Scintillator Structure and Manufacturing Method

Abstract

The technical problem to be solved by this invention is to reduce manufacturing costs and suppress the decrease in luminous output, or to reduce manufacturing costs and suppress the deterioration of afterglow characteristics. The solution is as follows: the scintillator structure comprises multiple units and a reflective material covering the multiple units. Each unit contains resin and a phosphor. The phosphor contains gadolinium oxysulfate, which contains terbium and cerium. The density of each unit is 4.4 g / cm³. 3 Above and below 5.0 g / cm 3 The thickness of each unit in the multiple units is between 0.5 mm and 1.8 mm. Alternatively, gadolinium oxysulfide contains praseodymium and cerium, and the density of each unit in the multiple units is 4.4 g / cm³. 3 Above 5.0g / cm 3 The thickness of each element in the multiple elements is between 0.3mm and 2.5mm.

Description

[0001] This case is filed on the date of application. July 2, 2021 Application number is 202110751880.6 The invention is named scintillation Structure and its manufacturing method The application for a divisional case. Technical Field

[0002] This invention relates to scintillator structures and methods for manufacturing the same, for example, to techniques applicable to scintillator structures having multiple units respectively containing resin and phosphor, and methods for manufacturing the same. Background Technology

[0003] Japanese Patent Application Publication No. 63-100391 (Patent Document 1) discloses a technology involving a phosphor molded body that mixes powder phosphor and epoxy resin.

[0004] Japanese Patent Application Publication No. 2-17489 (Patent Document 2) discloses a technique relating to a phosphor for use in a radiation detector.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 63-100391

[0008] Patent Document 2: Japanese Patent Application Publication No. 2-17489 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] A scintillator is a substance that absorbs the energy of radiation, such as X-rays and gamma rays, and produces visible light when irradiated. This scintillator is commercialized as a scintillator structure comprising a scintillator and reflective materials. X-ray detectors, which combine the scintillator structure with photoelectric conversion elements such as photodiodes, are used in medical equipment such as X-ray CT scanners, analytical equipment, non-destructive testing devices that utilize radiation, and radiation leak detection devices.

[0011] For example, the scintillator uses ceramics made of gadolinium oxysulfate (Gd₂O₂S). In this specification, gadolinium oxysulfate is referred to as "GOS". It should be noted that, strictly speaking, gadolinium oxysulfate itself emits almost no light; it emits light by incorporating praseodymium, terbium, etc. Therefore, in this specification, the term "GOS" implicitly refers to a substance (phosphor) that emits light by incorporating praseodymium, terbium, etc., within gadolinium oxysulfate itself. However, when it is necessary to explicitly state that gadolinium oxysulfate itself contains praseodymium, terbium, etc., it is sometimes described as "GOS containing praseodymium" or "GOS containing terbium".

[0012] Furthermore, when the scintillator is composed solely of "GOS," the "GOS" is made of ceramic. On the other hand, as described later, a technique was also investigated in which the scintillator is composed of a mixture of "GOS" and resin, in which case the "GOS" is made of powder. Therefore, in this specification, when it is not necessary to specifically specify ceramic and powder, it is sometimes simply referred to as "GOS." In contrast, when it is necessary to specify ceramic, it is called "GOS" ceramic. On the other hand, when it is necessary to specify powder, it is called "GOS" powder.

[0013] Compared to cadmium tungstate (CdWO4), "GOS" has the advantage of higher visible light emission output, but its manufacturing cost is higher.

[0014] Therefore, in order to reduce the manufacturing cost of scintillator structures, a mixture of "GOS" powder and resin was studied as a scintillator.

[0015] However, the inventors have recently discovered that when using a mixture of "GOS" powder and resin, there is still room for improvement from the viewpoint of the adhesion between the scintillator and the reflective material. Therefore, when using a mixture of "GOS" powder and resin as a scintillator, it is desirable to ensure the adhesion between the scintillator and the reflective material.

[0016] Technical solutions for solving technical problems

[0017] In one embodiment, the scintillator structure includes multiple cells and a reflective material covering the cells. Each cell contains a resin and a phosphor, the phosphor containing gadolinium oxysulfate. Furthermore, the interfacial tensile strength between each cell and the reflective material is 900 gf or higher.

[0018] Invention Effects

[0019] According to one implementation, the tightness of the scintillator and the reflective material can be ensured. Attached Figure Description

[0020] Figure 1 A diagram illustrating an X-ray detector.

[0021] Figure 2 A graph illustrating one factor contributing to the reduced light output in "resin GOS".

[0022] Figure 3 A graph showing the relationship between cell thickness and light output.

[0023] Figure 4 A graph showing the relationship between the density of the cell and its luminous output.

[0024] Figure 5A chart to represent the afterglow characteristics of "CWO".

[0025] Figure 6 A chart illustrating the afterglow characteristics of "GOS No. 3 resin".

[0026] Figure 7 A chart illustrating the afterglow characteristics of "GOS No. 1 resin".

[0027] Figure 8 A flowchart illustrating the manufacturing process of a scintillator structure.

[0028] Figure 9 A diagram illustrating the process from the cutting process to the reflective material coating process.

[0029] Figure 10 A graph was created to show the results of evaluating the wettability of epoxy resin by comparing the contact angles when epoxy resin was dropped onto the surface of "resin GOS" after various surface treatments.

[0030] Figure 11 The diagram illustrates how impregnation with titanium dioxide solution can improve wettability.

[0031] Figure 12 In the diagram, (a) is a cross-sectional view schematically showing the preparation process of the sample evaluated in the flexural test, and (b) is a top view schematically showing the preparation process of the sample evaluated in the flexural test.

[0032] Figure 13 In the diagram, (a) is a cross-sectional view showing the flexural test, and (b) is a top view showing the flexural test.

