JP2021143288A - Scintillator, radiation detector, and radiation imaging system - Google Patents

Abstract

To provide a scintillator material that has an emission peak wavelength appropriate to an optical receiver, a short DT, and an improved emission amount.SOLUTION: The problem is solved by using a scintillator material containing a scintillator satisfying the following general formula (1). (A1-a-bM1aM2b)x(Al1-cM3c)yOz (1) (In the formula (1), A contains at least one selected from the group consisting of Gd, Y, Lu and La, M1 represents an activator element different from A, M2 is different from A, M1, and contains at least one kind selected from the group consisting of Ca, Sr, Ba, Y, La, Sm, Gd, Dy, Ho and Lu, M3 contains at least Ga, Sc or In, and x, y, z, a, b, c independently satisfies 0.5≤x≤1.5, 0.5≤y≤1.5, 2≤z≤4, 0<a≤0.5, 0≤b≤0.9, 0<C≤0.8, respectively.)SELECTED DRAWING: Figure 1

Description

The present invention relates to a scintillator material that converts radiation into light, a radiation detector using this scintillator material, and a radiation imaging system.

The radiation inspection device is a device that irradiates a subject with radiation such as γ-rays, X-rays, and neutron rays, directly or indirectly converts the transmitted radiation into an electric signal, and performs imaging and the like. Radiation inspection equipment includes various fields and modes such as non-destructive inspection detectors such as non-destructive inspection detectors, resource exploration detectors, high-energy physical detectors, and diagnostic equipment such as medical image processing equipment. Used in.

In particular, in the medical field, in order to reduce the radiation exposure dose of a subject, there is a demand for a radiation detector that can obtain a brighter and clearer image with a smaller irradiation dose.

X-ray CT plays a fundamental and demanding role in the current medical diagnostic field. The current X-ray CT is an energy-integrated CT, and since it is read out as a current value after accumulating charges for a certain period of time, energy information cannot be obtained. Therefore, the obtained image is a monochrome image, and it is not possible to discriminate substances having the same CT value (line attenuation coefficient). Furthermore, there is a problem of exposure to X-rays of 10 mSV in one measurement. On the other hand, what is expected as the next-generation X-ray CT is photon counting CT (PCCT), which can acquire energy information by photon counting and enable energy discrimination. Further, by using the multi-pixel photon counter (MPPC) as a receiver, the exposure dose of one shooting can be significantly reduced to 0.1 mSV. However, in order to obtain a high-definition image, ^{a count rate of 107 to 8} / counts / s / mm2 is required, and the reciprocal of this is a high fluorescence lifetime of 10 to 100 ns (scintillation decay time, hereinafter simply referred to as DT). May be stated) is required.

The radiation detector is a scintillator that converts radiation into light, and receives light from CCDs, photodetectors (PD), avalanche photodiodes (APD), multipixel photon counters (MPPC), etc. that convert the light emitted from the scintillator into electrical signals. Including vessels.

Typical scintillator materials that convert radiation such as X-rays and γ-rays into light are Gd ₂ O ₂ S: Pr ³⁺ , Ce ³⁺ (GOS), CsI: Tl ⁺ , Lu ₂ SiO ₅ : Ce ^3+. (LSO), (Lu, Y) ₂ SiO ₅ : Ce ³⁺ (LYSO), Gd ₃ (Al, Ga) ₅ O ₁₂ (GAGG), Gemstone ™ and the like are known.
All of these materials exhibit a sufficient amount of light emission (10000 MeV or more) and have sufficiently high radiation stopping power. The Lu-containing raw material is expensive.

In recent years, in the medical field, photon counting CT, which significantly reduces the exposure dose of a subject by using MPPC, has attracted attention. In photon counting CT, a scintillator material showing a very short DT is required in order to obtain a high-definition image and reduce the irradiation amount, but the DT of the above-mentioned conventional scintillator materials is 30 ns or more. Therefore, there is a need for a scintillator material that exhibits a shorter DT. Further, since those using Lu are expensive, there is a demand for a scintillator material that can be manufactured at low cost.

Under these circumstances, yttrium aluminum perovskite (YAP) represented by _{YAlO 3} has been tried as a scintillator material for medical use. The DT of this scintillator is around 25 ns (Non-Patent Document 1).
However, since yttrium (Y) is a light element in YAP, the effective atomic number Z _eff of the entire compound is as low as about 32, and the X-ray stopping power is low. In order to obtain sufficient X-ray stopping power, the scintillator block must be enlarged, and there are problems such as a decrease in efficiency due to scattering.

