Scintillator structure, x-ray detector, and x-ray inspection device

Abstract

The present invention improves the reliability of a scintillator structure. This scintillator structure comprises multiple cells and a reflective layer covering the multiple cells. The reflective layer comprises a resin and reflective particles. The resin is a polyolefin without double bonds.

Description

Scintillator structure, X-ray detector, and X-ray inspection device

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to a scintillator structure, an X-ray detector, and an X-ray inspection device. For example, the present disclosure relates to a scintillator structure having a plurality of cells and a reflective layer.

[0002] Japanese Patent Application Laid-Open No. 2022-179793 (Patent Document 1) describes a technique relating to a scintillator structure having a plurality of cells each containing an epoxy resin and a phosphor.

[0003] Japanese Patent Application Laid-Open No. 2022-158410 (Patent Document 2) describes a scintillator structure having a plurality of cells each containing a resin and a phosphor, in which the resin exhibits a decrease in total light transmittance for light having a wavelength of 542 nm of less than 8% after being irradiated with X-rays at a dose of 100 kGy.

[0004] Japanese Patent Laid-Open Publication No. 2023-89270 (Patent Document 3) describes that in a scintillator array comprising a resin and a phosphor, the resin is made of a hydrogenated epoxy resin or an epoxy silicone resin.

[0005] JP 2022-179793 A JP 2022-158410 A JP 2023-89270 A

[0006] A scintillator is a material that absorbs the energy of radiation, such as X-rays or gamma rays, and generates visible light when it is exposed to the radiation. Scintillators are commercially available as scintillator structures that include a scintillator and a reflective layer. X-ray detectors that combine a scintillator structure with a light-receiving element such as a photodiode are used in, for example, medical equipment such as X-ray CT scanners, analytical equipment, non-destructive testing devices that use radiation, and radiation leakage testing devices.

[0007] For example, the scintillator may contain gadolinium oxysulfide (Gd ２ O ２In this specification, gadolinium oxysulfide is referred to as "GOS." Strictly speaking, gadolinium oxysulfide itself hardly emits light, but it emits light when gadolinium oxysulfide contains praseodymium, terbium, or the like. For this reason, the term "GOS" is used in this specification to implicitly refer to a substance (phosphor) that emits light when gadolinium oxysulfide itself contains praseodymium, terbium, or the like.

[0008] However, when it is necessary to explicitly indicate that gadolinium oxysulfide itself contains praseodymium, terbium, or the like, it is expressed as "GOS" containing praseodymium or "GOS" containing terbium.

[0009] Furthermore, when the scintillator is made of "GOS" alone, "GOS" is a ceramic. On the other hand, as will be described later, it is also being considered to use a scintillator as a mixture of "GOS" and resin. In this case, "GOS" is a powder. Therefore, in this specification, when there is no need to specifically distinguish between ceramic and powder, it will be referred to simply as "GOS." On the other hand, when it is necessary to specifically state the ceramic, it will be referred to as "GOS" ceramic. On the other hand, when it is necessary to specifically state the powder, it will be referred to as "GOS" powder.

[0010] This "GOS" is cadmium tungstate (CdWO ４ ) has the advantage of having a higher visible light emission output, but the manufacturing cost is high.

[0011] For this reason, in order to reduce the manufacturing cost of the scintillator structure, the use of a mixture of "GOS" powder and resin as the scintillator is being considered.

[0012] In this regard, improving reliability is a high-priority requirement for the scintillator structure, because improving the reliability of the scintillator structure can extend the life of the radiation detector. Therefore, the scintillator is required to have high radiation resistance in order to improve reliability. In particular, as described above, when the scintillator is made of a mixture of "GOS" powder and resin, it is desirable that the resin is resistant to deterioration when irradiated with radiation.

[0013] The scintillator structure also includes a reflective layer covering the scintillator. The reflective layer includes a resin and reflective particles. Therefore, it is desirable that the resin included in the reflective layer also be resistant to deterioration when irradiated with radiation. The above-described properties of the resin included in the reflective layer are desirable not only when the scintillator includes "GOS" powder and a resin, but also when the scintillator is a ceramic such as "GOS" ceramic.

[0014] An object of the present invention is to improve the reliability of the scintillator structure.

[0015] In one embodiment, the scintillator structure includes a plurality of cells and a reflective layer covering the plurality of cells, the reflective layer including a resin and reflective particles, the resin being a polyolefin having no double bonds.

[0016] In one embodiment, the scintillator structure includes a plurality of cells and a reflective layer covering the plurality of cells, the reflective layer including a resin and reflective particles, the resin exhibiting a decrease in total light transmittance of 1% or less for light having a wavelength of 542 nm after irradiation with an X-ray dose of 80 kGy.

[0017] In one embodiment, an X-ray detector includes the scintillator structure described above and a photodetector that generates a current from light generated in the scintillator structure.

[0018] In one embodiment, an X-ray inspection apparatus comprises an X-ray generator for generating X-rays and an X-ray detector as described above.

[0019] According to one embodiment, the reliability of the scintillator structure can be improved.

[0020] FIG. 1 is a diagram schematically showing an X-ray detection device. FIG. 2 is a diagram schematically showing an X-ray detector. FIG. 3 is a flowchart explaining the flow of a manufacturing process of a scintillator structure. FIG. 4 is a diagram schematically showing processes from a dicing process to a reflective material application process. FIG. 5 is a graph showing the relationship between X-ray dose and "total light transmittance" in each of an example and a comparative example. FIG. 6 is a diagram schematically showing an X-ray detector in a modified example. FIG. 7 is a diagram schematically showing an X-ray detector for explaining another example of the surface state of the reflective layer in a modified example. FIG. 8 is a diagram schematically showing an X-ray detector for explaining another example of the surface state of the reflective layer in a modified example. FIG. 9 is a flowchart explaining the flow of a first manufacturing method in a modified example. FIG. 10 is a flowchart explaining the flow of a second manufacturing method in a modified example. FIG. 11 is a flowchart explaining the flow of a third manufacturing method in a modified example.

[0021] In all the drawings for explaining the embodiments, the same components are generally designated by the same reference numerals, and repeated explanations thereof will be omitted. In addition, hatching may be used even in plan views to make the drawings easier to understand.

