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  • C09K11/7767—Chalcogenides
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  • C09K11/7771—Oxysulfides
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/2018—Scintillation-photodiode combinations
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/202—Measuring radiation intensity with scintillation detectors the detector being a crystal
  • G01T1/2023—Selection of materials
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  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
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  • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
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  • C04B2235/44—Metal salt constituents or additives chosen for the nature of the anions, e.g. hydrides or acetylacetonate
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  • C04B35/6455—Hot isostatic pressing

Definitions

• Embodiments of the present invention relate to ceramic scintillators, methods for manufacturing ceramic scintillators, radiation detectors, and radiation inspection devices.
• X-ray CT equipment In fields such as medical diagnosis or industrial non-destructive testing, tests are performed using radiation testing equipment such as X-ray tomography equipment (hereinafter referred to as "X-ray CT equipment").
• X-ray CT equipment is equipped with an X-ray tube (X-ray source) that irradiates a fan-shaped fan beam of X-rays, and an X-ray detector with multiple X-ray detection elements arranged in parallel, and is structured such that the X-ray tube and X-ray detector are arranged opposite each other so that the tomographic plane of the object to be inspected is at the center.
• X-ray CT equipment is equipped with an X-ray tube (X-ray source) that irradiates a fan-shaped fan beam of X-rays, and an X-ray detector with multiple X-ray detection elements arranged in parallel, and is structured such that the X-ray tube and X-ray detector are arranged opposite each other so that the tomographic plane of the
• the X-ray tube and X-ray detector are rotated while irradiating the object to be inspected with fan beam X-rays, and the intensity of the X-rays that pass through the object to be inspected is measured by the X-ray detector to collect X-ray absorption data.
• the obtained X-ray absorption data is then analyzed by a computer to reconstruct a tomographic image of the object to be inspected.
• a detector using a solid scintillator that emits visible light or the like when stimulated by X-rays is often used.
• the resolution of the X-ray CT device can be further improved.
• a ceramic scintillator made of a sintered body of a rare earth oxysulfide such as Gd 2 O 2 S:Pr has a large X-ray absorption coefficient, excellent luminous efficiency, and a short afterglow of luminescence, and is therefore suitable as a scintillator material for the X-ray detector.
• rare earth oxysulfide phosphor powder is sintered using a hot press method or HIP (hot isostatic pressing) method, and the resulting high-density sintered body is then cut into the desired shape and dimensions using a blade saw or wire saw to obtain scintillator pieces that are used as this type of ceramic scintillator.
• HIP hot isostatic pressing
• Ceramic scintillators are required to have transparency in order to obtain high detection sensitivity.
• the pressure during sintering causes distortion inside the sintered body, and the composition of the sintered body is often slightly deviated from the stoichiometric ratio, resulting in blackish coloring.
• the crystals on the cut surface are crushed, resulting in a crushed layer of about 3 ⁇ m to 5 ⁇ m from the surface, or a colored layer may be generated due to the pressure during cutting.
• the internal distortion of the sintered body, internal coloring due to composition fluctuation, or the crushed layer or colored layer generated during cutting may reduce the light output and stability of the ceramic scintillator and may be a factor in increasing the afterglow time. Therefore, in the conventional manufacturing process of ceramic scintillators, after cutting out scintillator pieces from a rare earth oxysulfide sintered body, heat treatment is performed in various atmospheres (see, for example, Patent Documents 2 and 3).
• Patent Document 3 describes a technology in which a rare earth oxysulfide sintered body and oxysulfide powder are contained in a substantially sealed container, which is placed in a normal atmospheric firing furnace and heat-treated at a temperature of 900°C to 1200°C, and sulfur and oxygen (e.g., SO2 or SO3 ) generated by decomposition of the oxysulfide powder during this heat treatment are reacted with the rare earth oxysulfide sintered body, thereby removing coloration and internal distortion of the sintered body.
