JPH06201834A - Ceramic scintillator - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide a ceramic scintillator which has a high detection sensitivity and is capable of always maintaining and exhibiting stable luminous efficiency by completely removing coloring and crystal lattice distortion. [Structure] A rare earth oxysulfide sintered body is used as a main body, and the surface thereof has a thickness of at least one of rare earth oxide and rare earth oxysulfate and a rare earth oxysulfide.
It is characterized in that it is integrally coated with a layer not exceeding 3 μm, and yet another form is a rare earth oxysulfide sintered body in a nitrogen-based or argon-based atmosphere containing 0.5 to 200 ppm by volume of oxygen, By heat treatment at 800 to 1300 ℃, at least one of rare earth oxides and rare earth oxysulfates formed integrally on the surface and the coating layer consisting of rare earth oxysulfides with a thickness not exceeding 3 μm are removed by etching. It is characterized by being formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic scintillator suitable for a radiation detector for detecting radiation such as X-rays and γ-rays.

[0002]

2. Description of the Related Art A scintillator is a material that emits visible light or an electromagnetic wave having a wavelength close to visible light when stimulated by radiation such as X-rays. As a scintillation counter, for example, an X-ray CT apparatus (X-ray tomography apparatus) ) Radiation detector. FIG. 4 is a cross-sectional view showing a schematic configuration of a radiation detector in an X-ray CT apparatus. Reference numeral 1 is a scintillator, and 2 is a photodiode optically arranged on one main surface of the scintillator 1. Then, the output of the photodiode 2 corresponding to the amount of visible light emitted by the scintillator 1 is computer-processed to be imaged by the stimulation of X-rays incident from the direction of the arrow through the exhibitor. . Reference numeral 3 denotes a radiation transmissive visible light reflection film. Therefore, this type of scintillator 1 is required to have luminous efficiency (sensitivity) due to stimulation with X-rays, short afterblowing, and small decrease in light output due to exposure to strong X-rays (stability). Will be.

Conventionally, as such a scintillator,
For example, single crystals of NaI, CsI, CdWO ₄ , BaFCl: E
u, LaOBr: Tb, CsI: Tl, CaWO ₄ and CdWO ₄ sintered body (see Japanese Patent Publication No. 59-45022), cubic rare earth oxide ceramics (see Japanese Patent Publication No. 59-27283), Gd ₂ O ₂
Rare earth oxysulfide ceramics such as S: Pr and Gd ₂ O ₂ S: (Tb, Pr) (see JP-A-58-204088) are known.

Among these scintillators, especially Pr, T
b, activated rare earth oxysulfide ceramics such as _{Eu (M 1-x Pr x} ) 2 O 2 S, (M 1-y Tb y) 2 O 2 S, (M
_1-z Eu _z ) ₂ O ₂ S (where M is at least one rare earth element selected from the group of Y, La, and Gd) is suitable as a scintillator because of its high luminous efficiency. . In particular, rare earth oxysulfide ceramics in which M in the above formula is Gd have a large X-ray absorption coefficient and are therefore desirable as scintillators for X-ray detection. The activation concentration of Pr
If the activation concentration y of x, Tb and the activation concentration z of Eu are too low or too high, the luminous efficiency will decrease, so 0.0001 ≤ x ≤ 0.
005, 0.001 ≤ y ≤ 0.2, 0.001 ≤ z ≤ 0.2.

In order to obtain high detection sensitivity, this type of ceramic scintillator is required to be translucent. In response to such purposes and requirements, the rare earth oxysulfide ceramics are, for example, The raw material powder is sintered by using a hot pressing method or a HIP (hot isostatic pressing) method, and the ceramic sintered body is cut into a desired shape and size with a blade saw or a wire saw, and a scintillator (element) Is used as.

