JP7056720B2 - Scintillator structure and its manufacturing method - Google Patents

Description

The present invention relates to a scintillator structure and a method for producing the scintillator structure, and the present invention relates to, for example, a scintillator structure having a plurality of cells including a resin and a phosphor, respectively, and an effective technique applied to the method for producing the scintillator structure.

Japanese Patent Application Laid-Open No. 63-100391 (Patent Document 1) describes a technique relating to a phosphor molded body in which a powder phosphor and an epoxy resin are mixed.

Japanese Patent Application Laid-Open No. 2-17489 (Patent Document 2) describes a technique relating to a fluorescent substance 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 absorbs the energy of radiation and generates visible light when exposed to radiation typified by X-rays and gamma rays. This scintillator has been commercialized as a scintillator structure including a scintillator and a reflective material, and an X-ray detector in which the scintillator structure and a photoelectric conversion element such as a photodiode are combined is, for example, a medical device such as an X-ray CT. It is used in analytical equipment, non-destructive inspection equipment using radiation, radiation leakage inspection equipment, etc.

For example, ceramics made of gadolinium acid sulfide (Gd ₂ O ₂ S) are used for the scintillator. Here, in the present specification, gadolinium acid sulfide will be referred to as "GOS". Strictly speaking, the gadolinium sulfide itself hardly emits light, but emits light by containing praseodymium, terbium, or the like in the gadolinium sulfide. For this reason, the term "GOS" in the present specification implicitly intends to use a substance (fluorescent substance) that contains praseodymium, terbium, or the like in the gadolinium sulfide itself and emits light. However, when it is necessary to explicitly indicate that the gadolinium sulfide itself contains praseodymium, terbium, etc., it may be expressed as "GOS" containing praseodymium or "GOS" containing terbium.

When the scintillator is composed of "GOS" alone, "GOS" is composed of ceramic. On the other hand, as will be described later, it is also considered to configure the scintillator with a mixture of "GOS" and a resin, and in this case, "GOS" is composed of powder. Therefore, in the present specification, when it is not necessary to specify ceramic and powder in particular, it is simply expressed as "GOS". On the other hand, when it is necessary to specify the ceramic, it is called "GOS" ceramic. On the other hand, when it is necessary to specify the powder, it will be called "GOS" powder.

This "GOS" has the advantage that the emission output of visible light is larger than that of cadmium tungstate (CdWO ₄ ), but the manufacturing cost is high.

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

However, the present inventor has newly found that the use of a mixture of "GOS" powder and a resin can reduce the manufacturing cost, while the afterglow characteristics deteriorate depending on the "GOS" powder used. Therefore, when a mixture of "GOS" powder and resin is used as a scintillator, it is desired to suppress deterioration of afterglow characteristics.

The 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 contains a resin and a phosphor, and the phosphor is composed of a gadolinium acid sulfide 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.

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

In all the drawings for explaining the embodiments, the same members are designated by the same reference numerals in principle, and the repeated description thereof will be omitted. In addition, in order to make the drawing easier to understand, hatching may be added even if it is a plan view.

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

In FIG. 1, the X-ray detector 100 has 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 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, for example, a photoelectric conversion element typified by a photodiode.

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 the present specification, the material obtained by mixing the "GOS" powder constituting the phosphor 11a and the resin 11b may be referred to as "resin GOS". That is, the scintillator 11 in the present embodiment is composed of "resin GOS". The phosphor 11a is a gadolinium acid sulfide containing praseodymium, terbium, and the like, and the resin 11b is, for example, an epoxy resin. Further, the reflective material 12 is made of an epoxy resin containing titanium oxide.

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

That is, when X-rays are incident on the scintillator 11 of the scintillator structure 10, the 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. After that, 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. By such a mechanism, the scintillator 11 absorbs X-rays and generates visible light.

Then, some visible light of the visible light generated from the scintillator 11 is directly incident on the light receiving element 20, and the other visible light of the visible light generated from the scintillator 11 is the scintillator. The light is collected by the light receiving element 20 while repeating the reflection by the reflective material 12 covering the 11.

