JP2022140222A - Scintillator material, radiation detection device, and method of manufacturing scintillator material - Google Patents

Abstract

To provide a scintillator material which has superior moisture resistance and is capable of emitting visible light well in the presence of radiation, and to provide a radiation detection device and a method of manufacturing the scintillator material.SOLUTION: A scintillator material that emits visible light when excited by radiation is provided. The scintillator material has a cristobalite structure with partially crystallized silica. SrI2:Eu2+, a phosphor material, is entrapped in the cristobalite structure to form a nanocomposite. The cristobalite structure contains an alkali metal ion.SELECTED DRAWING: Figure 1

Description

The present invention relates to a scintillator material, a radiation detection device, and a method for manufacturing a scintillator material.

Iodides such as NaI:Tl and CaI:Tl have been conventionally used in radiation detectors as scintillator materials that emit visible light when excited by radiation. The iodide-based scintillator material has deliquescent property to take in moisture in the air and hydrate, and must be sealed in a highly airtight container for use. Therefore, in a conventional radiation detection device, an iodide-based scintillator material and a light detection unit are sealed in a container, which is an aluminum can. Visible light was detected by the detector.

However, since a very small amount of water vapor in the outside air enters the container through the joint between the container and the window member, the iodide-based scintillator hydrates and deteriorates. and proper maintenance. In addition, in order to suppress the intrusion of moisture into the container, it is necessary to seal the container with a high degree of airtightness.

Therefore, in Patent Document 1, it is proposed to incorporate SrI ₂ :Eu ²⁺ , which is a phosphor material, into the cristobalite structure and use a nanocomposite scintillator material to improve moisture resistance.

JP 2019-074358 A

However, in the technique of Patent Document ₁ , it is necessary to incorporate _{SrI 2} :Eu ²⁺ into the cristobalite structure to form a nanocomposite ^. It was difficult to increase the amount of emitted light by increasing it.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the conventional problems described above, and an object of the present invention is to provide a scintillator material, a radiation detection device, and a method for manufacturing the scintillator material which are excellent in moisture resistance and emit visible light favorably when exposed to radiation. and

In order to solve the above problems, the scintillator material of the present invention is a scintillator material that emits visible light when excited by radiation, has a cristobalite structure in which silica is partially crystallized, and is a phosphor material. SrI ₂ :Eu ²⁺ is incorporated into the cristobalite structure to form a nanocomposite, and the cristobalite structure contains alkali metal ions.

In such a scintillator material of the present invention, SrI ₂ :Eu ²⁺ is incorporated in the cristobalite structure and alkali metal ions are included, thereby improving the moisture resistance of the phosphor material and favorably transmitting visible light to radiation. Can emit light.

Further, in one aspect of the present invention, the alkali metal ion is Li, Na, K, Rb or Cs.

Further, in one aspect of the present invention, the alkali metal ion is contained at a ratio of 0.1 to 10 mol % with respect to Si contained in the cristobalite structure.

In one aspect of the present invention, the phosphor material is a single crystal or a polycrystal.

Moreover, in one aspect of the present invention, the silica is a porous body in which voids are distributed from the surface to the inside.

Further, in one aspect of the present invention, the porous body is an aggregate of SiO ₂ particles having an average particle size (D50) of 2 to 50 μm.

Moreover, in one aspect of the present invention, the SiO ₂ particles contain an alkali metal component.

In one aspect of the present invention, Sr ions are 0.9 to 15 mol %, I ions are 2.0 to 40 mol %, and Eu ions are 0.1 to 5.0 mol %, relative to Si contained in the cristobalite structure. % included.

A radiation detection apparatus according to the present invention includes any one of the scintillator materials described above and a photodetector that detects a wavelength of 400 nm or more and 500 nm or less.

Further, the method for producing a scintillator material of the present invention includes a powder preparation step of forming a raw material powder containing SrI ₂ :Eu ²⁺ which is a phosphor material and an alkali metal material; The method is characterized by comprising a porous body forming step of forming silica, and a heat treatment step of bringing the porous body and the raw material powder into contact with each other and heat-treating them.

INDUSTRIAL APPLICABILITY The present invention can provide a scintillator material, a radiation detection device, and a method for producing a scintillator material that are excellent in moisture resistance and can emit visible light favorably when exposed to radiation.

1 is a schematic diagram showing the structure of a radiation detection device 10 using a scintillator material according to a first embodiment; FIG. FIG. 11 is a schematic diagram showing the structure of a radiation detection device 20 using a scintillator material according to a third embodiment; FIG. 2 is a schematic diagram showing a measuring device 30 for gamma ray absorption of scintillator material.

