JP7347625B2 - scintillator structure - Google Patents

Description

The present invention relates to a scintillator structure and a method for manufacturing the same, and for example, to a technique that is effective when applied to a scintillator structure having a plurality of cells each containing a resin and a phosphor, and a method for manufacturing the same.

JP-A-63-100391 (Patent Document 1) describes a technique related to a phosphor molded body in which a powdered phosphor and an epoxy resin are mixed.

Japanese Unexamined Patent Publication No. 2-17489 (Patent Document 2) describes a technology related to a phosphor used in a radiation detector.

Japanese Unexamined Patent Publication No. 63-100391 Japanese Unexamined Patent Publication No. 2-17489

A scintillator is a substance that, when exposed to radiation such as X-rays or gamma rays, absorbs the energy of the radiation and generates visible light. This scintillator has been commercialized as a scintillator structure that includes a scintillator and a reflective material, and an X-ray detector that combines the scintillator structure and a photoelectric conversion element such as a photodiode can be used for medical equipment such as X-ray CT, for example. It is used in analytical equipment, non-destructive testing equipment using radiation, radiation leakage testing equipment, etc.

For example, a ceramic made of gadolinium oxysulfide (Gd ₂ O ₂ S) is used for the scintillator. Here, in this specification, gadolinium oxysulfide will be referred to as "GOS". Strictly speaking, gadolinium oxysulfide itself hardly emits light, but when gadolinium oxysulfide contains praseodymium, terbium, or the like, it emits light. For this reason, in this specification, the word "GOS" is used to implicitly refer to a substance (phosphor) that emits light by containing praseodymium, terbium, or the like in gadolinium oxysulfide itself. However, if it is necessary to clearly indicate that gadolinium oxysulfide itself contains praseodymium, terbium, etc., it may be expressed as "GOS" containing praseodymium or "GOS" containing terbium.

Furthermore, when the scintillator is composed of a single "GOS", the "GOS" is composed of ceramic. On the other hand, as will be described later, constructing the scintillator from a mixture of "GOS" and resin is also being considered, and in this case "GOS" is composed of powder. Therefore, in this specification, when there is no need to specifically specify ceramic and powder, it is simply expressed as "GOS". On the other hand, when it is necessary to clearly identify ceramic, it is called "GOS" ceramic. On the other hand, when it is necessary to clearly identify the powder, it will be referred to as "GOS" powder.

This "GOS" has the advantage of having a higher visible light emission output than cadmium tungstate (CdWO ₄ ), but is expensive to manufacture.

For this reason, in order to reduce the manufacturing cost of scintillator structures, consideration has been given to using a mixture of "GOS" powder and resin as a scintillator.

However, the present inventors have newly discovered that while the use of a mixture of "GOS" powder and resin can reduce manufacturing costs, the afterglow properties may deteriorate depending on the "GOS" powder used. Therefore, when using a mixture of "GOS" powder and resin as a scintillator, it is desired to suppress deterioration of afterglow properties.

A scintillator structure in one embodiment includes a plurality of cells and a reflective material covering the plurality of cells. Here, each of the plurality of cells includes a resin and a phosphor, and the phosphor is made of gadolinium oxysulfide containing praseodymium and cerium. The density of each of the plurality of cells is 4.4 g/cm ³ or more and 5.0 g/cm ³ or less, and the thickness of each of the plurality of cells is 0.3 mm or more and 2.5 mm or less.

According to one embodiment, deterioration of afterglow characteristics can be suppressed while reducing manufacturing costs.

FIG. 2 is a diagram schematically showing an X-ray detector. FIG. 3 is a diagram illustrating a cause of a decrease in light emission output in "resin GOS". It is a graph showing the relationship between cell thickness and light emission output. It is a graph showing the relationship between the density of the cell itself and the light emission output. It is a graph showing the afterglow characteristics of "CWO". It is a graph showing the afterglow characteristics of "third resin GOS". It is a graph showing the afterglow characteristics of "first resin GOS". It is a flowchart explaining the flow of the manufacturing process of the scintillator structure. It is a figure which shows typically the process from a dicing process to a reflective material coating process. Graph showing the results of evaluating the wettability of epoxy resin by comparing the contact angle when epoxy resin is dropped onto the surface of "Resin GOS" after various surface treatments have been performed on the surface of "Resin GOS" It is. It is a figure explaining the improvement of wettability by titanium oxide liquid immersion treatment. (a) is a cross-sectional view schematically showing a manufacturing process of a sample to be evaluated by a bending test, and (b) is a top view schematically showing a manufacturing process of a sample to be evaluated by a bending test. (a) is a sectional view showing the state of the bending test, and (b) is a top view showing the state of the bending test. (a) is a table showing the conditions of surface treatment applied to the scintillator structure before forming the sample, and (b) is a table for the samples corresponding to each of "Condition 1" to "Condition 8". 2 is a graph showing the breaking strength measured by carrying out a bending test.

In all the drawings for explaining the embodiment, the same members are designated by the same reference numerals in principle, and repeated explanations thereof will be omitted. Note that, in order to make the drawings easier to understand, hatching may be added even in a plan view.

<Overview of X-ray detector>
FIG. 1 is a diagram schematically showing an X-ray detector.

