JP5904538B2 - Scintillator material and X-ray detector - Google Patents

Description

The present invention relates to scintillator materials and X-ray detectors.

  In recent years, X-ray detectors are used in various industries. An X-ray detector is a device that irradiates a measurement object with X-rays and sees through the measurement object or takes a tomographic image of the measurement object. It is applied as an X-ray foreign object detector, non-destructive inspection, X-ray CT (CT: Computed Tomography) apparatus and the like.

The X-ray foreign matter detector is a device that irradiates a measurement object with X-rays and detects foreign matters such as metal pieces, glass pieces, stone pieces and the like in the measurement object. X-ray CT is a device that images an object with X-rays from various angles and visualizes the internal structure of the object by performing reconstruction processing on a computer. In the X-ray foreign object detector and X-ray CT, a scintillator made of a material having a function of converting radiation such as X-rays into light is arranged. After the radiation transmitted through the measurement object is converted into light with the scintillator, The amount of transmitted radiation and the like are calculated by detecting light intensity and the like with a photodiode.

CdWO ₄ (CWO) is used as a scintillator material for the X-ray detector. This is because this material emits blue-green light by X-ray excitation, has a high light emission amount, is chemically stable, has excellent workability, and has little afterglow. However, harmful Cd is contained. Therefore, the development of safe alternative substances has been desired.

Examples of scintillator materials for positron emission tomography (PET) include Bi ₄ Ge ₃ O ₁₂ (BGO), Ce: Lu ₂ SiO ₅ (LSO), and Ce: (Lu _1-x Y _x ) ₂ SiO _5. (LYSO), Ce: (Lu _1-x Gd _x ) ₂ SiO ₅ (LGSO) is known (see, for example, Patent Documents 1 to 3, and Non-Patent Documents 1 to 5). BGO is a scintillator that has been used for a long time. However, since the amount of emitted light is small, LSO, LYSO, and LGSO are currently replaced by this market. However, since these materials contain Lu containing a radioisotope, the afterglow characteristics are not good and cannot be used as a substitute for CWO.

  Thus, there was no suitable scintillator material that could be a safe alternative to CWO.

JP 2007-16197 A JP-T-2004-532997 US Patent Publication US2006 / 0124854A1

M.M. D. Bioshooto et al., J. Biol. Of App. Phys. Vol. 99, 123520 (2006) Regarding BGO: Nuclear Instruments and Methods in Physics Research A 404 (1998) 413-417. Regarding LSO: Nuclear Instruments and Methods in Physics Research A 546 (2005) 33-36. Regarding LYSO: Nuclear Instruments and Methods in Physics Research A 564 (2006) 506-514. Regarding LGSO: Nuclear Instruments and Methods in Physics Research A 597 (2008) 238-241.

It is an object of the present invention to provide a high quantum efficiency scintillator material and X-ray detector that can be a safe substitute for CWO.

In view of the above circumstances, the present inventor succeeded in producing a fluoride single crystal containing a rare earth element and a Group 2 element by trial and error, and completed this research.
The present invention has the following configuration.

(1) a formula _{M 1-x RE x F 2} + x-w represented by the fluoride single crystal, M in Formula is Be, Mg, Ca, Sr, 1 or 2 or more selected from the group of Ba A scintillator material which is a Group 2 metal element, RE is a rare earth element, 0 <x ≦ 0.4, and 0 ≦ w ≦ 0.5.

(2) The scintillator material according to (1), wherein M is Ba and RE is Eu.
(3) The scintillator material according to (1) or (2), wherein 0.05 ≦ x ≦ 0.3.
(4) One or two or more of M is selected from the group consisting of Group 3 metal elements, Group 4 metal elements, Group 5 metal elements, Group 13 metal elements, and Group 14 metal elements The scintillator material according to any one of (1) to (3), wherein the scintillator material is substituted with an element.