[0006]

As described above, the ceramic scintillator composed of the rare earth oxysulfide sintered body is
It is obtained by cutting out from the polycrystalline sintered body by hot pressing or HIP. However, the following inconvenient problems are recognized in the ceramic scintillator of the rare earth oxysulfide sintered system. That is, after the step of cutting out from the polycrystalline sintered body, as shown in the scanning electron microscope photograph of FIG. 5, a surface crushed layer having a thickness of 1 to 3 μm colored brown due to pressure and crushing is produced. Also,
Distortion of the crystal lattice occurs inside and on the surface due to the pressure applied during sintering and the cutting process. The fact that the crystal lattice distortion is generated in this surface layer (surface crushed layer) can be understood from the fact that the X-ray diffraction width is wider than that of the powder. Further, the coloring of the surface layer and the distortion of the crystal lattice cause a decrease in translucency and the like, resulting in a large decrease in the luminous efficiency when excited by radiation such as X-rays. For example, the coloring (brown) of the surface layer not only reduces the light emission due to the radiation excitation in the surface layer but also absorbs the light emission on the inner side due to the radiation excitation, resulting in a decrease in the light emission efficiency. .

As a measure for reducing the luminous efficiency due to the coloring of the surface layer and the crystal lattice distortion, it has been proposed to forcibly wash away the surface layer with a corrosive liquid (Japanese Patent Laid-Open No. 2-2021).
No. 173088), the surface becomes uneven (step of grain of surface exposure is about 5 μm), and when incorporated in a photodetector such as a photodiode, there is a problem that matching of optical coupling is deteriorated. Moreover, in this case, since the lattice distortion inside the ceramic scintillator cannot be eliminated, there is a limit to the improvement / effect of the light emission output. As a countermeasure against this, it has been attempted to perform heat treatment at 800 to 1400 ° C in a mixed gas atmosphere of hydrogen or hydrogen sulfide and an inert gas (Japanese Patent Laid-Open No. 2-209987).
Although the line diffraction width is narrowed and the lattice distortion on the scintillator surface can be reduced, the coloring of the surface layer cannot be eliminated. In particular, when heat-treated at 1100 ° C or higher in a mixed gas atmosphere of hydrogen sulfide and an inert gas, orange gadolinium sulfide is formed on the surface, which in turn strengthens the coloring and makes it possible to utilize the luminous efficiency originally possessed by the scintillator. There is a problem that there is no.

The present invention has been made in consideration of such a situation, and is a ceramic scintillator that completely removes coloring and crystal lattice distortion, has high detection sensitivity, and constantly maintains and exhibits stable luminous efficiency. -For the purpose of providing data.

[0009]

A ceramic scintillator according to the present invention comprises a rare earth oxysulfide sintered body as a main body, and the surface thereof is at least one of rare earth oxide and rare earth oxysulfate, and a rare earth oxysulfide. Another feature is that the rare earth oxysulfide sintered body is made of a nitrogen-based material containing 0.5 to 200 ppm of oxygen by volume. Alternatively, the thickness of the rare earth oxysulfide and the rare earth oxide and / or the rare earth oxysulfate formed integrally on the surface after the heat treatment at 800 to 1200 ° C in an argon atmosphere exceeds 3 μm. It is characterized in that the coating layer which is not present is removed by etching.

