JP2022141118A - Scintillator structure and manufacturing method therefor - Google Patents

Abstract

To improve adhesion between a plurality of cells and a reflective material.SOLUTION: A scintillator structure 10 provided herein comprises a plurality of cells CL and a reflective material 12 covering the plurality of cells CL. Each of the plurality of cells CL contains a resin and a phosphor and is chemically coupled to the reflective material 12.SELECTED DRAWING: Figure 1

Description

The present invention relates to a scintillator structure and its manufacturing method, and for example, to a technique effectively applied to a scintillator structure having a plurality of cells each containing a resin and a phosphor and its manufacturing method.

Japanese Patent Laying-Open No. 2-17489 (Patent Document 1) describes a technique related to phosphors used in radiation detectors.

JP-A-2-17489

A scintillator is a substance that absorbs the energy of radiation and emits visible light when exposed to radiation such as X-rays and gamma rays. This scintillator is commercialized as a scintillator structure containing 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 is used for medical equipment such as X-ray CT, It is used in analysis equipment, non-destructive inspection equipment using radiation, radiation leakage inspection equipment, etc.

For example, scintillators use ceramics made of gadolinium oxysulfide (Gd ₂ O ₂ S). Here, in this specification, gadolinium oxysulfide will be referred to as "GOS". Strictly speaking, gadolinium oxysulfide itself hardly emits light, and gadolinium oxysulfide contains praseodymium, terbium, or the like to emit light. For this reason, the term "GOS" is used in this specification to imply a substance (phosphor) that emits light by containing praseodymium, terbium, or the like in gadolinium oxysulfide itself. 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.

Further, when the scintillator is composed of a single "GOS", the "GOS" is composed of ceramic. On the other hand, as will be described later, it is also under study to construct the scintillator from a mixture of "GOS" and resin, and in this case, "GOS" is composed of powder. Therefore, in this specification, when there is no need to specify ceramic and powder, the term "GOS" is simply used. In contrast, when it is necessary to specify the ceramic, it is referred to as a "GOS" ceramic. On the other hand, when it is necessary to specify 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 the manufacturing cost is high.

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

However, the present inventor has newly found that the use of a mixture of "GOS" powder and resin leaves room for improvement in terms of the adhesion between the cell composed of the scintillator and the reflective material. Therefore, when a mixture of "GOS" powder and resin is used as the scintillator, it is desired to ensure the adhesion between the cell composed of the scintillator and the reflector.

SUMMARY OF THE INVENTION An object of the present invention is to provide a scintillator structure capable of improving the adhesion between a plurality of cells and a reflective material, and a method of manufacturing the same.

A scintillator structure in one embodiment comprises a plurality of cells and a reflective material covering the plurality of cells. Here, each of the plurality of cells contains resin and phosphor, and each of the plurality of cells and the reflector are chemically bonded.

A method for manufacturing a scintillator structure according to one embodiment is a method for manufacturing a scintillator structure including a plurality of cells each containing a resin and a phosphor and a reflector covering the plurality of cells. The method for manufacturing this scintillator structure includes (a) a step of preparing a substrate made of a mixture of a resin and a phosphor, (b) a step of semi-crosslinking the substrate, and (c) separating the semi-crosslinked substrate into individual pieces. (d) forming a reflector covering the plurality of cells in a semi-crosslinked state; and (e) bridging the reflector while each of the plurality of cells is in a semi-crosslinked state. Prepare. At this time, in the step (e), each of the plurality of cells and the reflector are crosslinked.

According to one embodiment, it is possible to improve the adhesion between the plurality of cells and the reflector.

It is a figure which shows an X-ray detector typically. It is a flowchart which shows the manufacturing process in related technology. 4 is a flow chart showing a manufacturing process in the embodiment;

In principle, the same members are denoted by the same reference numerals throughout the drawings for describing the embodiments, and repeated description thereof will be omitted. In order to make the drawing easier to understand, even a plan view may be hatched.

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

In FIG. 1, an 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 scintillators 11 . On the other hand, the light receiving element 20 has a function of generating current from visible light generated by the scintillator 11, and is composed of a photoelectric conversion element represented by a photodiode, for example. The light receiving element 20 is provided, for example, on the support 30 and is provided corresponding to each of the scintillators 11 .