(5) A scintillator material according to any one of (1) to (4), wherein a part of RE is any one or more elements selected from the group of Sc, Y and rare earth elements .
(6) The scintillator material according to any one of (1) to (5), wherein a part of F is any one or more elements selected from the group of Cl, Br, and I.
(7) The scintillator material according to any one of (1) to (6), wherein the scintillator material has any one of a plate shape, a cubic shape, a linear shape, and a cylindrical shape.

(8) An X-ray detector comprising the scintillator material according to any one of (1) to (7) and a photodiode.

The scintillator material of the present invention comprises a fluoride single crystal represented by the chemical formula M _1-x RE _x F _{2 + x-w} , wherein M is selected from the group consisting of Be, Mg, Ca, Sr, and Ba. Or a group 2 or more group 2 metal element, RE is a rare earth element, 0 <x ≦ 0.4, and 0 ≦ w ≦ 0.5. And afterglow can be reduced. Thus, it can be used as a scintillator material for an X-ray detector that can be a safe substitute for CWO.

Moreover, since the X-ray detector of the present invention has the scintillator material of the present invention and a photodiode, it is a photodiode having a high absorbance of red light, and the scintillator emits light with high brightness by X-ray excitation. Light can be received efficiently and X-ray detection efficiency can be increased.

It is a photograph which shows Example 1 sample. It is a graph which shows the transmission spectrum of Example 1 sample. It is a graph which shows the emission spectrum of UV light excitation of Example 1 sample and Comparative Example 3 sample. It is a graph which shows the emission spectrum of the X-ray excitation of Example 1 sample. It is a graph which shows the quantum efficiency and reflectance of Si photodiode.

(Embodiment of the present invention)
Hereinafter, a scintillator material and an X-ray detector which are embodiments of the present invention will be described with reference to the accompanying drawings.

<Scintillator materials>
Scintillator material which is an embodiment of the invention, a formula _{M 1-x RE x F 2} + x-w represented by the fluoride single crystal, M is selected Be, Mg, Ca, Sr, from the group of Ba One or two or more Group 2 metal elements, RE is a rare earth element, 0 <x ≦ 0.4, and 0 ≦ w ≦ 0.5.

It is preferable that M is Ba and RE is Eu. Thereby, it can be set as the material which emits red light efficiently by X-ray excitation, and shows a scintillation characteristic.

Part of M is replaced with one or more elements selected from the group consisting of Group 3 metal elements, Group 4 metal elements, Group 5 metal elements, Group 13 metal elements, and Group 14 metal elements May be.
Further, a part of RE may be any one or more elements selected from the group of Sc, Y and rare earth elements.
Furthermore, a part of F may be any one or two or more elements selected from the group of Cl, Br, and I.
Even with these configurations, red light can be emitted with high quantum efficiency, and a single crystal with a large diameter can be generated.

The scintillator material is preferably in the shape of a plate, a cube, a line, or a column. Thereby, mounting to various apparatuses can be facilitated.

<Method for producing scintillator material>
The scintillator material according to the embodiment of the present invention can be grown by a melt solidification method, for example, as follows.
First, a predetermined material is weighed at a predetermined molar ratio.
Next, the weighed materials are mixed in a crucible, evacuated with a vacuum pump, then in a CF ₄ (> 99.99%) atmosphere, gradually dissolved, and then gradually cooled.
Through the above steps, it is possible to produce a formula _{M 1-x RE x F 2} + x-w scintillator material comprising a single crystal of fluoride which is represented by an embodiment of the present invention.

Further, it can be grown by the Czochralski (hereinafter, Cz) method, for example, as follows.
First, a predetermined material is weighed at a predetermined molar ratio, mixed in a crucible, and evacuated with a vacuum pump. After that, a CF ₄ (> 99.99%) atmosphere is gradually dissolved and gradually dissolved. Cooling to form a substantially disc-shaped single crystal.
Next, a rod-shaped seed crystal is cut out from the single crystal.

Next, after measuring a predetermined material at a predetermined molar ratio and mixing it in the crucible in the same manner as described above, the crucible is placed in the chamber, and then the vacuum in the chamber is made high vacuum to efficiently reduce the oxygen in the chamber. Then, the atmosphere is CF ₄ (> 99.99%).
Next, the crucible is heated by the high frequency coil connected to the high frequency oscillator (30 kW), and the mixed material is slowly melted in the crucible.