Further, the present invention provides a rare-earth oxide (M ₂ O ₃ ) and a rare-earth oxysulfate (M ₂ O ₂ SO) having good crystallinity.
₄ ) was made paying attention to the fact that it has no coloring property and exhibits transparency (light). That is, the rare earth oxysulfide (M ₂ O ₂ S) in the colored surface layer (surface crushed layer)
Is changed to a rare-earth oxide (M ₂ O ₃ ) or rare-earth oxysulfate (M ₂ O ₂ SO ₄ ) with good crystallinity, which is removed by etching if necessary, while reducing the internal crystal strain. I am trying. More specifically, the present invention was made based on the following findings. That is,
Conventionally, in high temperature oxidizing atmosphere, M
_{If 2} O ₂ S changes to M ₂ O ₃ and M ₂ O ₂ SO ₄ ,
It is considered that the emission efficiency may be reduced, the afterglow after the end of X-ray excitation may be long, and the emission output may be reduced by a large amount of X-ray irradiation. Excessively oxidized to a depth of 10 μm or more,
The surface became cloudy and the luminous efficiency was lowered, and a long red afterglow of the oxide was observed, which was not practical. For such consideration and observation, a surface layer (surface crushed layer) is formed when heat treatment is performed at 800 to 1300 ° C in a nitrogen or argon atmosphere containing 0.5 to 200 ppm by volume of oxygen (O ₂ ). A part of the colored M ₂ O ₂ S is composed of M ₂ O ₃ and M with good crystallinity.
₂ O ₂ SO ₄ not only improves the translucency but also increases the emission output under X-ray irradiation, and also causes the problem of long afterglow after the end of X-ray excitation and a large amount of X-rays. This is based on the unexpected finding that the problem of the decrease in the light emission output due to the line irradiation will be solved.

In the present invention, the rare earth oxysulfide sintered body (ceramic) contains M ₂ O ₂ S as a main component, and Md in the formula is exemplified by Gd, La, Y and Lu. , Used as a mixed system of one or more of these. Further, the rare earth element as the activator of the rare earth oxysulfide is, for example, one of Pr, Tb, Eu, Tm, or 2
More than one seed is used. As a specific example, Gd ₂ O ₂ S: Pr,
Gd ₂ O ₂ S: (Tb, Pr), (Y, Gd) ₂ O ₂ S: Pr, (Y, Gd) ₂ O ₂
S: (Tb, Pr), La ₂ O ₂ S: Tb, etc. are exemplified, and since this rare earth oxysulfide sintered body is required to have a light-transmitting property, for example, a hot press method or a HIP method is used. It is made.

In the present invention, when the thickness of the light-transmissive layer composed of M ₂ O ₃ , M ₂ O ₂ SO ₄ and M ₂ O ₂ S fine particles produced by the above heat treatment exceeds 3 μm, the afterglow Is long and the luminous efficiency of M ₂ O ₃ or M ₂ O ₂ SO ₄ is low, which is not preferable. The chemical composition of the M ₂ O ₃ or M ₂ O ₂ SO ₄ − M ₂ O ₂ S system forming this surface layer is S / M atomic ratio 1 / 2.1 to 1/80, S / O atomic ratio Number ratio 1 /
2.3 to 1/100, preferably S / M atomic ratio 1/5 to 1/60, S
The atomic ratio of / O is selected to be about 1/10 to 1/80. That is, the S / M atomic ratio is 1 / 2.1, and the S / O atomic ratio is 1 / 2.3.
If it is larger than the above range, it becomes difficult to eliminate the light brown coloration of the surface layer caused by the cutout, and it is observed that the luminous efficiency cannot be sufficiently improved. On the other hand, S / M
This is because when the atomic ratio of 1/80 and the atomic ratio of S / O are 1/100 or less, the afterglow is long and the emission efficiency tends to decrease.

The ceramic scintillator of the present invention is obtained by cutting a rare earth oxysulfide sintered body into a desired shape,
By subjecting to a heat treatment at 800 to 1300 ° C in a nitrogen or argon atmosphere containing 0.5 to 200 ppm of oxygen (O ₂ ) in a volume ratio, a part of M ₂ O ₂ S exhibiting a coloring property that forms a surface crushed layer, It has been changed to M ₂ O ₃ and M ₂ O ₂ SO ₄ with good crystallinity. Then, when the treatment temperature here is relatively high, or when the ceramic scintillator piece is directly exposed to the atmosphere, it is preferable to set the oxygen content ratio to one closer to the lower limit within the above range, and vice versa. When the temperature is relatively low, or when the ceramic scintillator piece is housed in a quartz container with a lid so as not to be directly exposed to the atmosphere, the oxygen content ratio is set to the one close to the upper limit within the above range. Preferably. In any case, if the oxygen content ratio exceeds 200 ppm, M ₂ O ₃ and M ₂ O ₂ SO ₄
It is recognized that the abrupt generation reaction of (3) occurs, particle growth occurs in the surface layer, light scattering becomes strong, and a white film-like foreign matter layer is easily formed. As a result, the light-transmitting property of the surface layer is lowered, and the luminous efficiency is lowered. At the same time, in addition to the emission of M ₂ O ₂ S, M ₂ O ₃ and M ₂ O ₂ SO with long afterglow and low luminous efficiency
Emission component ₄ is added, and improvement in luminous efficiency is likely to be impaired.

