JP2021098820A - Ceramic composition for scintillator, scintillator, and radiation detector - Google Patents

Abstract

To provide a novel material that can be used suitably as a scintillator material.SOLUTION: A ceramic composition for a scintillator is represented by a general formula A14-xSi2O7 N2:xA2, where A1 and A2 are different from each other; A1 represents at least one kind selected from a group consisting of Y, La, Gd, Tb and Lu; A2 represents Ce or Tb; and x satisfies 0.001<x<1.SELECTED DRAWING: None

Description

The present invention relates to a ceramic composition for a scintillator, a scintillator, and a radiation detection device including the scintillator.

The scintillator is made of a material that emits fluorescence (for example, visible light) when excited by irradiation with radiation. The scintillator is used as a detection element of a radiation detection device. The scintillator as a radiation detecting element is desired to be a molded body (bulk body) having a certain size rather than having a powdery form in order to increase the detection sensitivity.

As a bulk scintillator, a single crystal scintillator composed of _{CsI: Tl, CdWO 4} , NaI: Tl, Bi ₄ Ge ₃ O _{12, and the like is conventionally known.} Further, Patent No. 4959877 (Patent Document 1) describes a ceramic scintillator made of a sintered body of a gadolinium acid sulfide phosphor containing praseodymium. However, many of these existing scintillators do not have sufficient mechanical properties, and it is desired to enrich scintillators having good mechanical properties. Further, Japanese Patent Application Laid-Open No. 2018-178070 (Patent Document 2) _{lists rare earth-added Si 3} N ₄ as scintillators having good mechanical properties, but they have a small effective atomic number and X. The absorption efficiency of rays and γ-rays may not be sufficient.

Patent No. 4959877 JP-A-2018-178070

An object of the present invention is to provide a novel material that can be suitably used as a material for a scintillator.
Another object of the present invention is to provide a scintillator formed from the above scintillator material and a radiation detection device including the scintillator.

The present invention provides the following ceramic compositions for scintillators, scintillators and radiation detectors.
[1] The following general formula (1):
A ¹ _4-x Si ₂ O ₇ N ₂ : xA ² (1)
[During the ceremony,
A ¹ and A ² are different from each other
A ¹ represents at least one selected from the group consisting of Y, La, Gd, Tb and Lu.
A ² represents Ce or Tb.
x satisfies 0.001 <x <1. ]
Ceramic composition for scintillator represented by.
[2] A scintillator containing a sintered body of the ceramic composition for a scintillator according to [1].
[3] The scintillator according to [2], which is a sintered body of a molded product containing the ceramic composition for a scintillator.
[4] A radiation detection device including the scintillator according to [2] or [3] and a photodetector for detecting light emitted from the scintillator.

It is possible to provide a new material that can be suitably used as a material for a scintillator. Further, it is possible to provide a scintillator formed from the above scintillator material and a radiation detection device including the scintillator. Although the scintillator of the present invention has high mechanical properties, it has a _{large effective atomic number as compared with the rare earth-added Si 3} N _4, and can absorb X-rays and γ-rays more efficiently.

It is a figure which shows the emission spectrum when the scintillator of Experimental Example 31 is irradiated with X-rays. It is a figure which shows the emission spectrum when the scintillator of Experimental Example 59 was irradiated with X-rays.

In the present specification, the meanings of the following terms are as follows.
"Ceramics" refers to a sintered product of an inorganic compound or a sintered product of a molded product of an inorganic compound.
"Material for scintillator" means a material used for forming a scintillator.
The "scintillator" refers to a bulk body such as a member, a component, or an element composed of a substance (material) that emits fluorescence (for example, visible light) when excited by irradiation with radiation.
"Radiation" refers to X-rays, gamma rays, alpha rays, beta rays, neutron rays and the like.
The “sinterability” refers to a property that a dense sintered body is easily formed even at a lower sintering temperature, or a property that a denser sintered body is easily formed even at the same sintering temperature.
"Scintillator performance" means the performance as a scintillator, and refers to, for example, the property of being able to emit fluorescence with a higher emission intensity when the scintillator is irradiated with radiation.