Next, the rod-shaped seed crystal is brought into contact with the solution in the crucible from one end side, and then rotated around the central axis of the rod while being pulled up in the direction of the other end of the rod. A single crystal is grown. For example, the rotation speed is 1 to 50 rpm, and the pulling speed is 0.1 to 10 mm / h.
Thereby, a single crystal can be formed around the rod from one end side of the rod.

Next, the single crystal is cut into a predetermined shape. For example, a substantially cylindrical shape is used.
Next, a predetermined surface of the single crystal having a substantially cylindrical shape is polished by a predetermined method.
Through the above steps, it is possible to produce a formula _{M 1-x RE x F 2} + x-w scintillator material comprising a single crystal of fluoride which is represented by an embodiment of the present invention.

The single crystal can also be manufactured using a Bridgman method.
Crystal growth by the Bridgman method is, for example, as follows.
A predetermined material is weighed in a predetermined molar ratio in the crucible and stirred in the crucible, and then the crucible is placed in the chamber.
Thereafter, moisture is efficiently removed by making a high vacuum with a vacuum pump, and a resistance heating type heating source disposed around the crucible is energized while the high vacuum is maintained, thereby melting the material in the crucible. The heating source has a temperature gradient in which the upper side is higher than the melting point of the material and the lower side is lower than the melting point of the material.
After the material is dissolved, the crucible is moved from above the temperature higher than the melting point to below the temperature lower than the melting point. At this time, the solution having a melting point or a temperature lower than that becomes a single crystal, and the single crystal can be continuously grown by performing this continuously.

It is preferable to manufacture the scintillator material according to the embodiment of the present invention by the melt solidification method, the Cz method, or the Bridgman method. This is because a single crystal having easy and stable characteristics can be obtained.
In addition, since single crystals grown by these manufacturing methods have high stability and no phase transition, large single crystallization can be achieved because cracks during the cutting of the single crystal can be sufficiently suppressed, and generation of the second phase can also be suppressed. Is possible. In addition, the single crystal can be grown at a relatively low temperature, and the manufacturing cost can be reduced.

However, the production method is not limited to these methods, and the floating zone method (FZ: floating zone method), the micro pulling down method (μ-PD method: μ-Pulling Down method), the zone melting method (Zone melting method) Etc. may be used.

<X-ray detector>
An X-ray detector according to an embodiment of the present invention includes a scintillator material according to an embodiment of the present invention, and a photodiode. Thereby, it is possible to provide a highly sensitive X-ray detector having a scintillator material capable of emitting high-luminance red light by X-ray excitation and a photodiode that efficiently absorbs the red wavelength region.

Scintillator material is an embodiment of the present invention consists of the formula _{M 1-x RE x F 2} + x-w represented by the fluoride single crystal, M in Formula is Be, Mg, Ca, Sr, from the group of Ba One or more selected Group 2 metal elements, RE is a rare earth element, 0 <x ≦ 0.4, and 0 ≦ w ≦ 0.5. It can be used as a scintillator material for an X-ray detector that emits light with high quantum efficiency in the wavelength region of red light to near-infrared light by X-ray excitation, and high-sensitivity detection of X-rays becomes possible. Furthermore, since the single crystal body has high stability and no phase transition, cracks at the time of cutting out the single crystal body can be sufficiently suppressed, and generation of the second phase can be suppressed, so that a large single crystal can be formed. It has a high light emission amount, does not contain radioactive isotopes, and can reduce the afterglow. Thus, it can be used as a scintillator material for an X-ray detector that can be a safe substitute for CWO.

  Since the scintillator material according to the embodiment of the present invention has a structure in which M is Ba and RE is Eu, it can emit light with high quantum efficiency in the wavelength region of red light to near infrared light by X-ray excitation. .