[0033] Figure 14 In the table, (a) shows the conditions for surface treatment performed on the scintillator structure before the sample is formed, and (b) shows the fracture strength measured by performing flexural tests on the samples corresponding to "condition 1" to "condition 8" respectively.

[0034] Symbol Explanation

[0035] 10: Scintillator structure; 10A: Scintillator structure; 11: Scintillator; 11a: Phosphor; 11b: Resin; 20: Light-receiving element; 30: Processed modified layer; 100: X-ray detector; CL: Unit; FR: Outer frame; NL: Indenter; SP: Sample; WF substrate. Detailed Implementation

[0036] In all the figures used to illustrate the embodiments, the same symbols are generally used to label the same parts, and repeated descriptions are omitted. It should be noted that, for ease of understanding of the figures, even top views are sometimes marked with shading.

[0037] <Overview of X-ray detectors>

[0038] Figure 1 A diagram illustrating an X-ray detector.

[0039] exist Figure 1 In this X-ray detector 100, there is a scintillator structure 10 and a light-receiving element 20. The scintillator structure 10 is composed of a scintillator 11 that generates visible light from X-rays incident on the X-ray detector 100 and a reflective material 12 covering the scintillator 11. On the other hand, the light-receiving element 20 has the function of generating a current from the visible light generated by the scintillator 11, and is, for example, composed of a photoelectric conversion element represented by a photodiode.

[0040] The scintillator 11 has the function of absorbing X-rays to generate visible light, and is composed of a phosphor 11a and a resin 11b. Here, in this specification, the material obtained by mixing the "GOS" powder constituting the phosphor 11a and the resin 11b is sometimes referred to as "resin GOS". That is, the scintillator 11 in this embodiment is composed of "resin GOS". The phosphor 11a is gadolinium sulfide containing praseodymium, terbium, etc., and the resin 11b is, for example, epoxy resin. In addition, the reflective material 12 is composed of epoxy resin containing titanium oxide.

[0041] The X-ray detector thus constructed operates as shown below.

[0042] That is, when X-rays enter the scintillator 11 of the scintillator structure 10, electrons in the phosphor 11a constituting the scintillator 11 receive the energy of the X-rays and transition from the ground state to the excited state. Afterwards, the excited-state electrons transition back to the ground state. At this point, visible light equivalent to the energy difference between the excited state and the ground state is emitted. Through this mechanism, the scintillator 11 absorbs X-rays and produces visible light.

[0043] Subsequently, a portion of the visible light generated by the scintillator 11 is directly incident into the light-receiving element 20, while another portion of the visible light generated by the scintillator 11 is repeatedly reflected by the reflective material 12 covering the scintillator 11 and focused by the light-receiving element 20.

[0044] Next, when visible light is incident on a light-receiving element 20, such as a photodiode, the energy of the visible light excites electrons in the semiconductor material constituting the photodiode from the valence band to the conduction band. The current generated by these excited electrons flows through the photodiode. Subsequently, an X-ray image is obtained based on the current output from the photodiode. Thus, an X-ray image can be obtained using an X-ray detector 100.

[0045] <Reasons for using "GOS resin">

[0046] As described above, in this embodiment, "resin GOS" is used as the scintillator 11. The reason for this is explained below.

[0047] For example, cadmium tungstate (hereinafter referred to as "CWO") is used as the scintillator 11 constituting the scintillator structure 10, but this "CWO" contains cadmium, a substance restricted by the RoHS Directive / REACH. Therefore, "GOS" ceramic is used instead of the cadmium-containing "CWO" as the scintillator 11. Compared with "CWO", "GOS" ceramic has the advantage of high visible light emission output, but has the disadvantage of high manufacturing cost.

[0048] Therefore, from the perspective of reducing manufacturing costs, as the scintillator 11, it has been studied to use "resin GOS," which is obtained by mixing resin containing epoxy resin or the like with "GOS" powder, instead of "GOS" ceramic. That is, in order to suppress the increase in manufacturing costs caused by "GOS" ceramic, there is a trend towards using "resin GOS," which is cheaper than "GOS" ceramic, as the scintillator 11.

[0049] However, compared with "GOS" ceramic, "resin GOS" has a lower light output, so it is desirable to ensure light output when "resin GOS" is used as scintillator 11.

[0050] Factors that reduce light output

[0051] First, in "Resin GOS", the reason for the decrease in light output will be explained.

[0052] <<First Reason>>

[0053] "Resin GOS" is composed of a mixture of resin, such as epoxy resin, and "GOS" powder. Both epoxy resin and "GOS" powder are transparent to visible light. However, epoxy resin has higher transparency than "GOS". Therefore, "Resin GOS" has higher transparency than "GOS" ceramic. Considering this, the luminous output of the scintillator 11, which was originally thought to use "Resin GOS", should be higher than the luminous output of the scintillator 11 using "GOS" ceramic.

[0054] However, in practice, the light output of the scintillator 11 using "resin GOS" is lower than that of the scintillator 11 using "GOS" ceramic.

[0055] This is believed to be due to the following reason: In the "resin GOS", "GOS" powder is used, resulting in the total surface area of ​​the "GOS" powder constituting the "resin GOS" being greater than the total surface area of ​​the "GOS" ceramic. That is, in the "resin GOS", a large amount of "GOS" powder exists within the epoxy resin. Therefore, light emitted from the "GOS" powder, for example, after being emitted from the "GOS" powder into the epoxy resin, undergoes multiple scattering at the surface of the abundant "GOS" powder, with light absorption occurring at each scattering point. As a result, it is believed that light absorption is greater in the "resin GOS" than in the "GOS" ceramic, and therefore, the luminous output of the scintillator 11 using "resin GOS" is lower than that of the scintillator 11 using "GOS" ceramic. This is presumed to be the first reason for the reduced luminous output in the "resin GOS".