<Ceramics composition for scintillators>
The ceramic composition for a scintillator according to the present invention is a material for a scintillator, and has the following general formula (1):
A ¹ _4-x Si ₂ O ₇ N ₂ : xA ² (1)
[During the ceremony,
A ¹ and A ² are different from each other
A ¹ represents at least one selected from the group consisting of Y, La, Gd, Tb and Lu.
A ² represents Ce or Tb.
x satisfies 0.001 <x <1. ]
It is represented by. A ² plays a role as an activator. The scintillator formed from the composition can emit fluorescence associated with the 5d-4f electron orbit transition ^{of Ce 3+} ions or fluorescence associated with the 4f-4f electron orbit transition of ^{Tb 3+ ions by irradiation.}

Ceramic compositions for scintillators as oxides, nitrides and / or metals so that the final composition of the A ¹ , Si and A ^{2 elements is A 1} _4-x Si ₂ O ₇ N ₂ : xA ^{2, respectively.} It can be contained in a product.

Ceramic compositions for scintillators can contain components other than the ^{A 1} , Si and A ^{2 elements.} Examples of other components include unavoidable impurities that are unintentionally contained in the production process, additives that are intentionally added, and the like. The unavoidable impurities and additives may contain impurity elements such as carbon (C), aluminum (Al), and magnesium (Mg).
From the viewpoint of scintillator performance, the content of impurity elements in the scintillator ceramic composition shall be 20 parts by mass or less with respect to 100 parts by mass of the total amount of ^{A 14} _-x Si ₂ O ₇ N ₂ : xA ^2. Is preferable.
By containing the above-mentioned impurity element in the ceramic composition for scintillator, performance such as sinterability may be improved. However, if the above impurity elements are excessively contained, the scintillator performance tends to deteriorate. Therefore, the content of the impurity element is more preferably 10 parts by mass or less, still more preferably 5 parts by mass or less, based on 100 parts by mass of the total amount of ^{A 14} _-x Si ₂ O ₇ N ₂ : xA ^2. Is.

Examples of the additive include a sintering aid for improving the sinterability. The ceramic composition for scintillators can contain one or more sintering aids. Examples of the sintering aid include _{known sintering aids such as Al 2} O ₃ and Mg O.
However, when the ceramic composition for scintillator contains a lanthanoid compound (for example, a lanthanoid oxide), good sinterability tends to be obtained without further containing a sintering aid.

<Scintillator>
The scintillator according to the present invention is a sintered body of the ceramic composition for a scintillator, and preferably a sintered body (sintered bulk body) of a molded product containing the ceramic composition for a scintillator.

Since the scintillator according to the present invention is formed from the ceramic composition for a scintillator represented by the above formula (1), good scintillator performance can be exhibited.

^{When A 2} is Ce in the above formula (1), x is usually 0.0001 to 1 in the scintillator, and is preferably 0.001 to 0.1 from the viewpoint of enhancing the scintillator performance. ^{When A 2} is Tb in the above formula (1), x is usually 0.0001 to 1 in the scintillator, and is preferably 0.001 to 0.5 from the viewpoint of enhancing the scintillator performance.

<Manufacturing method of scintillator>
The scintillator can be manufactured, for example, by a method including the following steps.
Step of preparing ceramic composition for scintillator (first step),
A step of molding a ceramic composition for a scintillator to obtain a molded product (second step), and a step of sintering the molded product (third step).

(1) First Step scintillating ceramic composition is a composition represented by the general formula ^(1), as a source of A 1, Si and ^{A 2} elements, the final composition ^{A 1} _4-x It can be prepared by mixing each oxide, nitride and / or metal so as to be Si ₂ O ₇ N ₂ : xA ^2. The ^{sources of the A 1} , Si and A ² elements may be powders, respectively.

In order to improve the sinterability of the scintillator ceramic composition, the ^{particle size and particle shape of the raw material powder (additives such as A 1} , Si, A ² and / or a sintering aid) may be adjusted. Examples of the adjusting method include crushing and granulation. The pulverization method and the granulation method may be any method.

(2) Second Step This step is an arbitrary step provided as needed, but since the sinterability of the scintillator ceramic composition can be improved by increasing the density of the scintillator ceramic composition, the scintillator ceramic composition can be improved. It is preferable to provide this step of molding.

