JP2002275465A - Ceramic scintillator and method for producing the same, and radioactive ray detector and radioactive ray- surveying instrument by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an inner coloration of a sintered body which becomes a factor for increasing an afterglow time to be effectively eliminated while suppressing whitening of the surface of the sintered body which becomes the cause of the reduction of an optical output in a ceramic scintillator comprising the sintered body of an oxysulfide fluorophor of a rare earth. SOLUTION: This scintillator is obtained by sintering an oxysulfide fluorophor powder of the rare earth at first, cutting the sintered body, for example to form a desired shape or size, and reacting the sintered body with a reactive gas containing oxygen and sulfur, for example generated by the decomposition of an oxysulfide powder in a furnace in an inert gas atmosphere at 900-1,600 deg.C. When the ceramic scintillator comprises the sintered body of a Pr-activated gadolinium oxysulfide fluorophore, the sintered body of the Pr-activated gadolinium oxysulfide fluorophore has the body color satisfying the formulas: 0.32<=x<=0.38, and 0.83x+0.075<=y<=0.83x+0.095 when the body color is represented by chromaticity coordinates (x, y).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a ceramic scintillator for converting radiation into visible light, a method for manufacturing the same, and a radiation detector and a radiation inspection apparatus using the same.

[0002]

2. Description of the Related Art In the fields of medical diagnosis and industrial nondestructive inspection, inspections using a radiation inspection apparatus such as an X-ray tomography apparatus (hereinafter referred to as an X-ray CT apparatus) are performed. The X-ray CT apparatus includes an X-ray tube (X-ray source) for irradiating a fan-shaped fan beam X-ray and an X-ray detector having a large number of X-ray detection elements arranged in parallel. It has a structure in which it is arranged to face each other. In an X-ray CT apparatus, a subject is irradiated with a fan beam X-ray from an X-ray tube while rotating the subject, and the X-ray transmitted through the subject is rotated.
X-ray absorption data is collected with an X-ray detector. Thereafter, the tomographic image of the subject is reproduced by analyzing the X-ray absorption data by a computer.

As an X-ray detector of an X-ray CT apparatus, a detector using a solid scintillator, which emits visible light or the like in response to X-ray stimulation, as a detection element has been frequently used. In an X-ray detector using a solid scintillator,
Since it is easy to reduce the size of the line detection element and increase the number of channels, the resolution of the X-ray CT apparatus can be further increased. Various materials are known as a solid scintillator. In particular, a ceramic scintillator made of a sintered body of a rare earth oxysulfide such as Gd ₂ O ₂ S: Pr (see Japanese Patent Application Laid-Open No. 58-204088, etc.) It is suitable as a scintillator material for X-ray detectors because of its high X-ray absorption coefficient, excellent luminous efficiency, etc., and short afterglow of light emission.

Since this type of ceramic scintillator is required to have translucency in order to obtain high detection sensitivity, rare-earth oxysulfide powder is hot-pressed by H
By sintering by applying the IP (hot isostatic press) method and the like, and cutting out the obtained high-density sintered body into a desired shape and dimensions by using a blade saw or a wire saw,
Used as a scintillator chip.

[0005] When the rare earth oxysulfide powder is simply sintered, distortion occurs inside the sintered body due to the pressure during sintering, and the composition of the sintered body slightly deviates from the stoichiometric ratio. It will be colored black. Furthermore, when cutting the scintillator chip from the rare earth oxysulfide sintered body, the crystals on the cut surface are crushed,
A crushed layer of about 3 to 5 μm is formed, and a colored layer is formed due to the pressure at the time of cutting. The internal coloration due to the internal strain and composition fluctuation of such a sintered body, the crushed layer and the colored layer generated at the time of cutting, reduce the light output and stability of the ceramic scintillator, and increase the afterglow time. Become.

Therefore, in a conventional process for manufacturing a ceramic scintillator, a scintillator chip or the like is cut out from a rare earth oxysulfide sintered body and then heat-treated in various atmospheres (Japanese Patent Laid-Open No. 6-201834). And JP 20
00-171563). Of these, JP-A-2000-
No. 171563 discloses that a rare earth oxysulfide sintered body and an oxysulfide powder are housed in a substantially closed container, and this is placed in a normal air atmosphere firing furnace to reach 900 to 1200 ° C. A heat treatment is performed at a temperature within a range, and sulfur and oxygen (eg, SO ₂ or SO ₃ ) generated by decomposition of the oxysulfide powder during the heat treatment react with the rare earth oxysulfide sintered body, thereby coloring the sintered body, A technique for removing internal distortion and the like is described.

[0007]

Problems to be Solved by the Invention
The heat treatment method of the ceramic scintillator described in Japanese Patent No. 563 has a certain effect on the removal of a colored layer or the like generated at the time of internal coloring or cutting of the sintered body,
For example, when the particle size of the rare earth oxysulfide phosphor powder as the starting material is large, coloring (particularly internal coloring) cannot be completely removed at the above-mentioned temperature of 900 to 1200 ° C., and afterglow (afterglow) is reduced. Since it cannot be made sufficiently small, there is a problem that an artifact (pseudo image) occurs in an image obtained by an X-ray CT apparatus or the like.

Although it is considered effective to increase the heat treatment temperature for removing the internal coloring of the ceramic scintillator, the atmosphere in the furnace is not controlled by the heat treatment method described in the above-mentioned publication, and usually, Since the heat treatment is performed in a furnace in an air atmosphere, if the temperature exceeds 1200 ° C., the surface of the sintered body is whitened, and there is a problem that the light output of the ceramic scintillator is reduced.

To reduce the afterglow of the ceramic scintillator, a trace amount of cerium (Ce) is added to rare earth oxides such as gadolinium oxysulfide together with praseodymium (Pr).
It is known that activating is effective (see JP-A-56-151376 and JP-A-6-145655). However, since the properties of Ce change greatly with a small amount of addition, it is difficult to obtain uniform material properties.
It is desired that the afterglow time of a ceramic scintillator made of a rare earth oxide sintered body be shortened without adding chromium.