• SO2 or SO3 sulfur and oxygen
• the particle size of the starting rare earth oxysulfide phosphor powder is large, it may not be possible to completely remove the coloring (particularly the internal coloring) at temperatures of 900°C to 1200°C, and it may not be possible to sufficiently shorten the afterglow. As a result, there is a possibility that pseudo images (artifacts) may occur in images obtained by X-ray CT devices, etc., and there is room for improvement.
• An embodiment of the present invention provides a ceramic scintillator that suppresses an increase in afterglow time while suppressing a decrease in light output.
• a ceramic scintillator comprising a sintered body of a gadolinium oxysulfide phosphor containing praseodymium as a main activator,
• the body color of the sintered body is expressed in chromaticity coordinates (x, y) based on the CIE 1931 chromaticity value
• the sintered body has a color value of 0.4 ⁇ x ⁇ 0.505 (1).
• a ceramic scintillator having a body color that satisfies the above.
• the ceramic scintillator according to ⁇ 1> When the body color of the sintered body is expressed in chromaticity coordinates (x, y) based on the CIE 1931 chromaticity value, the sintered body has a color value of 0.4 ⁇ x ⁇ 0.42 (1a). and 0.83x + 0.075 ⁇ y ⁇ 0.83x + 0.095 ... (2) The ceramic scintillator has a body color that further satisfies the above requirements.
• the ceramic scintillator according to ⁇ 1> or ⁇ 2> The gadolinium oxysulfide phosphor is General formula: (Gd 1-ab Pr a Ce b ) 2 O 2 S (A) (In the formula, a is a number satisfying 0.0001 ⁇ a ⁇ 0.01, and b is a number satisfying 0 ⁇ b ⁇ 0.005.)
• a ceramic scintillator having a composition represented by the formula: ⁇ 4> A method for producing a ceramic scintillator according to any one of ⁇ 1> to ⁇ 3>, A heat treatment process is provided in which a reaction gas containing oxygen and sulfur is reacted with the sintered body in a heating furnace in an air atmosphere, The method for producing a ceramic scintillator, wherein the heat treatment time in the heat treatment step is 1 hour or more and 50 hours or less.
• a method for producing a ceramic scintillator according to the present invention The heat treatment step is carried out at a temperature in the range of 900° C. or more and 1600° C. or less.
• the method for producing a ceramic scintillator according to ⁇ 4> or ⁇ 5> The method for producing a ceramic scintillator, wherein the heat treatment step is carried out at a temperature in the range of more than 1100°C and less than 1300°C.
• ⁇ 7> ⁇ 4> to ⁇ 6> the method for producing a ceramic scintillator according to any one of the above, the sintered body and an oxysulfide powder are placed inside a container, and the heat treatment step is performed.
• ⁇ 8> ⁇ 7> A method for producing a ceramic scintillator according to the present invention,
• the container has a double or more layer structure including a first container and a second container inside the first container, the sintered body is placed inside the second container, the oxysulfide powder is placed outside the second container and inside the first container, and the heat treatment step is performed.
• the method for producing a ceramic scintillator according to ⁇ 7> or ⁇ 8> The method for producing a ceramic scintillator, wherein the oxysulfide powder is gadolinium oxysulfide powder.
• a radiation detector comprising the ceramic scintillator according to any one of ⁇ 1> to ⁇ 3>.
• ⁇ 11> ⁇ 10> A radiation inspection device comprising the radiation detector according to ⁇ 10>.
• FIG. 1 is a graph in which the body colors of the sintered bodies constituting the ceramic scintillators of the examples and comparative examples are plotted on xy chromaticity coordinates.
• FIG. 2 is a schematic diagram showing a state in which a heat treatment step is carried out using a double-structured container in the manufacturing method according to the embodiment.
• FIG. 3 is a schematic diagram showing the configuration of an X-ray detector as an example of a radiation detector according to an embodiment.
• FIG. 4 is a schematic diagram showing the configuration of an X-ray CT apparatus as an example of a radiation inspection apparatus according to an embodiment.
• the ceramic scintillator of the embodiment includes a sintered body of a gadolinium oxysulfide phosphor containing praseodymium (Pr) as a main activator.