The molded product can be obtained by press-molding (press-molding) the ceramic composition for a scintillator by, for example, a mechanical press, a hydraulic press, a hydraulic press, a cold isotropic press (CIP), or the like. The molding method is not limited to press molding, and a general ceramic molding method such as injection molding or tape molding may be used.

The press conditions in the press molding are not particularly limited, but in the case of mechanical press molding using a die, for example, the conditions can be ^{about 150 to 200 kgf / cm 2.} In the case of a cold isotropic press (CIP), for example, it can be performed under the condition of ^{1000 to 2000 kgf / cm 2.}

(3) Third Step This step is a step of sintering a molded product of a ceramic composition for a scintillator. The sintering method may be any ceramic sintering method such as normal pressure sintering, gas pressure sintering, hot press sintering, hot hydrostatic pressure pressure sintering, and pulse energization pressure sintering.

The conditions for gas pressure sintering are preferably set appropriately according to the composition of the molded product and the sintering apparatus used. The conditions for gas pressure sintering are, for example, a sintering temperature of 1700 to 1800 ° C. and a sintering time of 0.5 to 2 hours in a nitrogen atmosphere of 50 to 300 MPa.

The conditions for atmospheric pressure sintering are preferably set appropriately according to the composition of the molded product and the sintering apparatus used. The conditions for atmospheric sintering are, for example, a sintering temperature of 1700 to 1800 ° C. and a sintering time of 1 to 10 hours (for example, about 6 hours) in a nitrogen atmosphere of 0.2 to 5 MPa (for example, 0.8 MPa).

The sintered body (bulk scintillator) obtained by the sintering step may be processed. Examples of the processing process include a cutting process and a shape adjusting process such as a polishing process.

As described above, according to the ceramic composition for scintillators according to the present invention, when the composition contains a lanthanoid compound (for example, a lanthanoid oxide), good sinterability without further addition of a sintering aid is required. Tends to be obtained. It is presumed that the lanthanoid compound functions in the same manner as the sintering aid.
The fact that it is not necessary to further contain the sintering aid is advantageous in improving the scintillator performance. This is because the scintillator performance may be deteriorated when impurities other than the luminescent center element are added.

According to the above method, a bulk scintillator can be efficiently manufactured.
On the other hand, although a single crystal scintillator is conventionally known, the production efficiency is inferior because it takes time to generate a single crystal, and the shape freedom of the scintillator is inferior.
Oxides, acid sulfides, and halides are known as ceramic scintillators. However, oxides and acid sulfides are prone to oxygen defects in a reducing atmosphere, and many halides have unique problems such as high deliquescent properties.
The ceramic scintillator described in Patent Document 1, which is an acid sulfide, contains oxygen and sulfur as anions and Pr and Ce as activators, and these plurality of elements are contained at a predetermined concentration with good reproducibility. There is a manufacturing problem that it is not easy.

<Radiation detector>
The scintillator according to the present invention can be suitably applied to a radiation detection device.
The radiation detection device can include a scintillator according to the present invention and a photodetector for detecting light emitted from the scintillator.
Examples of the photodetector include a photomultiplier tube and a semiconductor light receiving element. Above all, from the viewpoint of manufacturing cost, the photodetector is preferably a silicon light receiving element.

Radiation detectors equipped with scintillators have a wide range of uses. Examples of such applications are baggage inspection at airports, medical diagnostic imaging and the like. If a position-sensitive light receiving element is used as a photodetector, it can also be used as an image pickup device for a radiation transmission image.

Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the present invention is not limited to these examples.

<Experimental Examples 1-35>
(1) Preparation of ceramic composition for scintillator As raw material powder, Si ₃ N ₄ (trade name: SN-9FWS) _{manufactured by Denka Co., Ltd. and SiO 2} (purity 99.9% by mass) manufactured by High Purity Chemical Laboratory Co., Ltd. ^{), Various A 1} oxides (Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Tb ₄ O ₇ , Lu ₂ O ₃ ) manufactured by High Purity Chemical Laboratory Co., Ltd., all having a purity of 99.9% by mass. _{) And CeO 2} (purity 99.9% by mass) manufactured by High Purity Chemical Laboratory Co., Ltd. were prepared.

