JP7593178B2 - Scintillator structure and method of manufacturing same - Google Patents

Description

The present invention relates to a scintillator structure and a manufacturing method thereof, for example, to a technology that is effective when applied to a scintillator structure having multiple cells, each of which contains a resin and a phosphor, and a manufacturing method thereof.

JP 2-17489 A (Patent Document 1) describes technology related to phosphors used in radiation detectors.

Japanese Unexamined Patent Publication No. 2-17489

A scintillator is a material that absorbs the energy of radiation, such as X-rays or gamma rays, and generates visible light when it is struck by the radiation. This scintillator is commercialized as a scintillator structure that includes a scintillator and a reflector, and X-ray detectors that combine a scintillator structure with a photoelectric conversion element such as a photodiode are used, for example, in medical equipment such as X-ray CT, analytical equipment, non-destructive testing equipment that uses radiation, and radiation leakage testing equipment.

For example, ceramics made of gadolinium oxysulfide (Gd ₂ O ₂ S) are used for the scintillator. Here, in this specification, gadolinium oxysulfide is referred to as "GOS". Strictly speaking, gadolinium oxysulfide itself hardly emits light, but emits light by making gadolinium oxysulfide contain praseodymium, terbium, etc. For this reason, the term "GOS" is used in this specification with the implicit intention of a substance (phosphor) that emits light by making gadolinium oxysulfide itself contain praseodymium, terbium, etc. However, when it is necessary to explicitly indicate that gadolinium oxysulfide itself contains praseodymium, terbium, etc., it may be expressed as "GOS" containing praseodymium or "GOS" containing terbium.

In addition, when the scintillator is made of "GOS" alone, the "GOS" is made of ceramic. On the other hand, as described below, it is also being considered to make the scintillator out of a mixture of "GOS" and resin, in which case the "GOS" is made of powder. Therefore, in this specification, when there is no need to specifically distinguish between ceramic and powder, it will simply be referred to as "GOS". In contrast, when it is necessary to specifically state the ceramic, it will be called "GOS" ceramic. On the other hand, when it is necessary to specifically state the powder, it will be called "GOS" powder.

While GOS has the advantage of having a greater visible light emission output than cadmium tungstate (CdWO ₄ ), it has a high manufacturing cost.

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

However, the inventor has newly discovered that when a mixture of "GOS" powder and resin is used, there is room for improvement in terms of adhesion between the cells made of the scintillator and the reflective material. Therefore, when using a mixture of "GOS" powder and resin as a scintillator, it is desirable to ensure adhesion between the cells made of the scintillator and the reflective material.

The object of the present invention is to provide a scintillator structure and a method for manufacturing the same that can improve the adhesion between multiple cells and a reflective material.

The scintillator structure in one embodiment includes a plurality of cells and a reflector covering the plurality of cells. Here, each of the plurality of cells includes a resin and a phosphor, and each of the plurality of cells is chemically bonded to the reflector.

In one embodiment, the method for manufacturing a scintillator structure includes a plurality of cells each containing a resin and a phosphor, and a reflective material covering the plurality of cells. The method for manufacturing the scintillator structure includes (a) a step of producing a substrate made of a mixture of resin and phosphor, (b) a step of semi-crosslinking the substrate, (c) a step of forming a plurality of cells by singulating the semi-crosslinked substrate, (d) a step of forming a reflective material covering the plurality of cells in a semi-crosslinked state, and (e) a step of crosslinking the reflective material while each of the plurality of cells is in a semi-crosslinked state. In this case, in the step (e), each of the plurality of cells is crosslinked with the reflective material.

According to one embodiment, the adhesion between multiple cells and the reflective material can be improved.

FIG. 1 is a diagram illustrating an X-ray detector. 1 is a flowchart showing a manufacturing process in the related art. 3 is a flowchart showing a manufacturing process according to the embodiment.

In all drawings used to explain the embodiments, the same components are generally given the same reference numerals, and repeated explanations will be omitted. In addition, hatching may be used even in plan views to make the drawings easier to understand.

<X-ray detector overview>
FIG. 1 is a diagram illustrating 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 plurality of scintillators 11 that generate visible light from X-rays incident on the X-ray detector 100, and a reflector 12 that covers each of the plurality of scintillators 11. On the other hand, the light receiving element 20 has a function of generating an electric current from the visible light generated by the scintillator 11, and is composed of a photoelectric conversion element such as a photodiode. The light receiving element 20 is provided, for example, on a support 30, and is provided corresponding to each of the plurality of scintillators 11.