[0022] <Outline of X-ray Inspection Apparatus> FIG. 1 is a diagram schematically showing an X-ray inspection apparatus 1. As shown in FIG.

[0023] The X-ray inspection device 1 has an X-ray generator 50, an X-ray detector 100, and a signal processing unit (not shown). The X-ray detector 100 has a scintillator structure 10 and a light receiving element 20. An object to be measured is placed between the X-ray generator 50 and the X-ray detector 100.

[0024] The X-ray generator 50 is configured to generate X-rays based on an electron beam generated by applying a voltage to a filament, for example. The X-ray detector 100 is configured to output an electrical signal based on incident X-rays. The signal processing unit is configured to acquire an image based on the electrical signal output from the X-ray detector 100. The signal processing unit is also configured to analyze the acquired image. In other words, the signal processing unit has an image acquisition unit and an image analysis unit.

[0025] In the X-ray inspection apparatus 1 configured as described above, the object to be measured is inspected as follows. That is, the object to be measured is irradiated with X-rays generated by the X-ray generator 50. Then, the X-rays that have passed through the object to be measured are incident on the X-ray detector 100. After that, the X-ray detector 100 generates an electrical signal from the X-rays. Next, an image is acquired based on the electrical signal generated by the X-ray detector 100. Subsequently, the acquired image is analyzed. Inspection of the object to be measured using the X-ray inspection apparatus 1 is performed in the manner described above.

[0026] <Outline of X-ray Detector> Next, the X-ray detector will be described.

[0027] FIG. 2 is a diagram schematically illustrating an X-ray detector.

[0028] 2 , the X-ray detector 100 has a scintillator structure 10 and a light-receiving element 20. The scintillator structure 10 includes a plurality of scintillators 11 that generate visible light from X-rays incident on the X-ray detector 100, and a reflective layer 12 that covers each of the plurality of scintillators 11. On the other hand, the light-receiving element 20 has a function of generating a current from the visible light generated by the scintillator 11. The light-receiving element 20 is, for example, a photodiode. The light-receiving element 20 is provided on, for example, a support 30, and is provided corresponding to each of the plurality of scintillators 11.

[0029] The scintillator 11 has the function of absorbing X-rays and generating visible light. The scintillator 11 includes a phosphor 11a and a resin 11b. Herein, the material obtained by mixing the "GOS" powder constituting the phosphor 11a with the resin 11b is referred to as "resin GOS" in this specification. In other words, the scintillator 11 in this embodiment is "resin GOS." The phosphor 11a is gadolinium oxysulfide containing praseodymium, terbium, and the like. The reflective layer 12 includes a resin 12b containing reflective particles 12a that are titanium oxide.

[0030] In recent years, as shown in Fig. 2 , in the scintillator structure 10, the scintillator 11 is divided into a plurality of cells (CL). That is, from the viewpoint of improving the resolution of X-ray images, the scintillator 11 is divided into a plurality of cells CL in accordance with each of a plurality of light receiving elements 20 (arraying the scintillators 11). In this manner, the scintillator structure 10 includes a plurality of cells CL and a reflective layer 12 that covers the plurality of cells CL. Specifically, the top surface and four side surfaces of the cell CL are covered with the reflective layer 12. On the other hand, the bottom surface of the cell CL is not covered with the reflective layer 12 because it needs to be in contact with the light receiving element 20.

[0031] The X-ray detector configured in this manner operates as follows.

[0032] That is, when X-rays are incident on the scintillator 11 of the scintillator structure 10, electrons in the phosphor 11a that constitutes the scintillator 11 receive the energy of the X-rays and transition from the ground state to an excited state. The excited state electrons then transition back to the ground state. At this time, visible light corresponding to the energy difference between the excited state and the ground state is emitted. Through this mechanism, the scintillator 11 absorbs X-rays and generates visible light.

[0033] Some of the visible light emitted from the scintillator 11 is directly incident on the light-receiving element 20. Another portion of the visible light emitted from the scintillator 11 is repeatedly reflected by the reflective layer 12 that covers the scintillator 11 and is then focused on the light-receiving element 20. When visible light is incident on the light-receiving element 20, which is, for example, a photodiode, the energy of the visible light excites electrons in the semiconductor material that makes up the photodiode from the valence band to the conduction band. This causes a current due to the electrons excited to the conduction band to flow in the photodiode. An X-ray image is then acquired based on the current output from the photodiode. In this way, an X-ray image can be acquired based on the electrical signal output from the X-ray detector 100.

[0034] 2 , the scintillator structure 10 has a rectangular parallelepiped-shaped scintillator 11 and a reflective layer 12 covering the scintillator 11. Here, the rectangular parallelepiped-shaped scintillator 11 is formed through processing steps such as a dicing step and a grinding step, and therefore a processed surface is formed on the surface of the rectangular parallelepiped shape. In other words, the "processed surface" refers to a surface that has been subjected to mechanical processing. Specifically, the "processed surface" includes a surface that has been ground with a grinding wheel to control the thickness of the scintillator structure 10, or a surface that has been cut from the scintillator structure 10 with a slicing blade to perform a dicing process.

[0035] For example, in a scintillator 11 using "resin GOS," the "processed surface" is defined as a surface where the resin is exposed and the GOS powder is broken. For example, FIG. 2 shows a schematic diagram of a scintillator 11 using "resin GOS," in which the interface between the scintillator 11 and the reflective layer 12 is the "processed surface." In this case, the "processed surface" includes a region where the resin 11b is cut and a region where the phosphor 11a (GOS powder) is broken. The X-ray detector 100 is constructed in this manner. The top surface, four side surfaces, and bottom surface of the cell CL correspond to the "processed surface."

[0036] <Reason for Using "Resin GOS"> As described above, in this embodiment, "resin GOS" is used as the scintillator 11. The reason for this will be described below.

[0037] For example, cadmium tungstate (hereinafter referred to as "CWO") is used as the scintillator 11 constituting the scintillator structure 10. This "CWO" contains cadmium, which is a substance subject to the RoHS Directive / REACH Regulation. For this reason, "GOS" ceramic has been used as the scintillator 11 instead of "CWO" containing cadmium. This "GOS" ceramic has the advantage of having a higher visible light emission output than "CWO," but has the disadvantage of higher manufacturing costs.