(First embodiment)
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or equivalent constituent elements, members, and processes shown in each drawing are denoted by the same reference numerals, and duplication of description will be omitted as appropriate. FIG. 1 is a schematic diagram showing the structure of a radiation detection device 10 using a scintillator material according to this embodiment. As shown in FIG. 1 , the radiation detection apparatus 10 includes a container 11 , a window member 12 , a scintillator material 13 , a photomultiplier tube 14 (PMT: PhotoMultiplier Tube), and a bleeder circuit 15 .

The container 11 is a substantially cylindrical member having an opening, and accommodates a scintillator material 13 , a photomultiplier tube 14 and a bleeder circuit 15 inside. A window member 12 is airtightly fixed to the opening with an adhesive or the like. Although the material constituting the container 11 is not limited, aluminum can be used as an example. Further, the shape of the container 11 is not limited to a cylindrical shape, and can be appropriately designed according to the shape and size of each member accommodated therein. A wiring hole (not shown) is formed in the container 11, and wiring is connected to the bleeder circuit 15 from the outside through the wiring hole.

The window member 12 is a plate-like member made of a radiation-transmitting material, and is arranged at the opening of the container 11 to hermetically seal the inside of the container 11 . A material for forming the window member 12 is not limited, and a known glass material can be used. Adhesive or the like is applied between the outer periphery of the window member 12 and the opening of the container 11, and is airtightly sealed to prevent water vapor from entering through the gap.

The scintillator material 13 is arranged between the window member 12 and the photomultiplier tube 14 and is a member containing a fluorescent material that emits visible light when irradiated with radiation. In this embodiment, as the fluorescent material, a nanocomposite is used in which single-crystal or polycrystalline SrI ₂ :Eu ²⁺ is incorporated into a cristobalite structure in which silica, which is a matrix phase, is partially crystallized. . Also, the cristobalite structure contains alkali metal ions.

The photomultiplier tube 14 is a member that detects a minute amount of photons and outputs an electrical signal. A known structure can be used for the photomultiplier tube 14. As an example, a photocathode, a plurality of secondary electron multiplying electrodes (dynodes), an anode, and other electrodes are placed in a high-vacuum glass container. Those with encapsulated structures can be used. A scintillator material 13 is arranged on the entrance window side of the photomultiplier tube 14, and a bleeder circuit 15 is connected to the output side.

The bleeder circuit 15 is a member that supplies voltage from the high-voltage power supply to the photomultiplier tube 14 through a plurality of dividing resistors and outputs current from the photomultiplier tube 14 . A plurality of voltages from a high voltage power supply are supplied to each dynode of photomultiplier tube 14 . The output of the bleeder circuit 15 is transmitted as a detection signal to an external signal processing section via wiring (not shown).

In the radiation detection apparatus 10 shown in FIG. 1, when radiation such as gamma rays is incident on the scintillator material 13 through the window member 12, the phosphor material in the scintillator material 13 is excited, and blue light with a wavelength range of 400 nm to 500 nm is emitted. Glow with light. Photons of blue light emitted by the scintillator material 13 reach the photocathode through the incident window of the photomultiplier tube 14 and are converted into electrons by the photocathode. When the electrons generated by the photocathode collide with the dynode, a large number of electrons are emitted by the voltage applied to the dynode. is amplified like an avalanche. The current generated by the electrons amplified by the photomultiplier tube 14 is transmitted as a detection signal to an external signal processing section via the bleeder circuit 15, and the signal processing section calculates the number of photons from the relationship between the photons, the current, and the detection signal. . Further, the signal processing unit calculates the intensity of radiation from the calculated number of photons.

Next, the phosphor material used for the scintillator material 13 of this embodiment will be described in further detail. Silica has an amorphous structure with a basic skeleton in which SiO ₄ tetrahedra are linked by Si—O—Si bonds. The bond angle of Si—O—Si has an angle of 145°±10°. When silica is heated, the coefficient of thermal expansion is small up to around 1000°C, but the coefficient of thermal expansion rises gently after around 1000°C. This is because active hydrogen is generated from OH groups on the surface of silica, and Si--O--Si bonds are broken and rearranged in a part of silica. At this time, the bond angle of Si--O--Si becomes 180°, and large voids are generated in the SiO ₄ connecting network. The voids become pockets for metal cations such as Sr ²⁺ , Cs ⁺ , Ca ²⁺ , Eu ²⁺ , Tl ⁺ , and anions such as halogens, and these ions are incorporated into the SiO ₄ connecting network.

By thermal diffusion of the taken ions, cations and anions combine to form ion crystal nuclei. Triggered by the generation of ion crystal nuclei, it is thought that silica in the matrix phase also crystallizes to form cristobalite. In this way, it is inferred that the incorporation of the luminescent metal halide salt and the crystallization of SiO ₂ occurred in parallel to produce a nanocomposite scintillator material.