The _{final composition of Si 3} N ₄ , SiO ₂ , CeO ₂ powder and ^{any of the above A 1} oxide powders is A ¹ _4-x Si ₂ O ₇ N ₂ : xCe (x = 0.001, 0. After mixing so as to be 005, 0.01, 0.05, 0.1, 0.5, 1), silicon nitride balls having a particle size of 10 mm are added so as to have the same volume as the raw material powder, and further ethanol is added. Was added so as to have a volume about 1.5 times that of the raw material powder as a whole, and mixed by a ball mill for 60 hours. The obtained slurry was dried by an evaporator and then pulverized using a mortar and a pestle. Then, the ceramic composition for a scintillator was obtained by classifying through a sieve having an opening of 425 μm.

(2) Preparation of Scintillator (Sintered Body) The ceramic composition for scintillator ^{was press-molded under the condition of 200 kgf / cm 2} to obtain a molded body having a cylindrical shape (diameter 10 mm × height 4 mm).
The obtained molded product was sintered under normal pressure under the conditions of 0.9 MPa, 1725 ° C., and 4 hours in a nitrogen atmosphere to obtain a cylindrical scintillator (sintered product).
The obtained sintered body had sufficient mechanical strength to evaluate the scintillator performance.

(3) Evaluation of scintillator The scintillator performance of the scintillator obtained above was evaluated. The scintillator performance was evaluated by measuring the emission intensity of fluorescence generated by irradiating the scintillator with X-rays. Specifically, it is as follows.

An X-ray generator (Monoblock XRB80P & N200X4550 manufactured by Spellman) was used as a radiation source, the tube voltage was 80 kV, the tube current was 1.2 mA, and the scintillator was irradiated with X-rays for 60 seconds.
The light emitted from the scintillator is propagated by an optical fiber (manufactured by Mitsubishi Electric Wire Co., Ltd., material STU) from the surface opposite to the surface irradiated with X-rays, and from a spectroscope (manufactured by ANDOR Co., Ltd., SR163i-UV) and a silicon light receiving element. The emission spectrum was measured with a measurement wavelength range of 200 to 700 nm and a wavelength step of 0.5 nm by wavelength-resolving and receiving light using a CCD (DU920P-BU2NC type manufactured by ANDOR).
From the obtained emission spectrum, a count value (unit: counts per second, cps) per second of measurement time was integrated in the range of 200 to 700 nm, and this was taken as the emission intensity. Table 1 shows the emission intensities of the scintillators of Experimental Examples 1 to 35.

Under the same measurement conditions as above, the spectrum was measured without installing a scintillator, and the count values for each wavelength were integrated in the wavelength range of about 200 to 700 nm. When this measurement was performed 10 times in total and the average value of the 10 integrated values was calculated, it was about 10 cps. Therefore, 10 cps was set as the background level, and the scintillator performance was evaluated based on whether or not a sufficiently high emission intensity was obtained with respect to this background level.

From Table 1, it can be seen that all the scintillators of Experimental Examples 1 to 35 show significantly higher emission intensity than the background level (10 cps).

FIG. 1 is a diagram showing an emission spectrum when the scintillator of Experimental Example 31 is irradiated with X-rays. From FIG. 1, it can be seen that the scintillator of Experimental Example 31 emits light at a peak wavelength of about 505 nm by X-ray irradiation.

<Experimental Examples 36-39>
5 parts by mass (Experimental Example 36), 10 parts by mass (Experimental Example 37), 20 parts by mass (Experimental Example 38) or 25 parts by mass with respect to 100 parts by mass of A ¹ _4-x Si ₂ O ₇ N _{2: xCe.} A ceramic composition for a scintillator was prepared in the same manner as in Experimental Example 31 except that _{Al 2} O ₃ (sintering aid) of Part (Experimental Example 39) was further added, and the same as in Experimental Example 31 except that this was used. Similarly, a cylindrical scintillator (sintered body) was obtained.

For the scintillators of Experimental Examples 36 to 39, the emission intensity when irradiated with X-rays was measured in the same manner as above. The results are shown in Table 2.

From Table 2, the emission intensity values were 401000, 380201, 358506, and 332565 cps, respectively, and no significant decrease in scintillation intensity was observed.

