WO2015053033A1 - セラミックスシンチレータ及びその製造方法、並びにシンチレータアレイ及び放射線検出器 - Google Patents
セラミックスシンチレータ及びその製造方法、並びにシンチレータアレイ及び放射線検出器 Download PDFInfo
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- WO2015053033A1 WO2015053033A1 PCT/JP2014/073915 JP2014073915W WO2015053033A1 WO 2015053033 A1 WO2015053033 A1 WO 2015053033A1 JP 2014073915 W JP2014073915 W JP 2014073915W WO 2015053033 A1 WO2015053033 A1 WO 2015053033A1
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Definitions
- the present invention relates to a ceramic scintillator suitable for a radiation detector such as an X-ray CT apparatus, a manufacturing method thereof, and a scintillator array and a radiation detector using the ceramic scintillator.
- CT apparatus computed tomography apparatus
- This CT apparatus is composed of an X-ray tube that generates a fan-shaped fan beam X-ray and an X-ray detector in which a large number of X-ray detection elements are arranged around the subject.
- the fan beam X-ray emitted from the X-ray tube is irradiated on the subject, the size of the X-ray transmitted through the subject is measured by an X-ray detector, and the data is analyzed by a computer, thereby analyzing the data within the tomographic plane. It has a function to display the status of.
- the X-ray absorption rate at each position on the tomographic plane irradiated with X-rays is calculated in the computer and an image corresponding to the absorption rate is visualized.
- a radiation detector for detecting ionizing radiation such as X-rays, rare earth oxy such as Gd 2 O 2 S, Y 2 O 2 S, Lu 2 O 2 S etc. using Pr, Ce, Eu, Tb, etc. as luminescent elements
- a radiation detector using a radiation detection element in which a ceramic scintillator sintered with sulfide powder and a silicon photodiode are combined has been developed and put into practical use.
- the radiation detection element can be reduced in size and the number of channels can be easily increased, so that an image with high resolution can be obtained.
- JP 2000-313619 discloses a method for producing a rare earth oxysulfide powder for use in a scintillator by suspending at least one rare earth oxide in water, 1 mol of sulfuric acid per 1 mol of rare earth oxide, or at least one rare earth.
- a method is disclosed in which a sulfate dissolved in accordance with the above is added, the resulting powdery precipitate is calcined, and the resulting rare earth oxysulfate is reduced.
- Japanese Patent Publication No. 2004-525848 discloses that a rare earth oxysulfide powder having a specific surface area of at least 10 m 2 / g is adjusted to a particle size of less than 10 ⁇ m by adding an organic pulverization liquid by a wet pulverization method.
- a powder body having a compact density of 40 to 60% is produced from the above, and the obtained powder body is sintered at a temperature of 1200 to 1450 ° C. in a vacuum or an inert gas at a normal pressure, thereby increasing the density.
- a method of manufacturing a translucent scintillator ceramic is disclosed.
- the rare earth oxysulfide powder obtained by the production method of JP-A-2000-313619 contains particles having a large particle size, a high-density sintered body cannot be obtained by pressureless sintering. Therefore, in order to obtain a high-density sintered body, it is necessary to sinter with a hot press or a hot isostatic press, which is costly.
- the particle size is adjusted by wet-grinding the rare earth oxysulfide with the addition of the organic pulverization liquid, but sulfur is released from the rare-earth oxysulfide during grinding, Lattice defects consisting of sulfur vacancies are introduced into the rare earth oxysulfide. Even after the rare earth oxysulfide is sintered to become a ceramic scintillator, the lattice defects remain, and the emission intensity of the ceramic scintillator is reduced.
- an object of the present invention is to provide a method for manufacturing a ceramic scintillator that suppresses a decrease in light emission intensity and easily obtains a high-density sintered body.
- Another object of the present invention is to provide a radiation detector suitable for a ceramic scintillator obtained by such a manufacturing method, and a scintillator array and an X-ray CT apparatus using the ceramic scintillator.
- the inventors added a grinding process before performing the reduction process to obtain the rare earth oxysulfide, rather than giving the grinding process after obtaining the rare earth oxysulfide powder.
- the inventors have obtained the knowledge that sulfur desorption can be suppressed while adjusting the particle diameter, thereby completing the present invention.
- a rare earth compound and sulfuric acid and / or sulfate are mixed and reacted to obtain a product, and the product is calcined to obtain a calcined powder.
- a calcining step, a reduction step of reducing the calcined powder to obtain a rare earth oxysulfide powder, a molding step of forming the rare earth oxysulfide powder to obtain a compact, and a sintering to sinter the compact A method for producing a ceramic scintillator including a sintering step, characterized by including a pulverizing step of adjusting the particle size of the product and / or calcined powder at least before the reduction step.
- a pulverization step for adjusting the particle size of the product after the mixing step it is preferable to calcine at 1000 ° C. or lower in the calcining step and to reduce at 900 ° C. or lower in the reduction step.