At the temperature at which nanocompositing of SiO ₂ proceeds, the temperature is too high to sublimate I in the raw material, making it difficult to incorporate a sufficient amount of SrI ₂ :Eu ²⁺ crystals. Therefore, it is important to synthesize I at a low temperature while suppressing the sublimation of I and to contain a large amount of SrI ₂ :Eu ²⁺ in the cristobalite structure.

Alkali metal ions contained in the cristobalite structure include Li, Na, K, Rb, and Cs. Further, the alkali metal ion contained in the cristobalite structure is preferably contained at a ratio of 0.01 mol or more and 1.00 mol or less (0.1 mol % or more and 10 mol % or less) with respect to 10 mol of Si.

If the alkali metal ion content is less than 0.1 mol %, the amount of SrI ₂ :Eu ²⁺ taken into the cristobalite structure is small, making it difficult to increase the radiation absorption rate and the emission intensity of visible light. In addition, when the alkali metal ion content is more than 10 mol %, the cristobalite structure cannot be formed, and SiO ₂ and alkali metal ions vitrify, making it difficult to incorporate SrI ₂ :Eu ²⁺ into the material, making it difficult to absorb radiation and emit visible light. become.

As described above, in the radiation detection apparatus 10 of the present embodiment, by using a nanocomposite containing alkali metal ions in which SrI ₂ :Eu ²⁺ is incorporated in the cristobalite structure as the scintillator material 13 , excellent moisture resistance is obtained. By detecting the visible light emitted by, it is possible to increase the detection sensitivity of radiation. Further, since the synthesis can be performed at a low temperature and the sublimation of I can be suppressed, a large amount of SrI ₂ :Eu ²⁺ can be contained in the cristobalite structure.

(Second embodiment)
Next, a second embodiment of the invention will be described. The description of the content that overlaps with the first embodiment is omitted. In this embodiment, a porous body of SiO ₂ is used as silica, which is the matrix phase of the scintillator material 13 .

The porous body is a molded body composed of silica, which is the matrix phase of the scintillator material, and voids are distributed from the surface to the inside of the silica. The shape and structure of the porous body are not limited, but a plate-like molded body having a thickness of about 1 mm to 5 mm can be used. The method of forming the porous body is not limited, but aggregates obtained by sintering SiO ₂ particles having an average particle diameter (D50) of 2 to 50 μm can be used. The filling ratio of silica contained in the porous body is preferably about 30 to 80% by volume. If the filling rate is less than 30%, the strength of the porous body is insufficient and handling becomes difficult, and if the filling rate exceeds 80%, it becomes difficult to incorporate the phosphor material inside the porous body. Become.

Moreover, in order to sinter the SiO ₂ particles to form aggregates, the SiO ₂ particles preferably contain an alkali metal component. Alkali metal components contained in the _SiO2 particles include Li, Na, K, Rb, and Cs. The content of the alkali metal component contained in the SiO ₂ particles is preferably 0.01 mol or more and 1.00 mol or less (0.1 mol % or more and 10 mol % or less) with respect to 10 mol of Si. By including an alkali metal component in the SiO ₂ particles, the SiO ₂ particles are sintered together, and a porous compact having voids between the particles can be obtained.

In the method for producing the scintillator material of the present embodiment, in the powder preparation step, the phosphor material SrI ₂ :Eu ²⁺ and the alkali metal material are prepared and pulverized/mixed in an inert gas atmosphere to form a raw material powder. . In addition, in the porous body forming step, a mixed powder of _SiO2 particles and an alkali metal material is prepared, pulverized/mixed in an inert gas atmosphere, and fired in an air atmosphere to form porous silica. . Next, in the heat treatment step, the raw material powder and the porous body are brought into contact with each other, heat-treated in an inert atmosphere, and fired to obtain a scintillator material. Although the method of contacting the raw material powder and the porous body is not limited, the porous body may be arranged on the raw material powder. Part of the silica of the porous body has a crystallized cristobalite structure by the heat treatment process, and the phosphor material SrI ₂ :Eu ²⁺ is incorporated into the cristobalite structure to form a nanocomposite. The cristobalite structure also contains alkali metal ions.

In the obtained scintillator material, the ratio of Sr ions is 0.9 to 15 mol%, I ions is 2.0 to 40 mol%, and Eu ions is 0.1 to 5.0 mol% with respect to Si contained in the cristobalite structure. is preferably included in If the ion content is less than these numerical ranges, the amount of SrI ₂ :Eu ²⁺ incorporated decreases, resulting in a decrease in light emission. Also, if the ion content is higher than these numerical ranges, excess elements seep out from the inside of the scintillator material, and cracks start from the seeped points, resulting in grain cracking. When grain cracking occurs, the SrI ₂ :Eu ²⁺ incorporated in the cristobalite structure is exposed to the atmosphere, resulting in a decrease in moisture resistance. Moreover, when the Sr ion content is 15 mol % or more, the amount of SrI incorporated into SiO ₂ decreases, resulting in a decrease in light emission performance. Also, even if the I ion content is 40 mol % or more, the amount of SrI incorporated into SiO ₂ decreases, resulting in a decrease in light emission performance. When the Eu ion content is 5.0 mol % or more, concentration quenching occurs, resulting in a decrease in light emission performance.