In FIG. 1, an X-ray detector 100 includes a scintillator structure 10 and a light receiving element 20. The scintillator structure 10 includes a scintillator 11 that generates visible light from X-rays incident on the X-ray detector 100, and a reflective material 12 that covers the scintillator 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, and is composed of a photoelectric conversion element represented by a photodiode, for example.

The scintillator 11 has a function of absorbing X-rays and generating visible light, and is composed of a phosphor 11a and a resin 11b. Here, in this specification, a material obtained by mixing "GOS" powder constituting the phosphor 11a and the resin 11b may be referred to as "resin GOS." In other words, the scintillator 11 in this embodiment is made of "resin GOS." The phosphor 11a is a gadolinium oxysulfide containing praseodymium, terbium, etc., and the resin 11b is, for example, an epoxy resin. Further, the reflective material 12 is made of epoxy resin containing titanium oxide.

The X-ray detector configured in this manner operates as shown below.

That is, when X-rays enter the scintillator 11 of the scintillator structure 10, the electrons in the phosphor 11a forming the scintillator 11 receive the energy of the X-rays and transition from the ground state to the excited state. Thereafter, the excited state electrons transition 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.

A part of the visible light emitted from the scintillator 11 directly enters the light receiving element 20, and another part of the visible light emitted from the scintillator 11 enters the scintillator. The light is focused on the light receiving element 20 while being repeatedly reflected by the reflective material 12 covering the light receiving element 11 .

Subsequently, when visible light is incident on the light-receiving element 20 composed of, for example, 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. As a result, a current caused by electrons excited in the conduction band flows through the photodiode. Then, an X-ray image is acquired based on the current output from the photodiode. In this way, the X-ray detector 100 can acquire an X-ray image.

<Reason for choosing “Resin GOS”>
As described above, in this embodiment, "resin GOS" is used as the scintillator 11. The reason for this will be explained below.

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, which is a substance subject to the RoHS Directive/REACH regulation. include. For this reason, "GOS" ceramic has been used as the scintillator 11 instead of "CWO" containing cadmium. This "GOS" ceramic has the advantage of higher visible light emission output than "CWO", but has the disadvantage of higher manufacturing cost.

Therefore, from the viewpoint of reducing manufacturing costs, instead of using "GOS" ceramic as the scintillator 11, it is being considered to use "resin GOS", which is a mixture of resin such as epoxy resin and "GOS" powder. There is. That is, in order to suppress the increase in manufacturing costs caused by "GOS" ceramics, there is a movement to use "resin GOS", which is cheaper than "GOS" ceramics, for the scintillator 11.

However, "resin GOS" has a lower light emission output than "GOS" ceramic, and even when "resin GOS" is employed as the scintillator 11, it is desired to ensure light emission output.

<Factors that reduce light output>
First, the cause of the decrease in light emission output in "resin GOS" will be explained.

<<First cause>>
"Resin GOS" is composed of a mixture of resin such as epoxy resin and "GOS" powder, for example. Both the epoxy resin and the "GOS" powder are transparent to visible light. In this regard, the light transmittance of epoxy resin is higher than that of "GOS". From this, the light transmittance of "resin GOS" is higher than that of "GOS" ceramic. Therefore, as a result of the light transmittance of "resin GOS" being higher than that of "GOS", at first glance, the light emitting output of scintillator 11 using "resin GOS" is lower than that of scintillator 11 using "GOS" ceramic. This is considered to be higher than the light emission output.

However, in reality, the light emitting output of the scintillator 11 using "resin GOS" is lower than the light emitting output of the scintillator 11 using "GOS" ceramic.

This is because "GOS" powder is used in "Resin GOS", and as a result, the total surface area of "GOS" powder that makes up "Resin GOS" is larger than the total surface area of "GOS" ceramic. This is thought to be due to this. In other words, in the case of "resin GOS", since a large amount of "GOS" powder is present in the epoxy resin, the light emitted by the "GOS" powder may be emitted from the "GOS" powder into the epoxy resin. Even if the light is emitted, it is then subjected to multiple scattering on the surface of the "GOS" powder present in large quantities, and light absorption occurs on the surface of the "GOS" powder each time it is scattered. As a result, the light absorption of "resin GOS" is greater than that of "GOS" ceramic, so the light emission output of scintillator 11 using "resin GOS" is higher than that of scintillator 11 using "GOS" ceramic. It is thought that the price will be higher. This is presumed to be the primary cause of the decrease in light emission output in "resin GOS".

<<Second cause>>
For example, as shown in FIG. 2, the scintillator structure 10 includes a rectangular parallelepiped-shaped scintillator 11 and a reflective material 12 that covers the scintillator 11. Here, since the rectangular parallelepiped-shaped scintillator 11 is formed through a processing process such as a dicing process or a grinding process, a processed surface is formed on the surface of the rectangular parallelepiped. That is, the "processed surface" refers to a surface that has been mechanically processed. Specifically, the "processed surface" includes a surface ground by a grinding wheel to thicken the workpiece, or a surface cut from the workpiece by a slicing blade to perform dicing. For example, in the scintillator 11 using "resin GOS", the "processed surface" is defined as a surface where a surface where the resin is exposed and a surface where the "GOS" powder is broken coexist. For example, the broken line shown in FIG. 1 schematically represents 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, it can be seen that on the "processed surface" there are regions where the resin 11b is cut and regions where the phosphor 11a ("GOS" powder) is broken. Note that the broken lines shown in FIG. 1 are drawn to clearly explain the structure of the "processed surface", and the broken lines are not intended to shrink the scintillator 11, but to indicate the size of the scintillator 11 surrounded by the broken lines. may be a size surrounded by a solid line.