Subsequently, for example, when visible light is incident on the light receiving element 20 composed of the photodiode, the electrons of the semiconductor material constituting the photodiode are excited from the valence band to the conduction band by the energy of the visible light. As a result, the current caused by the 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, according to the X-ray detector 100, an X-ray image can be acquired.

<Reason for adopting "Resin GOS">
As described above, in the present embodiment, "resin GOS" is adopted 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, and the "CWO" contains cadmium, which is a substance subject to the RoHS Directive / REACH regulation. include. For this reason, as the scintillator 11, "GOS" ceramic has been used instead of "CWO" containing cadmium. This "GOS" ceramic has the advantage that the emission output of visible light is higher than that of "CWO", but has the disadvantage that the manufacturing cost is high.

Therefore, from the viewpoint of reducing the manufacturing cost, it has been considered to use "resin GOS" as the scintillator 11 in which a resin made of an epoxy resin or the like and "GOS" powder are mixed, instead of the "GOS" ceramic. There is. That is, there is a movement to use "resin GOS", which is cheaper than "GOS" ceramic, for the scintillator 11 in order to suppress the increase in manufacturing cost due to "GOS" ceramic.

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

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

<< First cause >>
The "resin GOS" is composed of a mixture of a resin such as an epoxy resin and a "GOS" powder. And both the epoxy resin and the "GOS" powder have translucency with respect to visible light. In this respect, the translucency of the epoxy resin is higher than the translucency of "GOS". From this, the translucency of the "resin GOS" is higher than the translucency of the "GOS" ceramic. Therefore, as a result of the translucency of "resin GOS" being higher than that of "GOS", at first glance, the light emission output of the scintillator 11 using "resin GOS" is that of the scintillator 11 using "GOS" ceramic. It is considered to be higher than the emission output.

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

This is because, as a result of using the "GOS" powder in the "resin GOS", the total surface area of the "GOS" powder constituting the "resin GOS" is larger than the total surface area of the "GOS" ceramic. It is thought to be caused. That is, in the "resin GOS", since a large amount of "GOS" powder is present in the epoxy resin, the light emitted by the "GOS" powder can be emitted from the "GOS" powder into the epoxy resin. Even if it is emitted, it is subsequently multiple-scattered on the surface of a large amount of "GOS" powder, and light absorption occurs on the surface of the "GOS" powder each time it is scattered. As a result, since the "resin GOS" absorbs more light than the "GOS" ceramic, the light emission output of the scintillator 11 using the "resin GOS" is higher than the light emission output of the scintillator 11 using the "GOS" ceramic. It is expected to be higher. It is presumed that this is the first cause of the decrease in light emission output in "resin GOS".

<< Second cause >>
For example, as shown in FIG. 2, the scintillator structure 10 is composed of a rectangular parallelepiped scintillator 11 and a reflective material 12 that covers the scintillator 11. Here, since the rectangular parallelepiped scintillator 11 is formed through processing steps such as a dicing step and a grinding step, a machined surface is formed on the surface of the rectangular parallelepiped shape. That is, the "machined surface" means a surface that has been mechanically processed. Specifically, the "machined surface" includes a surface ground with a grinding wheel when thickening the work, or a surface cut with a slicing blade to perform a dicing process. For example, in the scintillator 11 using "resin GOS", the "processed surface" is defined as a surface in which the surface where the resin is exposed and the 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 the "resin GOS". In this case, it can be seen that in the "processed surface", a region where the resin 11b is cut and a region where the phosphor 11a ("GOS" powder) is broken are mixed. The broken line shown in FIG. 1 is drawn to explain the structure of the "machined surface" in an easy-to-understand manner, and is not intended to shrink the scintillator 11 by the broken line, but the size of the scintillator 11 surrounded by the broken line. May be the size enclosed by the solid line.

Since this machined surface receives mechanical damage due to the machined process, it becomes the machined alteration layer 30. The "processed alteration layer" is defined as a layer in which light reflection characteristics deteriorate and light is more easily absorbed than before mechanical processing due to mechanical damage caused by the mechanical processing process. Will be done. For example, as a specific example of the "processed alteration layer", a light absorption layer obtained by desulfurization of the sulfur component on the surface of the "GOS" powder can be mentioned.