As described above, in the scintillator material and the method for producing the scintillator material of the present embodiment, the silica, which is the matrix phase, is composed of a porous material. This increases the amount of SrI ₂ :Eu ²⁺ which is a phosphor material incorporated into the cristobalite structure, has excellent moisture resistance, can detect visible light emitted by radiation, and can increase radiation detection sensitivity.

(Third embodiment)
Next, a third embodiment of the invention will be described with reference to FIG. The description of the content that overlaps with the first embodiment is omitted. FIG. 2 is a schematic diagram showing the structure of a radiation detection device 20 using a scintillator material according to this embodiment. As shown in FIG. 2 , the radiation detection device 20 includes a light receiving element 21 and a scintillator material 23 .

The light receiving element 21 is a member that is made of a semiconductor material and generates electrons by receiving light. The light-receiving element 21 can use a known element and its material and structure are not limited. For example, a photodiode (PD) or an avalanche photodiode (APD: Avalanche Photo Diode) can be used. A wire is connected to an electrode (not shown) of the light receiving element 21, and a voltage or current corresponding to the intensity of light is output through the wire.

The scintillator material 23 is arranged on the light receiving surface side of the light receiving element 21 and is a member containing a fluorescent material that emits visible light when irradiated with radiation. As in the first embodiment, in this embodiment as well, a nanocomposite in which SrI ₂ :Eu ²⁺ is incorporated into a cristobalite structure and alkali metal ions are included is used as the scintillator material 23 .

In the radiation detection device 20 shown in FIG. 2, when radiation such as gamma rays is incident on the scintillator material 23, the phosphor material in the scintillator material 23 is excited and emits blue light with a wavelength range of 400 nm to 500 nm. Photons of blue light emitted by the scintillator material 23 reach the light receiving surface of the light receiving element 21, and current or voltage is transmitted as a detection signal to an external signal processing unit according to the intensity of the light. The signal processing unit calculates the number of photons and the intensity of radiation from the detection signal.

Also in the radiation detection apparatus 20 of the present embodiment, by using a nanocomposite in which SrI ₂ :Eu ²⁺ is incorporated in the cristobalite structure as the scintillator material 23 and contains alkali metal ions, visible light emitted by radiation is excellent in moisture resistance. can be detected and the detection sensitivity of radiation can be increased.

(Measurement of luminescence amount by gamma ray irradiation)
Materials of Examples 1 to 3 and Comparative Examples 1 to 4 shown below were used as the scintillator material 13 of the radiation detection apparatus shown in FIG. 1, and the amount of light emitted by gamma rays was measured. In this embodiment, 662 keV of ¹³⁷ Cs is used as the gamma ray source.

(Example 1)
The scintillator material 13 according to Example 1 has a cristobalite structure incorporated with SrI ₂ :Eu ²⁺ which is a phosphor material, and contains Na as an alkali metal ion. SiO ₂ , SrI ₂ (melting point 402° C.), NH ₄ I, EuF ₃ and NaI were prepared as raw materials, and their molar ratios were 10:0.46:0.08:0.04:0.02. After being accurately weighed, each raw material was placed in a quartz mortar in a nitrogen gas atmosphere and pulverized and mixed. After that, the mixed powder was placed in an alumina crucible and fired at 850° C. for 3 hours in a nitrogen atmosphere. The resulting fired product was carefully washed with warm pure water to remove free iodide ions, thereby obtaining the scintillator material 13 of Example 1. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, a luminescence amount of 26,500 [photons/Mev] was obtained. Since the raw material contained an alkali metal, the temperature for structuring cristobalite could be lowered to 850°C.

(Example 2)
The scintillator material 13 according to Example 2 has a cristobalite structure in which SrI ₂ :Eu ²⁺ , which is a phosphor material, is incorporated, and K is included as alkali metal ions. SiO ₂ , SrI ₂ , NH ₄ I, Eu ₂ O ₃ and KBr were prepared as raw materials and precisely weighed so that their molar ratios were 10:0.50:0.04:0.015:0.10. Then, each raw material was placed in a quartz mortar in a nitrogen gas atmosphere and pulverized and mixed. After that, the mixed powder was placed in an alumina crucible and fired at 850° C. for 3 hours in a nitrogen atmosphere. The obtained fired product was carefully washed with warm pure water to remove free iodide ions, and a scintillator material 13 of Example 2 was obtained. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, a luminescence amount of 22,300 [photons/Mev] was obtained.