After the surface layer (surface crushed layer) is made transparent and the coloring is removed, the translucent surface layer is removed by an etching treatment with a slightly slower corrosive solution, and the surface layer is adjacent to this surface layer. The steps of the grains (inside the scintillator element)
The luminous efficiency can also be improved by setting the thickness to 0.5 μm or less. Even when the surface layer is removed, the effect of improving the inside of the scintillator piece by the heat treatment, in other words, the effect of eliminating or reducing the crystal lattice distortion inside the scintillator piece remains, and the ceramic scintillator for radiation having high luminous efficiency (sensitivity) remains. Function as.

[0015]

In the present invention, a rare earth oxysulfide polycrystalline sintered body cut into a desired shape and having a thickness of 3 μm is used.
While the ceramic scintillator piece having the M ₂ O ₂ S surface layer (surface crushed layer) was colored light brown, for example, and exhibited the light transmittance spectrum as shown by the curve a in FIG. For example, in an atmosphere such as nitrogen or argon containing 0.5 to 200 ppm by volume of oxygen, 800 ° C to
Heat-treated at a temperature of 1300 ℃ to form a surface layer M ₂ O ₂ S
After changing a part of M ₂ O ₃ or M ₂ O ₂ SO ₄ , the light transmittance spectrum is shown by the curve A in FIG. 1, and the light transmittance is clearly improved. There is. Also,
Observation of the surface layer with a scanning electron micrograph showed that before heat treatment, the surface layer formed of fine crystal grains with a diameter of 1 μm or less or amorphous microcrystals (M ₂ O ₂ S) was 50 to 200 μm. Although it could be clearly distinguished from the inside of the scintillator composed of crystals with a diameter (grain), after the heat treatment, the shape of the fine crystals of the surface layer was square (M ₂ O ₃ or Partly changed to M ₂ O ₂ SO ₄ ) and has good crystallinity. The type of the compound forming the surface layer can be identified by measuring the X-ray diffraction pattern, and before the heat treatment, M ₂ O ₂
It consists only of S diffraction lines and has a wide line width, but after heat treatment, in addition to M ₂ O ₂ S diffraction lines, M ₂ O ₃ (cubic and monoclinic) and M ₂ O ₂ SO ₄ diffraction lines Also appears. Also, the above M
The diffraction line of ₂ O ₃ is mainly a cubic diffraction line, but when the heat treatment temperature exceeds 1100 ° C. or when the oxygen concentration is low, a monoclinic diffraction line appears. Here, conventionally known means, that is, heat treatment in a reducing atmosphere,
When performed at a temperature of about 00 ° C., the width of the diffraction line of M ₂ O ₂ S is narrowed, but this is very different from the fact that coloring could not be sufficiently removed.

Crystallization of the surface layer by heat treatment at 800 ° C. to 1300 ° C. in an atmosphere such as nitrogen or argon containing 0.5 to 200 ppm of oxygen just improves / improves coloring or permeability of the surface layer. Nonetheless, the above heat treatment also contributes to the light output inside the scintillator piece (inside the main body). For example, when the surface layer was corroded and removed before the heat treatment, the scintillator optical output was about 110%, whereas when the surface layer was corroded and removed after the heat treatment, the scintillator optical output was 110%.
˜150%, which suggests that the interior of the scintillator is also changing, eg, strain relief of the crystal lattice.