<Experimental Examples 40-67>
(1) Preparation of ceramic composition for scintillator As raw material powder, Si ₃ N ₄ (trade name: SN-9FWS) _{manufactured by Denka Co., Ltd. and SiO 2} (purity 99.9% by mass) manufactured by High Purity Chemical Co., Ltd. ^{, Various A 1} oxides manufactured by High Purity Chemical Laboratory Co., Ltd. (Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Lu ₂ O ₃ , all with a purity of 99.9% by mass), and Taka Co., Ltd. _{Tb 4} O ₇ (purity 99.9% by mass) manufactured by Purity Chemistry Laboratory was prepared.

The _{final composition of Si 3} N ₄ , SiO ₂ , Tb ₄ O ₇ powder and ^{any of the above A 1} oxide powders is A ¹ _4-x Si ₂ O ₇ N ₂ : xTb (x = 0.001, After mixing so as to be 0.005, 0.01, 0.05, 0.1, 0.5, 1), silicon nitride balls having a particle size of 10 mm were added so as to have the same volume as the raw material powder. Further, ethanol was added so as to have a volume about 1.5 times that of the raw material powder as a whole, and the mixture was mixed by a ball mill for 60 hours. The obtained slurry was dried by an evaporator and then pulverized using a mortar and a pestle. Then, the ceramic composition for a scintillator was obtained by classifying through a sieve having an opening of 425 μm.

(2) Preparation of Scintillator (Sintered Body) Scintillators (sintered body) of Experimental Examples 40 to 67 were produced in the same manner as in the procedure for producing the scintillator (sintered body) in Experimental Examples 1 to 35 described above. The obtained sintered body had sufficient mechanical strength to evaluate the scintillator performance.

(3) Evaluation of scintillators The scintillators of Experimental Examples 40 to 67 were evaluated in the same manner as the evaluation of the scintillators in Experimental Examples 1 to 35 described above. The results are shown in Table 3.

From Table 3, it can be seen that all the scintillators of Experimental Examples 40 to 67 show significantly higher emission intensity than the background level (10 cps).

FIG. 2 is a diagram showing an emission spectrum when the scintillator of Experimental Example 59 is irradiated with X-rays. From FIG. 2, it can be seen that the scintillator of Experimental Example 59 emits light at a peak wavelength of about 535 nm by X-ray irradiation.

<Experimental Examples 68-71>
5 parts by mass (Experimental Example 68), 10 parts by mass (Experimental Example 69), 20 parts by mass (Experimental Example 70) or 25 parts by mass with respect to 100 parts by mass of A ¹ _4-x Si ₂ O ₇ N _{2: xTb.} A ceramic composition for a scintillator was prepared in the same manner as in Experimental Example 59 except that _{Al 2} O ₃ (sintering aid) of Part (Experimental Example 71) was further added, and the same as Experimental Example 59 except that this was used. Similarly, a cylindrical scintillator (sintered body) was obtained.

For the scintillators of Experimental Examples 68 to 71, the emission intensity when irradiated with X-rays was measured in the same manner as above. The results are shown in Table 4.

From Table 4, the emission intensity values were 15623, 13651, 11026, and 8562 cps, respectively, and no significant decrease in scintillation intensity was observed.

The scintillator according to the present invention is expected as a new scintillator capable of having good scintillator performance and good productivity in place of the conventional scintillator such as a single crystal scintillator. The scintillator according to the present invention is suitable as a scintillator mounted on a radiation detection device.

Claims (4)

The following general formula (1):
A ¹ _4-x Si ₂ O ₇ N ₂ : xA ² (1)
[During the ceremony,
A ¹ and A ² are different from each other
A ¹ represents at least one selected from the group consisting of Y, La, Gd, Tb and Lu.
A ² represents Ce or Tb.
x satisfies 0.001 <x <1. ]
Ceramic composition for scintillator represented by. A scintillator containing a sintered body of the ceramic composition for a scintillator according to claim 1. The scintillator according to claim 2, which is a sintered product of a molded product containing the ceramic composition for a scintillator. A radiation detection apparatus comprising the scintillator according to claim 2 or 3 and a photodetector for detecting light emitted from the scintillator.

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