the dispersion treatment described above (e.g., using a ball mill, etc.), or it can be a commercially available dispersion.

[0192] When the coating solution is used to form a film, the coating is carried out in an inert atmosphere such as dry air or dry nitrogen. The dry atmosphere preferably has a relative humidity of 30% or less.

[0193] Furthermore, the solution coating method used to form the film can be a known coating method, such as dip coating, spin coating, spray coating, printing, flow coating, or a combination thereof. The film thickness can be controlled by changing the traction speed in dip coating or the substrate rotation speed in spin coating, or by changing the concentration of the coating solution.

[0194] The film can be cured by high-energy radiation such as light radiation or X-ray radiation, or by heating. High-energy radiation and heating can be combined for curing.

[0195] For high-energy radiation curing, the high-energy beam can be, but is not limited to, electron beams, X-rays, ultraviolet radiation, etc. When the high-energy beam is ultraviolet radiation, the preferred radiation wavelength range is 160 nm to 400 nm, and the preferred output range is 0.1 mW / cm². 2 Up to 2000mW / cm 2 To prevent oxidation of silsesquioxanes, an inert atmosphere, such as nitrogen, is preferred for curing. Heat curing can be performed at temperatures ranging from 50°C to 250°C, preferably from 80°C to 200°C, for 1 to 20 minutes.

[0196] Methods for evaluating membrane porosity and refractive index

[0197] The membrane porosity X (%) and porosity Y (%) can be calculated as follows.

[0198] First, a carbon film was coated onto the substrate using a Type 681 ion beam coater (manufactured by Gatan, Inc.), followed by ion beam sectioning (30 kV - 0.1 nA) in a focused ion beam processing apparatus (FIB-SEM, manufactured by FEI, Nova 600). Then, SEM images were acquired using a scanning electron microscope (hereinafter referred to as SEM) at an accelerating voltage of 2 kV.

[0199] The SEM image magnification allows observation of the entire film, at least in the thickness direction, and, for example, the shape of each hollow particle can be discerned. More specifically, the magnification ranges from approximately 50,000 to 200,000.

[0200] The membrane has a unit volume of 1000nm × 1000nm × 100nm (thickness direction). To calculate the porosity in the cross-sectional SEM image, the hollow particles and the voids between them are distinguished by binarization of the grayscale image, and the area of ​​each region is calculated. Image processing is performed using the image analysis software ImageJ (NIH Image, available from https: / / imagej.nih.gov / ij / ).

[0201] More specifically, porosity X (%) is calculated by multiplying the area A (%) of the hollow particles by the volume fraction Va of the internal voids relative to the total volume of the hollow particles: X = A × Va. Porosity Y (%) is Y = 100 - A.

[0202] The refractive index n of the low refractive index layer 104 can be calculated using equation (2) from X and Y calculated in this way.

[0203] <Film Thickness>

[0204] For example, the low refractive index layer 104 can have a thickness ranging from 100 nm to 3.5 μm or from 150 nm to 3 μm. The low refractive index layer 104 preferably has a thickness in the range of 300 nm to 2 μm. The lower limit of the preferred thickness is determined based on the fact that it is preferably equal to or greater than the emission wavelength of the scintillator to sufficiently increase the total internal reflection efficiency. To use a scintillator that emits light in the visible light region, the low refractive index layer preferably has a thickness of 300 nm or more. A low refractive index layer with a thickness of 2 μm or less is less likely to crack and has sufficient strength. The thickness of the low refractive index layer 104 can be determined from a cross-sectional SEM image, as described in the methods for evaluating film porosity and refractive index.

[0205] Radiation detector

[0206] like Figure 2 As illustrated, the scintillator unit 205 and the detection unit 206 for detecting light from the scintillator unit 205 can constitute a radiation detector 207. The detection unit 206 can be a silicon photomultiplier array (SiPMA), a complementary metal-oxide-semiconductor sensor (CMOS), a flat panel detector (FPD), etc.

[0207] The detection unit 206 is preferably in contact with the scintillator 201. Therefore, the detection unit 206 can effectively detect the light generated by the scintillator 201. The detection unit 206 is preferably paired with each scintillator 201. Therefore, the detection unit 206 can detect the light generated by each scintillator 201 individually.

[0208] Figure 2 The light extraction surface 208 is the surface of the scintillator unit 205 that emits light generated by the scintillator 201. Figure 2 In this configuration, the reflective layer 204 and the low-refractive-index layer 104 are approximately perpendicular to the light extraction surface 208. Therefore, multiple scintillators and multiple detection units paired with the scintillators are positioned via the reflective layer 204 and the low-refractive-index layer 104. Consequently, the light generated by the scintillators is detected by the paired detection units but is difficult to detect by unpaired detection units. This further reduces crosstalk.