[0017]

EXAMPLES Next, examples of the present invention will be described.

In the description of specific examples, the chemical composition of the surface layer of the ceramic scintillator was determined by EPMA analysis of the surface, or by removing the surface layer using an aqueous solution of hydrochloric acid and hydrogen peroxide as a corrosive solution and chemically analyzing this solution. It was Further, in this type of scintillator, characteristics other than the light emission output, such as short afterglow and small decrease in light output due to strong X-ray exposure, are important, and these points can be sufficiently satisfied in practical use. Met.

Example 1 A rare earth oxysulfide powder represented by the composition formula (Gd _0.999 Pr _0.001 ) ₂ O ₂ S was used as a raw material, and after molding by cold pressing, this molded body was placed in a metal airtight container. Enclose,
HIP under conditions of 1500 ° C x 2000 atm in argon atmosphere
Treated. After cooling, the ceramic sintered body was taken out from the metal airtight container, and a scintillator piece of 2 mm x 1 mm x 30 mm was cut out from this ceramic sintered body with a wire saw. According to the scanning electron microscope observation, the scintillator piece had a surface layer (surface crushed layer) having a thickness of 1 μm, was colored light brown, and had a light transmittance as shown by a curve a in FIG. Further, when the surface layer was subjected to X-ray diffraction,
Although the diffraction line width is wide as shown in (b), it is composed only of the diffraction lines of Gd ₂ O ₂ S, and the chemical composition of the surface layer is such that the atomic ratio of sulfur S to rare earth element M and sulfur S The atomic ratios with oxygen O were 1 / 2.0 and 1 / 2.1, respectively. further,
When the scintillator piece was irradiated with a tube voltage of 120 kVp and an X-ray of about 0.01 roentgen, the light output relative to the standard sample was 88%.
When the tube voltage was 120 kVp and 1500 X-rays were irradiated, and before and after that, about 0.01 X-rays were irradiated and the light output was compared, the light output retention rate was 98.2%.

Then, the above scintillator piece was placed in a quartz container, and 1000 ° C. in a nitrogen atmosphere containing 50 ppm of oxygen.
After that, heat treatment was performed for 10 hours to obtain a ceramic scintillator. This ceramic scintillator had a slightly light greenish body color due to the absorption of Pr, and the light transmittance was as shown by the curve A in FIG. Further, when the surface layer was subjected to X-ray diffraction, as shown in FIG. 3 (a), Gd ₂ O ₂ S having a sharp line width and Gd ₂ O ₃ and Gd ₂ O ₂ SO ₄ diffraction lines were obtained. Was made. Here, the diffraction intensity of Gd ₂ O ₂ S is (10
1) Plane line (2theta = 29.9 °), for cubic Gd ₂ O ₃
The (100) plane (2theta = 28.5 °) was 86%. The chemical composition of the surface layer was such that the atomic ratio of sulfur S to rare earth element M was 1/9, and the atomic ratio of sulfur S to oxygen O was 1/15. Further, the scintillator element has a tube voltage of 120 kVp,
When irradiated with X-rays of about 0.01 roentgen, the light output for the standard sample was 126%, which was a great improvement. The emission spectrum is composed of the emission lines of Gd ₂ O ₂ S: Pr, and the emission lines of Gd ₂ O ₃ : Pr and Gd ₂ O ₂ SO ₄ : Pr are Gd.
₂ O ₂ S: 0.1% or less of Pr emission line (not detectable),
It was small enough to be ignored in practical use. In addition, the tube voltage 12
It was exposed to X-rays of 0 kVp and 1500 roentgens, and about 0.
When the light output was compared by irradiating the X-ray of 01 roentgen, the light output retention rate was 98.5%.