This processed surface becomes a processed damaged layer 30 because it receives mechanical damage due to the processing process. "Processing-affected layer" is defined as a layer that has suffered mechanical damage caused by mechanical processing, resulting in its light reflection properties becoming worse than before mechanical processing and light being absorbed more easily. be done. For example, a specific example of the "process-affected layer" is a light absorption layer formed by desulfurization of the sulfur component on the surface of the "GOS" powder.

In this process-affected layer 30, visible light generated by the scintillator 11 is easily absorbed. That is, part of the generated visible light is absorbed by the process-affected layer 30 present in the scintillator 11, resulting in a decrease in light emission output. In other words, the formation of the process-affected layer 30 on the surface of the scintillator 11 is a factor in reducing the light emission output from the scintillator structure 10.

In particular, in recent years, as shown in FIG. 11 arrays). Then, the reflective material 12 is provided so as to cover the plurality of cells CL. Specifically, the top surface and four side surfaces of the cell CL are covered with a reflective material 12. On the other hand, the lower surface of the cell CL is not covered with the reflective material 12 because it needs to be brought into contact with the photodiode.

When the scintillator 11 is divided into a plurality of cells CL, the process-affected layer 30 is formed on the surface of each of the plurality of cells CL, so that the area of the process-affected layer 30 that occupies the scintillator structure 10A increases. As a result, in the multi-cell scintillator structure 10A, it is thought that the reduction in light emission output due to the damaged layer 30 becomes large.

The scintillator structure in this embodiment is based on a multi-cell scintillator structure 10A that can improve the resolution of X-ray images. For this reason, it is thought that the decrease in the light emission output due to the process-affected layer 30 becomes large, and it is therefore understood that it is important to take measures to maintain the light emission output.

Here, whether a "GOS" ceramic or "resin GOS" is used as the scintillator 11, the process-affected layer 30 is still formed on the surface of the scintillator 11. Therefore, regardless of whether the scintillator 11 is made of "GOS" ceramic or "resin GOS", it is considered that the light emission output decreases due to the process-affected layer 30.

Regarding this point, according to the inventor's study, the light emission output due to the process-altered layer 30 is lower when the scintillator 11 is made of "resin GOS" than when it is made from "GOS" ceramic. We have newly discovered that the decrease is significant.

The reason for this will be explained below. For example, "GOS" ceramic can be subjected to heat treatment even after it is singulated into cells CL. The heat treatment has a function of recovering the process-affected layer 30 formed due to mechanical damage. Therefore, when the scintillator 11 is made of "GOS" ceramic, it is possible to recover the process-affected layer 30 formed on the surface of the cell CL by applying heat treatment after cutting it into individual cells CL. It can be done. As a result, when the scintillator 11 is made of "GOS" ceramic, the heat treatment reduces the process-affected layer 30, so it is possible to suppress a decrease in light emission output due to the process-affected layer 30.

On the other hand, "resin GOS" is not ceramic but "GOS" powder hardened with resin, and it is difficult to heat-treat it. As a result, when the scintillator 11 is made of "resin GOS", the recovery effect of the process-affected layer 30 due to heat treatment cannot be obtained, so the reduction in light emission output due to the process-affected layer 30 becomes large. That is, unlike the "GOS" ceramic, "resin GOS" is difficult to heat-treat and cannot recover the process-affected layer 30, which is the second reason for reducing the light emission output from the scintillator structure 10A.

From the above, if the scintillator 11 is made of "resin GOS", the synergistic factor of the first cause due to the use of "GOS" powder and the second cause of difficulty in recovering the damaged layer 30 , the luminous output is lower than that of "GOS" ceramic.

Therefore, when "resin GOS" is used as the scintillator 11, it is inevitable that the light emission output will be essentially lower than that of "GOS" ceramic. However, the present inventor has obtained a new knowledge that when "resin GOS" is used as the scintillator 11, the light emission output changes depending on the thickness and density of the cell CL made of "resin GOS". That is, according to the new knowledge discovered by the present inventors, it is thought that by specifying the thickness and density of the cell CL, it is possible to ensure a certain level of light emission output even with "resin GOS".

Therefore, the thickness dependence and density dependence of the light emission output will be explained below.

<Thickness dependence of light emission output>
FIG. 3 is a graph showing the relationship between cell thickness and light emission output.

In FIG. 3, the horizontal axis shows the cell thickness, and the vertical axis shows the light emission output.

First, the "first GOS" is a "GOS" to which praseodymium (Pr) and cerium (Ce) are added. On the other hand, although not shown in FIG. 3, the "second GOS" is a "GOS" to which terbium (Tb) and cerium (Ce) are added.