[0209] (Methods for measuring reflectance)

[0210] Reflectivity includes absolute reflectivity and relative reflectivity. Absolute reflectivity is the ratio of the intensity of reflected light to the intensity of light of a certain wavelength incident on the sample. The angle of incidence is the angle between the incident light and the normal to the reflecting surface of the sample. The angle of reflection is the angle between the reflected light and the normal to the reflecting surface. In the measurement of absolute reflectivity, the intensity ratio is measured when the angle of incidence equals the angle of reflection.

[0211] Relative reflectance is based on the absolute reflectance of a sample. For example, the relative reflectance of two samples is the ratio of the absolute reflectance of one sample to the absolute reflectance of the other sample.

[0212] Exemplary Example

[0213] Although the scintillator unit according to the present invention will be described in detail in the following exemplary embodiments, the present invention is not limited to these exemplary embodiments.

[0214] (Exemplary Example 1)

[0215] The improvement in reflectivity of the low-refractive-index layer of the scintillator unit according to this exemplary embodiment was evaluated as follows. Figure 3This is a schematic bird's-eye view of the reflectance measurement sample according to the present invention. Figure 3 As shown in the diagram, the scintillator is processed so that θ1 is 40 degrees. An adhesive layer 202, a low refractive index layer 104, and a reflective layer 204 are then placed on the processed scintillator in sequence.

[0216] The low refractive index layer was formed using hollow silica particles. A coating solution for film formation was prepared using Thrulya 4110 (dispersion medium: IPA, silica solids content: 20.5%, number-average particle size per hollow particle: 60 nm, porosity per hollow particle: 45%, refractive index per hollow particle: 1.25) manufactured by JGC Catalysts and Chemicals Ltd. The silica solids content of the coating solution was adjusted to 6.0%. The coating solution was applied to the reflective layer for 10 seconds using a spin coating method at a rotation speed of 1000 rpm to form the low refractive index layer.

[0217] The low-refractive-index layer was ion-beam sliced ​​(30 kV - 0.1 nA) in a focused ion beam processing apparatus (FIB-SEM, manufactured by FEI Company, Nova 600). SEM images were then acquired using a scanning electron microscope (hereinafter referred to as SEM) at an accelerating voltage of 2 kV. The low-refractive-index layer was tightly bonded to the reflective layer and had a thickness of 0.5 μm. For the cross-sectional SEM images of the low-refractive-index layer, the hollow particles and the voids between them were distinguished by binarization of the grayscale images, and the area of ​​each region was calculated. Considering the calculated area of ​​the hollow particles and the volume fraction of the internal voids relative to the total volume of the hollow particles, the porosity of the low-refractive-index layer was calculated to be 67%. The refractive index of the low-refractive-index layer was calculated to be 1.15 using Equation (2), where ns is 1.46.

[0218] The reflective layer, on which the low-refractive-index layer is formed, is bonded to the scintillator (LSO) using an epoxy optical adhesive (refractive index 1.43). The amount of adhesive and the pressing pressure are adjusted to achieve an adhesive layer thickness of 2 μm. The reflective layer serves as a dielectric multilayer film.

[0219] As described below, absolute and relative reflectance were measured using VR670 and ARMN-735 manufactured by JASCO Corporation.

[0220] Figure 4A The diagram illustrates the following: along Figure 3 The cross-section intercepted by line A-A'. Figure 4AIn this experiment, incident light 401 is incident on reflective layer 204, and the intensity of reflected light 402 reflected by reflective layer 204 is measured. It is assumed that the reflection angle 404 of reflected light 402 is the same as the incident angle 403. The incident angle in the following measurements is the incident angle 403.

[0221] Relative reflectance is used in the following measurements. Figure 4B As illustrated, a spacer (not shown) is inserted between the reflective layer and the scintillator to form an air layer, and the absolute reflectivity of this structure is used as a reference for the relative reflectivity. The absolute reflectivity measured under each condition is divided by... Figure 4B The relative reflectance is calculated from the absolute reflectance. Figure 5A and Figure 5B This is an example of the measurement results of the relative reflectance spectrum.

[0222] (Comparative Example 1)

[0223] The sample is prepared in the same manner as in Exemplary Example 1, except that a low-refractive-index layer is not used. Therefore, as... Figure 4C As illustrated, a sample is prepared by stacking a scintillator 201, an adhesive layer 202, and a reflective layer 204. Relative reflectance is measured in the same manner as in Exemplary Example 1. Figure 5A and Figure 5B The measured relative reflectance spectrum is shown.

[0224] Figure 5A and Figure 5B The relative reflectance spectrum of Exemplary Example 1 shows that the reflectance at all wavelengths is higher than that of Comparative Example 1. Therefore, it can be understood that by sequentially arranging an adhesive layer and a low-refractive-index layer between the scintillator and the reflective layer, and on the scintillator, light can be easily reflected.