- the reduction is preferably performed at 900 ° C. or less in the reduction step.
- the mixing step is preferably mixed in a liquid and wet-pulverized in the pulverizing step.
- the rare earth compound is preferably at least one selected from the group consisting of rare earth oxides, hydroxides, halides, nitrates, sulfates, acetates, phosphates, and carbonates.
- the rare earth compound preferably contains at least gadolinium oxide or at least gadolinium oxide and praseodymium oxide.
- the rare earth compound a rare earth compound of one kind of rare earth element may be used, or a rare earth compound of a plurality of rare earth elements may be used. In the case of mixing a plurality of rare earth elements of rare earth elements, it is preferable that in the mixing step, the rare earth compounds having a small amount are added in order to an aqueous solution containing sulfate ions.
- an annealing step for annealing the sintered body is included after the sintering step.
- the ceramic scintillator of the present invention is obtained by the above method.
- the scintillator array and radiation detector of the present invention are characterized by including such a ceramic scintillator.
- the particle size can be adjusted and the desorption of sulfur can be suppressed. Therefore, a ceramic scintillator manufactured using such rare earth oxysulfide powder is composed of a high-density sintered body, has a large light emission intensity, and exhibits a highly sensitive response to radiation.
- One of the important features of the present invention is that it has been found that sulfur desorption can be suppressed by applying a pulverization step before the reduction step to obtain the rare earth oxysulfide powder. The reason is not clear, but before the reduction process to generate rare earth oxysulfide, it is a more stable compound than rare earth oxysulfide, and even if a grinding process is applied, sulfur desorption is suppressed. I guess it was.
- the present invention even if a powder having high sinterability is obtained by applying a pulverization process, the desorption of sulfur can be suppressed, so that the problem of decrease in the emission intensity of the obtained ceramic scintillator can be solved. It becomes.
- the ceramic scintillator of the present invention its manufacturing method, a scintillator array, and a radiation detector are explained in detail, the present invention is not limited to the following embodiment.
- FIG. 1 shows a flowchart of a method of manufacturing a ceramic scintillator according to a first embodiment of the present invention.
- the rare earth compound may be at least one selected from the group consisting of oxides, hydroxides, halides, nitrates, sulfates, acetates, phosphates and carbonates of rare earth elements.
- Rare earth oxides are particularly preferred as raw materials that are easy to obtain and chemically stable.
- Rare earth elements are scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium 17 elements of (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu) are shown.
- the rare earth compound powder a rare earth compound of one kind of rare earth elements among the rare earth elements may be used, or a rare earth compound of a plurality of rare earth elements may be used.
- the rare earth element is preferably gadolinium.
- the amount of sulfuric acid and / or sulfate added is desirably sufficient to obtain a rare earth oxysulfide of the general formula: RE 2 O 2 S (RE represents a rare earth element).
- the addition amount of sulfuric acid and / or sulfate may be 0.5 mol of sulfate ion per 1 mol of rare earth elements, and is more than 0.5 mol in consideration of component deviation due to sulfur desorption in the production process.
- the amount may be, for example, 0.5 to 1.75 mol. In particular, when the amount is 0.75 to 1.75 mol, rare earth oxysulfide powder with few different phases can be obtained.
- the rare earth element in addition to the rare earth element contained in the rare earth compound, includes a rare earth element contained in the sulfate when a sulfate containing the rare earth element is used.
- sulfate ions include sulfate ions contained in rare earth compounds when a rare earth compound containing sulfate ions is used.
- (1-2) Mixing Step In the mixing step, the rare earth compound and sulfuric acid or sulfate are mixed and reacted, and the produced product is recovered.
- a method of mixing the rare earth compound and sulfuric acid for example, (1) a method of adding a rare earth compound powder to sulfuric acid and stirring and reacting, and (2) adding a rare earth compound powder to water and stirring And a method of reacting by adding sulfuric acid.
- the concentration of sulfuric acid is not particularly limited, but from the viewpoint of the reaction rate with the rare earth compound, 0.1 to 2 mol of diluted sulfuric acid per liter of water is preferable.
- the rare earth compound powder may be added by known means. When adding a rare earth compound of a plurality of rare earth elements, it is preferable to add to the sulfuric acid in order from a rare earth compound with a small amount of rare earth elements. This is because the composition in the product is less likely to segregate by reacting and diffusing a rare amount of rare earth compound in advance.
- the concentration of the rare earth compound-water mixture is not particularly limited, but from the viewpoint of dispersibility with the rare earth compound (uniformity of composition) and reaction rate after addition of sulfuric acid, 0.05 to 1 per liter of water. 2 mol is preferred.
- the sulfuric acid concentration is preferably 10 to 98% by mass.
- the rare earth compound and sulfate When the rare earth compound and sulfate are mixed, fuming sulfuric acid, ammonium sulfate, or the like can be used as the sulfate, but it is desirable to use the same rare earth element sulfate as the rare earth oxysulfide powder.