Here, focusing on the light emission output of the "first GOS" and the "second GOS", the light emission output of the "second GOS" is higher than that of the "first GOS". In other words, the "first GOS" has a lower light emission output than the "second GOS". Note that the light emission output shown on the vertical axis of FIG. 3 is expressed as a percentage, with the light emission output of the "first GOS" having a thickness of 1.3 mm taken as 100%.

"Second resin GOS" is a mixture of "GOS" powder made of "second GOS" and epoxy resin.

"Third resin GOS" and "fourth resin GOS" are both a mixture of "GOS" powder consisting of "first GOS" and epoxy resin, and "third resin GOS" and "fourth resin GOS" The difference is density.

In FIG. 3, when paying attention to the curve of "first GOS", it can be seen that the light emission output of "first GOS" hardly depends on the thickness of the cell. On the other hand, in FIG. 3, if we pay attention to the respective curves of "second resin GOS" to "fourth resin GOS", we can see that the light emitting output of each of "second resin GOS" to "fourth resin GOS" depends on the thickness of the cell. It turns out that it depends on the

In the following, the thickness dependence of the light emission output of each of the "second resin GOS" to "fourth resin GOS" will be qualitatively explained. First, in a thinner thickness range, the luminous output increases as the thickness increases. This can be understood from the fact that in a thin range, as the thickness increases, the amount of "resin GOS" that absorbs incident X-rays and contributes to generating visible light increases. When the thickness increases to a certain extent, the amount of "resin GOS" that absorbs incident X-rays and contributes to generating visible light becomes saturated, while as the thickness increases, the translucency decreases and It is understood that as the thickness increases, the light emission output decreases due to the above-mentioned first and second causes becoming apparent.

<Density dependence of light emission output>
Next, the density dependence of light emission output will be explained.

FIG. 4 is a graph showing the relationship between the density of the cell itself and the light emission output.

In FIG. 4, the horizontal axis represents the density of scintillators constituting the cell, and the vertical axis represents the light emission output. Note that the light emission output on the vertical axis is expressed as a percentage, with the light emission output of the "first GOS" having a thickness of 1.5 mm taken as 100%.

Here, "density" refers to the density of the entire "resin GOS". In particular, in the case of "resin GOS", since the density of "GOS" powder is higher than that of epoxy resin, the following relationship holds true.

That is, a low density of "resin GOS" means that the amount of "GOS" powder is small and the amount of epoxy resin is large. In other words, a high density of "resin GOS" means a large amount of "GOS" powder and a small amount of epoxy resin.

In FIG. 4, the density of the "first resin GOS" (comparative example) is 5.0 (g/cm ³ ), while the density of the "second resin GOS" is 4.4 (g/cm ³ ). It is. That is, the density of the "second resin GOS" is lower than the density of the "first resin GOS." In other words, the density of the "first resin GOS" is higher than the density of the "second resin GOS."

As shown in FIG. 4, it can be seen that the lower the density, the higher the light emission output. This is because a lower density means a relatively larger amount of epoxy resin, which is more translucent than the "GOS" powder, so the absorption of visible light is reduced, resulting in a lower density. It is thought that the lower the value, the greater the light emission output. In other words, higher density means that the amount of "GOS" powder is greater than the amount of highly transparent epoxy resin, so the absorption of visible light in the "GOS" powder increases. As a result, it is thought that the higher the density, the lower the luminous output.

In the following, by constructing the scintillator 11 from "resin GOS", manufacturing costs can be reduced compared to the case where "GOS" ceramic is used as the scintillator 11, and the thickness dependence of the light emission output described above (see FIG. 3) will be explained. ) and the density dependence of the light emitting output (FIG. 4), we will discuss ways to improve the performance of the scintillator structure 10A. In other words, the points for improving the cost performance of the scintillator structure 10A will be explained.

Specifically, as points for improving the performance of the scintillator structure 10A, a first point from the viewpoint of ensuring light emission output and a second point from the viewpoint of ensuring afterglow characteristics will be explained respectively. I'll decide.

<Perspectives on securing light emission output (first point of improvement)>
As shown in FIG. 3, when looking at the thickness dependence of the light emission output in the "second resin GOS", for example, when the thickness is 0.5 mm or more and 1.8 mm or less, the "second resin GOS" The light emission output is higher than that of the "first GOS". In other words, the "second resin GOS" formed by mixing epoxy resin with the "GOS" powder made of the "second GOS" which has a higher luminescence output than the "first GOS" has a luminescence output higher than that of the "second GOS". Although it decreases, it is seen that by setting the cell thickness in the range of 0.5 mm or more and 1.8 mm or less, the light emission output can be made higher than that of the "first GOS". In other words, if the thickness of the cell made up of the "second resin GOS" is set in the range of 0.5 mm or more and 1.8 mm or less, the light emitting output of the "second resin GOS" can be made equal to or higher than that of the "first resin GOS". It is possible.

Next, as shown in FIG. 4, it can be seen that as the density of the cell itself becomes smaller, the light emission output improves. In particular, by setting the density to a range of 4.4 g/cm ³ or more and less than 5.0 g/cm ³ , when the light emission output of the "first GOS" with a thickness of 1.5 mm is set to "100%", " It can be seen that a light emission output of 125% or more can be obtained.