[0038] Therefore, from the viewpoint of reducing manufacturing costs, it is being considered to use "resin GOS," which is a mixture of resin and "GOS" powder, instead of "GOS" ceramic, as the scintillator 11. That is, in order to suppress the increase in manufacturing costs due to "GOS" ceramic, it is being considered to use "resin GOS," which is cheaper than "GOS" ceramic, for the scintillator 11.

[0039] Here, "resin GOS" includes a "first resin GOS" which is a mixture of "GOS" powder in which praseodymium (Pr) and cerium (Ce) have been added to gadolinium oxysulfide and a resin, and a "second resin GOS" which is a mixture of "GOS" powder in which terbium (Tb) and cerium (Ce) have been added to gadolinium oxysulfide and a resin.

[0040] Both the "first resin GOS" and the "second resin GOS" have the advantage of having higher light output than "CWO." Furthermore, the "first resin GOS" also has the advantage of having the same afterglow characteristics as "CWO." In other words, the performance of the scintillator structure 10 requires not only high light output but also good afterglow characteristics.

[0041] The afterglow characteristics will now be explained. The scintillator 11 constituting the scintillator structure 10 is a material that generates visible light when irradiated with X-rays. The mechanism by which the scintillator 11 generates visible light when irradiated with X-rays is as follows.

[0042] That is, when the scintillator 11 is irradiated with X-rays, electrons in the scintillator 11 receive energy from the X-rays and transition from a low-energy ground state to a high-energy excited state. The electrons in the excited state then transition to a low-energy ground state. At this time, most of the excited electrons immediately transition to the ground state. Meanwhile, some of the excited electrons transition to the ground state after a certain amount of time has passed.

[0043] The visible light generated by the transition of electrons from an excited state to a ground state after a certain amount of time has passed is called afterglow. In other words, afterglow is visible light generated when the transition from an excited state to a ground state occurs some time after the time of X-ray irradiation. A large amount of afterglow means that the intensity of the visible light generated is high even after a certain amount of time has passed since the X-ray irradiation. In this case, the afterglow generated by the previous X-ray irradiation remains until the next X-ray irradiation. Therefore, the remaining afterglow becomes noise. For this reason, it is desirable for the afterglow to be small. In other words, good afterglow characteristics mean small afterglow. In this regard, the afterglow characteristics of the "first resin GOS" are equivalent to those of the "CWO".

[0044] Therefore, "resin GOS" has the following advantages over "CWO" and is therefore superior as a scintillator 11 that can achieve both high performance and low manufacturing costs.

[0045] (1) "Resin GOS" has a higher light output than "CWO". (2) The afterglow characteristics of "First Resin GOS" are equivalent to those of "CWO". (3) "Resin GOS" does not use cadmium. (4) "Resin GOS" has a lower manufacturing cost than "CWO".

[0046] Cesium iodide (CsI) is used as the scintillator 11. In this regard, "resin GOS" has the following advantages over "CsI".

[0047] (1) "Second Resin GOS" has better X-ray stopping properties (ability to absorb X-rays) than "CsI". (2) The afterglow properties of "Second Resin GOS" are approximately 1 / 70 of "CsI". (3) "Resin GOS" is a stable material that does not deliquesce.

[0048] Furthermore, "resin GOS" has the following advantages over "GOS" ceramic. Specifically, "resin GOS" and "GOS" ceramic contain heavy metals such as Gd. These heavy metals are relatively expensive. Furthermore, there are concerns that heavy metals may have adverse effects on living organisms and the environment if they are leaked. Therefore, it is desirable for the scintillator 11 to contain as few heavy metals as possible. In this regard, "resin GOS," which is a mixture of "GOS" powder and resin, uses less "GOS" than bulk "GOS" ceramic. As a result, "resin GOS" can be used to construct a scintillator 11 with a lower heavy metal content than "GOS" ceramic. Therefore, "resin GOS" is superior to "GOS" ceramic in that it can provide a scintillator 11 with a lower heavy metal content. For these reasons, "resin GOS" is considered promising as a scintillator 11 that can achieve both high performance and low manufacturing costs.

[0049] <Specific Materials> Next, specific materials of the components that make up the scintillator structure 10 will be described.

[0050] <<Phosphor 11a>> The phosphor 11a used in this embodiment includes, for example, gadolinium oxysulfide or gadolinium-aluminum-gallium garnet (GGAG). Here, the gadolinium oxysulfide is, for example, “Gd ２ O ２ On the other hand, "GGAG" has a composition of Gd activated with at least one element selected from cerium (Ce) and praseodymium (Pr). １－ｘ Lu ｘ ) ３＋ａ (Ga ｕ Al １－ｕ ) ５－ａ O １２ The phosphor 11a has a main composition of (x=0 to 0.5, u=0.2 to 0.6, a=-0.05 to 0.15), but is not limited to a specific composition.

[0051] <<Resin 11b and Resin 12b>> The resins 11b and 12b are made of materials that are resistant to deterioration when irradiated with radiation. The materials of the resins 11b and 12b are a feature of this embodiment. This feature will be described later.

[0052] <<Reflective Particles 12a>> The constituent material of the reflective particles 12a is, for example, “TiO ２ ” (titanium oxide), “Al ２ O ３ " (aluminum oxide), "ZrO ２ Examples of the reflective particles 12a include white particles such as "rutile type TiO ２ The reflective particles 12a having the formula " are desirable particles having excellent light reflection efficiency. From the viewpoint of improving the light receiving efficiency of the light receiving element 20, the light reflectance of the reflective particles 12a is desirably 80% or more, and further, the light reflectance of the reflective particles 12a is desirably 90% or more. The composition of the reflective particles can be confirmed, for example, by examining the fracture surface of the reflective particles with SEM-EDX, i.e., scanning electron microscope-energy-dispersive X-ray spectroscopy.

[0053] <<Other Additives>> The resin 11b constituting the scintillator 11 and the reflective material constituting the reflective layer 12 may contain other additives in addition to the components described above.