The scintillator 11 has a 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 constituting the phosphor 11a and the resin 11b is sometimes called "resin GOS". That is, the scintillator 11 in this embodiment is made of "resin GOS". The phosphor 11a is gadolinium oxysulfide containing praseodymium, terbium, or the like, and the resin 11b is, for example, an epoxy resin. The reflector 12 is made of a 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 an X-ray image, the scintillator 11 is divided into a plurality of cells CL corresponding to each of the plurality of light receiving elements 20 (arraying of the scintillator 11). Thus, the scintillator structure 10 includes multiple cells CL and the reflector 12 covering the multiple cells CL. Specifically, the top surface and four side surfaces of the cell CL are covered with a reflector 12 . On the other hand, the bottom 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 .

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

That is, when X-rays are incident on the scintillator 11 of the scintillator structure 10, electrons in the phosphors 11a forming the scintillator 11 receive the energy of the X-rays and transition from the ground state to the excited state. The electrons in the excited state then 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.

A part of the visible light emitted from the scintillator 11 is directly incident on the light receiving element 20, and the other part of the visible light emitted by the scintillator 11 is emitted from the scintillator. The light is focused on the light receiving element 20 while being repeatedly reflected by the reflector 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, 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, a current due to electrons excited in the conduction band flows through the photodiode. An X-ray image is acquired based on the current output from the photodiode. Thus, 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 reflector 12 covering 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 processed surface is formed on the surface of the rectangular parallelepiped shape. That is, the term "processed surface" refers to a surface that has been mechanically processed. Specifically, the "machined surface" includes a surface ground with a grinding wheel to increase the thickness of the workpiece, or a surface obtained by cutting the workpiece with a slicing blade for dicing.

For example, in the scintillator 11 using the "resin GOS", the "processed surface" is defined as a surface where the resin is exposed and the surface where the "GOS" powder is fractured. For example, FIG. 1 schematically shows a scintillator 11 using "resin GOS" in which the interface between the scintillator 11 and the reflector 12 is a "processed surface". In this case, it can be seen that the "processed surface" includes a region where the resin 11b is cut and a region where the phosphor 11a ("GOS" powder) is broken. The X-ray detector 100 is configured in this manner.

<Reason for adopting “Resin GOS”>
As described above, "resin GOS" is used as the scintillator 11 in this embodiment. 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 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 an advantage over "CWO" in that it has a higher emission output of visible light, but has a disadvantage in that the manufacturing cost is higher.

Therefore, from the viewpoint of reducing the manufacturing cost, it is being considered to adopt "resin GOS", which is a mixture of resin such as epoxy resin and "GOS" powder, instead of "GOS" ceramic as the scintillator 11. 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.

Here, the "resin GOS" includes a "first resin GOS" obtained by mixing "GOS" powder obtained by adding praseodymium (Pr) and cerium (Ce) to gadolinium oxysulfide and an epoxy resin, and terbium (Tb ) and cerium (Ce) added to gadolinium oxysulfide, and “second resin GOS” obtained by mixing powder and epoxy resin.

Both the "first resin GOS" and the "second resin GOS" have the advantage of higher light output than "CWO". Furthermore, there is also the advantage that the afterglow characteristics of the "first resin GOS" are equivalent to those of the "CWO". In other words, the performance of the scintillator structure 10 is required not only to have a large emission output but also to have good afterglow characteristics.

Therefore, the afterglow characteristic will be described. The scintillator 11 forming the scintillator structure 10 is a material that emits visible light when exposed to X-rays. The mechanism by which the scintillator 11 generates visible light when exposed to X-rays is as follows. That is, when the scintillator 11 is irradiated with X-rays, electrons in the scintillator 11 receive energy from the X-rays and transition from a low-energy ground state to a high-energy excited state. 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 amount of time has passed. After a certain amount of time has passed, the visible light generated by the transition from the excited state to the ground state of electrons becomes afterglow. In other words, afterglow is visible light that occurs when a certain amount of time elapses after the timing of the transition from the excited state to the ground state after the X-ray irradiation. A large afterglow means that the intensity of the visible light generated until a certain amount of time has passed after the irradiation of X-rays 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 is small. In other words, good afterglow characteristics mean that the afterglow is small. In this regard, the afterglow characteristics of the "first resin GOS" are equivalent to those of "CWO". Therefore, "resin GOS" has the following advantages over "CWO", and is excellent as a scintillator 11 capable of achieving both performance and manufacturing cost.