In this processing alteration layer 30, visible light generated by the scintillator 11 is easily absorbed. That is, a part of the generated visible light is absorbed by the processing alteration layer 30 existing in the scintillator 11, and as a result, the emission output is lowered. That is, the formation of the processed alteration layer 30 on the surface of the scintillator 11 is one of the factors that reduce the light emission output from the scintillator structure 10.

In particular, in recent years, as shown in FIG. 2, from the viewpoint of improving the resolution of an X-ray image, the scintillator 11 is divided into a plurality of cell CLs according to each of a plurality of photodiodes (scintillator). 11 arraying). Then, the reflective material 12 is provided so as to cover the plurality of cells CL. Specifically, the upper surface and the four side surfaces of the cell CL are covered with the 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 in contact with the photodiode.

When the scintillator 11 is divided into a plurality of cell CLs, the processed alteration layer 30 is formed on the surface of each of the plurality of cell CLs, so that the area of the processed altered layer 30 in the scintillator structure 10A becomes large. As a result, in the multi-cell type scintillator structure 10A, it is considered that the decrease in light emission output due to the processed alteration layer 30 becomes large.

The scintillator structure in the present embodiment is premised on the multi-cell scintillator structure 10A capable of improving the resolution of the X-ray image. Therefore, it is considered that the decrease in the light emission output due to the processed alteration layer 30 becomes large, and it is important to take measures to maintain the light emission output.

Here, regardless of whether the "GOS" ceramic or the "resin GOS" is used as the scintillator 11, the processed alteration 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 emission output is lowered due to the processed alteration layer 30.

In this regard, according to the study of the present inventor, when the scintillator 11 is composed of "resin GOS", the emission output due to the processed alteration layer 30 is higher than when the scintillator 11 is composed of "GOS" ceramic. We have newly found that the decline will be large.

The reason for this will be explained below. For example, the "GOS" ceramic can be heat-treated even after being fragmented into the cell CL. The heat treatment has a function of recovering the work-altered layer 30 formed by mechanical damage. Therefore, when the scintillator 11 is made of "GOS" ceramic, the processed altered layer 30 formed on the surface of the cell CL can be recovered by subjecting the scintillator 11 to individual pieces in the cell CL and then heat-treating the scintillator 11. You can. As a result, when the scintillator 11 is made of "GOS" ceramic, the processed alteration layer 30 is reduced by the heat treatment, so that the decrease in light emission output due to the processed altered layer 30 can be suppressed.

On the other hand, "resin GOS" is not ceramics 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 processed alteration layer 30 by heat treatment cannot be obtained, so that the decrease in light emission output due to the processed altered layer 30 becomes large. That is, unlike the "GOS" ceramic, the "resin GOS" is difficult to heat-treat and the processed altered layer 30 cannot be recovered, which is the second reason for reducing the light emission output from the scintillator structure 10A.

From the above, when the scintillator 11 is composed of "resin GOS", there is a synergistic factor between the first cause caused by the use of the "GOS" powder and the second cause that it is difficult to recover the work-altered layer 30. , The emission output is lower than that of "GOS" ceramic.

Therefore, when "resin GOS" is used as the scintillator 11, it is inevitable that the emission output is essentially lower than that of "GOS" ceramic. However, the present inventor has acquired as a new finding 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 composed of "resin GOS". That is, according to the novel findings found by the present inventor, it is considered that by defining the thickness and density of the cell CL, it is possible to secure a certain amount of light emission output even with "resin GOS".

Therefore, in the following, the thickness dependence and the density dependence of the emission output will be described.

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

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

First, the "first GOS" is "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 outputs 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 emission output than the "second GOS". The light emission output shown on the vertical axis of FIG. 3 is shown as a percentage with the light emission output of the "first GOS" having a thickness of 1.3 mm as 100%.

The "second resin GOS" is a mixture of a "GOS" powder composed of the "second GOS" and an epoxy resin.