_{On the other hand, (Lu / Y) AlO 3} (LYAP) and (Lu / Gd) using a material having a composition in which the activating element of YAP was changed, or using lutetium (Lu) having a high X-ray stopping power in combination with Y or Gd. ) _{Attempts to use AlO 3} (LGAP) have also been reported, and these scintillators have achieved high luminescence (Patent Document 1).
There is also a report on a scintillator in which DT is shortened to 7 to 11 ns by combining a composition (Y / GAP) in which a part of Y is replaced with Gd in YAP and a method using two or more kinds of activating elements (Pr and Tb). (Patent Document 2).
However, the short DT scintillators described in the patent documents and non-patent documents have an emission peak wavelength of 230 to 285 nm for all of the scintillators in which the emission peak wavelength is described, and the high quantum efficiency of the receiver such as MPPC. It is far from. Further, there is no description in both documents about obtaining a scintillator having a short DT of 25 ns or less and a long emission peak wavelength.

Japanese Unexamined Patent Publication No. 2012-149223 Special Table 2018-536153

IEEE Transitions on Nuclear Science, 47: 860-864, 2000.

As described above, the conventional scintillator material showing a short DT applicable to PCCT and the like generally has an emission peak wavelength of about 350 nm at the longest, and light in this wavelength band is efficient in a receiver such as a CCD or MPPC. Since it is not often converted into an electric signal, there is a problem that the overall detection efficiency is low when it is used as a radiation detector. Further, YAP and GAP have low emission amounts of about 18,000 Ph / MeV and 9000 Ph / MeV, respectively, and there is a demand for a scintillator material showing a higher emission amount.

That is, an object to be solved by the present invention is to provide a scintillator material having a short DT, a high emission amount, and a long emission peak wavelength.

As a result of diligent studies in view of the above problems, the present inventor has found that the above problems can be solved by using a scintillator in which a part of Al of GAP is replaced with another element, and the present invention has been completed.
The present invention includes the following contents in one embodiment.
[1]: A scintillator including a scintillator having a composition satisfying the general formula (1).
(A _1-ab M ¹ _a M ² _b ) _x (Al _1-c M ³ _c ) _{y Oz} ... (1)
(In the formula (1), A contains at least one selected from the group consisting of Gd, Y, Lu and La, M ¹ represents an activating element different from A, and M ² is an element different from A and M ^1. At least one selected from the group consisting of Ca, Sr, Ba, Y, La, Sm, Gd, Dy, Ho, Lu, M ³ contains at least Ga, Sc or In, x, y, z. , A, b, and c are independently 0.5 ≦ x ≦ 1.5, 0.5 ≦ y ≦ 1.5, 2 ≦ z ≦ 4, 0 <a ≦ 0.5, 0 ≦ b ≦ 0. 9, 0 <c ≦ 0.8 is satisfied.)
[2]: The scintillator according to [1], wherein in the general formula (1), M ¹ contains any one or more of Ce, Pr, and Tb.
[3]: The scintillator according to [1] or [2], wherein 0.0001 ≦ a ≦ 0.2 in the general formula (1).
[4]: The scintillator according to any one of [1] to [3], wherein in the general formula (1), 0.1 ≦ c ≦ 0.5.
[5]: The scintillator according to any one of [1] to [4] ^{, wherein M 3} contains Ga or Sc in the general formula (1).
[6]: The scintillator according to any one of [1] to [5], which has a fluorescence lifetime (DT) of 25 ns or less when excited by Cs137-radiation.
[7]: The scintillator according to any one of [1] to [6], wherein the emission peak wavelength is 363 nm or more.
[8]: The scintillator according to any one of [1] to [7], wherein the ratio of the perovskite phase is 50% by mass or more when Rietveld analysis is performed on the powder X-ray diffraction peak.
[9]: A radiation detector comprising the scintillator material according to any one of [1] to [8].
[10]: A radiation inspection apparatus including the radiation detector according to [9].
[11]: The method for producing a scintillator material according to any one of [1] to [8], which comprises at least the following steps;
a) Steps to mix the ingredients,
b) A step of firing a powder or a molded product containing the mixed raw materials under the conditions of 800 ° C. or higher and 2000 ° C. or lower, 0.01 MPa or higher and 1000 MPa or lower, and 1 hour or longer and 24 hours or shorter.
[12]: The method for producing a scintillator material according to [11], further comprising the following steps c) or d).
c) Step of crushing the obtained sintered body to obtain a powder,
d) A step of melting the obtained sintered body and growing a single crystal from the obtained melt.
[13]: The method for producing a scintillator material according to any one of [1] to [8], which comprises at least the following steps.
e) Steps including the following e-1) or e-2);
e-1) After mixing each raw material, the step of melting the raw material mixture to obtain a melt,
e-2) A step of melting each raw material and then mixing the obtained melts to obtain a melt.
f) A step of growing a single crystal from the melt obtained in e).