- a method of mixing the rare earth compound and the sulfate for example, (3) a method of adding a sulfate to the brine, adding a powder of the rare earth compound to the obtained aqueous solution, stirring and reacting, and (4) adding the brine to the brine
- An example is a method in which a rare earth compound powder is added and stirred, and then an aqueous sulfate solution is added and reacted. Any known method can be used to add the sulfate.
- Reaction heat is generated by mixing rare earth compound powder and sulfate ions in water.
- the mixed solution together with the generated precipitation product may be heated to a predetermined temperature and maintained for a predetermined time. Heating promotes product generation.
- the generated precipitation product may be collected by heating and drying after separating the precipitation product from the mixed solution, or the liquid may be evaporated by heating together with the mixed solution. When the whole liquid mixture is heated, ripening proceeds at the same time, which is preferable because man-hours can be reduced.
- the obtained product has a composition mainly composed of a mixed salt of a rare earth sulfate and a rare earth compound or a rare earth sulfate, although it varies depending on the molar ratio of sulfuric acid or sulfate to be mixed with the rare earth compound.
- (1-3) Grinding step In the grinding step, the obtained product is ground to adjust the particle size.
- known means such as wet pulverization using a liquid such as water or ethanol, or dry pulverization not using the liquid as a medium can be used, but the apparatus is relatively inexpensive in consideration of the previous and subsequent processes.
- wet pulverization using a wet ball mill with good dispersibility and high pulverization efficiency is preferable.
- the product is put into the wet pulverization apparatus together with the reaction solution, and the pulverization step is performed by wet pulverization, so that drying of the obtained product can be omitted. Since the product is soft powder, it is easy to grind. Further, before the precipitated product is filtered from the mixed solution, wet pulverization may be performed in a state where the product is contained in the solution.
- the pulverized product obtained in the calcination process is calcined.
- the calcination step is preferably performed in air at atmospheric pressure.
- the calcination temperature is preferably from 300 to 1000 ° C., and more preferably from 600 to 900 ° C., because there is little variation in what is obtained after calcination.
- the calcining temperature is higher than 1000 ° C., the grain growth of the pulverized product is activated and a large deviation occurs in the particle diameter. If it is less than 300 ° C, the calcination reaction does not proceed sufficiently. Gases such as H 2 S and SO x containing sulfur generated at this time can be recovered by a known technique such as bubbling in a neutralized aqueous solution.
- the calcined powder obtained by calcining has a composition mainly composed of rare earth sulfate and rare earth oxysulfate or rare earth oxysulfate, although it varies depending on the molar ratio of sulfuric acid or sulfate to be mixed with the rare earth compound. .
- the calcined powder obtained by calcining in the reduction process is reduced using a gas such as hydrogen, hydrocarbons such as methane, propane, or the like as a reducing agent.
- the reduction treatment may include, for example, the reducing agent and an inert atmosphere such as nitrogen (N 2 ) or argon (Ar) depending on the reaction rate, and is preferably performed at a temperature of 900 ° C. or lower. Gases such as H 2 S and SO x containing sulfur generated at this time can also be recovered by a known technique such as bubbling in a neutralized aqueous solution.
- the reduction temperature is 900 ° C. or lower, the reduction treatment can be performed while suppressing grain growth of the calcined powder.
- the reduction time is preferably 1 to 180 minutes. If it is 900 ° C. or less, depending on the amount, a longer time may be used so that grain growth does not occur.
- the particle size is adjusted by pulverization before the reduction step, and the reduction treatment is performed under the condition that suppresses the increase of the particle size, thereby reducing the sulfur without causing desorption in the pulverization step.
- a rare earth oxysulfide having the desired particle size is obtained.
- the reduction temperature is set to 900 ° C. or lower, the grain growth of the calcined powder is suppressed, so that it is not necessary to perform the pulverization step again after the reduction. If the pulverization step is performed after reduction to rare earth oxysulfide, sulfur is lost and defects are likely to occur. You may perform the crushing process for crushing the rare earth oxysulfide particle
- the obtained rare earth oxysulfide powder is granulated to produce a granulated powder.
- a known method may be used for the granulation step.
- a granulated powder of rare earth oxysulfide a molded body is produced by a method known per se such as uniaxial pressing or cold isostatic pressing.
- the molding pressure is larger than the molding pressure for obtaining a molded body that can obtain a sufficient density in at least a subsequent sintering step, and smaller than the molding pressure at which desulfurization due to contact between powder particles during pressurization does not occur.
- a sintered body is obtained by sintering the obtained molded body in an inert atmosphere such as nitrogen (N 2 ) or argon (Ar).
- an inert atmosphere such as nitrogen (N 2 ) or argon (Ar).