[0054] <Considerations for Improvement> For example, epoxy resin is used as the resin contained in "resin GOS." This epoxy resin contains at least a base resin and a curing agent as constituent materials. For example, bisphenol A epoxy resin is often used as the base resin, and a phthalic anhydride curing agent such as methylhexahydrophthalic anhydride is often used as the curing agent. However, the present inventors have newly discovered that when a typical epoxy resin that uses bisphenol A epoxy resin as the base resin and a phthalic anhydride curing agent as the curing agent is used as the resin constituting "resin GOS," repeated exposure to radiation (X-rays) over a long period of time causes deterioration and discoloration.

[0055] The discoloration of the translucent resin means that the light absorption increases. As a result, the light transmittance decreases. Therefore, the light generated from the scintillator containing "resin GOS" is less likely to reach the light receiving element (photodiode). This reduces the detection performance of the X-ray detector.

[0056] In other words, according to the investigations of the present inventors, it has been found that if a general epoxy resin that uses a bisphenol A type epoxy resin as the main component and a phthalic anhydride curing agent as the curing agent is used as the resin that constitutes "Resin GOS," it is difficult to ensure stable detection performance over a long period of time in an X-ray detector.

[0057] Therefore, based on the above-mentioned new findings, in order to ensure the reliability of the X-ray detector over a long period of time, it is desirable to use a resin that is resistant to discoloration even when irradiated with X-rays over a long period of time as the resin constituting the "resin GOS" instead of the general epoxy resin described above. The inventors have therefore discovered a resin that is resistant to discoloration even when irradiated with X-rays over a long period of time and has excellent radiation resistance, which will be described below.

[0058] <Features of the embodiment> A feature of the present embodiment is that, instead of epoxy resin, a polyolefin having no double bonds is used as the resin contained in the "resin GOS" or the resin contained in the reflective material that constitutes the reflective layer. This makes it possible to provide a scintillator structure that can suppress the rate of decrease in "total light transmittance" that occurs due to radiation irradiation. As a result, the reliability of X-ray detectors that include the scintillator structure as a component can be ensured over a long period of time.

[0059] Polyolefins without double bonds are believed to be able to suppress the decrease in "total light transmittance" for the following reasons. This is because many polyolefins basically do not have double bonds. In other words, materials without double bonds in their molecules can suppress the decrease in "total light transmittance" caused by X-rays. For example, part of the energy of X-rays irradiated onto a material is absorbed by the material and used to break intermolecular bonds. When strong bonds such as double bonds are present in the molecule, more X-ray energy is absorbed. The more X-ray energy is absorbed, the greater the change in molecular structure. This makes the material more susceptible to discoloration due to changes in molecular structure. Discoloration of the material results in a decrease in "total light transmittance." Due to the above mechanism, materials with double bonds are more likely to experience a decrease in "total light transmittance." In this regard, many polyolefins do not have double bonds in their molecules. For this reason, polyolefins without double bonds suppress the decrease in "total light transmittance" more than materials with double bonds.

[0060] In other words, the present inventors have found that polyolefins having no double bonds are substances that can suppress the rate of decrease in "total light transmittance" caused by irradiation with radiation more effectively than epoxy resins. For example, by using polyolefins having no double bonds as the resin, the rate of decrease in "total light transmittance" for light having a wavelength of 542 nm after irradiation with X-rays at a dose of 80 kGy can be reduced to 1% or less.

[0061] Furthermore, by using a polyolefin having no double bonds as the resin, the decrease rate of the "total light transmittance" for light having a wavelength of 542 nm after irradiation with X-rays at a dose of 100 kGy can be reduced to 1% or less.

[0062] An example of a polyolefin having no double bonds is polymethylpentene. Examples of polymethylpentene include a commercially available product such as "TPX RT-18" manufactured by Mitsui Chemicals, Inc. By using polymethylpentene as a resin, it is possible to reduce the rate of decrease in "total light transmittance" for light having a wavelength of 542 nm to 1% or less after irradiation with X-rays at a dose of 80 kGy. Furthermore, by using polymethylpentene as a resin, it is possible to reduce the rate of decrease in "total light transmittance" for light having a wavelength of 542 nm to 1% or less after irradiation with X-rays at a dose of 100 kGy.

[0063] In addition to polymethylpentene, examples of polyolefins without double bonds include polyethylene and polypropylene. On the other hand, polyolefins also include substances that have double bonds in the molecule, such as poly-α-olefins. Therefore, polyolefins without double bonds do not include poly-α-olefins.

[0064] The presence of polymethylpentene, polyethylene, or polypropylene in the resin can be confirmed using a Fourier-transform infrared spectroscopy (FT-IR).

[0065] The term "total light transmittance" is used with the intention of including light that is scattered inside the scintillator and whose transmission direction deviates from the incident direction as transmitted light. In other words, "total light transmittance" represents the transmittance when it includes not only transmitted light that travels straight from the incident direction but also transmitted light that is scattered inside the scintillator and whose transmission direction deviates from the straight direction. In a scintillator structure, the scintillator cell is covered with a reflective layer. As a result, light scattered inside the cell is also repeatedly reflected and ultimately enters the light-receiving element located on the bottom of the cell. Therefore, light scattered inside the cell also contributes to detection by the light-receiving element. Taking this into consideration, the term "total light transmittance" is used. In other words, "total light transmittance" is used to evaluate radiation by taking into account all transmitted light that contributes to radiation detection.

[0066] The "total light transmittance" refers to the total light transmittance measured using light with a wavelength of 542 nm for a 1.5 mm thick sample. To measure the "total light transmittance," samples measuring 15 mm x 15 mm x 1.5 mm in length, width, and thickness were prepared, and the surfaces of the samples were mirror-finished before measuring the "total light transmittance" for each sample.

[0067] <Method for Manufacturing Scintillator Structure> Next, a method for manufacturing the scintillator structure will be described.

[0068] FIG. 3 is a flowchart illustrating the flow of the manufacturing process of the scintillator structure.

[0069] First, predetermined amounts of raw material powder and flux components are weighed and mixed (S101). The mixture is then loaded into a crucible and fired in an atmospheric furnace at 1300°C to 1400°C for 7 to 9 hours to produce "GOS" powder (S102). Flux components and impurities contained in the "GOS" powder are then removed by washing with hydrochloric acid and hot water (S103). Next, resin is dripped onto the "GOS" powder to allow it to penetrate the powder (S104). Next, the resin is cured (S105), and any resin not mixed with the "GOS" powder is removed (S106). This completes the formation of a scintillator containing "resin GOS."