Based on the above, on the premise that "resin GOS" which is a mixture of "GOS" powder made of "second GOS" and epoxy resin is used as the scintillator 11, the cell thickness should be set to 0.5 mm or more and 1.8 mm. By setting the density in the following range and setting the density of the cell itself in the range of 4.4g/ ^cm3 or more and less than 5.0g/ ^cm3 , even if it is a "resin GOS", the light emission output can be higher than that of the "1st GOS". Obtainable. In this way, while using a "resin GOS" that can reduce manufacturing costs, by setting the thickness range and density range within the above-mentioned ranges, it is possible to obtain a light emitting output higher than that of the "first GOS". It is. In other words, in order to secure light emitting output while using "resin GOS" which can reduce manufacturing costs, it is necessary to set the cell thickness in the range of 0.5 mm or more and 1.8 mm or less, and to reduce the density of the cell itself. This can be achieved by setting it in a range of 4.4 g/cm ³ or more and less than 5.0 g/cm ³ .

<Point of view to ensure afterglow characteristics (second point)>
The first point mentioned above is a point of improvement from the viewpoint of ensuring light emission output. On the other hand, the second point to be explained below is a point of improvement from the viewpoint of ensuring the afterglow characteristic. That is, the scintillator structure 10A is required not only to have a high light emission output but also to have good afterglow characteristics. Therefore, first, the afterglow characteristic will be explained.

The scintillator 11 constituting the scintillator structure 10A is a material that generates visible light when exposed to X-rays. The mechanism for generating visible light when exposed to X-rays in the scintillator 11 is as follows. That is, when the scintillator 11 is irradiated with X-rays, 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 to the ground state, which has lower energy. At this time, most of the excited electrons immediately transition to the ground state. On the other hand, some of the excited electrons transition to the ground state after a certain amount of time has passed. Visible light generated by the transition of electrons from the excited state to the ground state after a certain amount of time has passed becomes afterglow. In other words, afterglow is visible light that is generated when the timing of transition from an excited state to a ground state occurs after a certain amount of time has elapsed from the time when X-rays were irradiated. A large afterglow means that the intensity of visible light that is generated even after a certain amount of time has elapsed after X-ray irradiation is high. In this case, the afterglow generated by the previous X-ray irradiation remains until the next X-ray irradiation, and the remaining afterglow becomes noise. For this reason, it is desirable that the afterglow be small. In other words, good afterglow characteristics means that the afterglow is small.

Here, the afterglow characteristics differ depending on the type of scintillator 11. For example, FIG. 5 is a graph showing the afterglow characteristics of "CWO", and FIG. 6 is a graph showing the afterglow characteristics of "third resin GOS". Further, FIG. 7 is a graph showing the afterglow characteristics of the "first resin GOS".

In FIGS. 5 to 7, the vertical axis indicates the intensity of afterglow, while the horizontal axis indicates time. In FIGS. 5 to 7, it is shown that the greater the intensity of afterglow after time has elapsed, the worse the afterglow characteristics are. In other words, FIGS. 5 to 7 show that the smaller the intensity of the afterglow after the passage of time, the better the afterglow characteristics.

Focusing on this point and looking at FIGS. 5 to 7, the afterglow characteristics in FIG. 5 and the afterglow characteristics in FIG. 6 are almost the same and have good afterglow characteristics, while the afterglow characteristics in FIG. 7 are poor. I understand. In other words, while the afterglow characteristics of "CWO" shown in FIG. 5 and the afterglow characteristics of "third resin GOS" shown in FIG. 6 are both good, the afterglow characteristics of "first resin GOS" shown in FIG. I know it's bad.

In other words, from the viewpoint of light emission output, if the above-mentioned point 1 is realized, "2nd GOS" > "2nd resin GOS" > "1st resin GOS" > "1st GOS" > "4th resin GOS" > " There is a region where the relationship ``third resin GOS'' > ``CWO'' holds true.

On the other hand, referring to FIGS. 5 to 7, from the viewpoint of afterglow characteristics, the relationship "CWO"≒"third resin GOS"<"first resin GOS" holds true.

Therefore, for example, when focusing on "first resin GOS", "third resin GOS", and "CWO", "first resin GOS" is the most excellent from the viewpoint of light emission output. On the other hand, from the viewpoint of afterglow properties, "CWO" and "third resin GOS" are superior.

From this, in order to realize "resin GOS" with excellent afterglow properties, it is necessary to use "first resin GOS" or "second resin GOS" which is made by mixing epoxy resin with "GOS" powder consisting of "second GOS". It can be seen that "third resin GOS" and "fourth resin GOS" in which epoxy resin is mixed with "GOS" powder made of "first GOS" are more desirable than "first GOS". However, as shown in FIG. 3, the "third resin GOS" and the "fourth resin GOS" have lower light emission output than the "second resin GOS."

