JP7279383B2 - scintillator - Google Patents

Description

The present invention relates to a scintillator that transmits light emitted by phosphors through optical fibers.

Neutron detectors are an elemental technology that supports neutron utilization technology, and are used in security fields such as cargo inspection, academic research fields such as structural analysis by neutron diffraction, non-destructive inspection fields, and medical fields such as boron neutron capture therapy. With the development of neutron utilization technology, higher performance neutron detectors are required.

In addition, neutron detection is being considered to investigate the location of fuel debris in nuclear power plants after a severe accident. However, in a nuclear power plant after a severe accident, the intensity of gamma rays is high and the intensity of neutrons is low. For example, it is required to detect several neutrons/cm ² /sec under a gamma ray environment of several hundred Gy/h.

Techniques that can be used in a gamma ray environment include, for example, Patent Document 1. Patent Document 1 proposes a neutron scintillator in which phosphor is dispersed in a transparent resin, a wavelength shift fiber is passed through the resin, and light is transmitted from the wavelength shift fiber to a waveguide optical fiber. The wavelength-shifting fiber absorbs, for example, near-ultraviolet light from the phosphor, and propagates blue-violet emission shifted to a long wavelength to a PMT (photomultiplier tube). In the waveguide optical fiber, light entering from one side exits from the opposite side. However, with the wavelength shift fiber, the light incident from the side is isotropically re-emitted inside, so part of the emitted light enters the propagation mode and propagates through the wavelength shift fiber and the waveguide optical fiber.

JP 2016-003854 A

Here, the inventors previously applied for a scintillator that transmits light emitted by phosphors through optical fibers (Japanese Patent Application No. 2017-162132). In this scintillator, a transparent sphere containing phosphor particles is formed at the tip of the end face of the optical fiber. According to such a configuration, the emitted light of the phosphor can be collected from the "end surface" of the waveguide optical fiber without using the wavelength shift fiber, so that the wavelength shift fiber eliminates fluorescence generated by γ-rays. Therefore, pile-up due to γ-rays can be suppressed, and the n/γ discrimination ability can be enhanced.

The inventors also disclosed in the previous application that the transparent sphere described above is covered with a reflective material. As a result, it is possible to increase the probability that the light enters the optical fiber by reflecting the light in all directions, which is not going to enter the optical fiber and is about to be dispersed to the outside. However, when the inventors further examined the scintillator, there was a possibility that the signal intensity decreased due to the deterioration of the reflector when the scintillator was irradiated for a long time in a high gamma ray environment.

SUMMARY OF THE INVENTION In view of such problems, it is an object of the present invention to provide a scintillator capable of suppressing deterioration of a reflector in a high gamma ray environment and obtaining a high signal intensity.

In order to solve the above problems, a typical scintillator configuration according to the present invention is a scintillator that detects neutrons in a high gamma ray environment, in which phosphor particles are arranged at the tip of the end face of the optical fiber, and the phosphor A reflective material made of titanium dioxide is arranged around the particles.

By using titanium dioxide as the reflector as in the above configuration, it is possible to suppress deterioration of the reflector in a high gamma ray environment. Therefore, it is possible to obtain high signal strength over a long period of time.

The titanium dioxide is preferably composed of particles coated with aluminum oxide. As a result, deterioration of the reflector can be further suppressed, and the above effects can be enhanced.

A transparent sphere is formed at the end face of the tip of the optical fiber, the phosphor particles are enclosed in the transparent sphere, and at least the outside of the transparent sphere may be covered with a reflective material.

Alternatively, the phosphor particles may be directly adhered to the end surface of the tip of the optical fiber, and the outer periphery of the phosphor particles and the optical fiber may be covered with a reflective material.

ADVANTAGE OF THE INVENTION According to this invention, the scintillator which can suppress the deterioration of the reflecting material in the high gamma-ray environment, and can obtain high signal intensity can be provided.