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

Focusing on the curve of the "first GOS" in FIG. 3, it can be seen that the emission output of the "first GOS" hardly depends on the thickness of the cell. On the other hand, focusing on the curves of "second resin GOS" to "fourth resin GOS" in FIG. 3, each emission output of "second resin GOS" to "fourth resin GOS" is the thickness of the cell. It turns out that it depends on the plastic.

Hereinafter, the thickness dependence of each emission output of the "second resin GOS" to the "fourth resin GOS" will be qualitatively described. First, in the range where the thickness is thin, the light emission output increases as the thickness increases. This can be understood from the fact that in the thin range, the amount of "resin GOS" that contributes to the absorption of incident X-rays and the generation of visible light increases as the thickness increases. When the thickness becomes thick to some extent, the amount of "resin GOS" which absorbs the incident X-rays and contributes to the generation of visible light is saturated, while when the thickness becomes thick, the translucency decreases. It is understood that the light emission output decreases as the thickness increases due to the manifestation of the first cause and the second cause described above.

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

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

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

Here, the "density" means the density of the entire "resin GOS". In particular, in "resin GOS", the density of "GOS" powder is higher than that of epoxy resin, so that the following relationship is established.

That is, the 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, the high density of "resin GOS" means that the amount of "GOS" powder is large and the amount of epoxy resin is small.

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 ). 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 emission output increases as the density decreases. This means that the lower density means that the amount of highly translucent epoxy resin is relatively larger than that of the "GOS" powder, and as a result, the absorption of visible light is reduced, resulting in a higher density. It is considered that the lower the value, the larger the light emission output. In other words, the higher density means that the amount of "GOS" powder is higher than the amount of highly translucent epoxy resin, thus increasing the absorption of visible light in the "GOS" powder. As a result, it is considered that the emission output decreases as the density increases.

In the following, by configuring the scintillator 11 from "resin GOS", the manufacturing cost is reduced as compared with the case where the "GOS" ceramic is used as the scintillator 11, but the thickness dependence of the emission output described above (see FIG. 3). ) And the density dependence of the light emission output (FIG. 4), the points for improving the performance of the scintillator structure 10A will be described. In other words, a device for improving the cost performance of the scintillator structure 10A will be described.

Specifically, as the ingenuity to improve the performance of the scintillator structure 10A, the first ingenuity from the viewpoint of ensuring the light emission output and the second ingenuity from the viewpoint of ensuring the afterglow characteristics will be described. I will decide.

<Viewpoint to secure light emission output (first device)>
As shown in FIG. 3, 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 the light emission output of the "first GOS". That is, the "second resin GOS" formed by mixing an epoxy resin with the "GOS" powder composed of the "second GOS" having a larger emission output than the "first GOS" has a higher emission output than the "second GOS". Although it decreases, it can be seen that the emission output can be made higher than that of the "first GOS" by setting the cell thickness in the range of 0.5 mm or more and 1.8 mm or less. That is, if the thickness of the cell composed of the "second resin GOS" is set in the range of 0.5 mm or more and 1.8 mm or less, the emission output of the "second resin GOS" becomes equal to or more than that of the "first GOS". You can do it.

Next, as shown in FIG. 4, it can be seen that the emission output is improved as the density of the cell itself becomes smaller. In particular, when the density is set in the range of 4.4 g / cm ³ or more and less than 5.0 g / cm ³ , the emission output of the "first GOS" having 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.

From the above, on the premise that "resin GOS", which is a mixture of "GOS" powder made of "second GOS" and an epoxy resin, is used as the scintillator 11, the cell thickness is 0.5 mm or more and 1.8 mm or more. By setting the density of the cell itself to the range of 4.4 g / cm ³ or more and less than 5.0 g / cm ³ in addition to the following range, even if it is "resin GOS", the light emission output of "first GOS" or more can be obtained. Obtainable. In this way, while using the "resin GOS" that can reduce the manufacturing cost, by setting the thickness range and the density range to the above-mentioned ranges, it is possible to obtain a light emission output higher than that of the "first GOS". It is. That is, to secure the light emission output while using "resin GOS" that can reduce the manufacturing cost, the thickness of the cell is set in the range of 0.5 mm or more and 1.8 mm or less, and the density of the cell itself is adjusted. It can be realized by setting it in the range of 4.4 g / cm ³ or more and less than 5.0 g / cm ³ .