Examples 2 to 7 Regarding the heat treatment in the above-mentioned Example 1, the scintillator pieces after cutting were subjected to heat treatment by changing the oxygen concentration in the atmosphere, the heat treatment temperature and the heat treatment time.

The ceramic scintillator thus obtained
Similarly to the case of Example 1, the following table shows the results of measuring and evaluating the diffraction line intensity, the chemical composition of the surface-damaged layer, and the light output. In the X-ray diffraction of the surface layer, Gd
It shows that a part of ₂ O ₂ S is changed to Gd ₂ O ₃ . (Blank) Table Example Heat treatment conditions in atmosphere Diffraction line intensity Surface layer composition Light output Oxygen concentration Temperature ℃ Time h Gd ₂ O ₃ S / Gd S / O 2 150ppm 1000 8 120% 1/19 1/23 128 3 50ppm 1100 8 210% 1/27 1/38 138 4 100ppm 1100 8 300% 1/40 1/65 150 5 30ppm 1100 8 160% 1/20 1/26 155 6 30ppm 1000 3 10% 1 / 2.3 1 / 2.7 112 7 200ppm 900 5 40% 1 / 2.5 1/8 110 Example 8 A 2 mm × 1 mm × 30 mm scintillator piece was cut out from a ceramic sintered body manufactured (manufactured) in the same manner as in Example 1 with a wire saw. The scintillator piece was housed in a quartz container without a lid and heat-treated at 1100 ° C. for 3 hours in a nitrogen atmosphere containing 1 ppm of oxygen to obtain a ceramic scintillator.

This ceramic scintillator exhibited a body color due to light absorption of Pr, which was slightly greenish in color, and when the surface layer was subjected to X-ray diffraction, it consisted of diffraction lines of Gd ₂ O ₂ S and Gd ₂ O ₃ . Also, the intensity of the diffraction line is (10) of Gd ₂ O ₂ S.
1) Plane line (2theta = 29.9 °), for cubic Gd ₂ O ₃
The (100) plane (2theta = 28.5 °) was 70%. further,
The chemical composition of the surface layer is such that the atomic ratio of sulfur S to rare earth element M is 1/6 and the atomic ratio of sulfur S to oxygen O is 1/9. Light output to
At 160%, there was a significant improvement.

Examples 9 and 10 Starting material Gd ₂ O ₂ S: Pr in the case of Example 1 was replaced with Gd ₂
Except for replacing with O ₂ S: Tb or Gd ₂ O ₂ S: Eu, scintillator pieces of 2 mm × 1 mm × 30 mm were cut out with a wire saw from each ceramic sintered body manufactured (manufactured) in the same manner. The scintillator pieces of No. 2 were each housed in a quartz container with a lid, and heat-treated at 1000 ° C. for 20 hours in a nitrogen atmosphere containing 20 ppm of oxygen to obtain two types of ceramic scintillators.

In all of these ceramic scintillators, the surface layer has a good light-transmitting property, and when irradiated with X-rays, the light output is 150% or 180% of the light output of the scintillator piece before heat treatment. The values were shown, and both were significantly improved in light output.