The present invention can provide a scintillator material having a short DT, a high emission amount, and a long emission peak wavelength.

Further, by using the scintillator material, it is possible to provide a radiation detector and an inspection device that detect radiation with high sensitivity with a small dose.

It is a figure which shows the emission spectrum and absorption spectrum of Example 4. It is a figure which shows the emission spectrum and absorption spectrum of Example 7. It is a figure which shows the emission spectrum and absorption spectrum of Comparative Example 1.

Hereinafter, embodiments of the present invention will be illustrated, but the present invention is not limited to the following embodiments, and modifications can be made as long as the essence of the present invention is not impaired.

The scintillator according to the present invention (hereinafter, may be simply referred to as “scintillator”) satisfies the following formula (1).
(A _1-ab M ¹ _a M ² _b ) _x (Al _1-c M ³ _c ) _{y Oz} ... (1)
(In the formula (1), A contains at least one selected from the group consisting of Gd, Y, Lu and La, M ¹ represents an activating element different from A, and M ² is an element different from A and M ^1. At least one selected from the group consisting of Ca, Sr, Ba, Y, La, Sm, Gd, Dy, Ho, Lu, M ³ contains at least Ga, Sc or In, x, y, z. , A, b, and c are independently 0.5 ≦ x ≦ 1.5, 0.5 ≦ y ≦ 1.5, 2 ≦ z ≦ 4, 0 <a ≦ 0.5, 0 ≦ b ≦ 0. 9, 0 <c ≦ 0.8 is satisfied.)

In the general formula (1), A preferably contains Gd. By using Gd, which is inexpensive and has a large atomic number, the X-ray stopping power of the scintillator can be enhanced, the scintillator block can be miniaturized, the amount of light emitted can be increased by reducing scattering, and the scintillator can be manufactured at low cost. Can be obtained.

In the general formula (1), M ¹ represents an activating element, and for example, a rare earth element can be used. From the viewpoint of obtaining a short DT and a high amount of light emission, it is preferable to use Ce from the viewpoint of obtaining at least one of Ce, Pr, Tb and Eu, exhibiting a long emission peak wavelength, and obtaining a scintillator having a short DT. include. The ^{lower limit of a indicating the content of M 1} is not particularly limited, but is usually 0.000001 or more, preferably 0.00001 or more, more preferably 0.0001 or more, particularly preferably 0.001 or more, and usually 0. It is 7 or less, preferably 0.5 or less, more preferably 0.3 or less, still more preferably 0.2 or less, particularly preferably 0.1 or less, and particularly still more preferably 0.06 or less.

In the general formula (1), A may be used only with the above-mentioned elements, or may be substituted with other elements. M ² represents the substituting element, if the scintillator including the M ^2, M ² can be used such as alkaline earth elements, and rare earth elements. It preferably contains at least one or more of Ca, Sr, Ba, Y, La, Sm, Gd, Dy, Ho and Lu. The ^{b indicating the content of M 2} is usually 0.9 or less, preferably 0.7 or less, more preferably 0.6 or less, still more preferably 0.5 or less, and particularly preferably 0.4 or less. The lower limit is not particularly limited, and the smaller the number is, the more preferable it is when used. By using M ² in an appropriate type and content, a scintillator having a long emission peak wavelength, a short DT, and a high emission amount can be obtained.

In the general formula (1), M ³ may contain Ga, Sc, In and the like, preferably containing Ga or Sc, and more preferably containing Ga. The ^{c indicating the content of M 3} is usually 0.8 or less, preferably 0.7 or less, more preferably 0.5 or less, still more preferably 0.4 or less, and particularly preferably 0.35 or less. The lower limit is not particularly limited, but is usually 0.00001 or more, preferably 0.001 or more, more preferably 0.05 or more, and further preferably 0.1 or more. By containing an appropriate amount of M ³ , the amount of light emitted can be significantly improved, and the effect of shifting the emission peak wavelength to the longer wavelength side can be obtained. When M ³ is Ga, Sc, and In, the scintillators may be described as GAGP, GASP, and GAIP, respectively.

In the general formula (1), x ^{represents the total molar ratio of A, M 1} and M ^{2 in} the entire scintillator, and x is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more. It is usually 1.5 or less, preferably 1.3 or less, and more preferably 1.1 or less. y indicates the total molar ratio of Al and M ^{3 in} the entire scintillator, y is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, usually 1.5 or less, preferably 1.5 or less. It is 1.3 or less, more preferably 1.1 or less. z represents the molar ratio of oxygen (O) in the entire scintillator, where z is usually 2 or more, preferably 2.5 or more, more preferably 2.7 or more, usually 4 or less, preferably 3.5 or less, more preferably. It is 3.3 or less. When x, y, and z are in an appropriate range, a preferable crystal structure can be obtained.