[0056] <<Second Reason>>

[0057] For example, such as Figure 2 As shown, the scintillator structure 10 is composed of a cuboid-shaped scintillator 11 and a reflective material 12 covering the scintillator 11. Here, the cuboid-shaped scintillator 11 is formed through machining processes such as cutting and grinding, thus a machined surface is formed on the cuboid-shaped surface. That is, a "machined surface" refers to a surface that has been mechanically machined. Specifically, a "machined surface" includes a surface that has been ground using a grinding stone when thickening a workpiece, or a surface after the workpiece has been cut using a cutting tool for cutting purposes. For example, in a scintillator 11 using "resin GOS", a "machined surface" is defined as a surface that mixes surfaces with exposed resin and surfaces where "GOS" powder has broken. For example, in... Figure 1 The dashed lines schematically represent the case where the interface between the scintillator 11 and the reflective material 12 is a "processed surface" in the scintillator 11 using "resin GOS". In this case, the "processed surface" contains areas where the resin 11b is cut and areas where the phosphor 11a ("GOS" powder) is broken. It should be noted that in... Figure 1 The dashed lines shown are drawn to easily and clearly illustrate the composition of the "processed surface" and do not indicate that the scintillator 11 is contracted. The size of the scintillator 11 enclosed by the dashed lines can be the size enclosed by the solid lines.

[0058] The processed surface will become a processing modification layer 30 due to mechanical damage caused by the processing steps. A "processing modification layer" is defined as a layer that, due to mechanical damage caused by the machining process, ages its light reflection properties and becomes more prone to absorbing light compared to before machining. For example, a specific example of a "processing modification layer" is the light-absorbing layer generated by the desulfurization of sulfur components on the surface of "GOS" powder.

[0059] In this modified processing layer 30, visible light generated by the scintillator 11 is easily absorbed. That is, due to the presence of the modified processing layer 30 in the scintillator 11, a portion of the generated visible light is absorbed, resulting in a decrease in light emission output. In other words, the formation of the modified processing layer 30 on the surface of the scintillator 11 is a factor contributing to the decrease in light emission output from the scintillator structure 10.

[0060] In particular, in recent years, such as Figure 2 As shown, from the viewpoint of improving the resolution of X-ray images, the scintillator 11 is divided into multiple units CL (an array of scintillators 11) in conjunction with each of the multiple photodiodes. Furthermore, a reflective material 12 is provided to cover the multiple units CL. Specifically, the upper surface and four side surfaces of the unit CL are covered by the reflective material 12. On the other hand, the lower surface of the unit CL needs to contact the photodiodes, and therefore is not covered by the reflective material 12.

[0061] When the scintillator 11 is divided into multiple units CL, a processing modification layer 30 is formed on the surface of each unit of the multiple units CL. Therefore, the area occupied by the processing modification layer 30 in the scintillator structure 10A becomes larger. As a result, in the multi-unit type scintillator structure 10A, the reduction in light output caused by the processing modification layer 30 becomes larger.

[0062] In this embodiment, the scintillator structure is based on a multi-unit scintillator structure 10A that can improve the resolution of X-ray images. Therefore, it is assumed that the decrease in light output caused by the processing of the modified layer 30 will be greater, thus it is important to improve the light output in order to maintain it.

[0063] Here, regardless of whether "GOS" ceramic or "resin GOS" is used as the scintillator 11, the presence of the processing modification layer 30 on the surface of the scintillator 11 remains unchanged. Therefore, it is believed that a decrease in luminous output due to the processing modification layer 30 will occur when the scintillator 11 is made of either "GOS" ceramic or "resin GOS".

[0064] Regarding this, according to the inventors' research, a new discovery has been made: compared to the case where the scintillator 11 is made of "GOS" ceramic, the reduction in light output due to the processing of the modified layer 30 is greater in the case where the scintillator 11 is made of "resin GOS".

[0065] The reasons are explained below. For example, after the "GOS" ceramic is monolithically formed into unit CL, it can undergo heat treatment. Moreover, the heat treatment has the function of restoring the processing modification layer 30 formed due to mechanical damage. Therefore, when the scintillator 11 is made of "GOS" ceramic, after monolithically forming unit CL, the processing modification layer 30 formed on the surface of unit CL can be restored by performing heat treatment. Thus, when the scintillator 11 is made of "GOS" ceramic, the processing modification layer 30 can be reduced by heat treatment, thereby suppressing the reduction in light output caused by the processing modification layer 30.

[0066] In contrast, "resin GOS" is not ceramic, but rather a material made by curing "GOS" powder with resin, making it difficult to heat-treat. As a result, when the scintillator 11 is composed of "resin GOS", the effect of restoring the processed modification layer 30 through heat treatment cannot be achieved, thus increasing the reduction in luminous output caused by the processed modification layer 30. In other words, "resin GOS" is different from "GOS" ceramic; it is difficult to heat-treat and therefore the processed modification layer 30 cannot be restored. This is the second reason for the reduction in luminous output from the scintillator structure 10A.

[0067] Based on the above reasons, when the scintillator 11 is made of "resin GOS", the light output is further reduced compared to "GOS ceramic" due to the combined effect of the first reason caused by the use of "GOS" powder and the second reason that the recovery of the processing modification layer 30 becomes difficult.

[0068] Therefore, when using "resin GOS" as the scintillator 11, it is inherently unavoidable that the light output will be lower compared to "GOS" ceramic. However, the inventors have made a new discovery: when using "resin GOS" as the scintillator 11, the light output changes depending on the thickness and density of the unit CL made of "resin GOS". That is, according to the inventors' new insight, it can be considered that by specifying the thickness and density of the unit CL, even "resin GOS" can ensure a certain level of light output.

[0069] Therefore, the thickness and density dependence of the light output will be explained below.

[0070] <Thickness dependence of light output>

[0071] Figure 3 A graph showing the relationship between cell thickness and light output.