The present invention has been made to address such a problem, and a sintered body which causes an increase in afterglow time irrespective of the particle size of the rare earth oxysulfide phosphor powder as a starting material. It is possible to effectively remove internal coloring and the like of the ceramic scintillator which suppresses whitening of the surface of the sintered body which causes a decrease in light output, and by applying such a manufacturing method, It is an object of the present invention to provide a ceramic scintillator which is excellent in light output and has a reduced afterglow time, in particular, a ceramic scintillator which realizes short afterglow without adding Ce or the like. Further, it is an object of the present invention to provide a radiation detector and a radiation inspection apparatus that improve resolution and image accuracy by using such a ceramic scintillator, thereby improving medical diagnostic performance and nondestructive inspection accuracy. .

[0011]

The present inventors have developed a reaction gas containing sulfur and oxygen (such as SO ₂ or SO ₃₎ in order to remove internal coloring of a ceramic scintillator made of a rare earth oxysulfide sintered body. Containing gas) and the sintered body, that is, the surface of the sintered body was whitened when heat-treated at a high temperature. It was found that when the sintered body was heat-treated, the reaction between the sintered body and oxygen contained in the atmosphere in the furnace in a considerable amount was rapidly activated, and the surface of the sintered body was whitened as a result of oxidation.

The whitening due to oxidation of the surface of the sintered body causes a decrease in light output of the ceramic scintillator as described above. On the other hand, even if the rare earth oxysulfide sintered body is subjected to high-temperature heat treatment under the condition that does not contain oxygen at all (inert gas only), the internal coloring cannot be sufficiently removed, and the afterglow time of the ceramic scintillator is improved. It is not possible.

In consideration of the above-mentioned cause of whitening of the surface of the sintered body and improvement of the internal coloring, the whitening of the surface of the sintered body which causes a decrease in the light output of the scintillator is suppressed. As a result of various investigations on heat treatment conditions capable of effectively removing internal coloring of the body, etc., it was found that a rare earth oxysulfide sintered body and a gas containing sulfur and oxygen (for example, SO ₂ or SO ₃
), The atmosphere in the furnace when reacting with an inert gas atmosphere can prevent oxidation of the surface of the sintered body even when, for example, high-temperature heat treatment is performed. It has been found that it is possible to effectively remove, for example, the internal coloring of the sintered body, which causes the afterglow time to increase, after the maintenance.

The sintered body of the gadolinium oxysulfide phosphor has excellent light output by obtaining a specific body color based on the heat treatment as described above.
It has been found that a ceramic scintillator having a short afterglow time can be realized. That is, the body color of the sintered body constituting the ceramic scintillator is effective as a means for quantifying the internal coloring that causes an increase in afterglow time and the whitening of the surface that causes a decrease in light output. By controlling the body color of the sintered body within a specific range, it is possible to obtain a ceramic scintillator having excellent light output and a short afterglow time with good reproducibility.

The present invention is based on such findings. That is, the ceramic scintillator of the present invention is a ceramic scintillator comprising a sintered body of a gadolinium oxysulfide phosphor containing praseodymium (Pr) as a main activator, as described in claim 1. When the body color of the consolidated body is represented by chromaticity coordinates (x, y), the sintered body has a body color satisfying 0.32 ≦ x ≦ 0.38 and 0.83x + 0.075 ≦ y. In the ceramic scintillator of the present invention, the y value of the chromaticity coordinates representing the body color of the sintered body is further set to 0.83x
It is preferable that the range is + 0.075 ≦ y ≦ 0.83x + 0.095.

In the ceramic scintillator using the sintered body of the Pr-activated gadolinium oxysulfide phosphor specified in the present invention, when the body color of the sintered body is represented by chromaticity coordinates (x, y), Body color 0.32 ≦ x ≦ 0.38 and 0.83x + 0.07
Chromaticity in the range 5 ≦ y, further 0.32 ≦ x ≦ 0.38 and 0.8
When the chromaticity is in the range of 3x + 0.075 ≦ y ≦ 0.83x + 0.095, afterglow time can be reduced while achieving excellent light output.

In other words, the body color indicated in the range of the xy chromaticity coordinates (a very light green or yellowish green and highly transparent body color) is a coloring phenomenon of the Pr-activated gadolinium oxysulfide sintered body. In particular, this means that the internal coloring which causes an increase in the afterglow time is sufficiently removed, and that the surface of the sintered body which causes a decrease in light output is not whitened. Therefore, by using a Pr-activated gadolinium oxysulfide sintered body having such a body color, it is possible to provide a ceramic scintillator having excellent light output and a short afterglow time with good reproducibility.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a ceramic scintillator comprising: sintering a rare earth oxysulfide phosphor powder to produce a sintered body of the rare earth oxysulfide phosphor. And a heat treatment step of reacting a reaction gas containing oxygen and sulfur with the sintered body at a temperature in the range of 900 to 1600 ° C. in a furnace in an inert gas atmosphere. And The method for manufacturing a ceramic scintillator of the present invention is characterized in that the heat treatment is performed at a temperature in the range of more than 1200 ° C. and 1600 ° C. or less, particularly as described in claim 6.

As described above, when the rare earth oxysulfide sintered body is reacted with a gas containing sulfur and oxygen (eg, a gas containing SO ₂ or SO ₃ ), the atmosphere in the furnace is set to an inert gas atmosphere. Thereby, for example, even if high-temperature heat treatment is performed, oxidation of the surface of the sintered body can be prevented. Therefore, it is possible to effectively remove the internal coloring which causes an increase in the afterglow time while maintaining a good light output of the ceramic scintillator.

In the method for manufacturing a ceramic scintillator of the present invention, the reaction (heat treatment step) between the gas containing sulfur and oxygen and the rare earth oxysulfide sintered body can be carried out by various methods. As described, the sintered body and the oxysulfide powder are housed in a substantially sealed container, and the container is placed in a furnace in an inert gas atmosphere and housed in the container. It is preferable to carry out the heat treatment of the sintered body and the oxysulfide powder at the above-mentioned temperature. In this case, it is particularly preferable that the oxysulfide powder is made of a rare earth oxysulfide of the same type or different from the rare earth oxysulfide phosphor.

According to a twelfth aspect of the present invention, there is provided a radiation detector including the above-described ceramic scintillator of the present invention, and a fluorescent light generating means for causing the ceramic scintillator to emit light in response to incident radiation; Photoelectric conversion means for receiving light from the means and converting a light output into an electrical output.