- N 2 nitrogen
- Ar argon
- a jig such as a crucible or a setter to be used is preferably a stable material that is neither oxidized nor reduced at high temperatures.
- the sintering temperature is preferably 1300 to 1600 ° C, more preferably 1500 to 1600 ° C.
- the equipment without pressure structure or pressure structure such as HP or HIP is cheaper. Therefore, it is preferable to sinter at a pressure of about atmospheric pressure. Since the particle size of the rare earth oxysulfide powder is adjusted to be small by the pulverization process, a high-density sintered body can be obtained without performing pressure sintering. Further, the sintered body may be annealed in an inert atmosphere in order to remove distortion and the like of the obtained sintered body. The light emission intensity is further improved by annealing.
- the obtained sintered body can be used as a ceramic scintillator.
- the obtained sintered body is gadolinium oxysulfide using praseodymium as a light emitting element and cerium as an additive for adjusting afterglow. It becomes a ceramic scintillator. Since the rare earth oxysulfide obtained by the above process has few sulfur deficiencies and lattice defects in the pulverization process, the ceramic scintillator of the present invention produced using such a rare earth oxysulfide is composed of a high-density, translucent sintered body. It has a large emission intensity and shows a highly sensitive response to radiation.
- FIG. 2 shows a flowchart of a method for producing a rare earth oxysulfide according to a second embodiment of the present invention.
- the second embodiment is the same as the first embodiment except that the pulverization step is performed after the calcination step.
- the temperature may temporarily become high and some powder particles may grow, but in the second embodiment, the grown powder particles can also be pulverized together to adjust the particle size.
- the scintillator array of the present invention is formed by arranging a plurality of scintillators on a scintillator substrate provided with a reflective material.
- a known scintillator array configuration / manufacturing method can be used.
- the obtained ceramic scintillator is fixed to a support plate via a double-sided adhesive sheet, a groove is formed in the scintillator substrate to form a grooved scintillator substrate having a plurality of scintillator cells, and the groove is used for a reflector. It can be manufactured by filling a liquid curable resin, curing the liquid curable resin to form a cured scintillator cell resin, and then peeling the double-sided pressure-sensitive adhesive sheet from the cured scintillator cell resin.
- the radiation detector of the present invention includes the above scintillator and a detection element such as a silicon photodiode for detecting light emission of the scintillator.
- a detection element such as a silicon photodiode for detecting light emission of the scintillator.
- the light emitting surface of the scintillator array using the ceramic scintillator obtained by the above-described method and the light receiving surface of the light receiving element face each other and can be manufactured by bonding with an optical resin.
- This radiation detector is preferably mounted on a medical diagnostic imaging apparatus such as X-ray CT and PET (Positron Emission Tomography) / CT.
- the ceramic scintillator, the manufacturing method thereof, the scintillator array, and the radiation detector of the present invention are not limited to the following examples.
- Example 1 A ceramic scintillator was manufactured based on the first embodiment in which the product obtained in the mixing step was pulverized.
- Reduction step The calcined powder was put in an alumina crucible, and the reduction treatment was performed by using a reduction furnace in a hydrogen atmosphere and holding at 800 ° C. for 3 hours in a hydrogen gas atmosphere. H 2 O gas and H 2 S gas generated during the reduction treatment were treated with a gas treatment device. Rare earth oxysulfide (Gd, Pr, Ce) 2 O 2 S was obtained by this reduction reaction.
- the rare earth oxysulfide was pressure-molded at 49 MPa using a uniaxial pressure molding machine, vacuum-sealed in a vinyl bag, and pressure-molded at 294 MPa with a CIP molding machine.
- Example 2 A ceramic scintillator was manufactured under the same conditions as in Example 1 except that the order of the pulverization step (3) and the calcination step (4) was changed based on the second embodiment for pulverizing the calcined product.
- reaction product obtained in the mixing step (2) was placed in an alumina crucible and calcined at 900 ° C. for 1 hour in air at atmospheric pressure using a GOS calcining furnace.
- the H 2 O gas and SO 3 gas generated during the reaction were processed with a gas processing apparatus.
- the obtained calcined product (100 g) was placed in a ball mill together with ethanol (200 g) and wet-ground at 100 rpm for 15 hours.
- the pulverized slurry was dried at 100 ° C. for 4 to 6 hours.
- the dried product was further pulverized using a mortar until it passed through a sieve having an opening of 500 ⁇ m, whereby a fine-particle calcined product was obtained.
- a reduction step (5), a forming step (6) and a sintering step (7) were carried out in the same manner as in Example 1 to obtain a ceramic scintillator.
- Comparative Example 1 A ceramic scintillator was produced under the same conditions as in Example 1 except that the pulverization step (3) was not performed.
- Comparative Example 2 An example in which the pulverization step is performed after the reduction step is shown below.
- the weighing step (1), the mixing step (2), the calcining step (4), and the reduction step (5) were performed in this order in the same manner as in Example 1.