[0072] exist Figure 3 In the diagram, the horizontal axis represents the thickness of the unit, and the vertical axis represents the light output.

[0073] First, "GOS 1" refers to a "GOS" containing praseodymium (Pr) and cerium (Ce). On the other hand, although in Figure 3 It is not shown in the text, but “2nd GOS” refers to a “GOS” with added terbium (Tb) and cerium (Ce).

[0074] Here, focusing on the light output of "1st GOS" and "2nd GOS", the light output of "2nd GOS" is higher than that of "1st GOS". In other words, the light output of "1st GOS" is lower than that of "2nd GOS". It should be noted that... Figure 3 The luminous output shown on the vertical axis is expressed as a percentage, with the luminous output of the 1.3mm thick "1st GOS" as 100%.

[0075] "Second Resin GOS" is a mixture of "GOS" powder and epoxy resin, which is composed of "Second GOS".

[0076] Both "3rd Resin GOS" and "4th Resin GOS" are mixtures of "GOS" powder composed of "1st GOS" and epoxy resin. The difference between "3rd Resin GOS" and "4th Resin GOS" lies in their density.

[0077] exist Figure 3 In the context of the curve for the "1st GOS," it can be observed that the light output of the "1st GOS" is almost independent of the cell thickness. On the other hand, in... Figure 3 In the study, when looking at the curves of "2nd Resin GOS" to "4th Resin GOS", it can be seen that the light output of "2nd Resin GOS" to "4th Resin GOS" depends on the thickness of the cell.

[0078] The following is a qualitative explanation of the thickness dependence of the luminescence output of each of the "Second Resin GOS" to "Fourth Resin GOS". First, within the range of thinness, the luminescence output increases with increasing thickness. This can be understood as the amount of "resin GOS" that helps absorb incident X-rays and generate visible light increases with increasing thickness within the range of thinness. Furthermore, it can be understood that when the thickness reaches a certain level, the amount of "resin GOS" that helps absorb incident X-rays and generate visible light reaches saturation, and as the thickness increases, light transmittance decreases, and the first and second reasons mentioned above become significant, thus resulting in a decrease in luminescence output with increasing thickness.

[0079] <Density dependence of light output>

[0080] Next, the density dependence of the light output will be explained.

[0081] Figure 4 It is a graph showing the relationship between the density of the cell itself and the light output.

[0082] exist Figure 4 In the diagram, the horizontal axis represents the density of the scintillators constituting the unit, and the vertical axis represents the light output. It should be noted that the light output on the vertical axis is shown as a percentage, with the light output of the "1st GOS" with a thickness of 1.5mm taken as 100%.

[0083] Here, "density" refers to the overall density of "GOS resin". In particular, compared to epoxy resin, "GOS" powder has a higher density, thus the following relationship can be established.

[0084] In other words, a low density of "GOS resin" means that there is a small amount of "GOS" powder and a large amount of epoxy resin. Conversely, a high density of "GOS resin" means that there is a large amount of "GOS" powder and a small amount of epoxy resin.

[0085] exist Figure 4 In this example, the density of "Resin 1 GOS" (comparative example) is 5.0 g / cm³. 3 On the other hand, the density of "Second Resin GOS" is 4.4 g / cm³. 3 That is, the density of "second resin GOS" is lower than the density of "first resin GOS". In other words, the density of "first resin GOS" is higher than the density of "second resin GOS".

[0086] like Figure 4 As shown, the luminous output increases with decreasing density. This is believed to be because: lower density means that the amount of highly transparent epoxy resin is relatively larger compared to the "GOS" powder, thus reducing visible light absorption. As a result, lower density leads to higher luminous output. In other words, higher density means that the amount of "GOS" powder is greater than the amount of highly transparent epoxy resin, thus increasing visible light absorption within the "GOS" powder. As a result, higher density leads to lower luminous output.

[0087] Below, the following improvements will be explained: by using "resin GOS" to construct the scintillator 11, compared to using "GOS" ceramic as the scintillator 11, manufacturing costs can be reduced, and based on the aforementioned thickness dependence of light output (see...). Figure 3 ) and density dependence of luminous output ( Figure 4 This improves the performance of the scintillator structure 10A. In other words, it explains the improvements made to enhance the cost-effectiveness of the scintillator structure 10A.

[0088] Specifically, as improvements to enhance the performance of the scintillator structure 10A, the first improvement from the viewpoint of ensuring light output and the second improvement from the viewpoint of ensuring afterglow characteristics will be explained.

[0089] <From the perspective of ensuring light output (first improvement point)>

[0090] like Figure 3 As shown, regarding the thickness dependence of the luminescence output of the "second resin GOS", for example, when the thickness is between 0.5 mm and 1.8 mm, the luminescence output of the "second resin GOS" is higher than that of the "first GOS". In other words, although the luminescence output of the "second resin GOS" formed by mixing epoxy resin into a "GOS" powder composed of a "second GOS" with a higher luminescence output than the "first GOS" is lower than that of the "first GOS", by setting the unit thickness to between 0.5 mm and 1.8 mm, the luminescence output can be higher than that of the "first GOS". In other words, by setting the thickness of the unit composed of the "second resin GOS" to between 0.5 mm and 1.8 mm, the luminescence output of the "second resin GOS" can reach or exceed that of the "first GOS".

[0091] Next, as Figure 4 As shown, decreasing the density of the cell itself can improve the luminous output. Specifically, by reducing the density to 4.4 g / cm³... 3 Above and below 5.0 g / cm 3 Within the range, when the light output of the "1st GOS" with a thickness of 1.5mm is set to "100%", a light output of "more than 125%" can be obtained.