The crystal structure of the scintillator is not particularly limited, but garnet, pyrochlore, perovskite and the like may be used, and the proportion of the perovskite phase preferably occupies a certain level or more. The ratio (phase content) of the perovskite phase is usually 40% by mass or more, preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 75% by mass or more, particularly preferably 80% or more, particularly. It is preferably 85% by mass or more, most preferably 90% by mass or more, and the upper limit is not particularly limited and may be 100%. Since the proportion of the perovskite phase in the region is sufficiently high and the perovskite phase is the main component, the characteristics of the perovskite phase dominate regardless of the proportion of other phases, and a very short DT is produced with a high emission amount. The scintillator material shown can be obtained.
The phase content of the crystal structure and each crystal structure phase was determined with respect to the obtained powder X-ray diffraction peak after measuring the powder X-ray diffraction peak using a powdery scintillator to identify the phase. It can be obtained by performing Rietveld analysis using the peaks of the phase. When the scintillator has a shape other than powder, the powder X-ray diffraction peak measurement can be performed after pulverizing to obtain powder.

The effective atomic number Z _eff of the scintillator is usually 40 or more, preferably 45 or more, more preferably 50 or more, and further preferably 55 or more. It is possible to provide a scintillator material showing a high X-ray stopping power due to a high _{Z eff.}

The scintillator is excited by irradiation with ionizing radiation and emits light. The wavelength that emits the strongest light in the emission spectrum and peaks on the waveform (emission peak wavelength) is usually 350 nm or more, preferably 360 nm or more, more preferably 363 nm or more, still more preferably 365 nm or more, and particularly preferably 370 nm or more. Yes, usually 700 nm or less, preferably 600 nm or less. Examples of ionizing radiation include X-rays, γ-rays, α-rays, and neutron rays. When the emission peak wavelength is in this range, it is possible to obtain a scintillator capable of emitting light that is efficiently converted into an electric signal by the receiver. Irradiation, ultraviolet irradiation, or the like can be used to measure the emission peak wavelength. In the present specification, photoexcitation is performed by the method of Examples described later, an emission spectrum at an excitation wavelength with high excitation efficiency is observed, and the peak wavelength in the spectrum is evaluated as the emission peak wavelength of the scintillator.

The fluorescence lifetime (scintillation decay time, DT) of the scintillator according to the present invention is usually 30 ns or less, preferably 25 ns or less, more preferably 20 ns or less, still more preferably 15 ns or less. The lower limit is not particularly limited, but is usually 1 ns or more. When MPPC is used as the receiver, it is preferably 10 ns or more. Having the DT in this range can provide a scintillator that enables radiation conversion with high time resolution.
A method of measuring DT will be illustrated. The scintillator is irradiated with radiation, the light emitted by the scintillator is converted into electric charges by a receiver, and then a signal is output using an oscilloscope. Assuming that the time when the irradiation of the scintillator is stopped is t = 0, the signal intensity usually decreases exponentially with the passage of time after the irradiation is stopped. In the present specification, the signal output by the above method is plotted on the axis of signal intensity and time, and fitting using a quadratic exponential function is performed to derive an equation expressing the relationship between signal intensity and time. From the above equation, the time t at which the signal intensity decays to 1 / e of the maximum intensity is calculated, and the time t is defined as the fluorescence lifetime (DT).

When the fluorescence from the scintillator has a plurality of components having different DTs, the plot is a composite of waveforms corresponding to the plurality of components, but each component can be decomposed and grasped by performing the fitting. can. In the present specification, for convenience, each component is referred to as a 1st component, a 2nd component, and so on in order from the one having the shortest DT.
Further, for each component, the value obtained by integrating the signal intensity with time in the plot centered on the signal intensity and time is obtained, and the integrated value of each component is obtained when the total of the integrated values of each component is 100%. It can be evaluated as the relative ratio of the components.

The amount of light emitted from the scintillator according to the present invention is usually 10,000 Ph / MeV or more, more preferably 20,000 Ph / MeV or more.