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

In recent years, as shown in FIG. 1, in the scintillator structure 10, the scintillator 11 is divided into a plurality of cells (CL). That is, from the viewpoint of improving the resolution of X-ray images, the scintillator 11 is divided into a plurality of cells CL in accordance with each of the plurality of light receiving elements 20 (arraying the scintillator 11). In this way, the scintillator structure 10 includes a plurality of cells CL and a reflector 12 that covers the plurality of cells CL. Specifically, the upper surface and four side surfaces of the cell CL are covered with the reflector 12. On the other hand, the lower surface of the cell CL is not covered with the reflector 12 because it needs to be in contact with the light receiving element 20.

An X-ray detector configured in this way operates as follows:

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

Then, a portion of the visible light generated from the scintillator 11 is directly incident on the light receiving element 20, while another portion of the visible light generated from the scintillator 11 is repeatedly reflected by the reflector 12 that covers the scintillator 11 and is focused on the light receiving element 20. Next, when visible light is incident on the light receiving element 20, which is composed of, for example, a photodiode, the energy of this visible light excites electrons in the semiconductor material that composes the photodiode from the valence band to the conduction band. This causes a current due to the electrons excited to the conduction band to flow in the photodiode. 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.

For example, as shown in FIG. 1, the scintillator structure 10 is composed of a rectangular parallelepiped scintillator 11 and a reflective material 12 that covers the scintillator 11. Here, the rectangular parallelepiped scintillator 11 is formed through processing steps such as a dicing process and a grinding process, and therefore a processed surface is formed on the surface of the rectangular parallelepiped shape. In other words, the "processed surface" refers to a surface that has been mechanically processed. Specifically, the "processed surface" includes a surface that has been ground with a grinding wheel when performing thickness adjustment of the workpiece, or a surface where the workpiece has been cut with a slicing blade to perform a dicing process.

For example, in a scintillator 11 that uses "resin GOS," the "machined surface" is defined as a surface that includes a mixture of a surface where the resin is exposed and a surface where the "GOS" powder has been broken. For example, FIG. 1 shows a schematic representation of a scintillator 11 that uses "resin GOS," where the interface between the scintillator 11 and the reflector 12 is the "machined surface." In this case, it can be seen that the "machined surface" includes a mixture of an area where the resin 11b has been cut and an area where the phosphor 11a (the "GOS" powder) has been broken. In this manner, the X-ray detector 100 is constructed.

<Reasons for using "resin GOS">
As described above, in this embodiment, "resin GOS" is used as the scintillator 11. The reason for this will be described below.

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

Therefore, from the perspective of reducing manufacturing costs, it is being considered to use "resin GOS", which is a mixture of "GOS" powder and a resin such as epoxy resin, as the scintillator 11, instead of "GOS" ceramic. In other words, 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 costs caused by "GOS" ceramic.

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

The "first resin GOS" and the "second resin GOS" both have the advantage of having a higher light emission output than "CWO". Furthermore, the "first resin GOS" also has the advantage that the afterglow characteristics are equivalent to those of "CWO". In other words, the performance of the scintillator structure 10 requires not only high light emission output but also good afterglow characteristics.

Now, the afterglow characteristics will be explained. The scintillator 11 constituting the scintillator structure 10 is a material that generates visible light when it is irradiated with X-rays. The mechanism by which the scintillator 11 generates visible light when it is irradiated with 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 a low-energy ground state. At this time, most of the excited electrons immediately transition to the ground state. On the other hand, some of the excited electrons transition to the ground state after a certain amount of time has passed. The visible light generated by the transition of the electrons from the excited state to the ground state that occurs after this certain amount of time has passed becomes the afterglow. In other words, the afterglow is visible light that is generated when the timing of the transition from the excited state to the ground state occurs after a certain amount of time has passed from the time of irradiation with X-rays. And, the fact that this afterglow is large means that the intensity of the visible light generated until a certain amount of time has passed after 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 for the afterglow to be small. In other words, good afterglow characteristics mean small afterglow. In this regard, the afterglow characteristics of the "first resin GOS" are equivalent to those of the "CWO". Therefore, compared to "CWO", "resin GOS" has the following advantages, making it an excellent scintillator 11 that can achieve both performance and manufacturing costs.

(1) "Resin GOS" has a higher light output than "CWO."
(2) The afterglow characteristics of the "first resin GOS" are equivalent to those of the "CWO".
(3) Cadmium is not used in "Resin GOS".
(4) "Resin GOS" has lower manufacturing costs than "CWO".