It is a figure explaining the structure of the scintillator concerning this embodiment. It is a figure explaining the whole structure of a neutron detector. 4 is a graph for explaining the degree of deterioration of reflectance due to reflectors. It is a figure explaining selection of titanium dioxide. FIG. 4 is a diagram for explaining measurement results of peak values of element 1 and element 2; FIG. 10 is a diagram illustrating another configuration of a scintillator;

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in these embodiments are merely examples for facilitating understanding of the invention, and do not limit the invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals to omit redundant description, and elements that are not directly related to the present invention are illustrated or described. omitted.

FIG. 1 is a diagram illustrating the configuration of a scintillator 100 according to this embodiment. In the scintillator 100 shown in FIG. 1, a transparent sphere 104 containing particles of phosphor 102 is formed at the tip of the end face 10a of the optical fiber 10 for waveguide. As a result, phosphor particles are arranged at the tip of the end surface of the tip of the optical fiber 10 .

The optical fiber 10 comprises a core 12 that transmits light, a clad 14 that forms an interface that totally reflects the light passing through the core 12, and a buffer 16 that coats these. The core 12 and the clad 14 are made of silica glass or plastic, and the refractive index of the core 12 is slightly higher than that of the clad 14 . The buffer 16 can be made of polyimide, silicone resin, fluororesin, high-strength fiber, or the like, but any of them does not affect the present invention.

A phosphor that reacts to neutrons is used for the phosphor 102 . The phosphor is preferably a particle made of an inorganic substance that contains a neutron-capturing isotope and emits fluorescence, and that the inorganic substance itself is understood as a chemical substance. Specifically, an inorganic phosphor containing at least one neutron capture isotope selected from lithium 6 and boron 10 can be suitably employed.

The composition of the phosphor 102 is not particularly limited, and a conventionally known inorganic phosphor in the form of particles can be used. Specific examples include Eu: LiCaAlF ₆ , Eu, Na: LiCaAlF ₆ , Eu: LiSrAlF ₆ , Ce: LiCaAlF 6 , Ce, Na: LiCaAlF ₆ , Ce: LiSrAlF ₆ , Ce: LiYF ₄ , _Tb : _LiYF4 , Eu:LiI, _Ce : _Li6Gd ( _BO3 ) _{3 ,} Ce:LiCs2YCl6 _{, Ce} :LiCs2YBr6 _, Ce:LiCs2LaCl6 _{, Ce} :LiCs2LaBr6 _, Ce: _{LiCs2CeCl6 . _ _ _ _ _ _ _}

Further, for the phosphor 102, a converter that reacts to neutrons and a phosphor that does not react to neutrons may be used in combination. As a specific example of the converter, an inorganic substance containing at least one neutron-capturing isotope selected from lithium 6 and boron 10 is preferred, and LiF is particularly preferred. As the phosphor that does not react to neutrons, conventionally known phosphors can be used without particular limitation, and more specifically, Ag:ZnS, Eu:CaF ₂ and the like can be preferably used. That is, LiF—Eu:CaF ₂ can be suitably used for the phosphor 102 .

The transparent sphere 104 is a mass made of transparent resin or glass. Although it is called a "sphere", it does not have to be a geometrically strict sphere, and may have slight distortions or depressions, or may be spindle-shaped or waterdrop-shaped. The transparent sphere 104 is formed at the tip end face 10 a of the optical fiber 10 . The tip of the optical fiber 10 may be buried in the transparent sphere 104, but it is preferable that the end surface 10a does not reach the center of the transparent sphere 104. FIG. That is, it is preferable that the length of the optical fiber 10 embedded in the transparent sphere 104 is equal to or shorter than the radius of the substantially spherical transparent sphere 104 .

Also, the refractive index nL of the transparent sphere 104 is preferably smaller than the refractive index nQ of the core 12 . As a result, the light incident on the end face 10a from the transparent sphere 104 is refracted in the axial direction of the fiber, so that the light can be easily contained within the total reflection angle.