According to a thirteenth aspect of the present invention, there is provided a radiation inspection apparatus for irradiating a radiation to an object to be inspected, and detecting radiation transmitted through the object to be inspected.
It is characterized by comprising the above-mentioned radiation detector of the present invention. The radiation inspection apparatus according to the present invention is, for example, an X-ray C
This is effective for improving the resolution and accuracy of the T apparatus, and further contributes to the practical use of a multi-tomographic image type X-ray CT apparatus.

[0023]

Embodiments of the present invention will be described below.

The ceramic scintillator of the present invention comprises a sintered body of gadolinium oxysulfide phosphor containing praseodymium (Pr) as a main activator. Such gadolinium oxysulfide phosphor represented by the general _{formula: (Gd 1-ab Pr a} Ce b) 2 O 2 S ... (1) ( wherein, a is 0.0001 ≦ a ≦ 0.01, b is 0 ≦ b ≦ Which is a number that satisfies 0.005). Note that a part of Gd may be replaced by another rare earth element (at least one element selected from Y, La and Lu), and the replacement amount is 30 mol%.
It is preferable to set the following.

A Pr-activated or Pr- and Ce-activated gadolinium oxysulfide phosphor has a large X-ray absorption coefficient and an excellent light output, and thus is particularly effective as a means for generating fluorescence of a radiation detector. The content of Pr as the main activator is preferably in the range of 0.0001 to 0.01 as the value of a in the above formula (1). The value of a indicating the Pr content is 0.
If it is less than 0001, the effect as the main activator cannot be sufficiently obtained, and the luminous efficiency decreases. On the other hand, even if the value of a exceeds 0.01, the luminous efficiency decreases. The value of a indicating the Pr content is
More preferably, it is in the range of 0.0002 to 0.005.

In the gadolinium oxysulfide phosphor described above, in addition to Pr as the main activator, a small amount of Ce, which has an effect of suppressing afterglow, may be contained as a coactivator.
The content of Ce as a coactivator is determined by the above formula (1) b
Is preferably 0.005 or less. If the value of b indicating the Ce content exceeds 0.005, the light output will be reduced.

As will be described later in detail, according to the present invention, the afterglow time of the ceramic scintillator can be sufficiently reduced without adding Ce, and the gadolinium oxysulfide phosphor is substantially made of Ce. By not adding, it is easy to obtain uniform material properties, and the light output can be improved. Therefore, the ceramic scintillator of the present invention has a general formula: (Gd ₁ -aP _a ) ₂ O ₂ S (2) wherein a is a number satisfying 0.0001 ≦ a ≦ 0.01. It is more preferable to use a gadolinium oxysulfide phosphor having a composition represented by the following formula:

In the ceramic scintillator of the present invention, the above-mentioned sintered body of the Pr-activated or Pr- and Ce-activated gadolinium oxysulfide phosphor (hereinafter collectively referred to as a Pr-activated gadolinium oxysulfide sintered body) is used. Body color, CIE
When represented by chromaticity coordinates (x, y) based on the chromaticity value, P
The r-activated gadolinium oxysulfide sintered body has a body color satisfying the chromaticity coordinates of 0.32 ≦ x ≦ 0.38 (3) 0.83x + 0.075 ≦ y (4).

FIG. 1 is a graph in which body colors of Pr-activated gadolinium oxysulfide sintered bodies of Examples and Comparative Examples of the present invention described later are measured, and xy chromaticity coordinates of these body colors are plotted. The body color of the gadolinium oxysulfide sintered body in the present invention shows xy chromaticity in a 10 ° visual field. The xy chromaticity is measured using a spectrophotometer CM-3500d (trade name, manufactured by Minolta Co., Ltd.), selecting a D65 light source as the irradiation light, adopting a regular reflection light-incorporating method, and using a measurement diameter of 8 mm. And Before the heat treatment step, the surface of the measurement sample was polished with an abrasive having a count of 700 or more to a thickness of 1.0 mm ± 0.1 mm. The measurement sample was placed in close contact with the spectrometer window, and an inner black cylindrical box called a zero calibration box was placed on the side of the measurement sample opposite to the spectrometer window. The body color of the gadolinium oxysulfide sintered body in the present invention indicates the xy chromaticity value thus measured.

As described above, the Pr-activated gadolinium oxysulfide sintered body satisfies the chromaticity coordinates represented by the above-mentioned equations (3) and (4) (ultra-green or yellow-green, Having a high transparency) means that the internal coloring of the Pr-activated gadolinium oxysulfide sintered body, which causes an increase in afterglow time, is sufficiently removed, and the firing, which causes a decrease in light output, is performed. It means that the surface of the condensed matter has not been whitened. Therefore, by using a Pr-activated gadolinium oxysulfide sintered body having such a body color, it is possible to provide a ceramic scintillator having excellent light output and a short afterglow time with good reproducibility.

That is, in the xy chromaticity coordinates indicating the body color of the Pr-activated gadolinium oxysulfide sintered body, when the x value is less than 0.32, the opacity (whiteness) increases. In a ceramic scintillator using such an opaque Pr-activated gadolinium oxysulfide sintered body, light scattering occurs, so that the light output upon irradiation with X-rays or the like is reduced. Various factors can be considered for the opacity of the sintered body, and in particular, whitening caused by oxidation of the surface of the sintered body can be mentioned. In the present invention, for example, by preventing oxidation of the surface of a sintered body based on a manufacturing method described in detail later, it is possible to obtain a highly transparent Pr-activated gadolinium oxysulfide sintered body with good reproducibility. Making it possible.

On the other hand, when the value x of the body color of the Pr-activated gadolinium oxysulfide sintered body exceeds 0.38, the color tone of yellow becomes stronger as a whole of the sintered body, which also reduces the light output of the ceramic scintillator. When a small amount of Ce is added to the Pr-activated gadolinium oxysulfide sintered body, the x value of the xy chromaticity coordinate indicating the body color tends to increase, but when the x value is 0.38 or less, the light output of the ceramic scintillator is reduced. Can be kept good.

In the xy chromaticity coordinates indicating the body color of the Pr-activated gadolinium oxysulfide sintered body, the y value is as described above (4).
(0.83x + 0.075> y: y = 0.8 in FIG. 1)
Chromaticity below the line of 3x + 0.075) means that the color tone of the entire sintered body is dark. This means that the coloring generated during sintering or processing of the Pr-activated gadolinium oxysulfide sintered body, particularly the internal coloring, has not been sufficiently removed, so that the ceramic scintillator using the same has a long afterglow time. This will lead to an increase.