(Example 3)
The scintillator material 13 according to Example 3 incorporates SrI ₂ :Eu ²⁺ as a phosphor material into the cristobalite structure and contains Cs as alkali metal ions. SiO ₂ , SrI ₂ , NH ₄ I, EuI ₃ and CsCl were prepared as raw materials and precisely weighed so that their molar ratios were 10:0.40:0.10:0.06:1.80, Each raw material was placed in a quartz mortar in a nitrogen gas atmosphere and pulverized and mixed. After that, the mixed powder was placed in an alumina crucible and fired at 900° C. for 3 hours in a nitrogen atmosphere. The obtained fired product was carefully washed with warm pure water to remove free iodide ions, and a scintillator material 13 of Example 3 was obtained. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, a luminescence amount of 20,100 [photons/Mev] was obtained.

(Comparative example 1)
The scintillator material 13 according to Comparative Example 1 incorporates SrI ₂ :Eu ²⁺ which is a phosphor material into the cristobalite structure and does not contain alkali metal ions. SiO ₂ , SrI ₂ , NH ₄ I, EuF ₃ and CsCl were prepared as raw materials and precisely weighed so that the molar ratio of these was 10:0.46:0.28:0.04. It was placed in a quartz mortar and ground and mixed in a gas atmosphere. After that, the mixed powder was placed in an alumina crucible and fired at 1000° C. for 3 hours in a nitrogen atmosphere. The obtained fired product was carefully washed with warm pure water to remove free iodide ions, and a scintillator material 13 of Comparative Example 1 was obtained. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus shown in FIG. 1, an amount of luminescence of 12,000 [photons/Mev] was obtained.

(Comparative example 2)
The scintillator material 13 according to Comparative Example 2 contains excess Na as alkali metal ions. SiO ₂ , SrI ₂ , NH ₄ I, EuF ₃ and NaI were prepared as raw materials and precisely weighed so that their molar ratios were 10:0.41:0.04:0.02:2.40, Each raw material was placed in a quartz mortar in a nitrogen gas atmosphere and pulverized and mixed. After that, the mixed powder was placed in an alumina crucible and fired at 850° C. for 3 hours in a nitrogen atmosphere. The resulting baked product was carefully washed with warm pure water to remove free iodide ions, and a scintillator material 13 of Comparative Example 2 was obtained. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, the luminescence amount was 0 [photons/Mev].

(Comparative Example 3)
The scintillator material 13 according to Comparative Example 3 has SrI ₂ :Eu ²⁺ , which is a phosphor material, incorporated into the cristobalite structure, and contains a trace amount of Na as alkali metal ions. SiO ₂ , SrI ₂ , NH ₄ I, EuI ₃ and NaI were prepared as raw materials and precisely weighed so that the molar ratio of these was 10:0.38:0.02:0.01:0.01, Each raw material was placed in a quartz mortar in a nitrogen gas atmosphere and pulverized and mixed. After that, the mixed powder was placed in an alumina crucible and fired at 850° C. for 3 hours in a nitrogen atmosphere. The resulting baked product was carefully washed with warm pure water to remove free iodide ions, and a scintillator material 13 of Comparative Example 3 was obtained. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, a luminescence amount of 12,200 [photons/Mev] was obtained.

(Comparative Example 4)
A commercially available BGO (Bi ₄ Ge ₃ O ₁₂ ) was used as the scintillator material 13 . When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, a luminescence amount of 15,000 [photons/Mev] was obtained.

Table 1 shows the measurement results of the amount of light emitted by gamma ray irradiation in Examples 1 to 3 and Comparative Examples 1 to 4. As shown in Table 1, in Examples 1 to 3 containing alkali metal ions in the cristobalite structure, the luminescence amount was significantly improved as compared with Comparative Example 1 containing no alkali metal ions and Comparative Example 4 using commercially available BGO. ing. In addition, in Comparative Example 2, which was produced by excessively containing Na, which is an alkali metal ion, the phosphor material SrI ₂ :Eu ²⁺ was not incorporated into the cristobalite structure as described later, and radiation was absorbed to emit visible light. Not able to emit light. Further, in Comparative Example 3 containing a trace amount of alkali metal ions, only the same amount of light emission as in Comparative Example 1 was obtained.

(Measurement of gamma ray absorption in scintillator material)
Next, the gamma ray absorbance of the scintillator materials produced in Examples 1 to 3 and Comparative Examples 1 to 3 was measured. FIG. 3 is a schematic diagram showing an apparatus 30 for measuring the gamma ray absorptance of scintillator materials. As shown in FIG. 3 , the gamma ray absorptance measuring device 30 includes a photomultiplier tube 31 , a detection scintillator 32 , an evaluation sample 33 , a light shielding sheet 34 and a radiation source 35 .