[0092] From the above, it can be seen that, as the scintillator 11, a "resin GOS" is used, which is made by mixing epoxy resin into "GOS" powder composed of "second GOS". Under this premise, the density of the unit itself is set to 4.4 g / cm³ by making the thickness of the unit range from 0.5 mm to 1.8 mm. 3 Above and below 5.0 g / cm 3 This range allows for a light output of "1st GOS" or higher, even with "resin GOS". By using "resin GOS" that reduces manufacturing costs and setting the thickness and density ranges as described above, a light output of "1st GOS" or higher can be achieved. Specifically, by using "resin GOS" that reduces manufacturing costs and ensuring such light output, the cell thickness is set to a range of 0.5mm to 1.8mm, and the cell density is set to 4.4g / cm³. 3 Above and below 5.0 g / cm 3 This can be achieved within a certain range.

[0093] <The viewpoint of ensuring afterglow characteristics (2nd improvement point)>

[0094] The first improvement mentioned above is an improvement from the perspective of ensuring light output. In contrast, the second improvement described below is an improvement from the perspective of ensuring afterglow characteristics. That is, the performance of the scintillator structure 10A requires not only a large light output but also good afterglow characteristics. Therefore, the afterglow characteristics will be explained first.

[0095] The scintillator 11, constituting the scintillator structure 10A, is a material that produces visible light when irradiated by X-rays. The mechanism by which the scintillator 11 produces visible light when irradiated by X-rays is as follows: When X-rays irradiate the scintillator 11, electrons within the scintillator 11 receive energy from the X-rays and transition from a low-energy ground state to a high-energy excited state. Then, the electrons in the excited state transition back to the low-energy ground state. At this time, most of the excited electrons immediately transition to the ground state. On the other hand, some of the excited electrons transition back to the ground state after a certain period of time. The visible light produced by the transitions from the excited state to the ground state that occur after this certain period of time is called afterglow. In other words, afterglow refers to the visible light produced when the transition from the excited state to the ground state occurs a certain period of time after the X-ray irradiation. Moreover, a large afterglow means that even after X-ray irradiation, the intensity of the visible light produced until a certain period of time is relatively large. In this situation, afterglow from the previous X-ray irradiation will remain until the next X-ray exposure, and this residual afterglow will become noise. Therefore, low afterglow is desirable. In other words, good afterglow characteristics mean low afterglow.

[0096] Here, the afterglow characteristics vary depending on the type of scintillator 11. For example, Figure 5 A chart to represent the afterglow characteristics of "CWO". Figure 6 A graph illustrating the afterglow characteristics of "GOS No. 3 resin". Additionally, Figure 7 A chart illustrating the afterglow characteristics of "GOS No. 1 resin".

[0097] exist Figures 5-7 In the diagram, the vertical axis represents the intensity of the afterglow, and the horizontal axis represents time. Figures 5-7 In this context, the intensity of the afterglow increases over time, indicating a worse afterglow characteristic. In other words, in... Figures 5-7 The value in the middle indicates that the intensity of the afterglow is lower after a certain period of time, and the better the afterglow characteristics are.

[0098] Looking at it from this perspective again Figures 5-7 At that time, it can be known Figure 5 Afterglow characteristics and Figure 6 Its afterglow characteristics are almost identical to those of a good afterglow characteristic, while Figure 7 Its afterglow characteristics are poor. In other words, Figure 5 The afterglow characteristics of the "CWO" shown are similar to Figure 6The afterglow characteristics of the "third resin GOS" shown are all good, while Figure 7 The "first resin GOS" shown has poor afterglow characteristics.

[0099] In other words, from the perspective of light output, when the above-mentioned improvement point 1 is achieved, there exists a region where the following relationship can hold: "2nd GOS" > "2nd Resin GOS" > "1st Resin GOS" > "1st GOS" > "4th Resin GOS" > "3rd Resin GOS" > "CWO".

[0100] In contrast, refer to Figures 5-7 From the perspective of afterglow characteristics, the following relationship holds: "CWO" ≈ "3rd Resin GOS" < "1st Resin GOS".

[0101] Therefore, considering, for example, "First Resin GOS", "Third Resin GOS" and "CWO", "First Resin GOS" is the most superior from the viewpoint of luminous output. In contrast, from the viewpoint of afterglow characteristics, "CWO" and "Third Resin GOS" are superior.

[0102] Therefore, in order to achieve "resin GOS" with excellent afterglow characteristics, "third resin GOS" and "fourth resin GOS" formed by mixing epoxy resin into "GOS" powder composed of "second GOS" are more preferred than "first resin GOS" and "second resin GOS" formed by mixing epoxy resin into "GOS" powder composed of "second GOS". However, as Figure 3 As shown, the light output of "3rd Resin GOS" and "4th Resin GOS" is lower than that of "2nd Resin GOS".

[0103] Therefore, it is hoped that "third resin GOS" and "fourth resin GOS" will be used to ensure afterglow characteristics while maximizing luminous output. Regarding this point, it is believed that... Figure 3 In this context, based on the premise of using "resin GOS" which is made by mixing epoxy resin into "GOS" powder composed of "first GOS", the thickness of the unit is made in the range of 0.3 mm to 2.5 mm, and from... Figure 4 By analogy, the density of the unit itself is 4.4 g / cm³. 3 Above 5.0g / cm 3While the luminous output is lower than that of the "2nd GOS", a luminous output of "CWO" or higher can be achieved within the following range. Thus, by using a "resin GOS" that reduces manufacturing costs and has good afterglow characteristics, and by setting the thickness and density ranges as described above, a luminous output of "CWO" or higher can be obtained. In other words, by using a "resin GOS" that reduces manufacturing costs and has good afterglow characteristics while ensuring good luminous output, it is possible to set the cell thickness to a range of 0.3 mm to 2.5 mm and set the cell density to 4.4 g / cm³. 3 Above 5.0g / cm 3 The following range shall be used to achieve this.