In other words, the Pr-activated gadolinium oxysulfide sintered body whose y value satisfies the above equation (4) (y =
(Sintered body having chromaticity above the straight line of 0.83x + 0.075)
Since the internal coloring is sufficiently removed, the afterglow time of a ceramic scintillator using such a Pr-activated gadolinium oxysulfide sintered body can be sufficiently shortened. Incidentally, also in the gadolinium oxysulfide phosphor (sintered body) activated with Ce in addition to Pr, the afterglow time is sufficiently short because the y value of the body color satisfies the above equation (4). A ceramic scintillator can be obtained.

The upper limit of the y value of the xy chromaticity coordinates indicating the body color of the Pr-activated gadolinium oxysulfide sintered body is not necessarily limited. That is, when the x value of the xy chromaticity coordinates is within the range of the above equation (3), an increase in the y value means that a green color tone becomes strong. On the other hand, since the Pr-activated gadolinium oxysulfide phosphor has the same color emission spectrum, the light output of the ceramic scintillator does not decrease so much even if the green color tone of the body color becomes strong.

In the body color of the Pr-activated gadolinium oxysulfide sintered body, the above-mentioned green color tone mainly depends on the Pr concentration. Therefore, in consideration of a practical Pr concentration and obtaining a scintillator with a higher output, the y value of the body color of the Pr-activated gadolinium oxysulfide sintered body is y ≧ 0.83x + 0.
095 is preferable. That is, the Pr-activated gadolinium oxysulfide sintered body has a body color that satisfies the above-mentioned expression (3) and also satisfies the range of 0.83x + 0.075 ≦ y ≦ 0.83x + 0.095 (5). It is preferred to have.

Here, in the ceramic scintillator of the present invention, by sufficiently removing the internal coloring of the Pr-activated gadolinium oxysulfide sintered body, the afterglow time can be sufficiently reduced without substantially adding Ce. can do. Further, the gadolinium oxysulfide phosphor is substantially made of Ce.
By not adding, it is easy to obtain uniform material properties, and the light output can be improved. Therefore, the ceramic scintillator of the present invention has
It is more preferable to use a gadolinium oxysulfide phosphor having a composition represented by the formula (2).

At this time, the body color of the Pr-activated gadolinium oxysulfide sintered body is such that the x value of the xy chromaticity coordinates is lower than that in the case where Ce is added, so that 0.32 ≦ x ≦ 0.35 (6) It is preferred to have a range of x values. When the x value of the xy chromaticity coordinate indicating the body color of the Pr-activated gadolinium oxysulfide sintered body satisfies the above-mentioned expression (6), a particularly large light output can be obtained with good reproducibility. That is, in the ceramic scintillator of the present invention, a Pr-activated gadolinium oxysulfide sintered body to which Ce is not substantially added is used, and such a Pr-activated gadolinium oxysulfide sintered body is described above (6). It is desirable to have a body color that satisfies the x value of the expression and the y value of the expression (5).

In the Pr-activated gadolinium oxysulfide sintered body constituting the ceramic scintillator of the present invention, it is preferable that characteristics other than the above-mentioned body color be equal to or higher than those of a normal ceramic scintillator. For example, the density of the sintered body that affects the light transmittance is preferably 99.5% or more in relative density with respect to the true density. When the relative density of the Pr-activated gadolinium oxysulfide sintered body is less than 99.5%, light scattering is likely to occur, and thus the light transmittance and light output of the ceramic scintillator are likely to decrease.

Next, details of the method for manufacturing the ceramic scintillator of the present invention will be described. The production method of the present invention
Although it is suitable for the production of the ceramic scintillator made of the Pr-activated gadolinium oxysulfide sintered body described above, the ceramic scintillator made of the sintered body of various rare earth oxysulfide phosphors is not necessarily limited thereto. Can be applied to manufacturing.

That is, the method of manufacturing the ceramic scintillator of the present invention is not limited to the Pr-activated gadolinium oxysulfide sintered body, but includes praseodymium (Pr), terbium (Tb),
It is applicable when manufacturing a ceramic scintillator made of a sintered body of a rare earth oxysulfide phosphor containing europium (Eu) or the like as a main activator.

Such a rare earth oxysulfide phosphor has a general formula: (M _{1 -z} R _z ) ₂ O ₂ S (7) (where M is selected from Gd, Y, La and Lu) At least one element, R represents at least one element selected from Pr, Tb and Eu, and z is 0.0001 ≦ z ≦
0.1, which is a number that satisfies 0.1). The rare earth oxysulfide phosphor is composed of cerium (Ce), neodymium (Nd), samarium (Sm), dysprosium (D
y), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) or the like may be contained as a co-activator.

In the production method of the present invention, first, a raw material powder of a rare earth oxysulfide phosphor such as a Pr-activated (or Pr- and Ce-activated) gadolinium oxysulfide phosphor is prepared. That is, a predetermined amount of each rare earth element such as Gd or Pr is weighed and sufficiently mixed. At this time, an oxide such as gadolinium oxide or praseodymium oxide is used as each starting material. As a mixture of these starting materials, it is preferable to use a uniform mixed oxide obtained by calcining oxalic acid coprecipitated salt or the like.

Next, a sulfurizing agent such as sulfur (S) powder and A ₃ P
O ₄ or A ₂ CO ₃ (A is Li, Na, K, Rb and Cs
And at least one element selected from the following) and a sufficient mixing. 11
After calcination at a temperature of 00 to 1300 ° C. for 5 to 10 hours, the resultant is washed with an acid and water to obtain a rare earth oxysulfide phosphor powder.

The thus obtained rare earth oxysulfide phosphor powder is used as a raw material for a sintered body which is a constituent material of a ceramic scintillator. In the present invention, the average particle diameter of the rare earth oxysulfide phosphor powder is not particularly limited. However, if the average particle diameter is too small, it becomes difficult to produce a large-sized sintered body, while if it is too large, the sintered body becomes too small. It is necessary to use a rare earth oxysulfide phosphor powder having an average particle diameter in the range of, for example, 1 to 50 μm, since it is necessary to raise the temperature to a higher temperature. The average particle diameter of the rare earth oxysulfide phosphor powder is more preferably in the range of 5 to 20 μm.