Therefore, it is desirable to secure the afterglow property and increase the light emission output as much as possible by employing the "third resin GOS" and the "fourth resin GOS." Regarding this point, in Fig. 3, the cell thickness is set to 0.3 mm or more and 2.5 mm or less, assuming that ``resin GOS'' is used, which is a mixture of epoxy resin and ``GOS'' powder made of ``first GOS.'' By making the density of the cell itself within the range of 4.4 g/cm ³ or more and 5.0 g/cm ³ or less based on the analogy of FIG. It is thought that it is possible to obtain a light emission output greater than "CWO". In this way, by setting the thickness range and density range within the above-mentioned ranges while using "resin GOS" which can reduce manufacturing costs and has good afterglow characteristics, it is possible to emit light exceeding "CWO". You can get the output. In other words, in order to reduce manufacturing costs and ensure luminous output while using "resin GOS" with good afterglow characteristics, the cell thickness is set in the range of 0.3 mm or more and 2.5 mm or less, Moreover, this can be achieved by setting the density of the cell itself to a range of 4.4 g/cm ³ or more and 5.0 g/cm ³ or less.

<Method for manufacturing scintillator structure>
Next, a method for manufacturing the scintillator structure 10 will be described.

FIG. 8 is a flowchart illustrating the flow of the manufacturing process of the scintillator structure.

In FIG. 8, first, after predetermined amounts of raw material powder and flux components are weighed and mixed (S101), this mixture is filled into a crucible and fired for 7 to 9 hours in an atmospheric furnace at 1300°C to 1400°C. (S102), “GOS” powder is generated. Then, flux components and impurities contained in the "GOS" powder are removed by washing using hydrochloric acid and hot water (S103). Next, by dropping the epoxy resin onto the "GOS" powder, the epoxy resin is impregnated into the "GOS" powder (S104). Next, after curing the epoxy resin (S105), the epoxy resin that is not mixed with the "GOS" powder is removed (S106). Thereby, a scintillator made of "resin GOS" can be formed.

Subsequently, the substrate on which the scintillator is formed is diced to separate the substrate into a plurality of cells (S107). After the plurality of individualized cells are rearranged (S108), a reflective material is applied to cover the plurality of cells (S109). Then, after cutting off unnecessary parts of the scintillator structure 10A (S110), the scintillator structure 10A that has passed the inspection is shipped (S111).

FIG. 9 is a diagram schematically showing the steps from the dicing step to the reflective material coating step.

As shown in FIG. 9, by dicing the substrate WF on which the scintillator made of "resin GOS" is formed, the substrate WF is separated into a plurality of cells CL. Then, the plurality of individualized cells CL are rearranged, for example, in a line. Thereafter, the outer frame FR is arranged so as to enclose the plurality of cells CL rearranged in a line. Next, a reflective material 12 made of, for example, an epoxy resin containing titanium oxide is applied so as to cover the plurality of cells CL arranged within the outer frame FR. After that, the outer frame FR is removed. In this way, scintillator structure 10A is manufactured.

Although FIG. 9 illustrates a linear scintillator structure 10A using 1×n cells as an example, the technical idea of this embodiment is not limited to this, and for example, It is also applicable to an array-like (matrix-like) scintillator structure using n×n cells.

<Characteristics of the manufacturing method>
Next, the features of the manufacturing method in this embodiment will be explained.

A feature of the manufacturing method of this embodiment is that the substrate WF on which the scintillator 11 is formed is completely singulated into a plurality of cells CL by full-cut dicing, and then the plurality of singulated cells CL are recycled. The scintillator structure 10A is manufactured by arranging the cells CL, and then coating the reflective material 12 so as to cover the rearranged plurality of cells CL.

Thereby, according to this embodiment, the interval between cells can be adjusted freely.

For example, there is a technique in which the substrate WF on which the scintillator 11 is formed is half-diced halfway, the reflective material 12 is applied, and then the half-diced substrate WF is ground to separate adjacent cells CL. According to this technique, since the interval between adjacent cells CL is determined by the cutting width of half dicing, it is possible to accurately determine the interval between adjacent cells CL. In other words, this technique does not allow the interval between cells CL to be changed freely.

Regarding this point, for example, some users of X-ray detectors want to arrange photodiodes, which are light-receiving elements, in a high density to obtain high-definition X-ray images, while others want to arrange photodiodes in a low density. There are also users who wish to obtain X-ray images over a wide range but not in high definition. In the former case, a plurality of cells CL constituting the scintillator structure 10A are also required to be arranged at a high density in correspondence with the photodiodes arranged at a high density. In this case, it is necessary to make the interval between cells CL very small. For example, when the interval between cells CL is made smaller than the cutting width of half dicing, a technique using half dicing cannot handle this. On the other hand, in the latter case as well, even if it is desired to make the interval between the cells CL larger than the width of half dicing, the technology using half dicing cannot handle this. In this way, with the technology using half dicing, the spacing between cells CL is uniformly determined by the shear width of half dicing, so it is not possible to freely adjust the spacing between cells CL according to the user's requirements. .

In contrast, in the present embodiment, the substrate WF on which the scintillator 11 is formed is singulated into a plurality of cells CL by full cut dicing instead of half dicing, and then the plurality of singulated cells CL are It's being rearranged. Thereby, according to the present embodiment, when rearranging a plurality of cells CL, it is possible to freely set the interval between adjacent cells CL.

Therefore, according to the present embodiment, the interval between the cells CL can be made smaller or larger than the cutting width of dicing, so the advantage is that the scintillator structure 10A can be flexibly manufactured to meet the needs of the user. is obtained.