[0070] Next, the scintillator substrate is diced into individual cells (S107). The cells are rearranged (S108), and then a reflective material is applied to cover the cells (S109). After unnecessary portions of the scintillator structure are cut off (S110), scintillator structures that have passed inspection are shipped (S111).

[0071] FIG. 4 is a diagram showing the steps from the dicing step to the reflective material application step.

[0072] As shown in FIG. 4 , a substrate WF on which a scintillator containing "resin GOS" is formed is diced, whereby the substrate WF is divided into a plurality of cells CL. The plurality of cells CL are then rearranged in a line. An outer frame FR is then arranged to enclose the rearranged plurality of cells CL. Next, a reflective material having, for example, polyolefin containing titanium oxide is applied so as to cover the plurality of cells CL arranged within the outer frame FR. The outer frame FR is then removed. This produces a scintillator structure 10A including a reflective layer 12.

[0073] 4 illustrates an example of a linear scintillator structure 10A using 1×n cells. However, the technical idea of ​​this embodiment is not limited to this. For example, the technical idea of ​​this embodiment can also be applied to an array-shaped (matrix-shaped) scintillator structure using n×m cells. Note that n and m are each any natural number.

[0074] In the present embodiment described above, for example, in the X-ray detector 100 shown in FIG. 2 , it is assumed that the resin 11b constituting a part of the scintillator 11 is a polyolefin having no double bonds. In particular, in the present embodiment, polymethylpentene is cited as a specific example of the resin 11b. However, the technical idea of ​​the present embodiment is not limited to this. For example, in the X-ray detector 100 shown in FIG. 2 , the resin 11b constituting a part of the scintillator 11 may be, for example, polyethylene or polypropylene.

[0075] <Examples> Detailed verification results that support the effects of the technical idea of ​​the present embodiment will be described below based on examples. Note that the technical idea of ​​the present embodiment is not limited to these examples.

[0076] First, the sample will be described.

[0077] <<Materials>> A resin substrate was prepared as a sample.

[0078] As the "GOS" powder, gadolinium oxysulfide (Gd ２ O ２ S) was used.

[0079] Table 1 shows the resin components in each of the examples and comparative examples.

[0080] As shown in Table 1, polymethylpentene was used in the examples, while bisphenol A diglycidyl ether was used as the base resin and methylhexahydrophthalic anhydride (Me-HHPA) was used as the curing agent in the comparative examples.

[0081] <<Sample Preparation>> The "resin substrate" in the comparative example was prepared by blending the base agent and curing agent at a ratio of base agent:curing agent = 100:90.8. For each of the "resin substrate" in the example and the "resin substrate" in the comparative example, samples were prepared under primary curing conditions (90°C, 15 hours) and secondary curing conditions (120°C, 2.5 hours) in the resin curing process. The shape of each prepared sample was 15 mm x 15 mm x 1.5 mm (length x width x thickness). The surface of each sample was mirror-finished.

[0082] <<Evaluation Method>> Each sample was irradiated with 100 kGy of X-rays, and then the "total light transmittance" for light having a wavelength of 542 nm was measured using a JASCO V-570 ultraviolet-visible-near-infrared spectrophotometer. Here, an integrating sphere device and a reflector were used to collect diffuse transmitted light and direct transmitted light into a detector to measure the "total light transmittance."

[0083] <<Evaluation Results>> FIG. 5 is a graph showing the evaluation results.

[0084] As shown in Figure 5, the initial "total light transmittance" before X-ray irradiation is around 90% in both the Example and the Comparative Example. On the other hand, when looking at the "total light transmittance" after irradiation with X-rays at a dose (irradiation amount) of 100 kGy, it remains unchanged at approximately 90% in the Example. In contrast, in the Comparative Example, the "total light transmittance" drops to approximately 70%.

[0085] Table 2 shows the values ​​of total light transmittance (%) corresponding to the dose (kGy) of "0," "80," and "100" shown on the horizontal axis of the graph in FIG.

[0086] Table 3 shows the results converted into "total light transmittance reduction rate (%)."

[0087] As shown in Table 3, after irradiating with X-rays at a dose of over 80 kGy up to a dose of 100 kGy, the reduction rate for the Example was 1%, while the reduction rate for the Comparative Example was 29%. Furthermore, after irradiating with X-rays at a dose of 80 kGy, the reduction rate for the Example was 1%, while the reduction rate for the Comparative Example was 21%.

[0088] The above results confirm that the "resin GOS" in the examples can suppress a decrease in "total light transmittance" even after irradiation with X-rays at doses of 80 kGy to 100 kGy. In particular, the results in Table 3 show that the "resin GOS" in the examples can achieve excellent performance, maintaining an initial total light transmittance of nearly 90% for light having a wavelength of 542 nm before X-ray irradiation, while achieving a decrease in total light transmittance of 1% or less for light having a wavelength of 542 nm after irradiation with X-rays at a dose of 100 kGy. Therefore, by using the "resin GOS" in the examples, a scintillator structure can be realized that suppresses the decrease in "total light transmittance" caused by radiation irradiation. This allows the scintillator structure included in the X-ray detector to include a resin as a component that maintains high transmittance even after long-term radiation exposure. As a result, the reliability of X-ray detectors and X-ray inspection devices equipped with X-ray detectors can be ensured over a long period of time. The X-ray inspection apparatus includes, for example, an X-ray computed tomography apparatus.

[0089] <Basic Concept of the Present Disclosure> The basic concept of the present disclosure is to use a polyolefin without double bonds as the resin contained in the "resin GOS" or the resin contained in the reflective material that constitutes the reflective layer, instead of an epoxy resin. In the above-described embodiment, a specific example of the basic concept is described focusing on the resin contained in the "resin GOS." In the following modified example, a specific example of the basic concept is described focusing on the resin contained in the reflective material that constitutes the reflective layer. In this case, the scintillator is not limited to a case that includes "GOS" powder and a resin. Therefore, in the modified example, the scintillator is described assuming that it is a ceramic, such as a "GOS" ceramic.