<Viewpoint to ensure afterglow characteristics (second device)>
The first device described above is a device from the viewpoint of ensuring the light emission output. On the other hand, the second ingenuity to be described below is an ingenuity from the viewpoint of ensuring the afterglow characteristics. That is, the performance of the scintillator structure 10A is required not only to have a large light emission output but also to have good afterglow characteristics. Therefore, first, the afterglow characteristics will be described.

The scintillator 11 constituting the scintillator structure 10A is a substance that generates visible light when exposed to X-rays. In the scintillator 11, the mechanism for generating visible light when exposed to X-rays is as follows. That is, when the scintillator 11 is irradiated with X-rays, the electrons in the scintillator 11 receive energy from the X-rays and transition from a low-energy ground state to a high-energy excited state. Then, the electrons in the excited state transition to the ground state with low 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 period of time. Visible light generated by the transition from the excited state of electrons to the ground state, which occurs after a certain amount of time has passed, becomes afterglow. That is, the afterglow is visible light generated when the timing of transition from the excited state to the ground state occurs after a certain amount of time has elapsed from the time when the X-ray is irradiated. The fact that this afterglow is large means that the intensity of visible light generated until a certain amount of time has elapsed even after the irradiation with X-rays is large. 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 is small. That is, good afterglow characteristics mean that the afterglow is small.

Here, the afterglow characteristics differ depending on the type of the 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 the time. 5 to 7 show that the higher the intensity of the afterglow after the passage of time, the worse the afterglow characteristics. In other words, in FIGS. 5 to 7, it is shown that the smaller the intensity of the afterglow after the passage of time, the better the afterglow characteristics.

Looking at FIGS. 5 to 7 focusing on this point, the afterglow characteristics of FIG. 5 and the afterglow characteristics of FIG. 6 are almost the same and the afterglow characteristics are good, while the afterglow characteristics of FIG. 7 are poor. I understand. That is, the afterglow characteristics of "CWO" shown in FIG. 5 and the afterglow characteristics of the "third resin GOS" shown in FIG. 6 are both good, while the afterglow characteristics of the "first resin GOS" shown in FIG. 7 are good. Turns out to be bad.

That is, from the viewpoint of light emission output, if the above-mentioned device 1 is realized, "2nd GOS"> "2nd resin GOS"> "1st resin GOS"> "1st GOS"> "4th resin GOS"> " There is a region where the relationship of "third resin GOS"> "CWO" is established.

On the other hand, referring to FIGS. 5 to 7, the relationship of “CWO” ≈ “third resin GOS” <“first resin GOS” is established from the viewpoint of afterglow characteristics.

Therefore, for example, 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 characteristics, "CWO" and "third resin GOS" are superior.

From this, in order to realize "resin GOS" having excellent afterglow characteristics, "first resin GOS" or "second resin GOS" in which an epoxy resin is mixed with "GOS" powder composed of "second GOS" It can be seen that "third resin GOS" and "fourth resin GOS", which are obtained by mixing an epoxy resin with "GOS" powder composed of "first GOS", are preferable. However, as shown in FIG. 3, the "third resin GOS" and the "fourth resin GOS" have a lower emission output than the "second resin GOS".

Therefore, it is desired to increase the light emission output as much as possible while ensuring the afterglow characteristics by adopting the "third resin GOS" or the "fourth resin GOS". In this regard, in FIG. 3, the cell thickness is 0.3 mm or more and 2.5 mm or less on the premise that "resin GOS" in which an epoxy resin is mixed with "GOS" powder composed of "first GOS" is used. By analogizing with Fig. 4, the density of the cell itself is set to the range of 4.4 g / cm ³ or more and 5.0 g / cm ³ or less, although it does not reach the emission output of "2nd GOS". It is considered that a light emission output of "CWO" or higher can be obtained. In this way, while using "resin GOS" that can reduce manufacturing costs and has good afterglow characteristics, by setting the thickness range and density range to the above-mentioned ranges, light emission of "CWO" or higher is achieved. You can get the output. That is, to secure the light emission output while using "resin GOS" which can reduce the manufacturing cost and has good afterglow characteristics, the cell thickness is set in the range of 0.3 mm or more and 2.5 mm or less. Moreover, it can be realized by setting the density of the cell itself in the range of 4.4 g / cm ³ or more and 5.0 g / cm ³ or less.