  Since the scintillator material according to the embodiment of the present invention has a configuration of 0.05 ≦ x ≦ 0.3, it can emit light with high quantum efficiency in the wavelength region of red light to near infrared light by X-ray excitation. .

  In the scintillator material according to the embodiment of the present invention, a part of M is selected from the group consisting of Group 3 metal elements, Group 4 metal elements, Group 5 metal elements, Group 13 metal elements, and Group 14 metal elements. Therefore, cracks can be sufficiently suppressed, and generation of the second phase can also be suppressed, so that large-scale single crystallization can be achieved.

  Since the scintillator material according to the embodiment of the present invention has a configuration in which a part of RE is any one or more elements selected from the group of Sc, Y, and rare earth elements, cracks can be sufficiently suppressed. Since the generation of phases can be suppressed, large single crystallization is possible.

  Since the scintillator material according to the embodiment of the present invention has a configuration in which a part of F is one or more elements selected from the group of Cl, Br, and I, the second phase can be sufficiently suppressed. Therefore, large single crystallization is possible.

  Since the scintillator material according to the embodiment of the present invention has a plate shape, a cubic shape, a linear shape, or a cylindrical shape, it can be easily mounted on an X-ray detector.

  Since the X-ray detector according to the embodiment of the present invention has the scintillator material described above and a photodiode, the scintillator material that emits light in the wavelength region of red light to near infrared light, and red to near By combining a Si photodiode with high infrared light sensitivity, an X-ray detector with high detection efficiency can be obtained.

The scintillator material and the X-ray detector which are embodiments of the present invention are not limited to the above-described embodiments, and can be implemented with various modifications within the scope of the technical idea of the present invention. Specific examples of this embodiment are shown in the following examples. However, the present invention is not limited to these examples.

<Example 1 and Comparative Examples 1 to 3 Sample Preparation>
(Example 1)
First, BaF ₂ (shape: powder, purity: 99.99% or more) and EuF ₃ (shape: powder, purity: 99.99% or more) were prepared as raw materials.

Next, BaF ₂ and EuF ₃ were weighed. At this time, BaF ₂ : EuF ₃ (molar ratio) was set to 87.5: 12.5.
Next, the weighed BaF ₂ and EuF ₃ were mixed in a crucible, evacuated with a vacuum pump, then made into a CF ₄ (> 99.99%) atmosphere, gradually dissolved, and then gradually cooled. Then, a disk-like single crystal (Example 1 sample) was produced by the melt solidification method.
FIG. 1 is a photograph showing a sample of Example 1.
As shown in FIG. 1, the diameter of the single crystal of the sample of Example 1 was 4 cm. The thickness was 0.5 cm.

When the powder X-ray diffraction measurement of the sample of Example 1 was performed, it was identified as being single phase and represented by Ba _0.875 Eu _0.125 F _2.125 (charge composition). Hereinafter, this may be simply referred to as BaEuF. It was also confirmed that there was no residual BaF ₂ and EuF ₃ .

Next, a sample having a size of 1.5 × 1.5 × 4.5 mm ³ was cut out from the obtained single crystal.
Next, the entire surface of the cut sample was mirror-polished to obtain Example 1 sample for property evaluation.

(Comparative Examples 1-3)
A conventional scintillator material BGO (Comparative Example 1 sample), PET scintillator material LGSO (Comparative Example 2 sample), and LYSO (Comparative Example 3 sample) were prepared. After a sample having a size of 1.5 × 4.5 mm ³ was cut out, the entire surface of the cut out sample was mirror-polished to obtain Comparative Examples 1 to 3 samples for characteristic evaluation, respectively.

<Characteristic evaluation of Example 1 and Comparative Examples 1-3>
Next, the transmission spectrum of the sample of Example 1 was measured.
FIG. 2 is a graph showing a transmission spectrum of the sample of Example 1.
The transmittance was about 90% in the wavelength region of 400 to 1800 nm. The transmittance of light from visible light to near infrared region was high.