- the sintered body density of the ceramic scintillators of Example 1 and Example 2 and Comparative Example 1 and Comparative Example 2 was measured using the Archimedes method, and the luminescence intensity was measured using a tube voltage of a W target using a tube voltage. X-rays were generated under the conditions of 90 kV and tube current 20 mA, and this was irradiated to a ceramic scintillator and measured using a light receiving element of a Si photodiode. The luminescence intensity was relatively shown with the result of Example 2 as 100.
- the intensity measured using the light receiving element of the Si photodiode during X-ray irradiation was measured using the light receiving element of the Si photodiode after elapse of 3 milliseconds (ms) after the X-ray irradiation was stopped.
- the intensity is shown as “3 ms afterglow”.
- the results are shown in Table 1.
- the ceramic scintillator of Comparative Example 1 in which the pulverization process was not performed had a low sintered body density and a low light emission intensity.
- Comparative Example 2 in which the pulverization step was performed after the reduction step the sintered body density was high, but the emission intensity was low.
- ceramics manufactured using the reduced rare earth oxysulfide powder after adjusting the particle size by carrying out the pulverization step before the reduction step to obtain the rare earth oxysulfide, and suppressing the increase of the particle size It was found that the scintillator has a high density of the sintered body and a large light emission intensity. Inferring from the light emission mechanism of ceramic scintillators, the extremely large 3ms afterglow value is thought to be due to sulfur defects.
- Example 3 Weighing step (1), mixing step (2), grinding step (3) as in Example 1 except that 81.81 g of 96 mass% sulfuric acid was weighed in the weighing step and the grinding time was 40 hours in the grinding step.
- the rare earth oxysulfide powder was prepared by performing the calcination step (4) and the reduction step (5).
- a ceramic scintillator was produced in the same manner as in Example 1 using such rare earth oxysulfide powder.
- Example 4 The weighing step (1), the mixing step (2), the calcining step (4) as in Example 2 except that 81.81 g of 96 mass% sulfuric acid was weighed in the weighing step and the grinding time was 40 hours in the grinding step. ), Pulverization step (3), and reduction step (5) were performed to produce rare earth oxysulfide powder. A ceramic scintillator was produced in the same manner as in Example 2 using such rare earth oxysulfide powder.
- Comparative Example 3 Except for weighing 81.81 g of 96 mass% sulfuric acid in the weighing process, the weighing process (1), mixing process (2), calcining process (4) and reduction process (5) were carried out in the same manner as in Comparative Example 1. An oxysulfide powder was prepared. A ceramic scintillator was produced in the same manner as in Comparative Example 1 using such rare earth oxysulfide powder.
- Comparative Example 4 Weighing step (1), mixing step (2), calcining step (4) as in Comparative Example 2, except that 81.81 g of 96 mass% sulfuric acid was weighed in the weighing step and the grinding time was 40 hours in the grinding step. ) And reduction step (5), followed by a pulverization step to produce rare earth oxysulfide powder. A ceramic scintillator was produced in the same manner as in Comparative Example 2 using such rare earth oxysulfide powder.
- FIG. 3 shows the particle size distribution of the rare earth oxysulfide powders of Example 3, Example 4, Comparative Example 3, and Comparative Example 4.
- the particle size distribution was measured by a wet laser diffraction method using a particle size distribution measuring apparatus LA-950 manufactured by Horiba, Ltd.
- a dispersion medium in which hexametaphosphoric acid was dissolved as a dispersant in pure water was used. After dropping the sample, the sample was stirred and irradiated with ultrasonic waves for 10 minutes, and then the particle size distribution was measured.
- the particle diameter was distributed larger than that in the other examples.
- the particle size distribution after the reduction step is suppressed from becoming large by adjusting the particle size by the pulverization step before the reduction step for obtaining the rare earth oxysulfide powder.
- the average particle size of the rare earth oxysulfide powders of Examples 3 and 4 was larger than that of Comparative Example 4 because heat was applied in the reduction step after the pulverization step.
- Example 4 When the sintered body density, emission intensity, and 3 ms afterglow of the ceramic scintillators of Example 3, Example 4, Comparative Example 3, and Comparative Example 4 were determined by the same method as in Example 1, the same as in Examples 1 and 2 Results were obtained.
- the ceramic scintillator of Comparative Example 3 that did not perform the pulverization process had a low sintered body density and a low light emission intensity.
- Comparative Example 4 in which the pulverization step was performed after the reduction step the sintered body density was high, but the emission intensity was low. From this, it was found that the ceramic scintillators of Examples 3 and 4 had a larger average particle diameter than that of Comparative Example 4, but were excellent in emission intensity and 3 ms afterglow.
- a ceramic scintillator having a high density of the sintered body and a high light emission intensity can be obtained even if the amount of sulfuric acid in the weighing step is halved compared to Examples 1 and 2.