• Pr praseodymium
• a small amount of cerium (Ce), which is effective in suppressing afterglow, may be contained as a co-activator.
• gadolinium oxysulfide phosphors examples include: General formula: (Gd 1-ab Pr a Ce b ) 2 O 2 S...(A) (In the formula, a is a number satisfying 0.0001 ⁇ a ⁇ 0.01, and b is a number satisfying 0 ⁇ b ⁇ 0.005.)
• a part of Gd may be replaced with another rare earth element (such as at least one element selected from Y, La, and Lu), and in this case, the replacement amount is preferably 30 mol % or less.
• Gadolinium oxysulfide phosphors containing Pr as the main activator have a large X-ray absorption coefficient and provide excellent light output, and are therefore particularly effective as fluorescence generating materials for radiation detectors.
• the content of Pr as a main activator is preferably in the range of 0.0001 or more and 0.01 or less as the value of a in the above general formula (A). If the value of a indicating the Pr content is less than 0.0001, the effect as a main activator cannot be sufficiently obtained, and the luminous efficiency tends to decrease. On the other hand, if the value of a exceeds 0.01, the luminous efficiency tends to decrease.
• the value of a indicating the Pr content is in the range of 0.0002 or more and 0.005 or less.
• the content of Ce as a coactivator is preferably 0.005 or less as the value of b in the above general formula (A). If the value of b, which indicates the Ce content, exceeds 0.005, it may result in a decrease in light output, so care should be taken.
• the sintered body when the body color of the sintered body of the above-mentioned gadolinium oxysulfide phosphor (hereinafter simply referred to as the "sintered body") is expressed in chromaticity coordinates (x, y) based on the CIE1931 chromaticity value, the sintered body satisfies the following relationship: 0.4 ⁇ x ⁇ 0.505 ... (1) 0.83x+0.075 ⁇ y...(2-1) The body color satisfies the chromaticity coordinates of
• Figure 1 shows the xy chromaticity coordinates of each body color plotted after measuring the body color of the sintered body constituting the ceramic scintillator of Examples 1 to 7 and Comparative Examples 1 and 2 described below.
• the body color of the sintered body in the embodiment shows the xy chromaticity in a 10° field of view.
• This xy chromaticity is measured using a spectrophotometer CM-3500d (product name, manufactured by Minolta Co., Ltd.), selecting a D65 light source as the irradiating light, adopting the regular reflection light inclusion method, and measuring diameter of 8 mm.
• CM-3500d product name, manufactured by Minolta Co., Ltd.
• the surface of the measurement sample is polished with an abrasive of grit size 700 or more, and the thickness is 1.0 mm ⁇ 0.1 mm.
• the measurement sample is placed in close contact with the window of the spectroscope, and a cylindrical box with a black inner surface called a zero calibration box is placed on the opposite side of the measurement sample from the window of the spectroscope.
• the body color of the sintered body in the embodiment shows the xy chromaticity value measured in this way.
• the fact that the sintered body has a body color (yellow or very light orange with a highly transparent color tone) that satisfies the chromaticity coordinates expressed by the above formulas (1) and (2-1) means that the internal coloring of the sintered body, which is a factor in increasing the afterglow time, has been sufficiently removed, and that whitening of the sintered body surface, which is a cause of reduced light output, has not occurred. Therefore, by using a sintered body with such a body color, it is possible to reproducibly provide a ceramic scintillator that has excellent light output and a short afterglow time.
• the opacity degree of whiteness
• a ceramic scintillator using such an opaque sintered body light scattering occurs, resulting in a decrease in light output when irradiated with X-rays or the like.
• the sintered body can become opaque, but one particular example is whitening caused by oxidation of the sintered body surface.
• a highly transparent body color can be obtained with good reproducibility.
• the sum of the x and y values (x+y) is equal to or less than 1.
• the maximum value of the x value is approximately 0.505. Therefore, the upper limit of the x value in the xy chromaticity coordinates in this embodiment is 0.505, as represented by the above formula (1).