In addition, cesium iodide (CsI) is used as the scintillator 11, but "resin GOS" has the following advantages over "CsI".

(1) The "second resin GOS" has better X-ray stopping properties than "CsI."
(2) The afterglow characteristics of the "second resin GOS" are approximately 1/70 of "CsI".
(3) "Resin GOS" is a stable substance that does not deliquesce.

Furthermore, "resin GOS" has the following advantages over "GOS" ceramic. That is, "resin GOS" and "GOS" ceramic contain heavy metals such as "Gd", "Ga" and "Bi". These heavy metals are relatively expensive and there are concerns that they may have a negative impact on living organisms and the environment if they are leaked. Therefore, it is desirable for the scintillator 11 to contain as few heavy metals as possible. In this regard, "resin GOS", which is composed of a mixture of "GOS" powder and resin, uses less "GOS" than "GOS" ceramic, which is a bulk material. This means that "resin GOS" can be used to construct a scintillator 11 with a lower heavy metal content than "GOS" ceramic. From this, it can be said that "resin GOS" is superior to "GOS" ceramic in that it can provide a scintillator 11 with a lower heavy metal content.

For these reasons, "resin GOS" is seen as a promising scintillator 11 that can achieve both high performance and low manufacturing costs.

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

<<Phosphor 11a>>
The phosphor 11a used in this embodiment is composed of, for example, gadolinium oxysulfide or gadolinium-aluminum-gallium garnet (GGAG). Here, gadolinium oxysulfide has a composition of "Gd ₂ O _{2 S} " activated with at least one selected from praseodymium (Pr), cerium (Ce) or terbium (Tb). On the other hand, "GGAG" has a main composition of (Gd _1-x Lu _x ) _3+a (Ga _u Al _1-u ) _5-a O ₁₂ (x=0 to 0.5, u=0.2 to 0.6, a=-0.05 to 0.15) activated with at least one selected from cerium (Ce) or praseodymium (Pr). However, the phosphor 11a is not limited to a specific composition.

<<Resin 11b and Resin 12b>>
Resin 11b and resin 12b are made of a resin having light transmitting properties. In particular, resin 11b and resin 12b desirably have a light transmittance of 85% or more in the wavelength range of 450 nm to 650 nm. For example, resin 11b and resin 12b may be epoxy resin, polyester resin, acrylic resin, silicone resin, vinyl resin, etc. These resins may be used alone or in combination of two or more types.

<<Reflective particles 12a>>
Examples of the constituent material of the reflective particles 12a include white particles such as " _TiO2 " (titanium oxide), " _Al2O3 " (aluminum oxide), and " _ZrO2 " ₍ zirconium oxide). The reflective particles 12a may be, for example, a mixture of bulk or powder and resin. In particular, the reflective particles 12a made of "rutile type TiO ₂ " are desirable because they have excellent light reflection efficiency. From the viewpoint of improving the light receiving efficiency of the light receiving element 20, the light reflectance of the reflective particles 12a is preferably 80% or more, and more preferably 90% or more. desirable.

<<Other additives>>
In addition to the above-mentioned components, other additives may be blended into the scintillator 11 and the reflective material 12. For example, it is desirable to blend a curing catalyst in order to shorten the curing time of the resin.

<Consideration of improvements>
The inventors have examined the scintillator structure 10 having the above-mentioned configuration and have newly found room for improvement as described below, which will be described below. That is, the inventors have newly found that the scintillator structure 10 may be used in a high-temperature and high-humidity environment, and in this case, peeling is likely to occur at the interface between the scintillator 11 and the reflector 12. Thus, there is room for improvement in the scintillator structure 10 from the viewpoint of improving reliability. Therefore, in this embodiment, some ingenuity has been implemented to address the above-mentioned room for improvement. The technical idea of this embodiment in which this ingenuity has been implemented will be described below.

<Basic Concept of the Embodiment>
The basic idea of the present embodiment is to chemically bond the scintillator 11 and the reflector 12. This allows the interface between the scintillator 11 and the reflector 12 to be strongly chemically bonded, and as a result, even if the scintillator structure 10 is used in a high-temperature and high-humidity environment, peeling at the interface between the scintillator 11 and the reflector 12 can be suppressed. In other words, according to this basic idea, the reliability of the scintillator structure 10 can be improved.