The scintillator according to the present invention is irradiated with X-rays, and the light emission intensity 20 ms after the time when the light emission intensity reaches the maximum value (hereinafter, may be referred to as afterglow intensity) is set to 1 with the maximum value of the light emission intensity as 1. It is usually 2000 ppm or less, preferably 1500 ppm or less, more preferably 1000 ppm or less, and the lower limit is not particularly limited, and the smaller the value, the more preferable. The emission intensity (afterglow intensity) after 40 ms is usually 600 ppm or less, preferably 500 ppm or less, more preferably 400 ppm or less, still more preferably 300 ppm or less, and particularly preferably 200 ppm or less, with the maximum value of the emission intensity as 1. The lower limit is not particularly limited, and the smaller the value, the more preferable. When the afterglow intensity is sufficiently low, a scintillator having a higher time resolution and providing a sharp radiographic image can be obtained. The emission intensity can be determined by the photon counting method described in the examples.

Hereinafter, the raw materials used for the scintillator according to the present invention will be illustrated.
The raw material used is not particularly limited as long as the scintillator according to the present invention can be obtained, and for example, oxides, halides, inorganic acid salts and the like of each constituent atom can be used. For example, regarding Gd, Y, Lu, La, Al, Ga, and Sc, Gd ₂ O ₃ , Y ₂ O ₃ , Lu ₂ O ₃ , La ₂ O ₃ or La (OH) ₃ , Al ₂ O ₃ , Ga, respectively. ₂ O ₃ , Sc ₂ O _{3, and the} like can be used. The purity of each raw material is usually 90% by mass or more, preferably 99% by mass or more, and the upper limit is not particularly limited. As O, an O atom contained in the oxide of each element may be used.
The mode of the raw material is not particularly limited as long as the scintillator according to the present invention can be obtained, but for example, a powdery material can be used.

Next, a method for manufacturing the scintillator according to the present invention will be illustrated. The raw materials are weighed so as to obtain the desired composition, mixed sufficiently, placed in a heat-resistant container, and then fired at a predetermined temperature and in an atmosphere to obtain a desired powder. After firing, annealing may be performed for the purpose of removing defects, filling oxygen deficiencies with oxygen, or adjusting the valence of Ce.

<Raw material mixing process>
The method of mixing the raw materials is not particularly limited, and a generally used method can be applied, and either a dry mixing method or a wet mixing method may be used.
Examples of the dry mixing method include mixing using a ball mill or the like. You may mix using a mortar and pestle.
As a wet mixing method, for example, a solvent such as water or an organic solvent is added to the raw material, mixed using a milk bowl and a milk stick to prepare a dispersion solution or a slurry, and then dried by spray drying, heat drying, natural drying or the like. There is a way to make it. The organic solvent is not particularly limited, but for example, acetone, ethanol and the like can be used.

<Baking process>
The raw material mixture is usually obtained in the form of a powder (mixed powder). The mixture can also be calcined as a powder. Alternatively, a method may be used in which the obtained molded product is fired after molding the powder. In the present specification, for convenience, a product obtained by firing as a powder is referred to as a fired powder, and a product obtained by firing a molded product after molding before firing is referred to as a sintered body.
The calcined powder obtained in this step may be used to obtain a sintered body, or may be used as it is as a completed scintillator. Alternatively, it can be used as a starting material for growing a single crystal.
When molding the powder before firing, the molding method is not particularly limited, and for example, uniaxial molding using a hydraulic press and a mold, cold isotropic pressure pressing method (CIP), and the like can be used. By performing the molding, the contact area between the powder particles is increased, and a fired body having a high density can be obtained.

The firing temperature, pressure, and time are not particularly limited as long as the scintillator according to the present invention can be obtained, and it is preferable that the temperature and time are such that the mixed raw materials sufficiently react, but the temperature is usually 800 ° C. or higher. It is preferably 1000 ° C. or higher, more 1200 ° C. or higher, usually 2000 ° C. or lower, preferably 1800 ° C. or lower, and more preferably 1600 ° C. or lower. The pressure is usually 0.01 MPa or more and 1000 MPa or less. The time is usually 1 hour or more, preferably 2 hours or more, usually 24 hours or less, preferably 18 hours or less. If the synthesis temperature is too low or the time is too short, the synthesis will not proceed sufficiently. Conversely, if the synthesis temperature is too high or the time is too long, an unfavorable reaction will occur, or an element that easily evaporates, such as oxygen. May be detached.

The atmosphere at the time of firing is not particularly limited as long as the scintillator according to the present invention can be obtained, but it is preferable to perform firing in an appropriately suitable atmosphere in consideration of the stability of the material, reaction vessel, furnace material and the like. For example, an atmospheric atmosphere, an argon atmosphere, and a nitrogen atmosphere can be mentioned. The material of the heat-resistant container used for firing is not particularly limited, but an inert material that does not react with the raw material and the scintillator material is preferable. For example, alumina, BN, Mo and the like can be used.