The photomultiplier tube 31 is a member that detects a minute amount of photons and outputs an electrical signal. The scintillator 32 for detection is arranged at the entrance window of the photomultiplier tube 31, is a member containing BGO, and is excited by the radiation emitted from the radiation source 35 to emit visible light. The evaluation sample 33 is the scintillator material produced in Examples 1 to 3 and Comparative Examples 1 to 3 described above, and is arranged between the photomultiplier tube 31 and the scintillator 32 for detection. The light shielding sheet 34 is a sheet-like member made of a material that blocks visible light and transmits radiation, and is arranged to cover the entrance window of the photomultiplier tube 31 and the detection scintillator 32 . Also, the light shielding sheet 34 is sandwiched between the scintillator 32 for detection and the evaluation sample 33 . The radiation source 35 is a device for irradiating radiation, and uses 60 keV of ²⁴¹ Am in this embodiment.

In the measurement apparatus 30 shown in FIG. 3, gamma rays emitted from the radiation source 35 pass through the evaluation sample 33 and the light shielding sheet 34 and reach the scintillator 32 for detection. In the detection scintillator 32, BGO is excited by gamma rays to emit visible light. Photons emitted by the detection scintillator 32 reach the photomultiplier tube 14 and are output to the signal processing section as a detection signal. The signal processor calculates the number of photons based on the detection signal.

At this time, the phosphor material is also excited by the gamma rays incident on the evaluation sample 33 and emits visible light. Only the light emitted at 32 is obtained. Therefore, by comparing the number of photons detected by the photomultiplier tube 31, the amount of gamma rays absorbed by the evaluation sample 33 can be measured.

In the measurement apparatus 30 shown in FIG. 3, the amount of light emitted from the scintillator 32 for detection is measured by the photomultiplier tube 31 with the evaluation sample 33 removed, and this is used as a reference value. In the measuring device 30, the amount of light emitted from the scintillator 32 for detection is measured by the photomultiplier tube 31 while the evaluation samples 33 of Examples 1 to 3 and Comparative Examples 1 to 3 are placed. Absorption was calculated. Here, the gamma ray absorption rate _{R A} is the ratio _R (N _B / _NA ), and calculated as R _A = (100-R)%.

As shown in Table 2, in Examples 1 to 3, the scintillator material of Evaluation Sample 33 absorbed about 20% or more of gamma rays, and SrI ₂ :Eu ²⁺ which is a phosphor material containing alkali metal ions in the cristobalite structure. It can be seen that the is well incorporated and can be excited by radiation with high efficiency to emit visible light. On the other hand, in Comparative Example 1 containing no alkali metal and Comparative Example 3 containing a small amount of alkali metal ions, the absorption of gamma rays was about 12%, indicating that the efficiency of emitting visible light by excitation with radiation is low. . Moreover, in Comparative Example 2, which was produced by containing an excessive amount of alkali metal ions, SrI ₂ :Eu ²⁺ was not incorporated, so radiation was hardly absorbed.

(Analysis results of Examples 1 to 3 and Comparative Examples 1 to 3)
Next, the scintillator materials produced in Examples 1 to 3 and Comparative Examples 1 to 3 were measured for the ratio of the contained elements using flame atomic absorption spectrophotometry. A fluorescent X-ray device (RIX1000 manufactured by Rigaku Corporation) was used for the measurement. Monochromator, 2θ measurement range [deg. ], step width [deg. ] is shown in Table 3. Table 4 shows the measurement results of Examples 1 to 3 and Comparative Examples 1 to 3. In Table 4, the amount of each element in the scintillator material is shown in mol when the amount of Si element is 10 mol. Therefore, the value obtained by multiplying the numerical value shown in Table 4 by 10 is the mol % with respect to Si.

As shown in Table 4, in Examples 1 to 3, Na, K, and Cs, which are alkali metal ions, are 0.01 mol (0.1 mol %), 0.05 mol (0.5 mol %), and 0.90 mol ( 9.0 mol %), and accordingly the amounts of Sr and I are greater than in Comparative Examples 1-3. Therefore, it can be seen that when the cristobalite structure contains 0.1 to 10 mol % of alkali metal ions with respect to Si, the amount of SrI ₂ :Eu ²⁺ , which is the phosphor material, can be increased. In Comparative Example 1, alkali metal ions are not contained, and in Comparative Example 3, the amount of Na, which is an alkali metal ion, is as small as 0.005 mol (0.05 mol%). is smaller than ~3.

In Comparative Example 2, SrI ₂ contained in the raw material was not detected in the sample (ND: Not Detectable). In other words, since 1.20 mol (12.0 mol %) of Na, which is an alkali metal ion, is excessively contained, SiO ₂ and Na are vitrified, and a cristobalite structure cannot be formed. It can be confirmed that a certain SrI ₂ :Eu ²⁺ is not incorporated.