<Manufacturing method of scintillator structure>
Subsequently, a method for manufacturing the scintillator structure 10 will be described.

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

In FIG. 8, first, a predetermined amount of the raw material powder and the flux component are weighed and mixed (S101), and then the mixture is filled in a crucible and fired in an air furnace at 1300 ° C to 1400 ° C for 7 to 9 hours. (S102), "GOS" powder is produced. Then, the flux component and impurities contained in the "GOS" powder are removed by washing with hydrochloric acid and warm water (S103). Next, the epoxy resin is impregnated into the "GOS" powder by dropping the epoxy resin into the "GOS" powder (S104). Next, after the epoxy resin is cured (S105), the epoxy resin that is not mixed with the "GOS" powder is removed (S106). This makes it possible to form a scintillator made of "resin GOS".

Subsequently, the substrate on which the scintillator is formed is diced to individualize the substrate into a plurality of cells (S107). After the plurality of individualized cells are rearranged (S108), a reflective material is applied so as to cover the plurality of cells (S109). Then, after cutting the unnecessary portion 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 a process from the dicing process to the reflective material coating process.

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

In FIG. 9, a line-shaped scintillator structure 10A using 1 × n cells is described as an example, but the technical idea in the present embodiment is not limited to this, for example. It can also be applied to an array-shaped (matrix-shaped) scintillator structure using n × n cells.

<Characteristics of manufacturing method>
Next, the feature points in the manufacturing method in this embodiment will be described.

The characteristic feature of the manufacturing method in the present embodiment is that the substrate WF on which the scintillator 11 is formed is completely separated into a plurality of cell CLs by full-cut dicing, and then the separated plurality of cell CLs are re-individed. The point is to manufacture the scintillator structure 10A by applying the reflective material 12 so as to cover the plurality of rearranged cells CL after the arrangement.

Thereby, according to the present embodiment, the spacing between cells can be freely adjusted.

For example, there is a technique of half-dicing a substrate WF on which a scintillator 11 is formed, applying a reflective material 12, and then grinding the half-diced substrate WF to separate cells CL adjacent to each other. According to this technique, since the distance between the cells CL adjacent to each other is determined by the cutting width of the half dicing, the distance between the cells CL adjacent to each other can be accurately determined. This means that, on the flip side, this technique cannot freely change the spacing between cell CLs.

Regarding this point, for example, depending on the user of the X-ray detector, there is a user who wants to acquire a high-definition X-ray image by arranging a photodiode as a light receiving element at a high density, and a photodiode is arranged at a low density. There are also users who want to acquire a wide range of X-ray images, although they are not high-definition. In the former case, it is required to arrange a plurality of cells CL constituting the scintillator structure 10A at a high density corresponding to the photodiodes arranged at a high density. In this case, it is necessary to make the interval between the cells CL very small. For example, when the interval between cell CLs is made smaller than the cutting width of half dicing, the technique using half dicing cannot cope with it. On the other hand, also in the latter case, even if the cell CL spacing is desired to be larger than the width of the half dicing, the technique using the half dicing cannot cope with it. In this way, in the technique using half dicing, the interval between cell CLs is uniformly determined by the shear width of half dicing, so that the interval between cell CLs cannot be freely adjusted according to the user's request. ..

On the other hand, in the present embodiment, the substrate WF on which the scintillator 11 is formed is separated into a plurality of cell CLs by full-cut dicing instead of half dicing, and then the separated plurality of cell CLs are used. It is rearranged. Thereby, according to the present embodiment, when rearranging a plurality of cell CLs, the spacing between the adjacent cell CLs can be freely set.