<Annealing process>
In obtaining the calcined powder according to the present invention, annealing may be performed after calcining for the purpose of repairing defects, filling oxygen deficiencies with oxygen, and adjusting the valence of the activating element. Various conditions such as temperature, pressure, and atmosphere in the annealing step are not particularly limited as long as the scintillator according to the present invention can be obtained, but the temperature is usually 500 ° C. or higher, preferably 600 ° C. or higher, more preferably 700 ° C. or higher. , Usually 2000 ° C. or lower, preferably 1800 ° C. or lower, more preferably 1600 ° C. or lower. The pressure is usually 0.01 MPa or more and 1000 MPa or less. The atmosphere is not particularly limited, and for example, the atmosphere can be used, an inert gas such as nitrogen or argon can be used, or a gas in which various elements are mixed can be used. From the viewpoint of filling oxygen deficiency with oxygen, oxygen is preferably contained. By going through this step, light absorption due to defects can be reduced.

When the scintillator is obtained as a single crystal, for example, it is obtained by melting the fired powder obtained by the above-mentioned firing or the powder obtained by crushing the sintered body by heating and growing the single crystal from the melt. Can be done. The container and atmosphere at the time of producing the single crystal can be appropriately selected from the same viewpoint as in the production of the sintered body. Alternatively, a melt is prepared by melting each starting material by heating and then mixing it without going through a firing step, or by mixing each starting material and melting it by heating, and using the melt alone. It can also be obtained by growing crystals. The method for growing a single crystal is not particularly limited, and a general Czochralski method, Bridgeman method, micro-pulling method, EFG method, zone melt method, Fz method, skull melt method and the like can be used. For the purpose of lowering the melting point, the flux method or the like can also be used. When growing large crystals, the Czochralski method and the Bridgeman method are preferable.

When the scintillator according to the present invention is obtained as a powder, the method is not particularly limited. For example, the calcined powder obtained by the above firing may be used as it is as a powder scintillator, or the sintered obtained by calcining after molding. You may obtain it by crushing the body.

The scintillator can be used as a radiation detector by combining it with a receiver that converts the light emitted by the scintillator into an electric signal. When used in radiation detector applications, the scintillator may be in the form of powder, sintered body, or single crystal. Photomultiplier tubes (PMTs), photodiodes (PDs) or avalanche photodiodes (APDs), multipixel photon counters (MPPCs) (also known as silicon photomultipliers (Si-)) are used in radiation detectors. PM))) is used.

Furthermore, by providing these radiation detectors, it can also be used as a radiation inspection system or inspection device. Examples of the radiation inspection device include a non-destructive inspection detector such as a non-destructive inspection detector, a resource exploration detector, a high-energy physical detector, and a diagnostic device such as a medical image processing device. Examples of medical image processing devices include devices such as X-ray CT, PET (positron emission tomography), and SPECT (single photon emission tomography). X-ray CT has evolved from existing X-ray CT to dual energy CT, and photon counting CT is expected as a next-generation CT.

The form of the scintillator is not particularly limited, and may be powder, sintered body, or single crystal, and a form suitable for each application and purpose is preferable. For example, in an X-ray CT apparatus, a single crystal or a sintered block can be considered.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples.

<Examples 1 to 7><Comparative example 1>
Gd ₂ O ₃ (purity 99.99% by mass), Al ₂ O ₃ (purity 99.99% by mass), Ga ₂ O ₃ (purity 99.99% by mass), Sc ₂ O ₃ (purity 99.99% by mass) ), CeO ₂ (purity 99.99% by mass) is used as a raw material, and each powdered raw material is contained in ethanol so that the molar ratio of each element of Gd, Ce, Al, Ga, Sc is as shown in Table 1 below. Mixed in. The obtained powdery raw material mixture was uniaxially pressure-pressed at 100 MPa to form pellets. The molded product was fired in the atmosphere at normal pressure at 1500 ° C. for 4 hours to obtain a sintered body. Then, the sintered body was crushed with a mortar and a pestle to obtain a powdery scintillator sample (hereinafter, also referred to as a powder sample).

<Calculation method of effective atomic number Z _{eff>
Z eff} in the element ratio in Table 1 was calculated with x = 1, y = 1, and z = 3. _{In the calculation, the Z eff} of the compound represented by the following formula (3) was calculated with a coefficient k = 4 based on the following formulas (4) and (5). In the following formulas and explanations of the formulas, "*" is a symbol meaning that the left and right values are integrated.
The results are shown in Table 1.