[0104] <Manufacturing Method of Scintillator Structure>

[0105] Next, the manufacturing method of the scintillator structure 10 will be described.

[0106] Figure 8 A flowchart illustrating the manufacturing process of a scintillator structure.

[0107] exist Figure 8 First, a specified amount of raw material powder and flux components are weighed and mixed (S101). This mixture is then filled into a crucible and fired in an atmospheric furnace at 1300°C–1400°C for 7–9 hours (S102), thereby generating "GOS" powder. Next, the flux components and impurities in the "GOS" powder are removed by washing with hydrochloric acid and warm water (S103). Then, epoxy resin is added dropwise to the "GOS" powder, impregnating it with epoxy resin (S104). After the epoxy resin is cured (S105), any epoxy resin not mixed with the "GOS" powder is removed (S106). Thus, a scintillator composed of "resin GOS" can be formed.

[0108] Next, the substrate on which the scintillator is formed is cut, thereby monolithizing the substrate into multiple units (S107). After the monolithized multiple units are rearranged (S108), a reflective material is coated on the multiple units in a manner that covers them (S109). Then, after cutting off the parts that are not needed as scintillator structure 10A (S110), the inspected scintillator structure 10A is shipped (S111).

[0109] Figure 9 This diagram schematically illustrates the process from the cutting process to the coating of reflective material.

[0110] like Figure 9As shown, a substrate WF, on which a scintillator made of "resin GOS" is formed, is cut, and the substrate WF is monolithically divided into multiple units CL. Then, the monolithically divided units CL are rearranged, for example, in a linear arrangement. Next, an outer frame FR is arranged to enclose the multiple units CL arranged in a linear arrangement. Then, a reflective material 12, for example, an epoxy resin containing titanium oxide, is coated to cover the multiple units CL disposed within the outer frame FR. Afterward, the outer frame FR is removed. This manufactures a scintillator structure 10A.

[0111] It should be noted that, in Figure 9 The example given is a linear scintillator structure 10A using 1×n units, but the technical concept in this embodiment is not limited to this. For example, it is also preferably applicable to an array-shaped (matrix-shaped) scintillator structure using n×n units.

[0112] <Characteristics in manufacturing process>

[0113] Next, the key features of the manufacturing process in this embodiment will be explained.

[0114] The characteristic of the manufacturing method in this embodiment is that after the substrate WF on which the scintillator 11 is formed is completely monolithized into multiple units CL by full cutting, the monolithized multiple units CL are rearranged, and then the reflective material 12 is coated to cover the rearranged multiple units CL to manufacture the scintillator structure 10A.

[0115] Therefore, according to this embodiment, the spacing between units can be freely adjusted.

[0116] For example, there is a technique where a substrate WF with a scintillator 11 is half-cut, a reflective material 12 is applied, and then the half-cut substrate WF is ground to separate adjacent cells CL. Using this technique, the spacing between adjacent cells CL can be determined by the cutting width of the half-cut, thus allowing for precise determination of the spacing between adjacent cells CL. Conversely, this technique does not allow for flexible modification of the spacing between cells CL.

[0117] Regarding this, for example, the needs of X-ray detector users vary. Some users require a high-density arrangement of photodiodes, which serve as light-receiving elements, to obtain high-resolution X-ray images, while others require a low-density arrangement of photodiodes to obtain X-ray images that, while not high-resolution, have a wide range. In the former case, it is required that the multiple units CL constituting the scintillator structure 10A also be arranged at a high density, corresponding to the high-density arrangement of photodiodes. In this case, the spacing between the unit CLs needs to be very small. For example, if the spacing between the unit CLs needs to be smaller than the cut width of a half-cut, the half-cut technique cannot meet this requirement. On the other hand, in the latter case, even if the spacing between the unit CLs needs to be larger than the width of a half-cut, the half-cut technique cannot meet this requirement. Thus, in the half-cut technique, since the spacing between the unit CLs is fixed to a constant value by the cut width of the half-cut, the spacing between the unit CLs cannot be freely adjusted according to the user's requirements.

[0118] In contrast, in this embodiment, instead of a half-cut, the substrate WF on which the scintillator 11 is formed is completely cut into multiple units CL, and then these multiple units CL are rearranged. Therefore, using this embodiment, the spacing between adjacent units CL can be freely set when rearranging the multiple units CL.

[0119] Therefore, according to this embodiment, the spacing between the units CL can be adjusted to be greater than or less than the cutting width, thus achieving the advantage that the scintillator structure 10A can be flexibly manufactured to meet the user's needs.

[0120] Furthermore, according to this embodiment, the following advantages can be obtained. That is, in the technique using partial cutting, the separation unit CL is finally cut by a grinding process.

[0121] In this respect, in this embodiment, multiple scintillator cells (CLs) are monolithically processed by full cutting. Therefore, the grinding process required to separate the multiple CLs in subsequent processes is eliminated. This means that the grinding process for separating the multiple CLs can be reduced. As a result, the manufacturing method of the scintillator structure 10A in this embodiment has the advantage of simplified manufacturing processes.

[0122] <The viewpoint of attempting to improve the tightness (3rd improvement point)>

[0123] For example, the scintillator structure 10A, which is manufactured as a finished product through the above manufacturing process, is subjected to a constant temperature and high humidity test to ensure its reliability.

[0124] Here, when conducting a constant temperature and humidity test on the scintillator structure 10A made of "resin GOS" in the scintillator 11, it was confirmed that the pass rate in the constant temperature and humidity test decreased. Regarding this, the inventors have newly discovered that the decrease in the adhesion between the scintillator 11 made of "resin GOS" and the reflective material 12 leads to the decrease in the pass rate in the constant temperature and humidity test. Therefore, in this embodiment, from the viewpoint of improving the reliability of the scintillator structure 10A, an improvement has been implemented to improve the adhesion between the scintillator 11 made of "resin GOS" and the reflective material 12. This improvement will be explained below.