In particular, in this embodiment, the basic idea of chemically bonding the scintillator 11 and the reflector 12 can be realized, for example, by bridging each of the multiple cells CL consisting of the scintillator 11 with the reflector 12. In other words, in this embodiment, the above-mentioned basic idea is embodied by bridging each of the multiple cells CL with the reflector 12. As a result, according to this embodiment, the interface between the resin 11b of the multiple cells CL and the resin 12b of the reflector 12 is firmly bonded by bridging, and therefore, according to this embodiment, the adhesion between each of the multiple cells CL and the reflector 12 is improved, thereby achieving a remarkable effect of improving the reliability of the scintillator structure 10.

The following describes, using related technology, how we arrived at the idea of bridging each of the multiple cells CL made of the scintillator 11 with the reflector 12 in order to realize the idea of chemically bonding the scintillator 11 with the reflector 12.

In this specification, "related technology" refers to technology that is not publicly known, but has problems that the inventor has discovered, and is the premise of the present invention.

Figure 2 is a flow chart explaining a method for manufacturing a scintillator structure in the related art. In Figure 2, first, a substrate made of "resin GOS", which is a mixture of "GOS" powder and resin, is produced (S101). Then, the substrate is completely cross-linked by using a cross-linking reaction (S102). At this time, the cross-linking reaction is carried out until it is completely completed, and as a result, the "resin GOS" constituting the substrate is completely cross-linked. After that, the substrate is divided into individual pieces to obtain multiple cells made of the cross-linked "resin GOS" (S103). Next, a reflective material is formed to cover the multiple cells (S104), and then the reflective material is completely cross-linked by using a cross-linking reaction (S105). In this manner, a scintillator structure can be manufactured.

Here, in the related technology, the crosslinking reaction in the "resin GOS" is completed, and then the crosslinking reaction in the reflective material is performed. In other words, in the related technology, the crosslinking reaction in the "resin GOS" and the crosslinking reaction in the reflective material are performed independently and separately without being linked. For this reason, while the related technology can crosslink each of the "resin GOS" and the reflective material, it cannot crosslink the interface between the "resin GOS" and the reflective material. Therefore, the inventor speculates that, in the related technology, it is difficult to improve the adhesion between the "resin GOS" and the reflective material, and therefore, when the scintillator structure is used in a high-temperature and high-humidity environment, peeling is likely to occur at the interface between the "resin GOS" and the reflective material 12. On the other hand, the inventor has found a new finding that if the crosslinking reaction in the "resin GOS" and the crosslinking reaction in the reflective material can be performed in association with each other, the interface between the "resin GOS" and the reflective material can also be crosslinked, thereby improving the adhesion between the "resin GOS" and the reflective material.

The inventor has therefore devised a method for producing a scintillator structure that improves adhesion between the "resin GOS" and the reflective material by linking the crosslinking reaction of the "resin GOS" with the crosslinking reaction of the reflective material, thereby crosslinking the interface between the "resin GOS" and the reflective material. The method for producing a scintillator structure that has been devised by the inventor is the method for producing a scintillator structure in this embodiment, and the method for producing a scintillator structure in this embodiment will be described below.

<Method of manufacturing scintillator structure according to embodiment>
FIG. 3 is a flow chart illustrating the flow of the manufacturing process for the scintillator structure 10.

In FIG. 3, first, a predetermined amount of raw powder and flux components are weighed and mixed, and then the mixture is filled into a crucible and baked in an atmospheric furnace at 1300°C to 1400°C for 7 to 9 hours to produce "GOS" powder. Flux components and impurities contained in the "GOS" powder are then removed by washing with hydrochloric acid and hot water. Next, epoxy resin is dripped onto the "GOS" powder to allow the "GOS" powder to be saturated with epoxy resin. This produces a substrate made of "resin GOS" (S201). Next, crosslinking is performed on the substrate made of "resin GOS". At this time, in this embodiment, the substrate is not completely crosslinked, but the substrate is put into a semi-crosslinked state (S202). This allows the scintillator 11 made of semi-crosslinked "resin GOS" to be formed.

Here, the term "semi-crosslinked state" is defined as a state in which the chemical reaction (crosslinking reaction) has not yet been completely completed, and includes, for example, a gel state. In particular, the term "semi-crosslinked state" as used herein refers to a state in which the gel fraction is 80% or more and 95% or less. This is because if the gel fraction is less than 80%, it is difficult to maintain the shape of the individualized cells, while if the gel fraction exceeds 95%, reactivity is poor.

This gel fraction can be calculated using the formula below:

Gel fraction (%)=mass after drying/initial mass×100
The gel fraction is measured by the following procedure: First, the initial mass of the sample is measured, then the sample is immersed in a xylene solution for 24 hours, and the sample is taken out of the xylene solution and naturally dried overnight, and then vacuum dried, and the mass after drying is measured.