[0225] also, Figure 5A and Figure 5B The relative reflection spectra are shown at incident angles of 70 degrees and 74 degrees, respectively. Figure 5A and Figure 5B The comparison shows that the difference in relative reflectivity between Exemplary Example 1 and Comparative Example 1 increases with increasing incident angle. Figure 2 As illustrated, when the light extraction surface 208 is approximately perpendicular to the reflective layer 204, the relative reflectivity of Exemplary Example 1 is higher than that of Comparative Example 1. Therefore, it can be understood that by sequentially arranging an adhesive layer and a low-refractive-index layer between the scintillator and the reflective layer, and on the scintillator, light can be easily reflected.

[0226] As described above, the present invention can provide a radiation detector including a scintillator unit, wherein when the scintillator unit includes multiple scintillators, the radiation detector can reduce crosstalk.

[0227] This invention is not limited to these embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the scope of the invention is disclosed in the appended claims.

[0228] This application claims the benefit of Japanese Patent Application No. 2019-141822, filed on July 31, 2019, and No. 2020-127945, filed on July 29, 2020, the entire contents of which are incorporated herein by reference.

Claims

1. A scintillator unit, the scintillator unit comprising scintillators arranged in a two-dimensional pattern and a reflective layer between two scintillators of the plurality of scintillators, in, An adhesive layer and a low-refractive-index layer with a lower refractive index than the adhesive layer are sequentially disposed between the scintillator and the reflective layer, and on the scintillator. The thickness of the adhesive layer is in the range of 2 μm to 5 μm, and The low-refractive-index layer contains hollow particles.

2. The scintillator unit according to claim 1, wherein, The scintillator unit comprises, in sequence, a scintillator, an adhesive layer, a low refractive index layer, a reflective layer, a low refractive index layer, an adhesive layer, and a scintillator.

3. The scintillator unit according to claim 1 or 2, wherein, The reflective layer comprises a dielectric multilayer film.

4. The scintillator unit according to claim 1, wherein, The low-refractive-index layer is disposed approximately perpendicular to the light extraction surface of the scintillator unit.

5. The scintillator unit according to claim 1, wherein, The adhesive layer comprises at least one of epoxy resin, acrylic resin, and vinyl resin.

6. The scintillator unit according to claim 1, wherein, The refractive index of the adhesive layer is greater than 1.30 and less than 1.

70.

7. The scintillator unit according to claim 1, wherein, The low-refractive-index layer contains silicon dioxide.

8. The scintillator unit according to claim 1, wherein, The refractive index of the low-refractive-index layer is in the range of 1.10 to 1.

20.

9. The scintillator unit according to claim 1, wherein, The low-refractive-index layer has voids, and the porosity of the low-refractive-index layer is in the range of 60.0% to 95.0%.

10. The scintillator unit according to claim 1, wherein, The thickness of the low refractive index layer is in the range of 300 nm to 2 μm.

11. The scintillator unit according to claim 1, wherein, The hollow particles have an outer shell with a refractive index in the range of 1.35 to 1.

60.

12. The scintillator unit according to claim 1 or 11, wherein, The hollow particles are hollow silica particles.

13. The scintillator unit according to claim 1, wherein, The low-refractive-index layer contains vapor-phase silica particles.

14. A scintillator unit, the scintillator unit including a reflective layer between a plurality of scintillators, in, An adhesive layer and a low-refractive-index layer with a refractive index lower than that of the adhesive layer are sequentially disposed between the scintillator and the reflective layer, and on the scintillator. The low-refractive-index layer contains hollow particles.

15. The scintillator unit according to claim 14, wherein, The hollow particles have an outer shell with a refractive index in the range of 1.35 to 1.

60.

16. The scintillator unit according to claim 14 or 15, wherein, The hollow particles are hollow silicon dioxide particles.

17. A radiation detector, the radiation detector comprising: A scintillator unit, the scintillator unit comprising scintillators arranged in two dimensions and a reflective layer between two scintillators in a plurality of scintillators; and a detection unit configured to detect light generated from the scintillator. The scintillator unit comprises, between the scintillator and the reflective layer, and on the scintillator, an adhesive layer and a low-refractive-index layer with a refractive index lower than that of the adhesive layer, in sequence. The thickness of the adhesive layer is in the range of 2 μm to 5 μm, and The low-refractive-index layer contains hollow particles.

18. A radiation detector, the radiation detector comprising: A scintillator unit, the scintillator unit including a reflective layer between a plurality of scintillators; and a detection unit configured to detect light generated from the scintillators. The scintillator unit comprises, between the scintillator and the reflective layer, and on the scintillator, a bonding layer and a low-refractive-index layer with a refractive index lower than that of the bonding layer, in sequence. The low-refractive-index layer contains hollow particles.

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