Furthermore, according to this embodiment, the following advantages can also be obtained. That is, in the technique using half dicing, the cells CL are finally separated by a grinding process.

Regarding this point, in this embodiment, a plurality of cells CL are singulated by full-cut dicing. This eliminates the need for a grinding step to separate the plurality of cells CL in subsequent steps. This means that the grinding process for separating the plurality of cells CL can be reduced. As a result, the method for manufacturing the scintillator structure 10A according to the present embodiment has the advantage of simplifying the manufacturing process.

<Point of view for improving adhesion (third point of improvement)>
For example, a constant temperature and high humidity test is performed on the scintillator structure 10A, which is a completed product manufactured through the above-described manufacturing process, to ensure reliability.

Here, when a constant temperature and high humidity test was performed on the scintillator structure 10A using "resin GOS" for the scintillator 11, it was confirmed that the percentage of samples passing the constant temperature and high humidity test decreased. Regarding this point, the present inventor has newly discovered that the rate of passing the constant temperature and high humidity test decreases due to a decrease in the adhesion of the interface between the scintillator 11 made of "resin GOS" and the reflective material 12. Ta. Therefore, in this embodiment, from the viewpoint of improving the reliability of the scintillator structure 10A, measures are taken to improve the adhesion between the scintillator 11 made of "resin GOS" and the reflective material 12. This point will be explained below.

＜＜New findings＞＞
First, the novel knowledge discovered by the present inventor will be explained.

The new knowledge discovered by the present inventor is that if a surface treatment is applied to the surface of "resin GOS" before coating the reflective material 12 to cover the scintillator 11 made of "resin GOS", the surface It is a finding that a difference occurs in the adhesion force at the interface between the "resin GOS" and the reflective material 12 depending on the type of treatment. According to the present invention, the reason for the difference in the adhesion strength at the interface between the "resin GOS" and the reflective material 12 is that the wettability of the "resin GOS" to the reflective material 12 changes depending on the type of surface treatment applied to the surface of the "resin GOS". are guessing. From this, it can be considered that if the surface of the "resin GOS" is subjected to a surface treatment that can improve the wettability to the reflective material 12, the adhesion at the interface between the "resin GOS" and the reflective material 12 can be improved. That is, it is considered that by forming a surface treatment layer on the surfaces of the plurality of cells CL that are in contact with the reflective material 12, the adhesion at the interface between the "resin GOS" and the reflective material 12 can be improved. For example, it is thought that adhesion can be improved by forming a surface treatment layer on at least the side surfaces and top surfaces of each of the plurality of cells CL.

Therefore, we evaluated the wettability of various surface treatments to epoxy resin.

Figure 10 shows the wettability of epoxy resin evaluated by comparing the contact angle when epoxy resin was dropped onto the surface of "Resin GOS" after various surface treatments were performed on the surface of "Resin GOS". It is a graph showing the results.

In FIG. 10, various surface treatments include untreated, IPA treatment (isopropyl alcohol treatment), titanium oxide liquid immersion treatment, and pure water cleaning treatment.

As shown in FIG. 10, it can be seen that the contact angle varies depending on the surface treatment. This means that wettability varies depending on the type of surface treatment.

From the results shown in FIG. 10, it can be seen that the contact angle is the smallest when the epoxy resin is dropped onto the surface of the "resin GOS" after the surface of the "resin GOS" is subjected to titanium oxide liquid immersion treatment. This means that wettability to epoxy resin is most improved by performing titanium oxide liquid immersion treatment as surface treatment.

Therefore, it is presumed that if titanium oxide immersion treatment, which has the best wettability to epoxy resin, is performed, the adhesion at the interface between the "resin GOS" and the reflective material 12 will be increased. In other words, as shown in FIG. 11, when the titanium oxide immersion treatment is performed, titanium oxide adheres to the surface of the scintillator 11 made of "resin GOS", improving wettability and bonding the scintillator 11 and the reflective material 12. It is thought that as a result of the increase in area, the adhesion force at the interface between the scintillator 11 made of "resin GOS" and the reflective material 12 increases.

From the above, the points for improving the adhesion between the scintillator 11 made of "resin GOS" and the reflective material 12 are as follows: Before applying the reflective material 12 to cover the scintillator 11, On the other hand, the surface of the scintillator 11 is subjected to surface treatment to improve wettability. Specifically, this point is realized by subjecting the surface of the scintillator 11 to a titanium oxide liquid immersion treatment before applying the reflective material 12 to cover the scintillator 11.

<<Verification of effectiveness>>
In the following, before applying the reflective material 12 to cover the scintillator 11 made of "resin GOS", a titanium oxide liquid immersion treatment is performed on the surface of the scintillator 11, so that the interface between the scintillator 11 and the reflective material 12 is Verification results that support increased adhesion will be explained.

The present inventor believes that it is possible to quantitatively compare the adhesion force at the interface between the scintillator 11 and the reflective material 12 using the breaking strength of the bending test, Now that the force has been evaluated, the evaluation results from this bending test will be explained. Specifically, in this embodiment, the adhesion was evaluated by a bending test based on the three-point bending test specified in "JIS K7171." For example, in the figure shown in "JIS K7171", the load at which the sample breaks was measured under the conditions shown below.