(Example 4)
The scintillator material 13 according to Example 4 uses porous silica, has SrI ₂ :Eu ²⁺ , which is a phosphor material, incorporated into the cristobalite structure, and contains Na as alkali metal ions. First, in the porous body forming step, amorphous SiO ₂ and NaI were prepared, precisely weighed so that their molar ratio was 10/0.1, placed in a quartz mortar in a nitrogen gas atmosphere, and ground/mixed. After that, the mixed powder was uniaxially molded in a mold, and the molded body was placed in an inert container such as a platinum crucible and sintered at 700 ° C. for 1 hour in an air atmosphere to obtain a porous body with a diameter of 20 mm and a thickness of 3 mm. .

Next, in the powder preparation step, SrI ₂ , NH ₄ I, EuF ₃ and NaI were prepared as raw materials and refined so that their molar ratios were 0.46:0.08:0.04:0.02. Each raw material was weighed, placed in a quartz mortar in a nitrogen gas atmosphere, and pulverized and mixed to obtain a raw material powder.

After that, in the heat treatment step, the porous body was placed on the raw material powder and fired in a nitrogen atmosphere at 850° C. for 3 hours. After firing, the porous body placed on the raw material powder was taken out and washed with warm pure water to remove free iodide ions, thereby obtaining a scintillator material 13 of Example 4. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, a luminescence amount of 28,500 [photons/Mev] was obtained. Further, when the gamma ray absorption rate was measured by the method described above using the measuring device 30 of FIG. 3, the gamma ray absorption rate _RA was 26.3%.

(Example 5)
The scintillator material 13 according to Example 5 uses porous silica, has SrI ₂ :Eu ²⁺ , which is a phosphor material, incorporated into the cristobalite structure, and contains K as alkali metal ions. First, in the porous body forming step, amorphous SiO ₂ and KI were prepared, precisely weighed so that their molar ratio was 10/0.1, placed in a quartz mortar in a nitrogen gas atmosphere, and ground/mixed. After that, the mixed powder was placed on a quartz plate of φ20 mm and thickness of 2 mm, and heat-treated at 680° C. for 1 hour in an air atmosphere to obtain a porous body having a film thickness of 2 mm on the quartz plate.

Next, in the powder preparation process, SrI ₂ , NH ₄ I, Eu ₂ O ₃ and KBr are prepared as raw materials, and the molar ratio of these is 0.50:0.04:0.015:0.10. The raw materials were precisely weighed, put in a quartz mortar in a nitrogen gas atmosphere, and pulverized and mixed to obtain a raw material powder.

After that, in the heat treatment step, the porous body was placed on the raw material powder and fired in a nitrogen atmosphere at 850° C. for 3 hours. After firing, the porous body placed on the raw material powder was taken out and washed with warm pure water to remove free iodide ions, thereby obtaining a scintillator material 13 of Example 5. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, a luminescence amount of 24,300 [photons/Mev] was obtained. Further, when the gamma ray absorption rate was measured by the method described above using the measuring device 30 of FIG. 3, the gamma ray absorption rate _RA was 24.5%.

(Example 6)
The scintillator material 13 according to Example 6 uses porous silica, has a cristobalite structure in which SrI ₂ :Eu ²⁺ as a phosphor material is incorporated, and contains Cs as alkali metal ions. First, in the porous body forming step, amorphous SiO ₂ and CsI were prepared, precisely weighed so that their molar ratio was 10/0.1, placed in a quartz mortar in a nitrogen gas atmosphere, and ground/mixed. After that, the mixed powder was placed on a borosilicate glass having a diameter of 24 mm and a thickness of 1 mm, and fired at 650° C. for 1 hour in an air atmosphere to obtain a porous body having a film thickness of 0.5 mm on the borosilicate glass.

Next, in the powder preparation step, SrI ₂ , NH ₄ I, EuI ₃ and CsCl were prepared as raw materials and refined so that their molar ratios were 0.40:0.10:0.06:1.80. Each raw material was weighed, placed in a quartz mortar in a nitrogen gas atmosphere, and pulverized and mixed to obtain a raw material powder.

After that, in the heat treatment step, the porous body was placed on the raw material powder and fired in a nitrogen atmosphere at 700° C. for 10 hours. After firing, the porous body placed on the raw material powder was taken out and washed with warm pure water to remove free iodide ions, thereby obtaining a scintillator material 13 of Example 6. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, a luminescence amount of 22,100 [photons/Mev] was obtained. Further, when the gamma ray absorption rate was measured by the method described above using the measuring device 30 of FIG. 3, the gamma ray absorption rate _RA was 21.7%.