• the upper limit of the y value in the xy chromaticity coordinate is not necessarily limited.
• an increase in the y value means that the green tone becomes stronger.
• the gadolinium oxysulfide phosphor activated with Pr has a green emission spectrum, and even if the body color of the sintered body becomes stronger in green tone, the light output of the ceramic scintillator does not decrease significantly.
• the green hue is mainly determined by the Pr concentration. Therefore, in consideration of a practical Pr concentration and in order to obtain a higher output scintillator, the y value of the body color of the sintered body is y ⁇ 0.83x+0.095 ... (2-2) That is, the sintered body in the embodiment satisfies the x value in the above formula (1) and also satisfies the following: 0.83x+0.075 ⁇ y ⁇ 0.83x+0.095...(2) The body color satisfies the above.
• Sintered bodies that do not have a body color that satisfies the y value in the above formula (2) include sintered bodies in which the impurities contained therein are partially segregated. In particular, if elements that cause coloring are segregated in the sintered body, there is a risk that the performance as a scintillator will vary.
• Ce may or may not be added to the gadolinium oxysulfide phosphor.
• the afterglow time can be sufficiently shortened by sufficiently removing the internal coloring of the sintered body.
• the ceramic scintillator without adding Ce can suppress the exposure dose of the object to be inspected, it can be suitably used in an X-ray inspection device for medical diagnosis.
• Ce is added to the gadolinium oxysulfide phosphor
• the afterglow time can be further shortened. Therefore, when the gadolinium oxysulfide phosphor to which Ce is added is used in a radiation inspection device described below, it becomes easier to obtain a high-resolution image even when a large amount of X-rays is continuously irradiated.
• the ceramic scintillator to which Ce is added can be suitably used in an X-ray nondestructive inspection device for industrial use.
• the sintered body has a body color that satisfies the above formulas (1a) and (2).
• the x value tends to be small, being 0.42 or less. From the viewpoint of increasing the rotation rate of the heating furnace by shortening the heat treatment time and preventing an increase in production costs, it is preferable that the x value satisfies the above formula (1a).
• the x value of the xy chromaticity coordinates which indicates the body color of the sintered body, is preferably 0.407 or more, in order to obtain a greater light output.
• the color difference of the sintered body is preferably small.
• the difference between the x value at any point on the measurement surface of the xy chromaticity coordinates and the x value at any point 5 mm or more away from the said point is preferably 0.01 or less.
• the difference between the y value at any point on the measurement surface of the xy chromaticity coordinates and the y value at any point 5 mm or more away from the said point is also preferably 0.01 or less.
• the difference between the x value at any point on the measurement surface of the xy chromaticity coordinates and the x value at any point on the surface opposite to the measurement surface is preferably 0.01 or less.
• the difference between the y value at any point on the measurement surface of the xy chromaticity coordinates and the y value at any point on the surface opposite to the measurement surface is preferably 0.01 or less.
• the other characteristics other than the body color are equal to or better than those of conventional ceramic scintillators.
• the sintered body density which affects the light transmittance
• the relative density is 99.5% or more. If the relative density of the Pr-activated gadolinium oxysulfide sintered body is less than 99.5%, light scattering is likely to occur, and care should be taken as this may reduce the light transmittance or light output of the ceramic scintillator.
• the manufacturing method of the embodiment is suitable for manufacturing the ceramic scintillator described above, but is not necessarily limited thereto, and can be applied to manufacturing ceramic scintillators made of sintered bodies of various rare earth oxysulfide phosphors.
• gadolinium oxysulfide phosphor powder which is the raw material for the sintered body, is prepared. That is, each rare earth element such as Gd, Pr, Ce, etc. is weighed out in a predetermined amount and thoroughly mixed. At this time, an oxide such as gadolinium oxide or praseodymium oxide is used as each starting material. As a mixture of each starting material, it is preferable to use a uniform mixed oxide obtained by firing oxalic acid coprecipitate, etc.
• a sulfurizing agent such as sulfur (S) powder and a flux such as A3PO4 or A2CO3 (A is at least one element selected from Li, Na, K, Rb, and Cs) are added to the obtained mixture and mixed thoroughly.