A feature of the scintillator 100 of this embodiment is that the transparent spheres 104 are covered with a reflective material 106 . The reflector 106 is a film that transmits neutrons but reflects light. As a specific example of the reflector 106, a reflector formed by applying a titanium dioxide white pigment can be used. As a result, a reflector made of titanium dioxide is arranged around the particles of the phosphor 102 .

An example of the optical path is indicated by an arrow in FIG. When neutrons collide with phosphor 102 , light is emitted in all directions from phosphor 102 . Some of the light directly enters the end face 10a from the phosphor 102, but part of it collides with the reflector 106 as indicated by the arrow. The light is diffusely reflected by the reflector 106, and part of it enters the end surface 10a as indicated by the arrow. This can increase the number of photons that can be transmitted.

According to the above configuration, the light emitted from the phosphor 102 can be collected from the "end surface 10a" of the waveguide optical fiber 10 without using a wavelength shifting fiber. Since no wavelength-shifting fiber is used, fluorescence generated by γ-rays in the wavelength-shifting fiber can be eliminated, pile-up due to γ-rays can be suppressed, and n/γ discrimination performance can be improved.

FIG. 2 is a diagram illustrating the overall configuration of the neutron detector 200. As shown in FIG. For testing, a neutron source 20 using Cf-252 and a γ-ray source 22 using Co-60 are used. The neutron detector 200 has the scintillator 100 attached to the tip of the optical fiber 10 and guides fluorescence to the photomultiplier tube 210 . The photomultiplier tube 210 converted the light into an electric signal, and the pulse height analyzer 230 obtained the pulse height value and the count value to evaluate the neutron sensitivity.

As the phosphor 102, LiF, which is a converter that reacts to neutrons, and Eu: _CaF2, which is a phosphor that does not react to neutrons, are used in combination. The phosphor is a material called a eutectic having a multi-layer structure in which a crystal layer of LiF and a crystal phase of Eu:CaF ₂ are laminated on the order of μm. Hereinafter, the phosphor will be referred to as LiF—Eu:CaF ₂ . A transparent sphere 104 was fabricated using LiF—Eu:CaF ₂ and a silicone resin having a refractive index of 1.41.

First, a small amount of a silicone resin precursor (liquid) was applied to the tip of the fiber, and the silicone resin was cured by heating. Next, LiF—Eu:CaF ₂ was attached around the silicone resin, and a small amount of a silicone resin precursor was applied and cured by heating. The operation was repeated until finally a transparent sphere encapsulating 0.5 mg of LiF—Eu:CaF2 was formed. Also, the size of the transparent sphere 104 was adjusted to be about 2 mm. According to this manufacturing method, the amount of phosphor particles contained in the transparent spheres can be arbitrarily adjusted, and a scintillator having desired characteristics can be manufactured with good reproducibility. As the reflector 106, a diffuse reflector formed by applying titanium dioxide was used.

By using titanium dioxide as the reflector 106 as in the present embodiment, deterioration of the reflector 106 in a high gamma ray environment can be suppressed. Therefore, it is possible to obtain high signal strength in the scintillator 100 .

FIG. 3 is a graph for explaining the degree of reflectance deterioration due to the reflector 106, in which the vertical axis represents the reflectance under a high gamma ray environment (10 kGy) and the horizontal axis represents the wavelength of light. As the reflecting material, titanium dioxide was used in the examples, and aluminum oxide, barium fluoride, barium sulfate, lanthanum fluoride, and magnesium oxide were used in the comparative examples.

As shown in FIG. 3, it can be understood that by using titanium dioxide as a reflector, high reflectance can be obtained in the wavelength region of 430 nm, which is the emission wavelength of LiF—Eu:CaF2. At this time, the titanium dioxide of the example hardly deteriorates as compared with each reflector of the comparative example. Therefore, according to the scintillator 100 of the present embodiment, deterioration of the reflector 106 can be suppressed in a high gamma ray environment, and high signal intensity can be obtained.

