JP5115860B2 - Manufacturing method of scintillator material powder - Google Patents

Description

  The present invention relates to a method for producing a scintillator material powder characterized by a firing process.

Manufacturing method of a scintillator material powder mainly composed of gd 2 _O 2 _S is Patent Document 1, disclosed in Patent Document 2. That is, the scintillator raw material powder such as Gd ₂ O ₃ and S is mixed with Na
A mixed powder obtained by mixing a sintering aid such as ₂ CO ₃ , Li ₂ B ₄ O ₇ , NaBF ₄ , K ₃ PO ₄ .3H ₂ O and a flux powder was placed in an alumina crucible, and the alumina cover was applied. ~
Bake for several hours at a temperature of 1250 ° C. After cooling, the fired body in the crucible is loosened while thoroughly washing with pure water, and is continuously washed with hydrochloric acid and warm water in a stirrer to obtain a scintillator material powder mainly composed of Gd ₂ O ₂ S.

Japanese Patent Laid-Open No. 7-41760 JP-A-7-252476

In the process of filling the alumina crucible with a mixed powder obtained by mixing the scintillator raw material powder with the firing aid and the flux powder and firing it, there are the following industrial problems. FIG. 4 is a schematic view showing how the mixed powder is fired. The mixed powder 2 is filled in an alumina crucible 1 and an alumina lid 3 is formed, followed by firing in a firing furnace 6 at a temperature of 1100 to 1400 ° C. for several hours (FIG. 4A).
). By firing, the reaction between the raw material powders proceeds, and a fired body 8 made of a scintillator material powder containing Gd ₂ O ₂ S as a main component and a flux residue is obtained.

However, the fired body 8 has a reaction layer 9 of a flux component and alumina formed on the surface in contact with the crucible 1 (FIG. 4B). Even if the fired body 8 is immersed in pure water or acid to dissolve the flux residue, the reaction layer 9 cannot be easily dissociated into the scintillator material powder and can only be discarded as loosening waste. That is, only the portion of the fired body 8 excluding the reaction layer 9 can be a scintillator material powder. If the reaction layer 9 formed on the fired body 8 can be made small, the yield of the scintillator material powder relative to the raw material can be increased, which is very preferable in terms of manufacturing cost.

For firing the mixed powder, an alumina crucible that is relatively inexpensive in production is used. However, in the firing using the crucible made of alumina, there is a problem that the Al component contained in the crucible is slightly mixed into the scintillator material powder and deteriorates the scintillator characteristics. Of the scintillator characteristics, the afterglow characteristic is greatly influenced by the Al mixing amount, and it is known that the afterglow characteristic deteriorates when the Al mixing amount is large. In a scintillator for high resolution X-ray CT apparatus that requires low afterglow characteristics, the problem is how to improve afterglow characteristics by reducing the amount of Al contamination.

Based on the above problems, the present invention can reduce the reaction layer formed on the scintillator fired body,
The present invention provides a method for producing scintillator material powder that can increase the yield of the scintillator material powder with respect to the mixed powder containing the scintillator raw material.

The present invention also provides a method for producing a scintillator material powder that can improve the characteristics of the scintillator material powder, particularly the afterglow characteristics, with less mixing of crucible components into the scintillator material powder.

In the method of manufacturing a scintillator material powder of the present invention, a step of mixing a scintillator raw material powder and a flux powder containing a baking aid to form a mixed powder, a step of forming a mixed powder to obtain a molded product, a lower surface of the molded product, It is characterized by a step of obtaining a scintillator fired body by firing so that the flux contained in the molded body is released downward and a scintillator fired body being loosened, and washing and drying to form a scintillator material powder.

Moreover, in the manufacturing method of the scintillator material powder of this invention, the process which mixes the scintillator raw material powder and the flux powder containing a baking auxiliary agent into a mixed powder, and fills the crucible with the mixed powder to obtain a molded body of the mixed powder. A step of attaching a lid having a convex portion on the inward surface to the crucible containing the molded body, a convex portion having the lid facing down on the crucible and a part of the lower surface of the molded body in the crucible provided on the inward surface of the lid A step of obtaining a scintillator fired body by firing so as to release the flux contained in the molded body supported by the part, a step of loosening the scintillator fired body taken out from the crucible, and washing and drying to form a scintillator material powder It is a feature.

Furthermore, the method for producing a scintillator material powder according to the present invention is characterized in that the mixed powder is calcined at a temperature lower than the firing temperature to obtain a molded body.

Further, the method for producing scintillator material powder of the present invention is characterized by using a crucible and a lid made of alumina.

Furthermore, the scintillator material powder manufacturing method of the present invention is characterized in that a convex portion having the same component as that of the scintillator material powder is provided on the inward surface of the lid.