(1) “Resin GOS” has a higher luminous output than “CWO”.
(2) The afterglow characteristics of the "first resin GOS" are equivalent to those of "CWO".
(3) “Resin GOS” does not use cadmium.
(4) "Resin GOS" has a lower manufacturing cost than "CWO".

Cesium iodide (CsI) is used as the scintillator 11, and the "resin GOS" has the following advantages over "CsI".

(1) "Second resin GOS" has better X-ray stopping properties than "CsI".
(2) The afterglow characteristic of the "second resin GOS" is about 1/70 of that of "CsI".
(3) "Resin GOS" is a stable substance with no deliquescence.

In addition, "resin GOS" has the following advantages over "GOS" ceramics. That is, "resin GOS" and "GOS" ceramics contain heavy metals such as "Gd", "Ga" or "Bi". These heavy metals are relatively expensive, and there is concern about adverse effects on living bodies and the environment when they flow out. Therefore, it is desirable that the scintillator 11 contains as little heavy metal as possible. In this regard, "resin GOS", which consists of a mixture of "GOS" powder and resin, uses less "GOS" than bulk "GOS" ceramic. This means that the "resin GOS" makes it possible to construct the scintillator 11 with less heavy metal content than the "GOS" ceramic. From this, it can be said that the "resin GOS" is superior to the "GOS" ceramic in that it can provide a scintillator 11 with a low heavy metal content.

From the above, the "resin GOS" is considered to be promising as the scintillator 11 capable of achieving both performance and manufacturing cost.

<Specific materials>
Next, specific materials for the constituent elements of 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, for example, praseodymium (Pr), cerium (Ce), and terbium (Tb). On the other hand, “GGAG” is (Gd _1-X Lu _x ) _3+a (Gau Al _{1-u ) 5-a} O activated with at least one selected from cerium (Ce), praseodymium (Pr), and the like. ₁₂ (x=0-0.5, u=0.2-0.6, a=-0.05-0.15). However, the phosphor 11a is not limited to a specific composition.

<<resin 11b and resin 12b>>
The resin 11b and the resin 12b are made of a translucent resin. In particular, it is desirable that the resin 11b and the resin 12b have a light transmittance of 85% or more in the wavelength range of 450 nm to 650 nm. Examples of resin 11b and resin 12b include epoxy resin, polyester resin, acrylic resin, silicone resin, and vinyl resin. One of these resins may be used alone, or two or more resins may be used in combination.

<<reflective particles 12a>>
Examples of the constituent material of the reflecting particles 12a include white particles such as “TiO ₂ ” (titanium oxide), “Al ₂ O ₃ ” (aluminum oxide), and “ZrO ₂ ” (zirconium oxide). Here, for the reflecting particles 12a, for example, bulk or a mixture of powder and resin can be used. In particular, the reflective particles 12a made of “rutile-type TiO ₂ ” are desirable because they are excellent in light reflection efficiency. From the viewpoint of improving the light receiving efficiency of the light receiving element 20, the light reflectance of the reflective particles 12a is desirably 80% or more, and the light reflectance of the reflective particles 12a is desirably 90% or more. .

<<Other Additives>>
The scintillator 11 and the reflector 12 may contain other additives in addition to the components described above. For example, it is desirable to add a curing catalyst to shorten the curing time of the resin.

<Consideration of improvement>
As a result of examination of the scintillator structure 10 having the configuration described above, the present inventor newly found room for improvement as described below. This point will now be described. That is, the scintillator structure 10 may be used in a high-temperature and high-humidity environment. Found it. Thus, the scintillator structure 10 has room for improvement from the viewpoint of improving reliability. Therefore, in the present embodiment, measures are taken to address the room for improvement described above. In the following, the technical idea of this embodiment with this ingenuity will be described.

<Basic idea in the embodiment>
The basic idea of this embodiment is to chemically bond the scintillator 11 and the reflector 12 together. As a result, the interface between the scintillator 11 and the reflective material 12 can be strongly chemically bonded. Separation at the interface with the reflector 12 can be suppressed. That is, according to the basic idea, the reliability of the scintillator structure 10 can be improved.