- Example 5 A ceramic scintillator was produced in the same manner as in Example 3 except that water was used in place of ethanol as a grinding solvent in the grinding step, and grinding was performed for 15 hours.
- the sintered body density of the obtained ceramic scintillator was 7.34 g / cm 3 , the emission intensity was 101%, and the 3 ms afterglow was 181 ppm. Therefore, even when water is used in place of ethanol as a grinding solvent in the grinding process, a ceramic scintillator consisting of a high-density sintered body, having a large light emission intensity and showing a highly sensitive response to radiation is obtained. It was confirmed that
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Abstract
Description
本発明の第1の実施形態によるセラミックスシンチレータの製造方法のフローチャートを図1に示す。
まず秤量工程にて、所定の量の希土類化合物粉末と硫酸又は硫酸塩とを準備する。希土類化合物は希土類元素の酸化物、水酸化物、ハロゲン化物、硝酸塩、硫酸塩、酢酸塩、リン酸塩及び炭酸塩からなる群から選択される少なくとも1つを用いることができるが、高純度が得やすく、かつ化学的に安定な原料として、希土類元素の酸化物が特に好ましい。
混合工程にて、希土類化合物と硫酸又は硫酸塩とを混合して反応させ、生成した生成物を回収する。希土類化合物と硫酸を混合する方法としては、例えば、(1) 硫酸に希土類化合物の粉末を添加し、攪拌して反応させる方法と、(2) 水に希土類化合物の粉末を添加し、攪拌した後、硫酸を添加して反応させる方法が挙げられる。
粉砕工程にて、得られた生成物を粉砕し、粒度を調節する。生成物の粉砕は水やエタノールなどの液体を媒体とした湿式粉砕や、液体を媒体としない乾式粉砕等の公知の手段を用いることができるが、前後の工程を考慮し、装置が比較的安価で、分散性も良く、粉砕効率も高い湿式ボールミルを用いた湿式粉砕であるのが好ましい。
仮焼工程にて、得られた粉砕物を仮焼する。仮焼工程は大気圧の空気中で行うのが好ましい。仮焼温度は300~1000℃が好ましく、600~900℃であれば、仮焼後に得られるもののばらつきがすくなくなるため、より好ましい。仮焼温度が1000℃超であると粉砕物の粒成長が活性化して粒径に大きなズレが生じる。300℃未満では仮焼の反応が十分に進まない。このとき発生した硫黄を含むH2SやSOxなどのガスは、中和水溶液中にてバブリングするなどの公知の技術で回収できる。
還元工程にて、仮焼により得られた仮焼粉を、還元剤として水素やメタン、プロパン等の炭化水素等のガス等を使用して、還元処理する。還元処理は、例えば前記還元剤と、反応速度に応じて窒素(N2)やアルゴン(Ar)のような不活性雰囲気を含んでいても良く、900℃以下の温度で行うのが好ましい。このときに発生する硫黄を含むH2SやSOxなどのガスも、中和水溶液中にてバブリングするなどの公知の技術で回収できる。還元温度が900℃以下であると、仮焼粉の粒成長を抑制しつつ、還元処理を行うことができる。還元時間は1~180分であるのが好ましい。900℃以下であれば量に応じて、粒成長しない程度に、より長い時間でも構わない。
得られた希土類オキシ硫化物粉末を造粒し、造粒粉末を生成する。造粒工程は公知の方法を用いて良い。希土類オキシ硫化物の造粒粉末を用いて、一軸プレスや冷間等方圧加圧等のそれ自体は公知な方法を用いて成形体を作製する。成形圧は、少なくとも後の焼結工程において十分な密度が得られる成形体を得るための成形圧より大きく、加圧時の粉末粒子同士の接触による脱硫が発生しない成形圧より小さい。