Example 11 A scintillator piece of 2 mm × 1 mm × 30 mm was cut out with a wire saw from a ceramic sintered body manufactured (produced) in the same manner as in Example 1, and the scintillator piece was covered with a quartz container with a lid. The ceramic scintillator was housed inside and heat-treated at 1000 ° C. for 8 hours in a nitrogen atmosphere containing 150 ppm of oxygen. Then, the ceramic scintillator was immersed in a corrosive liquid prepared by mixing concentrated hydrochloric acid 1, hydrogen peroxide and pure water 1 for 10 minutes to remove the surface layer by etching, and then thoroughly washed with water. When the exposed surface was observed with a scanning electron microscope, the surface layer was almost completely removed, and the average step difference between adjacent grains on the exposed surface was 0.2 μm. The ceramic scintillator thus obtained had a light green body color and had a slightly lowered light-transmitting property due to light scattering caused by the small irregularities on the etching-exposed surface. When the exposed surface was subjected to X-ray diffraction, it consisted only of diffraction lines of Gd ₂ O ₂ S with a sharp line width. The chemical composition of the exposed surface was sulfur S and rare earth element M.
And the atomic ratio of sulfur S to oxygen O was 1 / 2.0. Furthermore, when this ceramic scintillator was irradiated with an X-ray of about 0.01 roentgen at a tube voltage of 120 kVp, the light output for the standard sample was 145%,
The light output was significantly improved / compared with the light output before the heat treatment. And, even when the etching exposed surface is combined with a photodiode, it is possible to achieve a matching that is optically satisfactory. Comparative Example 1

Manufacturing (manufacturing) in the same manner as in the first embodiment
2mm x 1mm with a wire saw from the sintered ceramics
Scintillator pieces of × 30 mm were cut out, the scintillator pieces were placed in a quartz container, and heat-treated at 1000 ° C. for 10 hours in a nitrogen atmosphere containing 2% hydrogen to obtain a ceramic scintillator.

The ceramic scintillator thus obtained had a light brownish greenish body color, and the light transmittance was improved as compared with that before the heat treatment, but its degree was low and insufficient. That is, when the surface layer was subjected to X-ray diffraction, Gd ₂
It consists of a sharp diffraction line of O ₂ S, and a slight monoclinic Gd ₂ O ₃ phase is recognized, and its intensity is (1) of Gd ₂ O ₂ S.
It was less than 1% with respect to the line of (01) plane (2theta = 29.9 °). The chemical composition of the surface layer is sulfur S and rare earth element M.
And the atomic ratio of sulfur S and oxygen O was 1 / 2.08. Furthermore, when this ceramic scintillator was irradiated with X-rays of about 0.01 roentgen at a tube voltage of 120 kVp, the light output was 89% with respect to the standard sample, but the degree of improvement compared to the light output before the heat treatment was It was significantly inferior to the case of the invention (for example, Example 4).

Comparative Example 2 A scintillator piece of 2 mm × 1 mm × 30 mm was cut out with a wire saw from a ceramic sintered body produced (manufactured) in the same manner as in Example 1, and the scintillator piece was made into a quartz container without a lid. After heat-treating at 1000 ℃ for 10 hours in a nitrogen atmosphere containing 2% hydrogen, oxygen is further added.
Heat treatment was performed at 1000 ° C. for 30 minutes in a nitrogen atmosphere containing 300 ppm to obtain a ceramic scintillator. Observation of this ceramic scintillator with a scanning electron microscope revealed that it had a surface phase with a thickness of about 4 μm. The ceramic scintillator thus obtained had a white powdery film formed on the surface, and when subjected to X-ray diffraction, Gd ₂ O ₃ and
Gd ₂ O ₂ OS ₄ is composed of diffraction lines with a sharp line width, and the chemical composition of the surface layer is such that the atomic ratio of sulfur S to rare earth element M and the number of atoms of sulfur S and oxygen O. Ratio 1
% Or less. Furthermore, the emission spectrum of this ceramic scintillator when irradiated with X-rays is Gd ₂ O ₃ : P
The red luminescence of r was added, and the yellow tint was stronger than that of Gd ₂ O ₂ S. Furthermore, when this ceramic scintillator was irradiated with X-rays of about 0.01 roentgen at a tube voltage of 120 kVp, the light output was 110% with respect to the standard sample, which was an improvement over the light output before the heat treatment. The glow became long and not suitable for practical use.