[0090] <Modifications> <<Configuration of X-ray detector>> FIG. 6 is a diagram schematically showing an X-ray detector.

[0091] 6 , the X-ray detector 200A includes a scintillator structure 10 and a light-receiving element 20. The scintillator structure 10 has a plurality of scintillators 11 and a reflective layer 12. The scintillators 11 generate visible light from X-rays incident on the X-ray detector 200A. The reflective layer 12 covers each of the plurality of scintillators 11. On the other hand, the light-receiving element 20 has a function of generating a current from the visible light generated by the scintillators 11. The light-receiving element 20 is, for example, a photodiode. The light-receiving element 20 is provided, for example, on a support 30, and is provided corresponding to each of the plurality of scintillators 11.

[0092] The scintillator 11 has a function of absorbing X-rays and generating visible light, and includes a phosphor 11c.

[0093] The phosphor 11c is made of at least one material selected from, for example, gadolinium oxysulfide, yttrium-gallium-aluminum garnet (YGAG), and gadolinium-aluminum-gallium garnet (GGAG).

[0094] "YGAG" has, for example, a composition activated with cerium (Ce) as its main composition.

[0095] The main composition is as follows:

[0096] (Y １－ｘ－ｚ Gd ｘ Ce ｚ ) ３＋ａ (Al １－ｕ Ga ｕ ) ５－ａ O １２ 0≦a≦0.1, 0.15≦x≦0.3, 0.002≦z≦0.015, and 0.35≦u≦0.55.

[0097] "GGAG" has, as its main composition, a composition activated with at least one element selected from, for example, cerium (Ce) and praseodymium (Pr).

[0098] The main composition is as follows:

[0099] (Gd １－ｘ Lu ｘ )３＋ａ (Ga ｕ Al １－ｕ ) ５－ａ O １２ 0≦x≦0.5, 0.2≦u≦0.6, and −0.05≦a≦0.15.

[0100] Thus, in a variant, the scintillator 11 is a "GOS" ceramic, a "YGAG" ceramic, or a "GGAG" ceramic, etc.

[0101] In the scintillator structure 10, the scintillator 11 is divided into a plurality of cells (CL). That is, from the viewpoint of improving the resolution of X-ray images, the scintillator 11 is divided into a plurality of cells CL in accordance with each of the plurality of light receiving elements 20 (arraying the scintillators 11). In this manner, the scintillator structure 10 includes a plurality of cells CL and a reflective layer 12 covering the plurality of cells CL. Specifically, the upper surface 11u and four side surfaces 11s of the cell CL are covered with the reflective layer 12. On the other hand, the lower surface 11w of the cell CL needs to be in contact with the light receiving element 20. Alternatively, the lower surface 11w of the cell CL needs to face the light receiving element via a transparent adhesive. For this reason, the lower surface 11w of the cell CL is not covered with the reflective layer 12.

[0102] The reflective layer 12 includes a resin 12b containing reflective particles 12a made of titanium oxide. The resin 12b is a polyolefin without a double bond. Examples of polyolefins without a double bond include polymethylpentene, polyethylene, and polypropylene. As a result, the resin 12b contained in the reflective material constituting the reflective layer 12 does not have a double bond. As a result, changes in molecular structure are less likely to occur. Therefore, according to the modified example, the resin 12b is less likely to discolor. As a result, a decrease in reflectance due to coloring of the resin 12b is suppressed. In particular, the top surface 11u and four side surfaces 11s of the cell CL are covered with the resin 12b. Therefore, a decrease in reflectance due to coloring of the resin 12b is suppressed on the top surface 11u and four side surfaces 11s of the cell CL. In this way, light reflected by the reflective particles 12a via the resin 12b in the reflective layer 12 is more likely to reach the light-receiving element 20.

[0103] The reflective layer 12 has an upper surface 12u, a side surface 12s, and a lower surface 12w. Various surface states of the upper surface 12u, the side surface 12s, and the lower surface 12w can be realized depending on the manufacturing method of the scintillator structure 10. In this case, if the resin 12b is a polyolefin having no double bonds, a decrease in reflectance due to coloration of the resin 12b is suppressed.

[0104] An example of the surface state of the reflective layer 12 will be described below.

[0105] 6, each of the upper surface 12u, the side surface 12s, and the lower surface 12w is made up of a surface of the resin 12b. The "surface of the resin 12b" is a surface of the reflective particles 12a that does not have a fracture surface. The "surface of the resin 12b" is intended to be a surface that is formed, for example, by hardening the applied resin 12b while facing another member.

[0106] 7 is a diagram schematically illustrating an X-ray detector 200B to explain another example of the surface state of the reflective layer 12. As shown in FIG. 7, the upper surface 12u is composed of a "surface of resin 12b" and a "fracture surface caused by broken reflective particles 12c." In contrast, each of the side surface 12s and the lower surface 12w is composed of a "surface of resin 12b." The surfaces composed of the "surface of resin 12b" and the "fracture surface caused by broken reflective particles 12c" are assumed to be, for example, ground or polished surfaces.

[0107] As another example of the surface state of the reflective layer 12 (not shown), in an X-ray detector, the lower surface 12w is composed of a "surface of resin 12b" and a "fracture surface caused by broken reflective particles 12c." In contrast, the upper surface 12u and the side surface 12s are each composed of a "surface of resin 12b." The surface composed of the "surface of resin 12b" and the "fracture surface caused by broken reflective particles 12c" is assumed to be, for example, a ground or polished surface.

[0108] As another example of the surface state of the reflective layer 12 (not shown), in an X-ray detector, the upper surface 12u and the lower surface 12w are composed of a "surface of resin 12b" and a "fracture surface caused by broken reflective particles 12c." In contrast, the side surface 12s is composed of a "surface of resin 12b." The surface composed of the "surface of resin 12b" and a "fracture surface caused by broken reflective particles 12c" is assumed to be, for example, a ground or polished surface.

[0109] Fig. 8 is a diagram schematically illustrating an X-ray detector 200C to explain another example of the surface state of the reflective layer 12. As shown in Fig. 8, each of the upper surface 12u, the side surface 12s, and the lower surface 12w is composed of a "surface of the resin 12b" and a "fracture surface caused by broken reflective particles 12c." That is, in Fig. 8, each of the upper surface 12u, the side surface 12s, and the lower surface 12w is, for example, a ground or polished surface.