Further, in the present invention, even when a rare earth oxysulfide phosphor powder having an average particle diameter of 20 μm or more is used, the internal coloring of the sintered body can be satisfactorily removed by the heat treatment described later. In other words, using a rare earth oxysulfide phosphor powder having a relatively large average particle size,
Even when the light output is improved, the afterglow time due to internal coloring or the like can be sufficiently reduced.

Next, the above-mentioned rare earth oxysulfide phosphor powder is sintered to produce a rare earth oxysulfide phosphor sintered body (rare earth oxysulfide sintered body) which is a constituent material of the ceramic scintillator. . In sintering the rare earth oxysulfide phosphor powder, a known sintering method such as hot pressing or HIP can be applied, but in particular, a high density rare earth oxysulfide sintered body can be easily obtained. Because it is possible, H
It is preferable to perform the sintering step by applying the IP method.

The sintering step to which the HIP method is applied is carried out by first forming a rare earth oxysulfide phosphor powder into an appropriate shape by a rubber press, filling and enclosing in a metal container or the like, and performing an HIP process. The HIP conditions at this time are HIP temperature of 1400 to 1600 ° C., HIP pressure of 98 MPa or more, HI
The P time is preferably 1 to 10 hours. By performing the HIP treatment under such conditions, for example, a rare earth oxysulfide sintered body having a relative density (density ratio to true density) of 99.5% or more can be obtained with good reproducibility. The relative density of the sintered body is
If it is less than 99.5%, characteristics such as light transmittance and light output required for the ceramic scintillator cannot be satisfied.

Next, the obtained high-density rare earth oxysulfide sintered body is cut into a desired shape and size using a blade saw, a wire saw, or the like to obtain a scintillator chip or the like. Here, in the rare earth oxysulfide sintered body, internal coloring occurs due to internal strain due to the pressure during sintering, or due to the composition of the sintered body slightly deviating from the stoichiometric ratio. Further, when chips or the like are cut out from the sintered body, a colored layer is formed on the surface due to pressure at the time of cutting or the like. These coloring phenomena lower the light output and stability of the ceramic scintillator, and increase the afterglow time.

Therefore, after cutting into a desired shape from the rare earth oxysulfide sintered body, heat treatment is performed for the purpose of restoring light output and removing coloring. In this heat treatment step, for example, in a furnace in an inert gas atmosphere such as nitrogen gas or argon gas, a reaction gas containing oxygen and sulfur and, for example, a rare earth oxysulfide sintered body after cutting processing is 900 to 1600. This is a step of reacting at a temperature in the range of ° C. Specifically, a vessel that can be substantially sealed is placed in a furnace in an inert gas atmosphere, and a reaction gas containing oxygen and sulfur and a rare earth oxysulfide sintered body after cutting are placed in the vessel. Is reacted.

As described above, the reaction gas containing oxygen and sulfur and the rare earth oxysulfide sintered body after the cutting process are 900-1600.
By reacting at a temperature in the range of ℃, internal strain of the sintered body generated at the time of sintering is alleviated, and oxygen deficiency and sulfur deficiency can be filled, so the internal coloring of the rare earth oxysulfide sintered body Can be removed. Further, the coloring layer and the like generated at the time of cutting are also removed at the same time.

In the production method of the present invention, the reaction between the reaction gas containing oxygen and sulfur and the rare earth oxysulfide sintered body is performed in a furnace in an inert gas atmosphere. Even when the (heat treatment temperature) is set to a high temperature exceeding, for example, 1200 ° C., the surface of the sintered body is not oxidized, thereby preventing the surface of the sintered body from being whitened, which causes a decrease in light output. Can be. Therefore, it is possible to provide a ceramic scintillator having excellent light output and stability and a short afterglow time with good reproducibility.

The heat treatment for the above reaction is 900-1600.
Performed at a temperature in the range of ° C. If the heat treatment temperature is lower than 900 ° C., oxygen and sulfur are not sufficiently diffused into the rare earth oxysulfide sintered body, and the effect of removing internal coloring cannot be sufficiently obtained. On the other hand, when the heat treatment temperature exceeds 1600 ° C., the crystal grains of the rare earth oxysulfide sintered body become coarse, and the processed shape cannot be maintained. In particular, in the production method of the present invention,
The heat treatment is preferably performed in a high temperature range of 1600 ° C. or less.

That is, in the production method of the present invention,
As described above, the problems associated with the conventional high-temperature heat treatment (oxidation of the sintered body surface and associated whitening) are prevented by setting the atmosphere in the furnace to an inert gas atmosphere. The heat treatment can be performed in a high temperature range exceeding the effective 1200 ° C. and not more than 1600 ° C. In other words, according to the production method of the present invention, the reaction temperature (heat treatment temperature) is set to 1200
By setting the temperature to be higher than 1600 ° C. and lower than 1600 ° C., the whitening of the surface of the sintered body can be prevented and the internal coloring can be more completely removed, so that the afterglow time of the ceramic scintillator is further reduced. In addition, it is possible to maintain a good light output.

The heat treatment time is appropriately set according to the heat treatment temperature, the state of the sintered body to be treated, the concentration and type of the reaction gas, etc., but is practically in the range of 2 to 50 hours. Is preferred. If the heat treatment time is less than 2 hours, the internal coloring may not be sufficiently removed in some cases. On the other hand, if the heat treatment time is set to be longer than 50 hours, no further effect is obtained, and the production cost is increased.

As described above, in the heat treatment step of the present invention, a reaction gas containing oxygen and sulfur is used. Although the method for producing such a gas is not particularly limited,
In order to obtain a gas having an appropriate concentration of oxygen and sulfur, it is preferable to use oxysulfide powder as a source of a reaction gas. That is, the rare earth oxysulfide sintered body and the oxysulfide powder are housed in a container that can be substantially sealed, and this container is placed in a furnace in an inert gas atmosphere to perform heat treatment. As a result, the oxysulfide powder decomposes at or near the heat treatment temperature to generate SO _x gas such as SO ₂ or SO ₃ or a mixed gas of oxygen and sulfur. In the present invention, the reaction gas thus obtained is preferably reacted with the rare earth oxysulfide sintered body at the above-mentioned temperature.

Here, as a source of the reaction gas, a mixed powder obtained by mixing an oxide powder and a sulfide powder at a predetermined composition ratio may be used. Further, from the viewpoint that oxygen and sulfur are generated at the composition ratio of the rare earth oxysulfide phosphor, it is desirable to use a rare earth oxysulfide powder as a source of the reaction gas. At this time, the rare earth oxysulfide powder may be a compound of the same type and composition as the rare earth oxysulfide phosphor, or may be a compound of a different or different composition. Further, the rare earth oxysulfide powder may be a pure compound or a compound having a phosphor composition containing an activator.