FIG. 4 is a diagram explaining the selection of titanium dioxide. Of the two types of titanium dioxide shown in FIG. 4, the titanium dioxide commercially available as paint consists of particles coated with aluminum oxide on the surface, and the overall titanium dioxide purity is around 95%. On the other hand, the reagent titanium dioxide is not surface-treated and has a purity of 99.99%.

As shown in FIG. 4, element 1 was fabricated using uncoated titanium dioxide, and element 2 was fabricated using aluminum oxide-coated titanium dioxide, and the crest values thereof were measured. When the crest value of each of the element 1 and the element 2 was measured, the crest value of the element 1 not coated with aluminum oxide was higher.

FIG. 5 is a diagram for explaining the measurement results of the crest values of the element 1 and the element 2. FIG. FIG. 5(a) is a diagram showing the measurement results of the initial peak values of the element 1 and the element 2, and FIG. Fig. 3 shows the relative signal strength of . As shown in FIG. 5A, the element 1 has a higher peak value than the element 2 at the initial peak value. On the other hand, as shown in FIG. 5B, the element 2 deteriorates less than the element 1 in terms of relative signal strength over time. That is, the element 2 is less likely to deteriorate over time than the element 1.

From this, it can be seen that in the case of a scintillator to be used for a long period of time, it is preferable to use titanium dioxide coated with aluminum oxide, as in element 2, as a reflective material. On the other hand, in the case of a scintillator for short-term or medium-term use, it is preferable to use high-purity titanium dioxide as the reflector, as in the element 1, because it is not necessary to consider deterioration over time.

FIG. 6 is a diagram explaining another configuration of the scintillator according to the present invention. In the scintillator 100A shown in FIG. 6, the particles of the phosphor 102 are directly adhered to the end face of the tip of the optical fiber 10. In the scintillator 100A shown in FIG. The particles of the phosphor 102 and the outer periphery of the optical fiber 10 are covered with a reflective material 106 .

The number of particles of the phosphor 102 can be appropriately set according to the relationship between the diameter of the particles and the diameter of the optical fiber 10, and can be set to 1 to 10, for example. The adhesive may be any transparent material, and the same adhesive as that constituting the transparent sphere 104 can be used. As a specific example, a transparent resin such as silicone or glass can be used.

The configuration of FIG. 6 has the advantage that the tip can be made thinner than the case where the transparent sphere 104 shown in FIG. 1 is used. In addition, since the tip end is not thicker than the optical fiber 10, when a large number of optical fibers 10 are bundled, they can be easily accommodated and easily handled. On the other hand, when using the transparent sphere 104, the amount of the phosphor 102 can be increased, so there is an advantage that the sensitivity can be improved.

Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such examples. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope described in the claims, and these also belong to the technical scope of the present invention. Understood.

INDUSTRIAL APPLICABILITY The present invention can be used as a scintillator that transmits light emitted by phosphors through optical fibers.

DESCRIPTION OF SYMBOLS 10... Optical fiber, 10a... End face, 12... Core, 14... Clad, 16... Buffer, 20... Neutron beam source, 22... γ-ray source, 100, 100A... Scintillator, 102... Phosphor, 104... Transparent sphere, 106 ... reflector, 200 ... neutron detector, 210 ... photomultiplier tube, 230 ... pulse height analyzer

Claims (2)

In a scintillator that detects neutrons in a high gamma ray environment,
A transparent sphere is formed at the tip of the optical fiber,
encapsulating a plurality of phosphor particles near the surface of the transparent sphere;
A scintillator , wherein the surface of the transparent sphere is coated with a reflective material made of titanium dioxide . 2. The scintillator of claim 1, wherein said titanium dioxide comprises particles coated with aluminum oxide.

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