[0125] <<New Insights>>

[0126] First, the new insights discovered by the inventors will be explained.

[0127] The inventors have discovered a new insight: when a surface treatment is applied to the surface of the "resin GOS" before coating the reflective material 12 onto the scintillator 11 made of "resin GOS", the type of surface treatment affects the adhesion strength at the interface between the "resin GOS" and the reflective material 12. Furthermore, the inventors speculate that the difference in adhesion strength at the interface between the "resin GOS" and the reflective material 12 is due to variations in the wettability of the "resin GOS" to the reflective material 12 caused by different types of surface treatments applied to the surface of the "resin GOS". Therefore, it is reasonable to assume that applying a surface treatment that improves the wettability of the reflective material 12 to the surface of the "resin GOS" can improve the adhesion strength at the interface between the "resin GOS" and the reflective material 12. In other words, it is reasonable to assume that forming a surface treatment layer on the surface of each of the multiple unit cells CL that contacts the reflective material 12 can improve the adhesion strength at the interface between the "resin GOS" and the reflective material 12. For example, it is believed that forming a surface treatment layer on at least the side and top surfaces of each unit in a multi-unit CL can improve the adhesion.

[0128] Therefore, the wettability of various surface treatments to epoxy resin was evaluated.

[0129] Figure 10 A graph was created to show the results of evaluating the wettability of epoxy resin by comparing the contact angles when epoxy resin was dropped onto the surface of "resin GOS" after various surface treatments.

[0130] exist Figure 10 Among various surface treatments, there are untreated, IPA treatment (isopropanol treatment), titanium dioxide immersion treatment, and pure water cleaning treatment.

[0131] like Figure 10As shown, the contact angle varies depending on the surface treatment. This indicates that different types of surface treatments can alter the wettability.

[0132] Moreover, from Figure 10 The results show that after impregnating the surface of "Resin GOS" with titanium dioxide solution, the contact angle when epoxy resin is dropped onto the surface of "Resin GOS" is minimized. This means that impregnation with titanium dioxide solution as a surface treatment can best improve the wettability of epoxy resin.

[0133] Therefore, it is speculated that when titanium dioxide impregnation treatment, which has the best wettability to epoxy resin, is applied, the interfacial adhesion between the "resin GOS" and the reflective material 12 can be increased. In other words, it can be considered that: Figure 11 As shown, when titanium oxide impregnation treatment is performed, titanium oxide is attached to the surface of the scintillator 11 made of "resin GOS", thereby improving wettability and increasing the bonding area between the scintillator 11 and the reflective material 12. As a result, the adhesion force at the interface between the scintillator 11 made of "resin GOS" and the reflective material 12 becomes higher.

[0134] As can be seen from the above, the improvement in enhancing the adhesion between the scintillator 11 made of "resin GOS" and the reflective material 12 lies in performing a surface treatment on the surface of the scintillator 11 to improve its wettability to the reflective material 12 before coating the reflective material 12 in a manner that coats the scintillator 11. Specifically, this improvement is achieved by impregnating the surface of the scintillator 11 with titanium dioxide solution before coating the reflective material 12 in a manner that coats the scintillator 11.

[0135] <<Verification of Effect>>

[0136] The following explains the results showing that, before coating the reflective material 12 with a scintillator 11 made of "resin GOS", the adhesion between the scintillator 11 and the reflective material 12 is increased by impregnating the surface of the scintillator 11 with titanium oxide solution.

[0137] The inventors believe that the bonding force at the interface between the scintillator 11 and the reflective material 12 can be quantitatively compared by measuring the fracture strength through a flexural strength test. This invention describes the evaluation results using the flexural strength test, which was used to evaluate the bonding force at the interface between the scintillator 11 and the reflective material 12. Specifically, in this embodiment, the bonding force was evaluated using a flexural strength test based on the three-point bending test specified in JISK 7171. For example, in the figure shown in JISK 7171, the load at which the sample fractured was measured under the conditions shown below.

[0138] Sample shape (length, thickness, width): 50mm × 6.2mm × 1.2mm

[0139] The front radius (R1) of the pressure head: 0.3mm

[0140] Radius of the support platform corner (R2): 0.3mm

[0141] The thickness (h) of the test piece (sample) is 6.2 mm.

[0142] Length (l) of the test piece (sample): 50 mm

[0143] Distance between pivots (L): 10mm

[0144] 1. Sample preparation

[0145] Figure 12 (a) is a schematic cross-sectional view showing the fabrication process of the sample being evaluated in the flexural strength test. Figure 12 (b) is a top view schematically showing the preparation process of the sample being evaluated in the flexural strength test.

[0146] like Figure 12 As shown in (a), a scintillator structure 10A is prepared by covering a plurality of arranged scintillators 11 with a reflective material 12. The upper surface of the scintillator structure 10A is ground, and as shown in (a). Figure 12 As shown in (b), the sample SP was fabricated by grinding the two side surfaces (long side) of the scintillator structure 10A.

[0147] Then, a constant temperature and high humidity test was conducted on the sample SP. This was done by immersing the sample in warm water at 80°C for 80 minutes. Afterwards, a flexural strength test was performed on the sample SP that had undergone the constant temperature and high humidity test.

[0148] 2. Flexural strength test

[0149] Figure 13 (a) is a cross-sectional view showing the flexural strength test. Figure 13 (b) is a top view showing the flexural strength test. For example... Figure 13 As shown in (a), the front end of the pressure head NL contacts the interface between the scintillator 11 and the reflective material, and as Figure 13 As shown in (b), the front end of the indenter NL is configured to be located at the center of the sample SP in the width direction.