AaBbCcDd ... (3)
(In the formula, A, B, C and D represent the first to fourth elements constituting the compound, respectively, and a, b, c and d are the elements A, B, C and D in the compound, respectively. The molar ratio is shown. In this formula, an example of four kinds of constituent elements is shown, but compounds having three or less kinds of constituent elements or five or more kinds of constituent elements can be similarly described using different alphabets. Any element contained in the compound instead of A, B, C, D, etc. can be indicated by m instead of M, a, b, c, d, etc.).

w _m = X (M) * m / Σ (X (M) * m) ... (4)
(In the formula (4), M represents an arbitrary element M in the compound represented by the formula (3), m represents the molar ratio m of the element M, and X (M) represents the atomic weight of the element M. Σ (X (M) * m) indicates that the values of (X (M) * m) in all the elements M contained in the compound represented by the formula (3) are totaled.) For example, the compound is When represented by AaBbCcDd, w _a = {(atomic weight of A) * a} / {(atomic weight of A) * a + (atomic weight of B) * b + (atomic weight of C) * c + (atomic weight of D) * d} Is.

Z _eff = [Σ {w _m * (Z _M ) ^k }] ^{(1 / K)}・ ・ ・ (5)
(In the formula (5), w _{m represents w m} represented by the formula (4) with respect to any element M represented by the formula (3), and Z _M represents the atomic number of the element M. Further, Σ [w _m * Z _M ^ k] means to sum the values _{of [w m} * Z _M ^ k] for all the elements M contained in the compound represented by the formula (3). ..

<Measurement of emission intensity when excited by X-rays>
After 200 mg of the powder sample was evenly spread on the bottom of a synthetic quartz petri dish having a diameter of 14.8 mm and a load of 8 mm, the powder sample was irradiated with pulse X-rays and the emission intensity was measured by a photon counting method. Specifically, X-rays were generated by applying 100 kV, 0.5 mA to an X-ray tube (tungsten). After irradiating the powder sample with X-rays, the weak light generated by the photomultiplier tube H13126 was detected and monitored using the Hamamatsu Photonics C12918 interface. The relative emission intensity of the powder sample according to each example was determined by setting the emission amount of the powder sample of Comparative Example 1 described later to 1. The results are shown in Table 1.

<Afterglow intensity>
Using the medical compact and lightweight portable X-ray imaging device PORTA as the X-ray source, the powder sample is irradiated with X-rays under the conditions of 100 kV, 20 mAs, and 16 mGy / s, and the emission intensity (afterglow intensity) after 20 ms and 40 ms is evaluated. bottom. The results are shown in Table 3.

<Measurement of emission peak wavelength>
Using an F-7000 (Hitachi, Ltd.) spectroscope, the powder sample was irradiated with light of 220 to 500 nm, the emission spectrum and the excitation spectrum were observed, and the emission peak wavelength was determined. The results are shown in Table 1 and FIGS.
In FIGS. 1 to 3, the dotted line shows the excitation spectrum of each scintillator, and the solid line shows the emission spectrum when light of 290 nm is absorbed. For example, em371 nm means that the emission peak wavelength when the excitation spectrum shown by the dotted line is shown is 371 nm. For example, ex290 nm means that the emission spectrum shown by the solid line is excited by light having a wavelength of 290 nm. Means that

<Fluorescence life (DT)>
The obtained powder sample was processed into powdery pellets by uniaxial molding under 100 MPa with a hydraulic press at room temperature for several tens of seconds, and then resintered under the conditions of air, normal pressure, 1000 ° C., and 2 hours. A sintered sample was obtained. The obtained sintered body sample was used to evaluate the fluorescence lifetime (DT) at the time of gamma ray excitation. A sintered sample was brought into close contact with a H7195 photomultiplier tube manufactured by Hamamatsu Photonics Co., Ltd. using an opt seal manufactured by Shin-Etsu Chemical Co., Ltd. The sintered body sample was irradiated with γ-rays using Cs-137 as an excitation source, and the signal intensity based on fluorescence during and after γ-ray irradiation was measured using an MSO54 5-BW-1000 oscilloscope manufactured by Tektronix. Based on the signal intensity, a plurality of components were separated by fitting using a quadratic exponential function, and the fluorescence lifetime (DT) of each component was calculated.
As a result, it was found that the fluorescence of each sintered sample was composed of two components having different DTs, so the relative ratio of the two components was determined by the method described above. The results are shown in Table 2. The short component of DT was evaluated as the 1st component, the long component was defined as the 2nd component, and the 1st component was evaluated as the DT of each scintillator.

<Specification of crystal structure and proportion>
The powder X-ray diffraction peak of the obtained powder sample was measured to identify the phase. As a result, the scintillators obtained were _three phases: GdAl (Ga) O 3 (GA (G) P, perovskite) phase, Gd ₄ Al ₂ O ₉ phase, and Gd ₃ Al ₂ Ga ₃ O ₁₂ (GAGG, garnet) phase. It was found that it was composed of. Rietveld analysis was performed on the obtained powder X-ray diffraction peak using the peaks of the three phases, and the phase content (mass%) of each phase was determined. The results are shown in Table 2.