In particular, in the present embodiment, the basic idea of chemically bonding the scintillator 11 and the reflector 12 is realized by, for example, bridging each of the plurality of cells CL composed of the scintillator 11 and the reflector 12. be able to. In other words, in the present embodiment, the basic idea described above is embodied by bridging each of the plurality of cells CL and the reflector 12 . Thus, according to the present embodiment, the interface between the resin 11b of the plurality of cells CL and the resin 12b of the reflector 12 is strongly bonded by cross-linking. By improving the adhesion to the scintillator structure 12, a remarkable effect of improving the reliability of the scintillator structure 10 can be obtained.

In the following, in embodying the idea of chemically bonding the scintillator 11 and the reflector 12, the background to the idea of bridging each of the plurality of cells CL composed of the scintillator 11 and the reflector 12 will be described. will be explained using

The term "related art" as used in this specification means a technology that is not a publicly known technology, but has a problem found by the inventor of the present application, and is a technology that is a premise of the present invention.

FIG. 2 is a flow chart illustrating a method for manufacturing a scintillator structure in related art. In FIG. 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 crosslinked by using a crosslinking 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, by separating the substrate into individual pieces, a plurality of cells composed of the crosslinked "resin GOS" are obtained (S103). Next, after forming a reflective material covering a plurality of cells (S104), the reflective material is completely crosslinked using a crosslinking reaction (S105). Thus, a scintillator structure can be manufactured.

Here, in the related art, the cross-linking reaction of the reflective material is carried out after the cross-linking reaction of the "resin GOS" is completed. That is, in the related art, the cross-linking reaction of the "resin GOS" and the cross-linking reaction of the reflector are performed independently without being associated with each other. Therefore, in the related art, each of the "resin GOS" and the reflector can be crosslinked, but the interface between the "resin GOS" and the reflector cannot be crosslinked. Therefore, in the related art, it is difficult to improve the adhesion between the "resin GOS" and the reflective material. The present inventor speculates that peeling is likely to occur at the interface between. To put it the other way around, the present inventor believes that if the cross-linking reaction of the "resin GOS" and the cross-linking reaction of the reflective material can be performed in association with each other, the interface between the "resin GOS" and the reflective material can also be cross-linked. The inventors have found a novel finding that it is possible to improve the adhesion between the "resin GOS" and the reflector.

Therefore, the present inventor has devised the related art based on the above-mentioned new findings. That is, the inventors of the present invention are able to crosslink the interface between the "resin GOS" and the reflector by linking the crosslinking reaction of the "resin GOS" with the crosslinking reaction of the reflector. A method for manufacturing a scintillator structure that can improve the adhesion between the resin "GOS" and the reflector has been devised. The scintillator structure manufacturing method conceived by the present inventor is the scintillator structure manufacturing method according to the present embodiment, and the scintillator structure manufacturing method according to the present embodiment will be described below.

<Manufacturing Method of Scintillator Structure in Embodiment>
FIG. 3 is a flow chart explaining the flow of the manufacturing process of the scintillator structure 10. As shown in FIG.

In FIG. 3, first, after weighing and mixing the raw material powder and the flux component in predetermined amounts, this mixture is filled in a crucible and fired in an atmospheric furnace at 1300° C. to 1400° C. for 7 to 9 hours to obtain a “GOS ” to produce a powder. Then, the flux component and impurities contained in the "GOS" powder are removed by washing using hydrochloric acid and warm water. Next, the "GOS" powder is impregnated with the epoxy resin by dripping the epoxy resin onto the "GOS" powder. Thus, a substrate made of "resin GOS" is produced (S201). Next, the substrate made of "resin GOS" is crosslinked. At this time, in the present embodiment, the substrate is not caused to undergo a complete cross-linking reaction, but to be in a semi-cross-linked state (S202). Thereby, the scintillator 11 made of the "resin GOS" in a semi-crosslinked state can be formed.

Here, the "semi-crosslinked state" is defined as a state in which the chemical reaction (crosslinking reaction) is not completely completed, and includes, for example, a gel state. In particular, the term "semi-crosslinked state" as used herein means 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%, the reactivity is poor.

This gel fraction can be calculated by the formula shown below.

Gel fraction (%) = mass after drying/initial mass x 100
Measurement of the gel fraction is performed by the following procedure. That is, first, the initial mass of the sample is measured. After that, the sample is immersed in a xylene solution for 24 hours, and the sample taken out of the xylene solution is naturally dried overnight and then vacuum-dried, and the post-drying mass is measured.