The rare earth oxysulfide sintered body and the oxysulfide powder (especially, the same or different rare earth oxysulfide powder) as the source of the reaction gas are not in direct contact with the phosphor and are in the same container. For example, by using a container having a double structure as shown in FIG. 2, the reaction can be easily controlled, and the internal coloring of the rare earth oxysulfide sintered body can be removed with good reproducibility. be able to.

FIG. 2 is a view showing a heat treatment state using a double-structure container according to an embodiment of the manufacturing method of the present invention. In the figure, 1 is a small crucible as a first container,
For example, the processed rare earth oxysulfide sintered body 2 is accommodated in the small crucible 1, and the small crucible 1 is closed with the small lid 3. Such a small crucible 1 is placed in a large crucible 4 as a second container, and an oxysulfide powder 5 such as a rare earth oxysulfide powder is filled around the small crucible 1 without gaps. In other words, the small crucible 1 containing the rare earth oxysulfide sintered body 2 is embedded in the oxysulfide powder 5. Thereafter, the large crucible 4 filled with the oxysulfide powder 5 is sealed with the large lid 6.

Then, the above-mentioned rare earth oxysulfide sintered body 2
Is placed in the heating furnace 7 and the atmosphere gas 8 in the heating furnace 7 is changed to an inert gas atmosphere. The heat treatment is performed at a temperature of not more than ℃. Such heat treatment, and gas generated by the decomposition of the rare earth oxysulfide sintered 2 and oxysulfide powder 5, that is, a gas containing oxygen and sulfur, for example, as a SO _x reaction, rare earth oxysulfide sintered The ceramic scintillator having a short afterglow time is obtained by removing the internal coloring and the like of No. 2. In addition, since the surface of the rare earth oxysulfide sintered body 2 does not become white during the heat treatment, excellent light output of the ceramic scintillator can be maintained.

As described above, according to the method for manufacturing a ceramic scintillator of the present invention, a ceramic scintillator having excellent light output and a reduced afterglow time can be obtained with good reproducibility. In particular, when a sintered body of a Pr-activated gadolinium oxysulfide phosphor is used as a constituent material of the ceramic scintillator, the body color is improved with good reproducibility as described above.
Since the color tone can be represented by the chromaticity coordinates, it is possible to more reliably obtain excellent light output and afterglow time.

Since the ceramic scintillator of the present invention or the ceramic scintillator obtained by the manufacturing method of the present invention has excellent light output and short afterglow time as described above, such a ceramic scintillator is used as a radiation detector. By using as a fluorescence generating means, it is possible to improve the detection sensitivity of radiation, suppress artifacts, and the like. This greatly contributes to downsizing and high resolution of the radiation detector.

Next, an embodiment of the radiation detector and the radiation inspection apparatus according to the present invention will be described with reference to FIGS.

FIG. 3 is a diagram showing a schematic configuration of an X-ray detector according to an embodiment of the radiation detector of the present invention. The X-ray detector 11 shown in FIG. 1 has a ceramic scintillator 12 as a fluorescence generating means. The ceramic scintillator 12 is, for example, a scintillator chip cut out of the above-described rare earth oxysulfide sintered body into a desired shape, or a scintillator block in which a plurality of segments further cut out therefrom are integrated in a number of vertical and horizontal directions.

A rectangular rod-shaped ceramic scintillator 12
Is covered with a reflection film 13 except for one surface, and a silicon photodiode 15 or the like is attached as a photoelectric conversion element via a bonding layer 14 to a surface not covered with the reflection film 13. When a scintillator block in which a large number of segments are integrated is used as the ceramic scintillator 12, a silicon photodiode 15 is arranged corresponding to each segment.

In the above-described X-ray detector 11, X-rays enter the ceramic scintillator 12, and the ceramic scintillator 12 emits light in accordance with the incident X-ray dose. Light emitted from the ceramic scintillator 12 is detected by the photodiode 15. That is, the output of light emitted based on the incident X-ray dose is converted into an electrical output by the photodiode 15 and then output to the output terminal 16.
From the computer of the X-ray CT apparatus.

FIG. 4 is a diagram showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the radiation inspection apparatus of the present invention. The X-ray CT apparatus 20 shown in FIG. 1 has the X-ray detector 11 of the above-described embodiment. The X-ray detector 11 includes a subject 21
Is attached to the inner wall of a cylinder in which the imaging part is placed. An X-ray tube 22 that emits X-rays is disposed substantially at the center of the arc to which the X-ray detector 11 is attached.

Between the X-ray detector 11 and the X-ray tube 22,
The fixed subject 21 is placed. The X-ray detector 11 and the X-ray tube 22 are
It is configured to rotate while taking a picture with a line. In this way, the image information of the subject 12 is collected three-dimensionally from different angles.

The signal obtained by the X-ray photography (the converted electric signal converted by the photodiode 15) is processed by the computer 23 and displayed on the display 24 as the subject image 25. The subject image 25 is, for example, a tomographic image of the subject 21. At this time, a multi-tomographic image type X-ray CT apparatus is configured by using a scintillator block in which a plurality of segments are integrated as the ceramic scintillator 12, whereby a plurality of tomographic images of the subject 12 can be simultaneously captured. Can be.
According to such a multi-tomographic image type X-ray CT apparatus, it is possible to three-dimensionally describe the imaging result.

In the X-ray CT apparatus 20 described above, since a ceramic scintillator having a short afterglow time is used, the appearance of artifacts (pseudo images) can be effectively prevented. Further, since the output from each ceramic scintillator is high, the resolution can be improved. These make it possible to greatly enhance the medical diagnostic capability of the X-ray CT apparatus 20.

The radiation inspection apparatus of the present invention is not limited to an X-ray inspection apparatus for medical diagnosis, but is applicable to an X-ray non-destructive inspection apparatus for industrial use. The present invention also contributes to improvement of inspection accuracy by the X-ray non-destructive inspection device.

[0072]

Next, specific examples of the present invention and evaluation results thereof will be described.