From this, according to the present embodiment, since the interval between the cell CLs can be made smaller or larger than the cutting width of the dicing, there is an advantage that the scintillator structure 10A corresponding to the user's needs can be flexibly manufactured. Is obtained.

Further, according to the present embodiment, the following advantages can be obtained. That is, in the technique using half dicing, the cell CL is finally separated by the grinding process.

In this regard, in the present embodiment, a plurality of cell CLs are individualized by full-cut dicing. This eliminates the need for a grinding process that separates a plurality of cell CLs in the subsequent process. This means that the grinding process for separating a plurality of cell CLs can be reduced. As a result, the method for manufacturing the scintillator structure 10A in the present embodiment can also obtain an advantage that the manufacturing process can be simplified.

<Viewpoint to improve adhesion (third device)>
For example, a constant temperature and high humidity test is performed on the scintillator structure 10A, which is a finished product manufactured through the above-mentioned manufacturing process, in order to ensure reliability.

Here, it was confirmed that when a constant temperature and high humidity test was performed on the scintillator structure 10A using "resin GOS" for the scintillator 11, the rate of passing the constant temperature and high humidity test decreased. In this regard, the present inventor has newly found that the rate of passing the constant temperature and high humidity test decreases due to the decrease in the adhesion at the interface between the scintillator 11 made of "resin GOS" and the reflective material 12. rice field. Therefore, in the present embodiment, from the viewpoint of improving the reliability of the scintillator structure 10A, a device for improving the adhesion between the scintillator 11 made of "resin GOS" and the reflective material 12 is taken. In the following, this device will be described.

<< New findings >>
First, the novel findings found by the present inventor will be described.

The novel finding found by the present inventor is that the surface of the "resin GOS" is surface-treated before the reflective material 12 is applied so as to cover the scintillator 11 made of the "resin GOS". It is a finding that the adhesion at the interface between the "resin GOS" and the reflective material 12 differs depending on the type of treatment. The present invention states that the cause of the difference in the adhesive force at the interface between the "resin GOS" and the reflective material 12 is that the wettability to the reflective material 12 changes depending on the type of surface treatment on the surface of the "resin GOS". Is 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 of the reflective material 12, the adhesive force at the interface between the "resin GOS" and the reflective material 12 can be improved. That is, it is considered that if the surface treatment layer is formed on the surface of the plurality of cells CL and 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 considered that the adhesion can be improved by forming a surface treatment layer on at least the side surface and the upper surface of each of the plurality of cells CL.

Therefore, the wettability to the epoxy resin was evaluated for various surface treatments.

In FIG. 10, the wettability with respect to the epoxy resin was evaluated by comparing the contact angles when the epoxy resin was dropped on the surface of the “resin GOS” after various surface treatments were applied to the surface of the “resin GOS”. It is a graph which shows the result.

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

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

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

Therefore, it is presumed that when the titanium oxide dipping treatment, which has the best wettability with respect to the epoxy resin, is carried out, the adhesive force at the interface between the "resin GOS" and the reflective material 12 is increased. That is, as shown in FIG. 11, when the titanium oxide immersion treatment is carried out, the wettability is improved by adhering titanium oxide to the surface of the scintillator 11 made of "resin GOS", and the scintillator 11 and the reflective material 12 adhere to each other. As a result of the increase in the area, it is considered that the adhesive force at the interface between the scintillator 11 made of "resin GOS" and the reflective material 12 is increased.

From the above, the device for improving the adhesion between the scintillator 11 made of "resin GOS" and the reflective material 12 is to apply the reflective material 12 to the reflective material 12 before applying the reflective material 12 so as to cover the scintillator 11. On the other hand, a surface treatment for improving wettability is performed on the surface of the scintillator 11. Specifically, this device is realized by performing a titanium oxide liquid immersion treatment on the surface of the scintillator 11 before applying the reflective material 12 so as to cover the scintillator 11.

<< Verification of effect >>
In the following, before the reflective material 12 is applied so as 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 formed. The verification results that support the high adhesion will be explained.