Sample shape (length, thickness, width): 50mm x 6.2mm x 1.2mm
Indenter tip radius (R1): 0.3mm
Support stand corner radius (R2): 0.3mm
Test piece (sample) thickness (h): 6.2mm
Test piece (sample) length (l): 50mm
Distance between fulcrums (L): 10mm

1. Preparation of sample Figure 12(a) is a cross-sectional view schematically showing the manufacturing process of the sample to be evaluated by the bending test, and Figure 12(b) is a cross-sectional view schematically showing the manufacturing process of the sample to be evaluated by the bending test. FIG.

As shown in FIG. 12(a), a scintillator structure 10A configured to cover a plurality of arranged scintillators 11 with a reflective material 12 is prepared, and the upper surface of this scintillator structure 10A is ground. As shown in (b), a sample SP is produced by grinding two side surfaces (long sides) of the scintillator structure 10A.

Then, a constant temperature and high humidity test is performed on this sample SP. Here, a constant temperature and high humidity test is performed by immersing the product in 80°C warm water for 80 minutes. Thereafter, a bending test is performed on the sample SP that has been subjected to the constant temperature and high humidity test.

2. Bending Test FIG. 13(a) is a cross-sectional view showing the bending test, and FIG. 13(b) is a top view showing the bending test. As shown in FIG. 13(a), the tip of the indenter NL is brought into contact with the interface between the scintillator 11 and the reflective material, and as shown in FIG. 13(b), the tip of the indenter NL is brought into contact with the interface of the sample SP. It is arranged so as to be located at the center in the width direction.

In the bending test, an indenter NL is pressed against the sample SP from above to measure the breaking strength when the sample SP is broken. It can be said that the higher the breaking strength, the higher the adhesion force at the interface between the scintillator 11 and the reflective material 12. That is, the adhesion force at the interface between the scintillator 11 and the reflective material 12 can be evaluated based on the breaking strength measured in the bending test. The evaluation results will be explained below.

Note that the measuring device used in the bending test includes, for example, a drive machine (FGS-50V-L: manufactured by SHIMPO) and a tension meter (FGC-5: manufactured by SHIMPO). Further, the number of measurement points on the sample used for measurement is three, and the breaking strength of the sample is evaluated by the average value at the three measurement points.

3. Evaluation Results FIG. 14 is a diagram showing the evaluation results of the bending test.

FIG. 14(a) is a table showing conditions for surface treatment performed on the scintillator structure 10A before forming the sample SP. In FIG. 14A, eight samples SP are fabricated by processing a scintillator structure 10A that has been surface-treated under eight conditions. For example, "Condition 1" indicates a condition in which the reflective material is applied after performing IPA treatment, titanium oxide liquid immersion treatment, and pure water cleaning as surface treatment. "Condition 2" indicates a condition in which a reflective material is applied without performing the above-mentioned surface treatment.

FIG. 14(b) is a graph showing the breaking strength measured by performing a bending test on samples SP corresponding to each of "Condition 1" to "Condition 8". As shown in FIG. 14(b), it can be seen that the breaking strength of sample SP subjected to titanium oxide liquid immersion treatment as surface treatment is higher. Specifically, it can be seen that in the sample SP subjected to the titanium oxide liquid immersion treatment, the breaking strength at the interface between the scintillator 11 and the reflective material 12 is 900 gf or more.

From this evaluation result, it was found that before applying the reflective material 12 to cover the scintillator 11 made of "resin GOS", the scintillator 11 and the reflective material 12 were It can be seen that this proves that the adhesion force at the interface is increased.

In addition, from the viewpoint of improving the adhesion of the interface between the scintillator 11 and the reflective material 12, the breaking strength of the interface is preferably 938 gf or more, more preferably 1059 gf or more, and more preferably 1182 gf or more. is desirable.

The invention made by the present inventor has been specifically explained based on the embodiments thereof, but the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the gist thereof. Needless to say.

10 scintillator structure 10A scintillator structure 11 scintillator 11a phosphor 11b resin 20 light receiving element 30 processing-affected layer 100 X-ray detector CL cell FR outer frame NL indenter SP sample WF substrate

Claims (4)

A scintillator structure comprising a plurality of cells and a reflective material covering the plurality of cells,
Each of the plurality of cells includes an epoxy resin and fluorescent powder ,
The fluorescent powder is made of gadolinium oxysulfide containing praseodymium and cerium,
The density of each of the plurality of cells is 4.4 g/cm ³ or more and less than 5.0 g/cm ³ ,
The thickness of each of the plurality of cells is 0.3 mm or more and 2.5 mm or less,
The upper surface of each of the plurality of cells is composed of a cross section of the fluorescent powder and the epoxy resin,
A scintillator structure , wherein a lower surface of each of the plurality of cells is composed of a cross section of the fluorescent powder and the epoxy resin . The scintillator structure according to claim 1,
A scintillator structure , wherein a side surface of each of the plurality of cells is composed of a cross section of the fluorescent powder and the epoxy resin . The scintillator structure according to claim 1,
A scintillator structure in which each of the plurality of cells has a rectangular parallelepiped shape. The scintillator structure according to claim 1,
The fluorescent powder is a scintillator structure that generates fluorescence when irradiated with X-rays.

Images