• the mixed powder is fired at a temperature of 1100°C to 1300°C for 5 hours to 10 hours, and then washed with acid and water to obtain a gadolinium oxysulfide phosphor powder.
• the gadolinium oxysulfide phosphor powder thus obtained is used as the raw material for the sintered body that is the constituent material of the ceramic scintillator.
• the average particle diameter of the gadolinium oxysulfide phosphor powder is not particularly limited, but if the average particle diameter is too small, it becomes difficult to produce a sintered body of a large shape, and if the average particle diameter is too large, a higher temperature is required during sintering. From this perspective, the average particle diameter of the gadolinium oxysulfide phosphor powder is preferably, for example, 1 ⁇ m or more and 50 ⁇ m or less, and more preferably 5 ⁇ m or more and 20 ⁇ m or less.
• the internal coloring of the sintered body can be effectively removed by the heat treatment described below.
• the afterglow time caused by internal coloring can be sufficiently shortened.
• the gadolinium oxysulfide phosphor powder is sintered to produce a sintered body that will be the constituent material of the ceramic scintillator.
• known sintering methods such as hot pressing or HIP can be applied. Of these, it is preferable to carry out sintering by applying the HIP method, from the viewpoint of easily obtaining a sintered body with a particularly high density.
• Sintering using the HIP method is carried out, for example, by first forming gadolinium oxysulfide phosphor powder into an appropriate shape using a rubber press, then filling and sealing it in a metal container or the like and carrying out HIP processing.
• the HIP conditions at this time are preferably a HIP temperature of 1300°C to 1600°C, a HIP pressure of 98 MPa or more, and a HIP time of 1 hour to 10 hours. It is more preferable that the HIP temperature is 1350°C to 1600°C.
• the obtained sintered body is cut into a desired shape and size using a blade saw or a wire saw to obtain a scintillator piece or the like.
• internal distortion may occur due to the pressure during sintering, or the composition of the sintered body may deviate slightly from the stoichiometric ratio, resulting in internal coloring.
• a colored layer may form on the surface due to the pressure applied during cutting.
• This heat treatment process is a process in which a reaction gas containing oxygen and sulfur is reacted with the sintered body after cutting in a heating furnace with an air atmosphere, for example. Specifically, a sealable container is placed in a furnace with an air atmosphere, and the reaction gas containing oxygen and sulfur is reacted with the sintered body after cutting in the container.
• an inert gas atmosphere such as nitrogen gas or argon gas may be used instead of the air atmosphere inside the heating furnace.
• an inert gas atmosphere such as nitrogen gas or argon gas
• the heat treatment is preferably carried out at a temperature in the range of 900° C. to 1600° C. In this way, the internal distortion of the sintered body caused during sintering is alleviated, and oxygen and sulfur vacancies can be filled, so that the internal coloring of the sintered body can be removed. Furthermore, the colored layer caused during cutting can also be removed at the same time. If the heat treatment temperature is less than 900° C., oxygen and sulfur may not be sufficiently diffused into the sintered body, and the effect of removing internal coloring may not be sufficiently obtained. On the other hand, if the heat treatment temperature exceeds 1600° C., the crystal grains of the sintered body may become coarse, and the processed shape may not be able to be maintained.
• the surface of the sintered body is not oxidized, and therefore whitening of the surface of the sintered body, which is a cause of a decrease in light output, can be prevented, even when the heat treatment temperature is set to a high temperature exceeding 1100° C. Therefore, it is possible to provide a ceramic scintillator with excellent light output and stability as well as a short afterglow time with good reproducibility.
• the heat treatment time is set appropriately depending on the heat treatment temperature, the state of the sintered body to be treated, the concentration of the reactive gas, the type of reactive gas, etc., but in practice it is preferably set in the range of 1 hour or more and 50 hours or less. If the heat treatment time is less than 1 hour, there is a risk that internal coloring may not be sufficiently removed in some cases. On the other hand, even if the heat treatment time is set to more than 50 hours, no further effect will be obtained and production costs will increase. In particular, in the manufacturing method of the embodiment, the heat treatment time is preferably 3 hours or more and 14 hours or less, and more preferably 5 hours or more and 7 hours or less.