得られた成形体を窒素(N2)やアルゴン(Ar)などの不活性雰囲気中で焼結することにより、焼結体が得られる。希土類オキシ硫化物は酸化雰囲気で加熱すると、酸化して希土類酸化物に変化し、還元雰囲気中で加熱すると、還元されて硫黄や酸素の欠陥ができるため、不活性雰囲気中で焼結することが好ましい。使用するルツボやセッターなどの治具は、高温で酸化も還元もせず、安定した材質が好ましい。焼結の温度は1300~1600℃が好ましく、1500~1600℃がより好ましい。このときHP(ホットプレス)やHIP(熱間等方圧プレス)などにより、加圧下で焼結しても良いが、HPやHIPのような加圧構造や耐圧構造を有しない装置のほうが安価であることなどから大気圧程度の圧力で焼結するのが好ましい。希土類オキシ硫化物粉末は粉砕工程により粒径が小さく調整されているため、加圧焼結を行わなくても高密度な焼結体を得ることができる。さらに、得られた焼結体の歪などを取り除くために不活性雰囲気中で焼結体をアニールしても良い。アニールすることで発光強度がさらに向上する。
本発明の第2の実施形態による希土類オキシ硫化物の製造方法のフローチャートを図2に示す。第2の実施形態は、粉砕工程を仮焼工程の後に行うこと以外は、第1の実施形態と同様である。仮焼工程において、一時的に高温になり一部の粉末粒子が成長することがあるが、第2の実施形態では成長した粉末粒子も一緒に粉砕し、粒度を調整することができる。
本発明のシンチレータアレイは、反射材を備えたシンチレータ基板に複数の上記シンチレータを配列してなる。シンチレータアレイの構成・製造方法は公知のものを用いることができる。例えば、得られたセラミックスシンチレータを、両面粘着シートを介して支持プレートに固定し、前記シンチレータ基板に溝を形成して複数のシンチレータセルを有する溝付きシンチレータ基板を形成し、前記溝に反射材用液状硬化性樹脂を充填し、前記液状硬化性樹脂を硬化させることによりシンチレータセル樹脂硬化体を形成し、次いで前記シンチレータセル樹脂硬化体から前記両面粘着シートを剥離することで製造することができる。
本発明の放射線検出器は、上記のシンチレータと、このシンチレータの発光を検出するシリコンフォトダイオード等の検出素子とを有する。このときシリコンフォトダイオードのアレイに対応させて、上記シンチレータアレイを用いることにより、効率的に放射線検出器を形成できるため好ましい。例えば、上述の方法で得たセラミックスシンチレータを用いたシンチレータアレイの発光面と受光素子の受光面を対向させて、光学樹脂で接着させることで製造することができる。この放射線検出器は、X線CT、PET(Positron Emission Tomography)/CTなどの医療用の画像診断装置に搭載することが好適である。発光強度が大きい本発明のシンチレータを用いることにより、X線に対し高感度で、応答性が高く、さらに安定性の優れた高性能の放射線検出器が得られる。
混合工程において得られた生成物を粉砕する第1の実施形態に基づいて、セラミックスシンチレータを製造した。
まず3Lビーカーに純水1600 mlを準備し、濃度96 mass%の硫酸163.62 gを秤量し、それを3Lビーカーの水に添加し、希硫酸を生成した。
3Lビーカーの希硫酸に硝酸セリウム0.0113 g、酸化プラセオジム0.2561 g及び酸化ガドリニウム290.00 gをこの順で添加した。希硫酸と硝酸セリウム、酸化プラセオジム及び酸化ガドリニウムが沈殿反応し、生成物が発生する。得られた懸濁液をスターラーで撹拌しつつ、ホットバスで90℃に加温し、150分間以上維持した。
ボールミルに生成物100 gとエタノール200 mlを入れ、100 rpmで15時間湿式粉砕した。粉砕後のスラリーを100℃で4~6時間乾燥した。乾燥した生成物を、乳鉢を用いて目開き500μmのふるいを通るまでさらに解砕することで、微粒子の生成物を得られた。
湿式粉砕した生成物をアルミナるつぼに入れ、大気雰囲気の電気炉を使用し、大気圧の空気中にて900℃で1時間仮焼を行った。反応時に発生したH2Oガス及びSO3ガスはガス処理装置で処理を行った。
アルミナるつぼに仮焼処理を行った粉末を入れ、水素雰囲気の還元炉を使用し、水素ガス雰囲気下で、800℃で3時間保持し、還元処理を行った。還元処理時に発生するH2Oガス及びH2Sガスはガス処理装置で処理した。この還元反応により希土類オキシ硫化物(Gd, Pr, Ce)2O2Sが得られた。
この希土類オキシ硫化物を一軸加圧成形機を用いて49 MPaで加圧成形後、ビニル袋に真空封止しCIP成形機にて294 MPaで加圧成形した。
得られた成形体を高温焼結炉を用いて、窒素雰囲気中で1500℃に保持し、焼結した。焼結体は微量酸素を含むアルゴン雰囲気中にて1100℃で2時間熱処理し、焼結時に生じた酸素欠陥を補填するアニール処理を行い、セラミックスシンチレータを得た。
仮焼物を粉砕する第2の実施形態に基づき、粉砕工程(3)と仮焼工程(4)の順番を入れ替えた以外は、実施例1と同様の条件でセラミックスシンチレータを製造した。
粉砕工程(3)を行わない以外は、実施例1と同様の条件でセラミックスシンチレータを製造した。
還元工程後に粉砕工程を行う例を以下に示す。秤量工程(1)及び混合工程(2)、仮焼工程(4)、還元工程(5)をこの順に実施例1と同様に行った。