[0150] In the flexural strength test, the indenter NL is pressed down on the sample SP from above, and the fracture strength of the sample SP when it breaks is measured. The higher the fracture strength, the stronger the adhesion between the scintillator 11 and the reflective material 12. In other words, the adhesion between the scintillator 11 and the reflective material 12 can be evaluated based on the fracture strength measured in the flexural strength test. The evaluation results are explained below.

[0151] It should be noted that the measuring apparatus used in the flexural strength test consists of, for example, a drive unit (FGS-50V-L: manufactured by SHIMPO) and a tension meter (FGC-5: manufactured by SHIMPO). Furthermore, three measurement points are used in the sample, and the breaking strength of the sample is evaluated by averaging the values ​​from these three measurement points.

[0152] 3. Evaluation Results

[0153] Figure 14 A graph representing the evaluation results of the flexural strength test.

[0154] Figure 14 Table (a) shows the surface treatment conditions performed on the scintillator structure 10A prior to the formation of sample SP. Figure 14 In (a), eight samples SP were fabricated by processing a scintillator structure 10A that underwent surface treatment under eight conditions. For example, "Condition 1" indicates a condition in which IPA treatment → titanium oxide immersion treatment → pure water rinsing was performed as a surface treatment, followed by coating with a reflective material. "Condition 2" indicates a condition in which the reflective material was coated without the above treatment as a surface treatment.

[0155] Figure 14 (b) is a graph showing the fracture strength determined by flexural tests performed on samples SP corresponding to conditions 1 through 8, respectively. Figure 14 As shown in (b), the fracture strength of sample SP, which underwent titanium dioxide immersion treatment as a surface treatment, increased. Specifically, in sample SP that underwent titanium dioxide immersion treatment, the fracture strength at the interface between scintillator 11 and reflective material 12 was 900 gf or higher.

[0156] The evaluation results demonstrate that by performing titanium dioxide immersion treatment on the surface of the scintillator 11 before coating the reflective material 12 with the scintillator 11 made of "resin GOS", the adhesion between the interface of the scintillator 11 and the reflective material 12 is increased.

[0157] It should be noted that, from the viewpoint of improving the adhesion of the interface between the scintillator 11 and the reflective material 12, the fracture strength of the interface is preferably 938 gf or more, and more preferably 1059 gf or more, and even more preferably 1182 gf or more.

[0158] The invention described above is based on its embodiments. However, the invention is not limited to the above embodiments, and it is self-evident that various changes can be made without departing from its spirit.

Claims

1. A scintillator structure, characterized in that: It includes multiple units and a reflective material covering the multiple units. Each of the plurality of units contains resin and phosphor. The phosphor contains gadolinium sulfide, which in turn contains terbium and cerium. The density of each of the plurality of units is 4.4 g / cm³. 3 Above and below 5.0 g / cm 3 , The thickness of each of the plurality of units is between 0.5 mm and 1.8 mm. The resin is epoxy resin. Each of the plurality of units is composed of a cuboid shape with a machined surface. Each of the plurality of units has a processing and modification layer. The modified processing layer is a layer whose light reflection properties have aged and become more prone to absorbing light due to mechanical damage caused by the machining process, compared to before the machining was carried out.

2. The scintillator structure as described in claim 1, characterized in that: The scintillator produces fluorescence when irradiated with X-rays.

3. A method for manufacturing a scintillator structure, characterized in that: The scintillator structure comprises multiple units and a reflective material covering the multiple units. Each of the plurality of units contains resin and phosphor. The manufacturing method includes: (a) The process of monolithizing the substrate into the plurality of units; (b) The process of arranging the monolithized units; and (c) The process of forming the reflective material by covering the plurality of units arranged in a manner. The phosphor contains gadolinium sulfide, which in turn contains terbium and cerium. The density of each of the plurality of units is 4.4 g / cm³. 3 Above and below 5.0 g / cm 3 , The thickness of each of the plurality of units is between 0.5 mm and 1.8 mm. The resin is epoxy resin. Each of the plurality of units is composed of a cuboid shape with a machined surface. Each of the plurality of units has a processing and modification layer. The modified processing layer is a layer whose light reflection properties have aged and become more prone to absorbing light due to mechanical damage caused by the machining process, compared to before the machining was carried out.

4. A scintillator structure, characterized in that: It includes multiple units and a reflective material covering the multiple units. Each of the plurality of units contains resin and phosphor. The phosphor contains gadolinium sulfide, which in turn contains praseodymium and cerium. The density of each of the plurality of units is 4.4 g / cm³. 3 Above 5.0g / cm 3 the following, The thickness of each of the plurality of units is between 0.3 mm and 2.5 mm. The resin is epoxy resin. Each of the plurality of units is composed of a cuboid shape with a machined surface. Each of the plurality of units has a processing and modification layer. The modified processing layer is a layer whose light reflection properties have aged and become more prone to absorbing light due to mechanical damage caused by the machining process, compared to before the machining was carried out.

5. The scintillator structure as described in claim 4, characterized in that: The scintillator produces fluorescence when irradiated with X-rays.

6. A method for manufacturing a scintillator structure, characterized in that: The scintillator structure comprises multiple units and a reflective material covering the multiple units. Each of the plurality of units contains resin and phosphor. The manufacturing method includes: (a) The process of monolithizing the substrate into the plurality of units; (b) The process of arranging the monolithized units; and (c) The process of forming the reflective material by covering the plurality of units arranged in a manner. The phosphor contains gadolinium sulfide, which in turn contains praseodymium and cerium. The density of each of the plurality of units is 4.4 g / cm³. 3 Above 5.0g / cm 3 the following, The thickness of each of the plurality of units is between 0.3 mm and 2.5 mm. The resin is epoxy resin. Each of the plurality of units is composed of a cuboid shape with a machined surface. Each of the plurality of units has a processing and modification layer. The modified processing layer is a layer whose light reflection properties have aged and become more prone to absorbing light due to mechanical damage caused by the machining process, compared to before the machining was carried out.

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