• the problems of the conventional technology associated with high-temperature heat treatment are prevented by adjusting the heat treatment time. Therefore, heat treatment can be performed at a high temperature of over 1100°C, which is effective for removing internal coloring.
• heat treatment time within a certain range, it is possible to prevent whitening of the sintered body surface and remove internal coloring, further shortening the afterglow time of the ceramic scintillator while maintaining good light output.
• a reaction gas containing oxygen and sulfur is used.
• the method for generating the reaction gas is not particularly limited, it is preferable to use an oxysulfide powder as a reaction gas source from the viewpoint of obtaining a reaction gas having an appropriate concentration of oxygen and sulfur.
• the sintered body and the oxysulfide powder are placed in a sealable container, and the container is placed in a heating furnace in an air atmosphere to perform a heat treatment.
• SOx gas e.g., SO2 or SO3
• a mixed gas of oxygen and sulfur is generated as a reaction gas.
• the oxysulfide powder which is the source of the reaction gas a mixed powder in which an oxide powder and a sulfide powder are mixed at a predetermined composition ratio may be used.
• a rare earth oxysulfide powder such as gadolinium oxysulfide (Gd 2 O 2 S) powder or yttrium oxysulfide (Y 2 O 2 S) powder may be used.
• gadolinium oxysulfide powder from the viewpoint of generating oxygen and sulfur at the composition ratio of the gadolinium oxysulfide phosphor, it is preferable to use gadolinium oxysulfide powder as the oxysulfide powder.
• the rare earth oxysulfide powder may be composed of a pure compound, or may have a composition including an activator, similar to the gadolinium oxysulfide phosphor.
• the sintered body and oxysulfide powder may be stored in a single-layered container so that they are not in direct contact with each other, but it is preferable to use a container with a double or more layers.
• a container with a double or more layers For example, by using a double-layered container as shown in Figure 2, the reaction can be easily controlled and the internal coloring of the sintered body can be removed with good reproducibility.
• FIG. 2 is a schematic diagram of a case where a heat treatment step is performed using a double-structured container in the manufacturing method of the embodiment.
• a scintillator piece for example a sintered body 2 after cutting, is placed inside a small crucible, which is a second container 1, and the opening of the second container 1 is covered with a small lid 3.
• the second container 1 is placed inside a large crucible, which is a first container 4, and the outside (surrounding) of the second container 1 is filled with oxysulfide powder 5 without any gaps.
• the second container 1 containing the sintered body 2 is embedded in the oxysulfide powder 5.
• the opening of the first container 4 is sealed with a large lid 6.
• the double-structured containers in which the sintered body 2 is accommodated in the second container 1 and the oxysulfide powder 5 is accommodated in the first container 4, are placed in a heating furnace 7, and the atmospheric gas 8 in the heating furnace 7 is, for example, air atmosphere, and heat treatment is performed at the above-mentioned temperature.
• a reaction gas e.g., a reaction gas containing oxygen and sulfur as SOx
• SOx oxygen and sulfur
• the manufacturing method of the embodiment allows the body color of the sintered body to be a desired color tone with good reproducibility, making it possible to reproducibly obtain a ceramic scintillator with excellent light output and short afterglow time.
• the ceramic scintillator of the embodiment or the ceramic scintillator obtained by the manufacturing method of the embodiment, has excellent light output and a short afterglow time. Therefore, by using such a ceramic scintillator as a fluorescence generating material in a radiation detector, it is possible to improve the radiation detection sensitivity and suppress false images. This contributes greatly to the miniaturization and high resolution of radiation detectors.
• FIG. 3 is a schematic diagram showing an X-ray detector, which is an example of a radiation detector according to an embodiment.
• the X-ray detector 11 shown in FIG. 3 has a ceramic scintillator 12 as a fluorescence generating material.