Next, the emission spectrum of UV light excitation of the samples of Example 1 and Comparative Example 3 (excitation wavelengths were Example 1: 391 nm and Comparative Example 3: 358 nm) was measured.
FIG. 3 is an emission spectrum of the sample of Example 1 and Comparative Example 3.
LYSO (Comparative Example 3 sample) showed blue to purple emission having an emission peak wavelength of 410 nm, whereas Example 1 sample had a first emission peak wavelength around 700 nm and a second emission around 590 nm. Red light was emitted having a peak wavelength, a third emission peak wavelength near 690 nm, a fourth emission peak wavelength near 620 nm, and a fifth emission peak wavelength near 645 nm.

Next, the emission spectrum of the X-ray excitation of the sample of Example 1 was measured. Cu was used as a target, and the condition was 100 mA.
FIG. 4 is a graph showing an emission spectrum of X-ray excitation of the sample of Example 1.
Ba _0.875 Eu _0.125 F _2.125 (Example 1 sample) is a first emission peak wavelength near 595 nm, a second emission peak wavelength near 702 nm, a third emission peak wavelength near 624 nm, It showed red emission having a fourth emission peak wavelength near 694 nm and a fifth emission peak wavelength near 655 nm.

Next, each of the samples of Example 1 and Comparative Examples 1 to 3 was irradiated with a predetermined excitation wavelength shown in Table 3, and the ratio of the obtained light intensity of the emitted light to the light intensity of the irradiated excitation light Quantum efficiency was calculated.
The quantum efficiency of the sample of Example 1 and Comparative Examples 1 to 3 was as shown in Table 1. The quantum efficiency of the sample of Example 1 (BaEuF) was 0.943, which was the best.

FIG. 5 is a graph showing an example of quantum efficiency and reflectance of a Si photodiode.
The reflectance of about 42% at a wavelength of 350 nm decreased as the wavelength increased, and the reflectance was almost 0% at 610 nm. When the wavelength was further increased, the reflectance increased and the reflectance was about 18% at 1100 nm.
The quantum efficiency is about 50% at a wavelength of 350 nm, and increases as the wavelength increases, and reaches about 95% at 640 nm. When the wavelength was further increased, it decreased and became about 5% at 1100 nm.

Therefore, as shown in FIGS. 3 and 4, the sample of Example 1 (BaEuF) emits light in the wavelength region of 580 nm to 710 nm where the reflectance of the Si photodiode is almost 0% and the quantum efficiency is 90% or more. Therefore, by combining the sample 1 sample (BaEuF) and the Si photodiode, the light emitted from the sample 1 sample (BaEuF) can be converted into electricity with high efficiency by the Si photodiode, and high sensitivity X-rays can be obtained. It can be a detector.

The scintillator material of the present invention is a safe substitute for CWO, which is a scintillator for X-ray detectors, and can be applied to X-ray foreign matter detectors and X-ray detectors such as X-ray CT and can be used in the radiation technology industry. There is.

Claims (4)

Consists formula _{M 1-x RE x F 2} + x-w represented by the fluoride single crystal, in Formula, wherein M is Ba, the RE is Eu, with 0.05 <x ≦ 0.3 A scintillator material, wherein 0 ≦ w ≦ 0.5, which is excited by X-rays and emits red light. Consists formula _{M 1-x RE x F 2} + x-w represented by the fluoride single crystal, in Formula, wherein M is, Ba and third group metal element, a Group 4 metal element, a Group 5 metal elements Any one or more elements selected from the group consisting of Group 13 metal elements and Group 14 metal elements, wherein RE is Eu, 0.05 < x ≦ 0.3, 0 A scintillator material that is ≦ w ≦ 0.5 and is excited by X-rays to emit red light.   The red emission includes a first emission peak wavelength of 595 nm, a second emission peak wavelength of 702 nm, a third emission peak wavelength of 624 nm, a fourth emission peak wavelength of 694 nm, and a fifth emission peak wavelength of 655 nm. The scintillator material according to claim 1, comprising: The scintillator material according to any one of claims 1 to 3, wherein the scintillator material has a plate shape, a cubic shape, a linear shape, or a cylindrical shape.