Subsequently, by dicing the substrate on which the scintillator 11 is formed, the substrate is separated into a plurality of cells CL (S203). After the plurality of singulated cells CL are rearranged, a reflector 12 is formed so as to cover the plurality of cells CL (S204). Then, the reflective material 12 is crosslinked (S205). At this time, not only the reflecting material 12 itself is crosslinked, but also the reflecting material 12 is chemically bonded to each of the plurality of semi-crosslinked cells CL in which the chemical reaction is not completely completed. That is, each of the plurality of cells CL and the reflector 12 are crosslinked. As a result, according to the present embodiment, the adhesion between each of the plurality of cells CL and the reflector 12 can be significantly improved. Then, after cutting the unnecessary portion of the scintillator structure 10, the scintillator structure 10 that has passed the inspection is shipped.

<Features of the embodiment>
The characteristic point of this embodiment is that the cross-linking reaction of the "resin GOS" and the cross-linking reaction of the reflector are not performed independently but are performed in association with each other, so that the "resin GOS" and the reflector are interlinked. is a point that also crosslinks the interface between Specifically, in the present embodiment, in order to associate the cross-linking reaction of the "resin GOS" with the cross-linking reaction of the reflector, the "semi-crosslinked state" before the cross-linking reaction of the "resin GOS" is completely completed is While maintaining, the substrate is singulated into a plurality of cells, and after forming a reflective material covering the plurality of cells, the reflective material is subjected to a cross-linking reaction. In this case, when a cross-linking reaction is caused in the reflector, the cross-linking reaction proceeds also in the plurality of cells in the “semi-crosslinked state”. This means that the cross-linking reaction of the "resin GOS" and the cross-linking reaction of the reflector are related to each other. As a result, the cross-linking reaction of each of the plurality of cells in the "semi-cross-linked state" and the reflector material proceeds simultaneously, and as a result, only the cross-linking reaction of each of the plurality of cells itself and the cross-linking reaction of the reflector itself Instead, a cross-linking reaction that connects each of the plurality of cells and the reflective material can also be generated. As a result, according to the present embodiment, each of the plurality of cells and the reflector are chemically bonded by cross-linking, so that the adhesion between each of the plurality of cells and the reflector can be improved. Therefore, according to the scintillator structure of the present embodiment, even if it is used in a high-temperature and high-humidity environment, it is possible to suppress the occurrence of delamination at the interface between each of the plurality of cells and the reflector. That is, according to this embodiment, the reliability of the scintillator structure can be improved.

Although the invention made by the present inventor has been specifically described based on the embodiment, the invention is not limited to the above embodiment, and can be variously modified without departing from the gist of the invention. Needless to say.

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 (7)

multiple cells and
a reflector covering the plurality of cells;
A scintillator structure comprising:
each of the plurality of cells includes a resin and a phosphor,
The scintillator structure, wherein each of the plurality of cells and the reflector are chemically bonded. The scintillator structure according to claim 1,
The scintillator structure, wherein each of the plurality of cells and the reflector are crosslinked. The scintillator structure according to claim 1 or 2,
The scintillator structure, wherein the reflective material includes translucent resin having translucency to light with a wavelength ranging from 450 nm to 650 nm. In the scintillator structure according to any one of claims 1 to 3,
The scintillator structure, wherein the phosphor contains gadolinium oxysulfide. A method for manufacturing a scintillator structure comprising a plurality of cells containing a resin and a phosphor and a reflective material covering each of the plurality of cells,
(a) preparing a substrate made of a mixture of resin and phosphor;
(b) semi-crosslinking the substrate;
(c) forming the plurality of cells by singulating the semi-crosslinked substrate;
(d) forming the reflector covering the plurality of semi-crosslinked cells;
(e) cross-linking the reflector while each of the plurality of cells is in a semi-cross-linked state;
with
The method of manufacturing a scintillator structure, wherein in the step (e), interfaces between each of the plurality of cells and the reflector are crosslinked. In the method for manufacturing a scintillator structure according to claim 5,
The method for manufacturing a scintillator structure, wherein each of the plurality of semi-crosslinked cells has a gel fraction of 80% or more and 95% or less. The method for manufacturing a scintillator structure according to claim 5 or 6,
In the method for producing a scintillator structure, the semi-crosslinked state is a state in which the crosslinking reaction is not completely completed.

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