Comparative Example 3 A scintillator piece of 2 mm × 1 mm × 30 mm was cut out with a wire saw from a ceramic sintered body produced (manufactured) in the same manner as in Example 1, and immediately subjected to no heat treatment, this scintillator piece was immediately cut. Was immersed in a corrosive liquid prepared by mixing concentrated hydrochloric acid 3 and nitric acid 1 for 30 minutes to remove the surface layer by etching, and then thoroughly washed with water. When the surface exposed by this etching was observed with a scanning electron microscope, the surface layer was almost completely removed.

The scintillator element thus obtained is
It had a light green body color, and the exposed surface had a low transparency (difference of about 5 μm) due to light scattering due to the uneven surface, and also had poor optical coupling with the photodiode. . Also, when the etched exposed surface was subjected to X-ray diffraction, it consisted only of diffraction lines having a sharp line width of Gd ₂ O ₂ S. Then, the tube voltage is applied to this scintillator element.
When irradiated with an X-ray of 120 kVp and about 0.01 roentgen, the light output with respect to the standard sample was 109%, which is an improvement / improvement as compared with the light output before the etching treatment, but it is inferior to the case of the present invention. It was

In the above, a ceramic scintillator having a Gd ₂ O ₂ S sintered body as a main body (matrix) has been exemplified.
The coloring of the surface layer (surface crushed layer) by cutting (cutting) from the sintered body is a phenomenon unique to rare earth oxysulfides (Gd ₂ O ₂ S, etc.). Therefore, in the Gd ₂ O ₂ S sintered body, when the scintillator main body (matrix) is a sintered body in which Gd is replaced by La, Y, etc., the same operation and effects can be obtained. it can.

[0033]

As described above, according to the present invention, since the material is processed into a required shape, a colored surface crush layer is generated due to an indispensable cutting processing, and a crystal strain is generated due to sintering under high pressure. The decrease in the light output caused by is eliminated (avoided), and rather, the detection sensitivity is greatly improved. On the other hand, the so-called afterglow is short, and the decrease in light output due to strong X-ray irradiation is greatly reduced / suppressed, and stable and highly reliable functions are maintained and exhibited. Therefore,
It can be said that the ceramic scintillator according to the present invention is suitable for a radiation detector such as an X-ray CT apparatus.

[Brief description of drawings]

FIG. 1 is a curve diagram showing the translucency of a ceramic scintillator according to the present invention and the translucency of a conventional ceramic scintillator in comparison.

FIG. 2 is a schematic diagram showing a crystal structure of a cut surface of a ceramic scintillator according to the present invention.

3A is an X-ray diffraction diagram of a surface layer of a ceramic scintillator according to the present invention, and FIG. 3B is an X-ray diffraction diagram of a surface layer of a conventional ceramic scintillator.

FIG. 4 is a cross-sectional view showing a schematic configuration of a radiation detector using a ceramic scintillator.

FIG. 5 is a micrograph showing a crystal structure of a cut surface of a conventional ceramic scintillator.

[Explanation of symbols]

1 ... Ceramic scintillator 2 ... Photodiode 3 ... Radiation transmissive visible light reflection film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuto Yokota 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Inside the Yokohama Works of Toshiba Corporation (72) Inventor Yukichi Fukuda 8th Shin-sugita-cho, Isogo-ku, Yokohama, Kanagawa Incorporated company Toshiba Yokohama Works (72) Inventor Yukiko Nishiyama 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research & Development Center

Claims (2)

[Claims] 1. A body of a rare earth oxysulfide sintered body,
A ceramic scintillator, the surface of which is integrally coated with a layer of at least one of rare earth oxides and rare earth oxysulfates, and a rare earth oxysulfide having a thickness not exceeding 3 μm. 2. A rare earth oxysulfide sintered body in volume ratio
At least one of rare earth oxides and rare earth oxysulfates formed integrally on the surface by heat treatment at 800 to 1300 ° C in a nitrogen or argon atmosphere containing 0.5 to 200ppm oxygen, and rare earth oxys A ceramic scintillator characterized by etching and removing a coating layer made of sulfide and having a thickness not exceeding 3 μm.