[0110] For example, if the lower surface 12w of the reflective layer has a fracture surface caused by the reflective particles 12c, the lower surface 12w corresponds to the processed surface. As a result, by using the lower surface 12w as the processed surface, the distances between the light receiving element 20 and the scintillator 11 can be made uniform.

[0111] For example, variations in the spacing (gaps) may result in variations in the effect of suppressing light leakage. In this regard, a configuration in which the lower surface 12w of the reflective layer has a fracture surface caused by the reflective particles 12c can make the spacing between the light receiving element 20 and the scintillator 11 uniform. As a result, a configuration in which the lower surface 12w of the reflective layer has a fracture surface caused by the reflective particles 12c can make it less likely that variations will occur in the effect of suppressing light leakage.

[0112] For example, if the upper surface 12u and the lower surface 12w of the reflective layer have fracture surfaces caused by the reflective particles 12c, the upper surface 12u and the lower surface 12w correspond to processed surfaces. By using the upper surface 12u and the lower surface 12w as processed surfaces, the distance between the upper surface 12u and the lower surface 12w (the height of the cells CL) can be made uniform. In other words, a configuration in which the upper surface 12u and the lower surface 12w of the reflective layer have fracture surfaces caused by the reflective particles 12c is desirable because it allows the heights of the multiple cells CL to be made uniform.

[0113] The modified example provides the following effect. That is, the modified example suppresses the decrease in reflectance caused by the coloring of the resin 12 b. That is, the light reflected by the reflective particles 12 a via the resin 12 b in the reflective layer 12 is more likely to reach the light receiving element 20.

[0114] <<Method of Manufacturing Scintillator Structure>> <<<First Manufacturing Method ("Groove Resin Application")>>> FIG. 9 is a flowchart illustrating the flow of the first manufacturing method.

[0115] First, predetermined amounts of raw material powder and flux components are weighed and mixed (S201). The mixture is then filled into a crucible and fired in an atmospheric furnace at 1300°C to 1400°C for 7 to 9 hours to produce "GOS" powder (S202). The flux components and impurities contained in the "GOS" powder are then removed by washing with hydrochloric acid and warm water (S203).

[0116] Next, the GOS powder is placed in a stainless steel can and pressed to obtain a molded body made of the GOS powder (S204). The SUS can containing the molded body is then evacuated and sealed. The SUS can is then subjected to a hot isostatic pressing (HIP) process in a HIP device, i.e., hot isostatic pressing, to reduce voids within the molded body (S205). During the HIP process, a heat treatment is performed at a temperature of, for example, 1300°C to 1600°C. This results in a sintered body (S206). The resulting sintered body is processed into a rectangular substrate to produce a GOS ceramic. In this way, a scintillator made of GOS ceramic can be formed.

[0117] Next, the scintillator substrate is diced to form multiple grooves, and then multiple other grooves are formed perpendicular to the multiple grooves. As a result, the area surrounded by the multiple grooves becomes a convex cell portion. In other words, the scintillator substrate is processed to have a flat substrate portion and multiple cell portions arranged on one surface of the substrate portion.

[0118] This processing is called "grooving" (S207).

[0119] Next, the inverted scintillator substrate is fixed to the upper surface of a supporting base substrate (a UV-transparent glass substrate) via a UV-peelable double-sided adhesive sheet. At this time, the end faces of each convex cell portion are fixed to the upper surface of the base substrate via the adhesive sheet. After that, the substrate portion is removed by cutting using a cutting machine. As a result, the multiple cell portions become multiple cells fixed to the upper surface of the base substrate via the adhesive sheet (S208).

[0120] Next, a reflective material is applied to cover the cells (S209). The reflective material may be, for example, a reflective material containing polyolefin containing titanium oxide.

[0121] After applying the reflective material, the adhesive sheet is peeled off by irradiating it with UV (ultraviolet) light. As a result, the base substrate and adhesive sheet can be removed. This results in a resin-cured substrate in which multiple cells are connected via the reflective material. Both sides of the resin-cured substrate are ground (S210). Before grinding begins, the resin-cured substrate is in the following state: On the side facing the adhesive sheet, the end faces of the multiple cells are almost exposed. On the other hand, on the side covered with the reflective material, the end faces of the multiple cells are not exposed. After grinding begins, the resin-cured substrate is in the following state: On the side facing the adhesive sheet, the end faces of the multiple cells are ground until they are aligned on a single plane (these end faces correspond to the light-emitting surface). On the other hand, on the side covered with the reflective material, the end faces of the multiple cells are ground until they are exposed and aligned on another single plane. These grinding steps make the heights of the multiple cells uniform.

[0122] Next, a new reflective material is applied to the side that was originally covered with the reflective material, thereby covering the multiple cells with the reflective material (S211). After that, only the side that was coated in S211 is ground to make the thickness of the reflective material uniform (S212). That is, the top surface of the reflective layer made of the reflective material is flattened. After cutting off unnecessary parts of the scintillator structure (S213), scintillator structures that have passed inspection are shipped (S214).

[0123] For example, the technical concept of the embodiments is an array (matrix) scintillator structure using n × m cells, where n and m are any natural numbers. The technical concept of the embodiments can also be applied to a line-shaped scintillator structure using 1 × n cells.

[0124] As described above, the scintillator structure according to the modified example can be manufactured using the first manufacturing method. The scintillator structure manufactured using the first manufacturing method suppresses the decrease in reflectance caused by the coloring of the resin in the reflective layer. In other words, light reflected by the reflective particles via the resin in the reflective layer is more likely to reach the light receiving element.

[0125] <<<<Second Manufacturing Method (Integrated Coating)>>> FIG. 10 is a flowchart illustrating the flow of the second manufacturing method.

[0126] In FIG. 10, the flow from S301 "powder mixing" to S310 "double-sided grinding" is the same as the flow from S201 "powder mixing" to S210 "double-sided grinding" in FIG.

[0127] However, the "grinding of both sides" in S310 of Fig. 10 differs from the "grinding of both sides" in S210 of Fig. 9 in that it is necessary to avoid exposing the cells on the side covered with the reflective material during grinding. In S310, the reflective material remaining after grinding is stopped becomes the reflective layer.