• the ceramic scintillator 12 is made of, for example, a scintillator piece cut into a desired shape from a sintered body, or a scintillator block in which multiple scintillator pieces are stacked vertically and horizontally.
• the rectangular rod-shaped ceramic scintillator 12 is covered with a reflective film 13 on all sides except one, and a photoelectric conversion element such as a silicon photodiode 15 is attached as a photoelectric conversion member to the side not covered by the reflective film 13 via an adhesive layer 14.
• a scintillator block made up of multiple scintillator pieces is used as the ceramic scintillator 12, the silicon photodiodes 15 are arranged to correspond to each scintillator piece.
• X-rays are incident on the ceramic scintillator 12, which emits light according to the amount of X-rays incident on it.
• the light emitted from the ceramic scintillator 12 is detected by a silicon photodiode 15.
• the output of the light emitted based on the amount of X-rays incident on it is converted into an electrical output by the silicon photodiode 15, and then sent from the output terminal 16 to, for example, the computer of the X-ray CT device.
• FIG. 4 is a schematic diagram showing an X-ray CT device, which is an example of a radiation inspection device according to an embodiment.
• the X-ray CT device 20 shown in FIG. 4 has the above-mentioned X-ray detector 11.
• the X-ray detector 11 is attached to the inner wall of a cylinder on which the imaging area of the inspected object 21 is placed.
• An X-ray tube 22 that emits X-rays is disposed approximately in the center of the arc on which the X-ray detector 11 is attached.
• a fixed object to be inspected 21 is placed between the X-ray detector 11 and the X-ray tube 22.
• the X-ray detector 11 and the X-ray tube 22 are configured to rotate around the fixed object to be inspected 21 while taking an image using X-rays. In this way, image information of the object to be inspected 21 is collected three-dimensionally from different angles.
• the signal obtained by X-ray photography (electrical signal converted by silicon photodiode 15) is processed by computer 23 and displayed on display 24 as specimen image 25.
• the specimen image 25 is, for example, a tomographic image of specimen 21.
• a scintillator block in which multiple scintillator pieces are integrated as ceramic scintillator 12
• a multi-tomographic image type X-ray CT device is constructed, which makes it possible to simultaneously capture multiple tomographic images of specimen 21.
• Such a multi-tomographic image type X-ray CT device can also depict the imaging results in three dimensions.
• the X-ray CT device 20 described above uses ceramic scintillators with a short afterglow time, which effectively prevents the appearance of false images.
• the output from each ceramic scintillator is high, which allows for improved resolution.
• the medical diagnostic capabilities of the X-ray CT device 20 can be significantly improved.
• the radiation inspection device of the embodiment is not limited to X-ray inspection devices for medical diagnosis, but can also be applied to X-ray non-destructive inspection devices for industrial use.
• the radiation inspection device of the embodiment also contributes to improving the inspection accuracy of X-ray non-destructive inspection devices.
• Gadolinium oxysulfide phosphor powder having an average particle size of 10 ⁇ m and a composition of (Gd 0.999 , Pr 0.001 ) 2 O 2 S was molded by a rubber press.
• the molded body was sealed in a Ta capsule and then set in a HIP processing device.
• Argon gas was sealed in the HIP processing device as a pressure medium, and a sintered body was produced by processing for 3 hours under conditions of a pressure of 148 MPa and a temperature of 1500°C. After cooling, the sintered body was taken out, and a rod-shaped sample of 1 ⁇ 2 ⁇ 30 mm was cut out from the sintered body with a blade saw to prepare a plurality of scintillator pieces.
• a plurality of scintillator pieces were placed in a second container (small crucible: capacity 500 cc) made of high purity alumina, and the opening of the second container was covered with a small lid.
• the double-structured container with the second container housed inside the first container was placed inside the heating furnace 7, and heat treatment was carried out for 1 hour in an air atmosphere.
• the oxysulfide powder packed inside the first container so as to cover the periphery of the second container was decomposed, generating a reaction gas containing oxygen and sulfur.