Furthermore, the method for producing a scintillator material powder of the present invention is characterized by producing a scintillator material powder containing Gd ₂ O ₂ S as a main component.

According to this invention, the reaction layer formed in a scintillator baking body can be made small in the baking process which manufactures a scintillator material powder. Since the yield of the scintillator material powder with respect to the scintillator raw material can be increased, it is possible to provide a scintillator material powder manufacturing method that is very preferable in terms of manufacturing cost.

It is a schematic diagram which shows the baking process which manufactures the scintillator material powder of an Example. It is a schematic diagram of the crucible and the container which can be used for the baking process of the scintillator material powder of an Example. It is a figure which shows the yield of the scintillator material powder of an Example, Al mixing amount, and afterglow characteristic. It is a schematic diagram which shows a mode that a scintillator material powder is baked by the conventional method.

Hereinafter, the present invention will be described in detail based on examples with reference to the drawings. In order to make the explanation easy to understand, the same reference numerals are used for the same parts and parts.

In this example, 333 g of Gd ₂ O ₃ , 0.35 g of Pr ₆ O ₁₂ and 105 g of S were used as the scintillator raw material powder, and Na ₂ CO ₃ was 96 as the baking aid and the flux powder.
g, 10 g of Li ₂ B ₄ O ₇ , 3 g of NaBF ₄ and 32 g of K ₃ PO ₄ .3H ₂ O were respectively weighed and then dry mixed to obtain a mixed powder. In the mixed powder, 1.3 g of Ce (NO ₃ ) _3
2 mL of 6H ₂ O dissolved in 500 cc pure water was added with a pipette.

Next, the process of filling the mixed powder into an alumina crucible and firing it will be described with reference to FIG. In this example, a pot-shaped crucible 1 made of alumina having a purity of 99% or more, a volume of 600 cc, and a wall thickness of 4 mm was used. First, 850 g of the above mixed powder 2 was weighed and poured into the crucible 1, and the surface was flattened by applying light vibrations, and then the surface was further lightly pressed (FIG. 1 (a)).

Next, a lid 3 made of alumina having a purity of 99% or more is attached to the crucible 1, and 1 in an air atmosphere.
Calcination was performed at 50 ° C. for 4 hours (FIG. 1B). The mixed powder 2 in the crucible 1 was slightly baked by calcination, and a molded body 4 having substantially the same shape as the inside of the crucible 1 was obtained. (Fig. 1 (c))

In this example, the mixed powder 2 was calcined at 150 ° C. lower than the firing temperature to obtain a molded body 4.
The mixed powder 2 may be mechanically pressed and formed to form the molded body 4. When forming the compact 1 by mechanically pressing and compacting it, it is necessary to examine the material of the forming jig so that the mixed powder is not contaminated with impurities.

Next, the lid 3 attached to the crucible 1 was removed, and instead the lid 3A provided with the convex portion 6 on the inward surface was attached with a ceramic adhesive. Both the convex portion 6 and the lid 3A are made of alumina having a purity of 99% or more. After attaching the lid 3A to the crucible 1, the molded body 4 in the crucible 1 is supported by the convex portion 5 provided on the inward surface of the lid 1A so that the lid 3A is downward with respect to the crucible 1. (FIG. 1 (d)).

In this embodiment, the convex portion 5 made of alumina having a purity of 99% or more is used, but the convex portion 5 made of a scintillator sintered body having the same component as that of the fired scintillator material powder may be used. In the scintillator material powder as in this example, mixing of trace elements is a scintillator characteristic (especially afterglow characteristic).
Leads to a significant deterioration of By making the convex part 5 the same component as the scintillator material powder, it is possible to prevent a trace component contained in the convex part 5 from being mixed into the scintillator material powder and to improve the scintillator characteristics of the sintered body.

Further, in this embodiment, the lid 3A to which the convex portion 5 is attached is used. However, as shown in FIG. 3A, a lid 3B in which the convex portion is provided on the inward surface with the crucible 1 may be used. . Further, as shown in FIG. 3B, a container 7 capable of collectively firing a large number of molded bodies 4 and a lid 3C provided with a plurality of convex portions 5 on the inward surface of the container 7 may be used. good. By using the lid and container as described above,
The workability of firing can be improved.

Finally, the molded body 4 in the crucible 1 is placed on the lid 3A so that the lid 3A is directed downward with respect to the crucible 1.
The molded body 4 in the crucible 1 was fired in the firing furnace 6 while being supported by the convex portions 5 provided on the inward surface (FIG. 1 (e)). Firing was performed at 1350 ° C. for 8 hours in an air atmosphere. During the firing reaction, the molded body 4 contracts in the direction of the block arrow in the figure, and the flux component contained in the molded body 4 flows out in the direction of the line arrow as a flux residue.