(Comparative Example 5)
The scintillator material 13 according to Comparative Example 5 uses a quartz plate having no voids inside and incorporates SrI ₂ :Eu ²⁺ , which is a phosphor material, into the cristobalite structure. SrI ₂ , NH ₄ I, and EuF ₃ were prepared as raw materials and precisely weighed so that their molar ratio was 0.46:0.28:0.04. It was added and pulverized and mixed. After that, a quartz plate was placed on the raw material powder and fired at 1000° C. for 3 hours in a nitrogen atmosphere. After firing, the porous body placed on the raw material powder was taken out and washed with warm pure water to remove free iodide ions, and a scintillator material 13 of Comparative Example 5 was obtained. When luminescence due to gamma ray irradiation was measured with the radiation detection apparatus of FIG. 1, a luminescence amount of 13,000 [photons/Mev] was obtained. Further, when the gamma ray absorption rate was measured by the method described above using the measuring device 30 of FIG. 3, the gamma ray absorption rate _RA was 14.1%.

For Examples 4 to 6 and Comparative Example 5, Table 5 shows the measurement results of the amount of light emitted by gamma ray irradiation using the radiation detection apparatus of FIG. Table 6 shows the measurement results of the gamma ray absorption rate _RA using the measuring apparatus 30 of FIG.

(Analysis results of Examples 4 to 6 and Comparative Example 5)
Next, with respect to the scintillator materials produced in Examples 4 to 6 and Comparative Example 5, the ratio of contained elements was measured using flame atomic absorption spectrophotometry. A fluorescent X-ray device (RIX1000 manufactured by Rigaku Corporation) was used for the measurement. Table 7 shows the measurement results of Examples 4 to 6 and Comparative Example 5. In Table 7, the amount of each element in the scintillator material is shown in mol when the amount of Si element is 10 mol. Therefore, the value obtained by multiplying the numerical value shown in Table 7 by 10 is the mol % with respect to Si.

As shown in Table 7, in Examples 4 to 6, Na, K, and Cs, which are alkali metal ions, are 0.01 mol (0.1 mol %), 0.05 mol (0.5 mol %), and 0.90 mol ( 9.0 mol %). It also contains Sr and I equal to or greater than those of Examples 1-3 shown in Table 4. Therefore, by using a porous body in which voids are distributed from the surface to the inside as the matrix phase silica, it is possible to increase the amount of the phosphor material SrI ₂ :Eu ²⁺ incorporated into the cristobalite structure. Thereby, the radiation absorption rate of the scintillator material 13 can be increased, and the amount of light emitted from the phosphor material can be improved.

The present invention is not limited to the above-described embodiments, but can be modified in various ways within the scope of the claims, and can be obtained by appropriately combining technical means disclosed in different embodiments. is also included in the technical scope of the present invention.

Reference Signs List 10, 20 Radiation detection device 30 Measuring device 11 Container 12 Window member 13, 23 Scintillator material 14, 31 Photomultiplier tube 15 Bleeder circuit 21 Light receiving element 32 Scintillator for detection 33 Evaluation sample 34 ... Shielding sheet 35 ... Radiation source

Claims (10)

A scintillator material that emits visible light when excited by radiation,
Having a cristobalite structure in which a part of silica is crystallized,
SrI ₂ :Eu ²⁺ which is a phosphor material is incorporated into the cristobalite structure to form a nanocomposite,
A scintillator material, wherein the cristobalite structure contains alkali metal ions. The scintillator material according to claim 1,
The scintillator material, wherein the alkali metal ion is Li, Na, K, Rb or Cs. The scintillator material according to claim 1 or 2,
A scintillator material, wherein the alkali metal ion is contained at a ratio of 0.1 to 10 mol % with respect to Si contained in the cristobalite structure. The scintillator material according to any one of claims 1 to 3,
A scintillator material comprising the phosphor material in the form of a single crystal or a polycrystal. The scintillator material according to any one of claims 1 to 4,
A scintillator material, wherein the silica is a porous body in which voids are distributed from the surface to the inside. The scintillator material according to claim 5,
The scintillator material, wherein the porous body is an aggregate of amorphous SiO ₂ particles having an average particle size (D50) of 2 to 50 μm. A scintillator material according to claim 6,
A scintillator material, wherein the _SiO2 particles contain an alkali metal component. The scintillator material according to any one of claims 5 to 7,
The cristobalite structure contains 0.9 to 15 mol% of Sr ions, 2.0 to 40 mol% of I ions, and 0.1 to 5.0 mol% of Eu ions relative to Si contained in the cristobalite structure. scintillator material. a scintillator material according to any one of claims 1 to 8;
1. A radiation detection apparatus comprising a photodetector that detects wavelengths of 400 nm or more and 500 nm or less. a powder preparation step of forming a raw material powder containing SrI ₂ :Eu ²⁺ as a phosphor material and an alkali metal material;
a porous body forming step of forming porous silica in which voids are distributed from the surface to the inside;
A method for producing a scintillator material, comprising: a heat treatment step in which the porous body and the raw material powder are brought into contact with each other and heat-treated.

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