• the ceramic scintillator of Example 1 consisting of a sintered body, was produced by reacting this reaction gas with the scintillator pieces.
• Example 2 A ceramic scintillator of Example 2 was produced in the same manner as in Example 1, except that the heat treatment was carried out for 5 hours.
• Example 3 A ceramic scintillator of Example 3 was produced in the same manner as in Example 1, except that the heat treatment was carried out for 7 hours.
• Example 4 A ceramic scintillator of Example 4 was produced in the same manner as in Example 1, except that the heat treatment was carried out for 10 hours.
• Example 5 A ceramic scintillator of Example 5 was produced in the same manner as in Example 1, except that the heat treatment was carried out for 12 hours.
• Example 6 A ceramic scintillator of Example 6 was produced in the same manner as in Example 1, except that the heat treatment was carried out for 14 hours.
• Comparative Example 1 A ceramic scintillator of Comparative Example 1 was produced in the same manner as in Example 1, except that the scintillator pieces were not subjected to heat treatment.
• Comparative Example 2 A ceramic scintillator of Comparative Example 2 was produced in the same manner as in Example 1, except that a gadolinium oxysulfide phosphor powder having a composition of (Gd 0.9989 , Pr 0.0009 , Ce 0.0002 ) 2 O 2 S was used instead of the gadolinium oxysulfide phosphor powder having a composition of (Gd 0.999 , Pr 0.001 ) 2 O 2 S.
• Example 7 A ceramic scintillator of Example 7 was produced in the same manner as in Comparative Example 2, except that the heat treatment was carried out for 5 hours.
• Fig. 1 is a graph plotting xy chromaticity coordinates showing the body colors of the ceramic scintillators of Examples 1 to 7 and Comparative Examples 1 and 2.
• ⁇ indicates the results of the Examples
• ⁇ indicates the results of the Comparative Examples.
• the body color was measured in the same manner at four arbitrary locations in addition to the above measurement locations.
• the body color was measured at a total of five locations on one surface (front surface) of the ceramic scintillator.
• the five measurement locations were 5 mm or more apart from each other.
• the body color was measured at five arbitrary locations 5 mm or more apart from each other on the surface opposite to the front surface (rear surface).
• the difference between the maximum and minimum x values at a total of 10 measurement locations was 0.01 or less, and the difference between the maximum and minimum y values at a total of 10 measurement locations was also 0.01 or less. That is, the color difference of the sintered body was small.
• the X-ray detectors shown in Fig. 3 were constructed for each of the ceramic scintillators of Examples 1 to 7 and Comparative Examples 1 and 2.
• the current value flowing through the silicon photodiode when the X-ray detector was irradiated with X-rays of 120 kVP and 200 mA was measured.
• the light output of the ceramic scintillators of Examples 1 to 7 and Comparative Examples 1 and 2 was determined as a relative value when the current value when a scintillator made of a single crystal of cadmium tungstate (CdWO 4 ) was used in the X-ray detector was set to 100.
• CdWO 4 cadmium tungstate
• the ceramic scintillators of Examples 1 to 7 had body colors that satisfied the above formulas (1) and (2).
• the light output was approximately 1.14 to 1.22 times greater, and the afterglow intensity after 10 ms was approximately 0.10 to 0.33 times smaller, compared to the ceramic scintillator of Comparative Example 1.
• the light output was approximately 1.13 times greater, and the afterglow intensity after 10 ms was approximately 0.33 times smaller, compared to the ceramic scintillator of Comparative Example 2.
• the ceramic scintillator of the embodiment suppresses an increase in the afterglow time while suppressing a decrease in light output.
• Second container small crucible
• Sintered body sintered body
• Small lid First container (large crucible)
• Oxysulfide powder Large lid 7
• Heating furnace Atmospheric gas
• X-ray detector 12
• Ceramic scintillator 13
• Reflecting film Adhesive layer
• Silicon photodiode 16
• Output terminal 20
• X-ray CT device 21
• Inspected object 22
• X-ray tube 23 23
• Computer 24 Display 25 Inspected object image

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