Example 1 First, the average particle size was 10 μm and (Gd _0.999 , Pr
_{0.001) 2} O ₂ prepared gadolinium oxysulfide phosphor powder S composition was formed the phosphor powder by rubber press. After the molded body was sealed in a capsule made of Ta, it was set in a HIP processing apparatus. Argon gas is sealed as a pressurized medium in a HIP processing apparatus, and the pressure is 148 MPa and the temperature is 15
The treatment was performed at 00 ° C. for 3 hours. After cooling, the Pr-containing gadolinium oxysulfide 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 produce a number of scintillator pieces.

Next, as shown in FIG. 2, about 100 scintillator pieces 2 were placed in a first container (small crucible: capacity: 500 cc) 1 made of high-purity alumina and covered with a lid 3. Further, a second container (large crucible) 4 made of high-purity alumina, which is slightly larger than the first container 1, is prepared, and the first container 1 containing the scintillator pieces 2 is arranged in the second container. At the same time, Gd ₂ O ₂ S powder as the oxysulfide powder 5 was filled around the first container 1 without gaps.

Next, the above-mentioned container having a double structure was placed in a heating furnace.
7 and a nitrogen gas of 6 m^Three/ h flow rate
Heat treatment was performed under the conditions of 1300 ° C. × 24 hours while flowing.
In this heat treatment step, the periphery of the first container 1 is covered.
Thus, the Gd filled in the second container 4_TwoO_TwoS powder 5
Partially decomposes near the heat treatment temperature described above.
O _xIt produces gas containing oxygen and sulfur such as gas
It is. Then, this reaction gas and the scintillator piece are
By reacting at the above heat treatment temperature, the purpose and
The resulting ceramic scintillator is obtained. Sera obtained
The mic scintillator was subjected to the characteristic evaluation described later.

Examples 2 to 10 In Example 1 described above, the composition and particle size of the rare earth oxysulfide phosphor powder, the temperature at the time of heat treatment, the composition of the oxysulfide powder to be filled, and the like were set to the conditions shown in Table 1. A ceramic scintillator was produced in the same manner as in Example 1 except for the change. That is, a scintillator piece cut out from each rare earth oxysulfide sintered body was subjected to heat treatment in the same manner as in Example 1 to obtain a ceramic scintillator. Each of the obtained ceramic scintillators was subjected to characteristic evaluation described later.

Comparative Example 1 The procedure of Example 1 was repeated except that the gadolinium oxysulfide sintered body was not heat-treated after cutting.
A ceramic scintillator was produced in the same manner as in the above. The ceramic scintillator thus obtained was subjected to the characteristic evaluation described later.

Comparative Example 2 In Example 1, the heat treatment of the cut gadolinium oxysulfide sintered body (scintillator piece) after cutting was performed in a heating furnace (heat treatment temperature 900 ° C.) in the atmosphere. A ceramic scintillator was produced in the same manner as in Example 1. The obtained ceramic scintillator was subjected to characteristic evaluation described later.

Comparative Example 3 In Example 1, the heat treatment of the cut gadolinium oxysulfide sintered body (scintillator piece) after cutting was performed in a heating furnace (heat treatment temperature of 1300 ° C.) in the atmosphere. A ceramic scintillator was produced in the same manner as in Example 1. The obtained ceramic scintillator was subjected to characteristic evaluation described later.

Comparative Example 4 In Example 1 described above, the gadolinium oxysulfide sintered body (scintillator piece) after cutting was simply supplied with nitrogen gas at 6 m ³ / cm ² .
A ceramic scintillator was produced in the same manner as in Example 1, except that the operation was performed in a heating furnace at a flow rate of h.
That is, heat treatment was performed in a heating furnace in a nitrogen gas atmosphere without filling the periphery of the crucible containing the scintillator pieces with the oxysulfide powder. The obtained ceramic scintillator was subjected to characteristic evaluation described later.

Comparative Example 5 In Example 1, the heat treatment temperature of the cut gadolinium oxysulfide sintered body (scintillator piece) was 800 ° C.
A ceramic scintillator was produced in the same manner as in Example 1 except for the following. The obtained ceramic scintillator was subjected to characteristic evaluation described later.

The above Examples 1 to 10 and Comparative Examples 1 to
The body color of each ceramic scintillator according to No. 5 was measured based on the method described above. Table 1 shows the chromaticity values (xy chromaticity coordinates) as the measurement results. FIG. 1 is a plot of xy chromaticity coordinates indicating the body color of each ceramic scintillator, where ○ indicates the result of the example and ● indicates the result of the comparative example.

Next, the X-ray detector 11 shown in FIG. 3 was constructed using each of the ceramic scintillators, and the current value flowing through the silicon photodiode when irradiating X-rays of 120 kVP and 200 mA was obtained as an optical output. . The light output is shown as a relative value when the light output when a scintillator made of a single crystal of cadmium tungstate (CdWO4) is used is 100. Further, the afterglow time of each ceramic scintillator was obtained as a ratio (%) of the luminescence intensity after 100 ms had elapsed after the X-ray irradiation was stopped to the luminescence intensity during X-ray irradiation. Table 1 also shows these measurement results.

[0084]

[Table 1]

As is clear from Table 1 and FIG. 1, the ceramic scintillators according to the respective examples have 0.32 ≦ x ≦ 0.38 and 0.83x + 0.075 ≦ y ≦ 0.8 in xy chromaticity coordinates, respectively.
The ceramic scintillator (Examples 1 to 8) having a body color satisfying 3x + 0.095 and further substantially not adding Ce has a body color satisfying 0.32 ≦ x ≦ 0.35. I understand.

It is clear that the ceramic scintillator according to each of the embodiments has excellent light output based on the above-mentioned body color and has a short afterglow time. In particular,
According to Examples 1 to 8, in the present invention, the afterglow time can be shortened without substantially adding Ce.

Further, it can be seen that the afterglow time of the ceramic scintillator is further shortened by setting the heat treatment temperature to a temperature exceeding 1200 ° C. Further, even in such a case, it is clear that the light output of the ceramic scintillator has not been reduced and the surface of the sintered body has not been whitened.

On the other hand, it is understood that the y values of the xy chromaticity coordinates indicating the body colors of all the ceramic scintillators according to the comparative examples are out of the range of the present invention. In particular, the ceramic scintillator of Comparative Example 3 in which the furnace atmosphere was set to the atmosphere and the heat treatment temperature was 1300 ° C.
It is clear that the x value of the chromaticity coordinate is less than 0.32, and the surface of the sintered body is whitened. As a result, in the ceramic scintillator of Comparative Example 3, the light output is only a value that is practically problematic.