The present inventor considers that it is possible to quantitatively compare the adhesion at the interface between the scintillator 11 and the reflector 12 by the breaking strength of the bending test, and the adhesion at the interface between the scintillator 11 and the reflector 12 by the bending test. Now that the force has been evaluated, the evaluation results of this anti-fold test will be explained. Specifically, in the present embodiment, the adhesion was evaluated by a bending test based on the three-point bending test defined 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): 50 mm x 6.2 mm x 1.2 mm
Indenter tip radius (R ₁ ): 0.3 mm
Support base corner radius (R ₂ ): 0.3 mm
Specimen (sample) thickness (h): 6.2 mm
Specimen (sample) length (l): 50 mm
Distance between fulcrums (L): 10 mm
1. 1. Sample Preparation FIG. 12 (a) is a cross-sectional view schematically showing a sample preparation process to be evaluated in a folding test, and FIG. 12 (b) is a schematic view of a sample preparation process to be evaluated in a folding test. It is a top view shown in.

As shown in FIG. 12A, 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 the scintillator structure 10A is ground and FIG. As shown in (b), a sample SP is prepared by grinding two side surfaces (long side 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 in warm water at 80 ° C. for 80 minutes. Then, an anti-folding test is performed on the sample SP that has been subjected to the constant temperature and high humidity test.

2. 2. Folding test FIG. 13 (a) is a cross-sectional view showing a state of the folding test, and FIG. 13 (b) is a top view showing a state of the folding 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 reflector, and as shown in FIG. 13 (b), the tip of the indenter NL is the sample SP. It is arranged so as to be located in the center in the width direction.

In the fracture resistance test, the indenter NL is pressed against the sample SP from above, and the breaking strength when the sample SP is broken is measured. It can be said that the higher the breaking strength, the higher the adhesion 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 reflector 12 can be evaluated based on the breaking strength measured in the bending resistance test. The evaluation results will be described below.

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

3. 3. Evaluation Results FIG. 14 is a diagram showing the evaluation results of the anti-fold test.

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

FIG. 14B is a graph showing the breaking strength measured by performing a bending test with respect to the sample SP corresponding to each of “Condition 1” to “Condition 8”. As shown in FIG. 14B, it can be seen that the breaking strength of the sample SP subjected to the titanium oxide liquid immersion treatment as the surface treatment is high. 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, before the reflective material 12 is applied so as to cover the scintillator 11 made of "resin GOS", the scintillator 11 and the reflective material 12 are subjected to a titanium oxide liquid immersion treatment on the surface of the scintillator 11. It can be seen that this is supported by the fact that the adhesion at the interface is high.

From the viewpoint of improving the adhesion 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 1182 gf or more. Is desirable.

Although the invention made by the present inventor has been specifically described above based on the embodiment thereof, the present invention is not limited to the embodiment and can be variously modified 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 processed alteration layer 100 X-ray detector CL cell FR outer frame NL indenter SP sample WF substrate

Claims (2)

With multiple cells
The reflective material that covers the plurality of cells and
A scintillator structure comprising
Each of the plurality of cells contains a resin and a phosphor.
The fluorophore consists of gadolinium acid sulfide 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.
The thickness of each of the plurality of cells is 0.3 mm or more and 2.5 mm or less.
Each of the plurality of cells has a processing alteration layer.
The processing alteration layer is a scintillator which is a layer in which light reflection characteristics are deteriorated and light is more easily absorbed than before mechanical processing due to mechanical damage caused by the mechanical processing process. Structure. A method for manufacturing a scintillator structure including a plurality of cells containing a resin and a phosphor, respectively, and a reflective material covering the plurality of cells.
(A) A step of separating the substrate into the plurality of cells.
(B) A step of arranging the plurality of separated cells.
(C) A step of forming the reflective material so as to cover the plurality of arranged cells.
Have,
The fluorophore consists of gadolinium acid sulfide 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.
A method for manufacturing a scintillator structure, wherein the thickness of each of the plurality of cells is 0.3 mm or more and 2.5 mm or less.

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