<Examples 8 to 15>
A scintillator sample was obtained in the same manner as in Example 1 except that the molar ratio of each element at the time of mixing the raw materials was as shown in Table 4. _{The calculated Z eff} was obtained from the molar ratio when the raw materials were mixed. In addition, the emission intensity of each of the obtained scintillator samples was measured in the same manner as in Example 1. The results are shown in Table 4.

※”N.D.”は”検出下限以下またはベースライン以下”を意味する。

* "ND" means "below the detection limit or below the baseline".

_{The calculated Z eff} of the scintillators according to the examples was as high as 57 to 58, and the crystal phase mainly showed a perovskite phase. Moreover, regardless of the content of the phase other than the perovskite phase, the DT was as short as 20 ns or less. Further, as shown in Examples 1 to 7, the scintillator according to the example replaces a part of the element of Al site with another element, so that the emission intensity is higher than that of Comparative Example 1 in which the substitution is not performed. In addition to the dramatic improvement, the emission peak wavelength was shifted to the long wavelength side up to 371 nm when Ga was used and 373 nm when Sc was used, as compared with 361 nm in Comparative Example 1.
When MPPC is used as the receiver, the DT of the scintillator is preferably 10 ns or more, but all the scintillators according to the examples satisfy this condition.

As described above, the present invention can provide a scintillator material having a short DT, a high emission amount, and a long emission peak wavelength.

Further, the present invention can provide a radiation detector and a radiation inspection device having a low dose and high sensitivity by using a scintillator satisfying the above characteristics.

Claims (13)

A scintillator comprising a scintillator having a composition satisfying the general formula (1).
(A _1-ab M ¹ _a M ² _b ) _x (Al _1-c M ³ _c ) _{y Oz} ... (1)
(In the formula (1), A contains at least one selected from the group consisting of Gd, Y, Lu and La, M ¹ represents an activating element different from A, and M ² is an element different from A and M ^1. At least one selected from the group consisting of Ca, Sr, Ba, Y, La, Sm, Gd, Dy, Ho, Lu, M ³ contains at least Ga, Sc or In, x, y, z. , A, b, and c are independently 0.5 ≦ x ≦ 1.5, 0.5 ≦ y ≦ 1.5, 2 ≦ z ≦ 4, 0 <a ≦ 0.5, 0 ≦ b ≦ 0. 9, 0 <c ≦ 0.8 is satisfied.) The scintillator according to claim 1, wherein in the general formula (1), M ¹ contains any one or more of Ce, Pr, and Tb. The scintillator according to claim 1 or 2, wherein in the general formula (1), 0.0001 ≦ a ≦ 0.2. The scintillator according to any one of claims 1 to 3, wherein in the general formula (1), 0.1 ≦ c ≦ 0.5. The scintillator according to any one of claims 1 to 4, wherein in the general formula (1), M ^{3 contains Ga or Sc.} Cs137-The scintillator according to any one of claims 1 to 5, which has a fluorescence lifetime (DT) of 25 ns or less when excited by radiation. The scintillator according to any one of claims 1 to 6, wherein the emission peak wavelength is 363 nm or more. The scintillator according to any one of claims 1 to 7, wherein the ratio of the perovskite phase is 50% by mass or more when Rietveld analysis is performed on the powder X-ray diffraction peak. A radiation detector comprising the scintillator material according to any one of claims 1 to 8. A radiation inspection apparatus including the radiation detector according to claim 9. The method for producing a scintillator material according to any one of claims 1 to 8, which comprises at least the following steps;
a) Steps to mix the ingredients,
b) A step of firing a powder or a molded product containing the mixed raw materials under the conditions of 800 ° C. or higher and 2000 ° C. or lower, 0.01 MPa or higher and 1000 MPa or lower, and 1 hour or longer and 24 hours or shorter. The method for producing a scintillator material according to claim 11, further comprising the following steps c) or d).
c) Step of crushing the obtained sintered body to obtain a powder,
d) A step of melting the obtained sintered body and growing a single crystal from the obtained melt. The method for producing a scintillator material according to any one of claims 1 to 8, which comprises at least the following steps.
e) Steps including the following e-1) or e-2);
e-1) After mixing each raw material, the step of melting the raw material mixture to obtain a melt,
e-2) A step of melting each raw material and then mixing the obtained melts to obtain a melt.
f) A step of growing a single crystal from the melt obtained in e).

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