Further, at 900 ° C. in a furnace in the atmosphere.
It can be seen from Comparative Example 2 in which the heat treatment was performed in the above, that the reduction of the afterglow time was insufficient. Further, Comparative Example 4 in which heat treatment was performed without filling the oxysulfide powder around the crucible containing the scintillator pieces and Comparative Example 5 in which the heat treatment temperature was less than 900 ° C., had a long afterglow time and a sintered body It can be seen that the internal coloring of was not sufficiently removed.

[0090]

As described above, according to the ceramic scintillator of the present invention, afterglow (afterglow) can be sufficiently reduced in addition to excellent light output (sensitivity characteristics). Therefore, according to the radiation detector and the radiation detection device of the present invention using such a ceramic scintillator, for example, it is possible to improve resolution, image accuracy, and the like.

[Brief description of the drawings]

FIG. 1 is a diagram in which body colors of ceramic scintillators (a rare earth oxysulfide sintered body after heat treatment) according to Examples and Comparative Examples of the present invention are plotted on xy chromaticity coordinates.

FIG. 2 is a view showing a heat treatment state using a double structure container according to an embodiment of the method for manufacturing a ceramic scintillator of the present invention.

FIG. 3 is a diagram showing a schematic configuration of an X-ray detector as one embodiment of the radiation detector of the present invention.

FIG. 4 is a diagram showing a schematic configuration of an X-ray CT apparatus as one embodiment of the radiation inspection apparatus of the present invention.

[Explanation of symbols]

1 ... first container, 2 ... rare earth oxysulfide sintered body after processing, 4 ... second container, 5 ... oxysulfide powder, 7 ... heating furnace, 8 ... furnace atmosphere , 11 ... X-ray detector, 12 ...
... ceramic scintillator, 15 ... photodiode, 20 ... X-ray CT device, 22 ... X-ray tube

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 31/09 H01L 31/00 A (72) Inventor Eiji Koyanatsu 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa, Japan Shares (72) Inventor Miwa Okumura 1385-1 Higashiyama, Shimoishi-kami, Otawara-shi, Tochigi Prefecture Inside the Toshiba Nasu Factory (72) Inventor Masaaki Tamaya 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki City, Kanagawa Prefecture F-term in Toshiba Research Consulting Co., Ltd. (reference) 2G088 EE02 FF02 GG10 JJ05 JJ37 4H001 CA08 XA08 XA16 XA64 YA58 YA59 5F088 AA01 BA01 BA20 BB07 EA04 JA17 LA08

Claims (13)

[Claims] 1. A ceramic scintillator comprising a sintered body of a gadolinium oxysulfide phosphor containing praseodymium as a main activator, wherein a body color of the sintered body is represented by chromaticity coordinates (x, y). When
The sintered body is 0.32 ≦ x ≦ 0.38 and 0.83x + 0.075 ≦ y
A ceramic scintillator having a body color satisfying the following. 2. The ceramic scintillator according to claim 1, wherein the y value of the chromaticity coordinates representing the body color of the sintered body is 0.83x + 0.07.
A ceramic scintillator characterized by satisfying 5 ≦ y ≦ 0.83x + 0.095. 3. The ceramic scintillator according to claim 1, wherein the gadolinium oxysulfide phosphor has a general formula: (Gd ₁ -abP _a CeC _b ) ₂ O ₂ S, wherein a is 0.0001. ≦ a ≦ 0.01, b is a number satisfying 0 ≦ b ≦ 0.005). 4. The ceramic scintillator according to claim 1, wherein the gadolinium oxysulfide phosphor has a general formula: (Gd ₁ -aP _a ) ₂ O ₂ S, wherein a and b are 0.0001. ≦ a ≦ 0.01), and the x value of chromaticity coordinates representing the body color of the sintered body is in the range of 0.32 ≦ x ≦ 0.35. A ceramic scintillator characterized by the following. 5. A sintering step of sintering the rare earth oxysulfide phosphor powder to produce a sintered body of the rare earth oxysulfide phosphor, and further comprising the step of: And a heat treatment step of reacting a reaction gas containing sulfur and the sintered body with the sintered body at a temperature in the range of 900 to 1600 ° C. 6. The method for manufacturing a ceramic scintillator according to claim 5, wherein the heat treatment step is performed at a temperature in a range from more than 1200 ° C. to 1600 ° C. or less. 7. The method for manufacturing a ceramic scintillator according to claim 5, wherein in the heat treatment step, the sintered body and the oxysulfide powder are contained in a substantially sealed container. A step of arranging a container in a furnace having the inert gas atmosphere, and a step of heat-treating the sintered body and the oxysulfide powder contained in the container at the temperature. Manufacturing method of ceramic scintillator. 8. The method for manufacturing a ceramic scintillator according to claim 7, wherein the sintered body is housed in a first container, and the first
Is disposed in a second container filled with oxysulfide powder, and the heat treatment is performed by disposing the container having the double structure in a furnace having the inert gas atmosphere. Manufacturing method of ceramic scintillator. 9. The method for manufacturing a ceramic scintillator according to claim 7, wherein the oxysulfide powder is made of a rare earth oxysulfide that is the same or different from the rare earth oxysulfide phosphor. Of manufacturing a ceramic scintillator. 10. The method according to claim 5, wherein:
The method for producing a ceramic scintillator according to claim 1, wherein the rare earth oxysulfide phosphor contains praseodymium as a main activator. 11. A method for producing a ceramic scintillator of claim 10, wherein the rare earth oxysulfide phosphor represented by the general _{formula: (Gd 1-ab Pr a} Ce b) in ₂ O ₂ S (wherein, a is 0.0001 ≦ a ≦ 0.01, b is a number satisfying 0 ≦ b ≦ 0.005). 12. The method according to claim 1, wherein:
And a fluorescence generating means for causing the ceramic scintillator to emit light in response to incident radiation, and a photoelectric conversion means for receiving light from the fluorescence generating means and converting an output of the light into an electrical output. A radiation detector. 13. A radiation source for irradiating radiation to an object to be inspected, and detecting radiation transmitted through the object to be inspected.
A radiation inspection apparatus, comprising: the radiation detector according to any one of the preceding claims.