[0128] 10 also differs from FIG. 9 in that "grinding both sides" in S310 is followed by "cutting off unnecessary parts" in S311 and "inspection and shipping" in S312. FIG. 10 does not include the steps corresponding to "applying reflective material" in S211 and "grinding only the coated side" in S212 in FIG. 9. Therefore, in the second manufacturing method shown in FIG. 10, the reflective material needs to be applied only once. As a result, the second manufacturing method can shorten the number of processes compared to the first manufacturing method.

[0129] As described above, the scintillator structure according to the modified example can be manufactured using the second manufacturing method. The scintillator structure manufactured using the second manufacturing method suppresses the decrease in reflectance caused by the coloring of the resin in the reflective layer. In other words, light reflected by the reflective particles via the resin in the reflective layer is more likely to reach the light receiving element.

[0130] <<<<Third Manufacturing Method ("Singulation Process")>>> FIG. 11 is a flowchart illustrating the flow of the third manufacturing method.

[0131] The flow of the manufacturing process shown in FIG. 11 is similar to the flow shown in FIG.

[0132] However, there are two differences between the two.

[0133] The first difference is that the steps related to the production of "resin GOS" are replaced with steps related to the production of "GOS" ceramic. Specifically, the process flow of "resin dripping" in S104, "resin curing" in S105, and "resin removal" in S106 in Fig. 3 is replaced with the process flow of "molding" in S404, "HIP treatment" in S405, and "sintering" in S406 in Fig. 11.

[0134] The second difference is that the step of "applying reflective material" in S109 in FIG. 3 is replaced with "applying reflective material" in S409 and "grinding both sides" in S410 in FIG. 11. However, in "grinding both sides" in S410 in FIG. 11, the side where the reflective material is applied is ground so as not to expose the cells. As a result, even in the third manufacturing method, the application of reflective material only needs to be done once. As a result, the third manufacturing method can shorten the process compared to the first manufacturing method.

[0135] <<<<When using "YGAG" ceramic or "GGAG" ceramic>>> When using "YGAG" ceramic or "GGAG" ceramic as the scintillator instead of "GOS" ceramic, the flow from starting from raw material powder to forming the scintillator in the explanations of Figures 9 to 11 is replaced with the method shown below.

[0136] First, a predetermined amount of raw material powder is weighed and mixed (e.g., corresponding to S201). Then, the raw material is pulverized using a pulverizer. Note that the step corresponding to "firing" in S202 and the step corresponding to "cleaning" in S203 are omitted.

[0137] Next, the obtained pulverized powder is placed in a mold of a molding machine and pressed. This produces a compact for YGAG (e.g., corresponding to S204). The compact is then introduced into a CIP machine and subjected to CIP (Cold Isostatic Pressing) processing, i.e., cold isostatic pressing. This reduces air bubbles (voids) within the compact (e.g., corresponding to S205).

[0138] The compact is then introduced into a sintering furnace, where the oxygen atmosphere and temperature are controlled. This converts the compact into a sintered body through heat treatment, for example, at temperatures of 1100°C to 1300°C (e.g., corresponding to S206). The resulting sintered body is processed into a rectangular substrate, resulting in a "YGAG" ceramic or "GGAG" ceramic. As a result, a scintillator made of "YGAG" ceramic or "GGAG" ceramic can be formed.

[0139] As described above, the third manufacturing method can be used to manufacture the scintillator structure of the modified example. The scintillator structure manufactured using the third manufacturing method suppresses the decrease in reflectance caused by the coloring of the resin in the reflective layer. In other words, light reflected by the reflective particles via the resin in the reflective layer is more likely to reach the light receiving element.

[0140] The invention made by the inventor has been specifically described above based on the embodiments thereof, but it goes without saying that the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the invention.

[0141] REFERENCE SIGNS LIST 10 Scintillator structure 10A Scintillator structure 11 Scintillator 11a Phosphor 11b Resin 11c Phosphor 11s Side surface 11u Top surface 11w Bottom surface 12 Reflective layer 12a Reflective particles 12b Resin 12c Reflective particles 12s Side surface 12u Top surface 12w Bottom surface 20 Light receiving element 100 X-ray detector 200A X-ray detector 200B X-ray detector 200C X-ray detector CL Cell FR Outer frame WF Substrate

Claims

1. A scintillator structure comprising: a plurality of cells; and a reflective layer covering the plurality of cells, wherein the reflective layer contains a resin and reflective particles, and the resin is a polyolefin having no double bonds.

2. A scintillator structure according to claim 1, wherein the resin is at least one resin selected from the group consisting of polymethylpentene, polyethylene, and polypropylene.

3. A scintillator structure comprising: a plurality of cells; and a reflective layer covering the plurality of cells, wherein the reflective layer contains a resin and reflective particles, and the resin has a decrease in total light transmittance for light having a wavelength of 542 nm of 1% or less after being irradiated with X-rays at a dose of 80 kGy.

4. A scintillator structure according to claim 3, wherein the resin exhibits a decrease in total light transmittance of 1% or less for light having a wavelength of 542 nm after irradiation with X-rays at a dose of 100 kGy.

5. A scintillator structure according to any one of claims 1 to 4, wherein each of the plurality of cells contains a phosphor and the resin.

6. A scintillator structure according to any one of claims 1 to 4, wherein each of the plurality of cells contains a phosphor.

7. An X-ray detector comprising: a scintillator structure according to any one of claims 1 to 4; and a light-receiving element that generates a current from light generated in the scintillator structure.

8. An X-ray detector comprising: a scintillator structure according to claim 5; and a light-receiving element that generates a current from light generated in the scintillator structure.

9. An X-ray detector comprising: a scintillator structure according to claim 6; and a light-receiving element that generates a current from light generated in the scintillator structure.

10. An X-ray inspection apparatus comprising: an X-ray generator that generates X-rays; and the X-ray detector according to claim 7.

11. An X-ray inspection apparatus comprising: an X-ray generator that generates X-rays; and the X-ray detector according to claim 8.

12. An X-ray inspection apparatus comprising: an X-ray generator that generates X-rays; and the X-ray detector according to claim 9.

Images