FIG. 1 (f) is a schematic diagram showing a state in the crucible 1 after firing. By providing the convex portion 5 on the lid 1A, the fired body 8 and the flux residue 7 were separated and generated. During the firing reaction, the molded body 4
Contracted and separated from the inner wall surface of the crucible 1, so that the reaction layer 9 was not generated at the portion where the molded body 4 and the crucible 1 were in contact as shown in FIG. 4.

The fired body 8 obtained in the above steps is immersed in pure water and loosened while washing away the flux residue and excess sulfur compound, and further washed with warm water, filtered, dried at low temperature, and Gd ₂ O _2.
A scintillator material powder containing S as a main component was obtained. In the unraveling operation of the fired body 8, almost all of the fired body 8 could be unraveled, and there was almost no amount discarded as unraveling glass.

FIG. 3 shows the amount of scintillator material powder and the yield rate with respect to the amount of the mixed powder when the firing step of this example is used. FIG. 3 also shows the amount of Al contained in the scintillator material powder and the afterglow characteristics of the scintillator material powder.

The amount of Al contained in the scintillator material powder is determined by dissolving the scintillator material powder in aqua regia.
Evaluated by CP analysis. Afterglow characteristics are obtained by irradiating the scintillator powder with X-rays with a tube voltage of 90 kV, detecting light emitted from the scintillator powder with a photodiode, and cutting off the X-ray with respect to the output current of the photodiode during X-ray irradiation. Evaluation was based on the ratio of the output current of the photodiode after 3 msec.

When the firing step of this example was used, about 402 g of scintillator material powder was obtained with respect to 850 g of mixed powder. The yield rate was about 47.3%. In the case of the mixing ratio of the scintillator raw material powder of this example, the theoretical maximum yield rate excluding the flux component is about 59%, so that a scintillator material powder having a theoretical maximum yield rate of about 80% was obtained. It will be. When a conventional baking process as a comparative example is used, about 339 g with respect to 850 g of mixed powder.
Only a scintillator powder was obtained, and the yield rate was about 39.9%. From the above comparison, it was confirmed that when the firing step of this example was used, about 19% more scintillator powder was obtained compared to the conventional firing step.

Further, the scintillator material powder of this example was able to reduce the amount of Al contained in the scintillator material powder of the comparative example to half or less. This is because the compact 4 and the crucible 1 during the firing reaction.
Since the inner wall surface of the metal plate is separated and only the convex portion 5 provided on the lid 3A comes into contact with the molded body 4, Al
It is thought that the amount of contamination has decreased. From the above, it was confirmed that the amount of Al mixed in the scintillator material powder can be reduced by using the firing step of this example.

Furthermore, the scintillator material powder of this example is compared with the scintillator material powder of the comparative example,
Afterglow could be reduced to less than half. This is considered because the amount of Al mixed in the scintillator material powder could be reduced. In a scintillator used for a high-resolution X-ray CT apparatus, it is preferable that the afterglow is small. It was confirmed that the scintillator material powder for a high-resolution X-ray CT apparatus with a small afterglow can be manufactured by using the firing step of this example.

1 crucible,
2 mixed powder,
3, 3A, 3B, 3C lid,
4 moldings,
5 Convex,
6 firing furnace,
7 Flux residue,
8 fired body,
9 Reaction layer.

Claims (6)

A step of mixing a scintillator raw material powder and a flux powder containing a firing aid to form a mixed powder;
Forming a mixed powder to obtain a molded body;
A step of obtaining a scintillator fired body by supporting a part of the lower surface of the molded body and firing so as to release the flux contained in the molded body downward;
A method for producing a scintillator material powder comprising a step of loosening a scintillator fired body and then washing and drying to form a scintillator material powder. A step of mixing a scintillator raw material powder and a flux powder containing a firing aid to form a mixed powder;
A step of filling the crucible with the mixed powder to obtain a molded body of the mixed powder;
Attaching a lid provided with a convex portion on the inward surface to a crucible containing a molded body;
Scintillator firing by firing with the lid facing down on the crucible, with a convex portion provided on the inward surface of the lid supporting a part of the lower surface of the molded body in the crucible so that the flux contained in the molded body is released downward Obtaining a body,
A method for producing a scintillator material powder comprising a step of loosening a scintillator fired body taken out from a crucible and then washing and drying to form a scintillator material powder. The method for producing a scintillator material powder according to claim 1 or 2, wherein the mixed powder is calcined at a temperature lower than a firing temperature to obtain a molded body. The method for producing scintillator material powder according to claim 2 , wherein a crucible and a lid made of alumina are used. The method for producing scintillator material powder according to claim 2 or 4, wherein a convex portion having the same component as that of the scintillator material powder is provided on an inward surface of the lid. The method for producing a scintillator material powder according to any one of claims 1 to 5 , wherein a scintillator material powder containing Gd ₂ O ₂ S as a main component is produced.

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