Then, the substrate on which the scintillator 11 is formed is diced to separate the substrate into a plurality of cells CL (S203). The separated cells CL are rearranged, and then the reflector 12 is formed to cover the cells CL (S204). Then, the reflector 12 is crosslinked (S205). At this time, not only is the reflector 12 itself crosslinked, but each of the cells CL in a semi-crosslinked state in which the chemical reaction has not yet been completed is chemically bonded to the reflector 12. In other words, each of the cells CL is crosslinked to the reflector 12. As a result, according to this embodiment, the adhesion between each of the cells CL and the reflector 12 can be significantly improved. Then, after unnecessary parts of the scintillator structure 10 are cut off, the scintillator structure 10 that has passed inspection is shipped.

<Features of the embodiment>
The feature of this embodiment is that the crosslinking reaction of the "resin GOS" and the crosslinking reaction of the reflective material are not performed independently, but are performed in association with each other, so that the interface between the "resin GOS" and the reflective material is also crosslinked. Specifically, in this embodiment, in order to associate the crosslinking reaction of the "resin GOS" and the crosslinking reaction of the reflective material with each other, the substrate is divided into a plurality of cells while maintaining the "semi-crosslinked state" before the crosslinking reaction of the "resin GOS" is completely completed, and a reflective material covering the plurality of cells is formed, and then a crosslinking reaction is caused on the reflective material. In this case, when a crosslinking reaction is caused on the reflective material, a crosslinking reaction also proceeds on the plurality of cells in the "semi-crosslinked state". This means that the crosslinking reaction of the "resin GOS" and the crosslinking reaction of the reflective material are associated with each other. As a result, the crosslinking reaction proceeds simultaneously on both the plurality of cells in the "semi-crosslinked state" and the reflective material, and thus not only the crosslinking reaction of each of the plurality of cells itself and the crosslinking reaction of the reflective material itself, but also the crosslinking reaction connecting each of the plurality of cells and the reflective material can be caused. As a result, according to this embodiment, each of the multiple cells is chemically bonded to the reflector by crosslinking, so that the adhesion between each of the multiple cells and the reflector can be improved. Therefore, according to the scintillator structure of this embodiment, even if it is used in a high-temperature and high-humidity environment, peeling at the interface between each of the multiple cells and the reflector can be suppressed. In other words, according to this embodiment, the reliability of the scintillator structure can be improved.

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

REFERENCE SIGNS LIST 10 Scintillator structure 11 Scintillator 11a Phosphor 11b Resin 12 Reflector 12a Reflective particle 12b Resin 20 Light receiving element 30 Support 100 X-ray detector CL Cell

Claims (8)

A scintillator structure comprising a plurality of cells and a reflector covering the plurality of cells,
Each of the plurality of cells includes a resin and a phosphor;
A scintillator structure, wherein each of the plurality of cells is chemically bonded to the reflective material on the top and side surfaces of the plurality of cells . 2. The scintillator structure of claim 1,
A scintillator structure, wherein each of the plurality of cells and the reflector are cross-linked. 3. The scintillator structure according to claim 1,
The scintillator structure includes a light-transmitting resin that is transmissive to light having a wavelength in the range of 450 nm to 650 nm, and reflective particles . 3. The scintillator structure according to claim 1,
The cell is a scintillator structure including a light-transmitting resin that is transmissive to light having a wavelength in the range of 450 nm to 650 nm, and the phosphor. The scintillator structure according to any one of claims 1 to 4 ,
The scintillator structure wherein the phosphor comprises gadolinium oxysulfide. A method for manufacturing a scintillator structure including a plurality of cells containing a resin and a phosphor and a reflective material covering each of the plurality of cells, the method comprising the steps of:
(a) preparing a substrate made of a mixture of a resin and a phosphor;
(b) semi-crosslinking the substrate;
(c) singulating the semi-crosslinked substrate to form the plurality of cells;
(d) forming the reflective material to cover the plurality of cells in a semi-crosslinked state;
(e) cross-linking the reflective material while each of the plurality of cells is in a semi-cross-linked state;
In the step (e), interfaces between each of the plurality of cells and the reflective material are cross-linked. 7. The method for producing a scintillator structure according to claim 6 ,
A method for manufacturing a scintillator structure, wherein each of the plurality of cells in the semi-crosslinked state has a gel fraction of 80% or more and 95% or less. 8. The method for producing a scintillator structure according to claim 6 , further comprising the steps of :
The semi-crosslinked state is a state in which the crosslinking reaction has not been completely completed.

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