秤量工程で濃度96 mass%の硫酸81.81 gを秤量し、粉砕工程で粉砕時間を40時間とした以外は実施例1と同様に秤量工程(1),混合工程(2),粉砕工程(3),仮焼工程(4) 及び還元工程(5)を行い、希土類オキシ硫化物粉末を作製した。かかる希土類オキシ硫化物粉末を用いて実施例1と同様にセラミックスシンチレータを作製した。
秤量工程で濃度96 mass%の硫酸81.81 gを秤量し、粉砕工程で粉砕時間を40時間とした以外は実施例2と同様に秤量工程(1),混合工程(2),仮焼工程(4),粉砕工程(3),及び還元工程(5)を行い、希土類オキシ硫化物粉末を作製した。かかる希土類オキシ硫化物粉末を用いて実施例2と同様にセラミックスシンチレータを作製した。
秤量工程で濃度96 mass%の硫酸81.81 gを秤量した以外は比較例1と同様に秤量工程(1),混合工程(2),仮焼工程(4)及び還元工程(5)を行い、希土類オキシ硫化物粉末を作製した。かかる希土類オキシ硫化物粉末を用いて比較例1と同様にセラミックスシンチレータを作製した。
秤量工程で濃度96 mass%の硫酸81.81 gを秤量し、粉砕工程で粉砕時間を40時間とした以外は比較例2と同様に秤量工程(1),混合工程(2),仮焼工程(4) 及び還元工程(5)を行った後、粉砕工程を行い、希土類オキシ硫化物粉末を作製した。かかる希土類オキシ硫化物粉末を用いて比較例2と同様にセラミックスシンチレータを作製した。
粉砕工程の粉砕溶媒としてエタノールの代わりに水を用いて、15時間粉砕した以外は実施例3と同様にセラミックスシンチレータを作製した。得られたセラミックスシンチレータの焼結体密度は7.34g/cm3であり、発光強度は101%であり、3ms残光は181ppmであった。このことから粉砕工程の粉砕溶媒としてエタノールの代わりに水を用いた場合でも、高密度な焼結体からなり、大きな発光強度を有し、放射線に対して高感度な応答を示すセラミックスシンチレータが得られることを確認した。
Claims (14)
- 希土類化合物と硫酸及び/又は硫酸塩とを混合して反応させ、生成物を得る混合工程と、
前記生成物を仮焼して仮焼粉を得る仮焼工程と、
前記仮焼粉を還元して希土類オキシ硫化物粉末を得る還元工程と、
前記希土類オキシ硫化物粉末を成形して成形体を得る成形工程と、
前記成形体を焼結する焼結工程と、
を含むセラミックスシンチレータの製造方法であって、
少なくとも還元工程より前に、生成物及び/又は仮焼粉の粒径を調整する粉砕工程を含む
ことを特徴とするセラミックスシンチレータの製造方法。 - 前記混合工程後に前記粉砕工程を行った後、前記仮焼工程において1000℃以下で仮焼し、前記還元工程において900℃以下で還元することを特徴とする請求項1に記載のセラミックスシンチレータの製造方法。
- 前記仮焼工程後に前記粉砕工程を行った後、前記還元工程において900℃以下で還元することを特徴とする請求項1に記載のセラミックスシンチレータの製造方法。
- 前記混合工程は液体中で混合し、前記粉砕工程において湿式粉砕することを特徴とする請求項1~3のいずれか1つに記載のセラミックスシンチレータの製造方法。
- 前記還元工程の後に、前記希土類オキシ硫化物粉末の粒径を調整する粉砕工程を含まないことを特徴とする請求項1~4のいずれか1つに記載のセラミックスシンチレータの製造方法。
- 前記焼結工程では成形体に大気圧を超える圧力を印加せず、且つ不活性雰囲気中で焼結することを特徴とする請求項1~5のいずれか1つに記載のセラミックスシンチレータの製造方法。
- 前記希土類化合物は、希土類元素の酸化物、水酸化物、ハロゲン化物、硝酸塩、硫酸塩、酢酸塩、リン酸塩、及び炭酸塩からなる群から選択される少なくとも一つであることを特徴とする請求項1~6のいずれか1つに記載のセラミックスシンチレータの製造方法。
- 前記希土類化合物は少なくとも酸化ガドリニウムを含むことを特徴とする請求項7に記載のセラミックスシンチレータの製造方法。
- 前記希土類化合物は少なくとも酸化ガドリニウム及び酸化プラセオジムを含むことを特徴とする請求項7に記載のセラミックスシンチレータの製造方法。
- 前記混合工程において、複数の希土類元素の希土類化合物を硫酸及び/又は硫酸塩に添加して混合する際、量の少ない希土類化合物から順に添加することを特徴とする請求項1~9のいずれか1つに記載のセラミックスシンチレータの製造方法。
- 前記焼結体をアニールするアニール工程をさらに含むことを特徴とする請求項1~10のいずれか1つに記載のセラミックスシンチレータの製造方法。
- 請求項1~11のいずれか1つに記載の方法で製造されたセラミックスシンチレータ。
- 請求項12に記載のセラミックスシンチレータを備えたシンチレータアレイ。
- 請求項12に記載のセラミックスシンチレータを備えた放射線検出器。
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