JP2018132314A - Neutron scintillator, neutron detector, and neutron detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutron scintillator, neutron detector, and neutron detection method capable of accurately measuring neutrons even in a field with a high dose of a gamma-ray to be background noise.SOLUTION: A neutron scintillator includes as components: a resin composition including inorganic phosphor particles containing at least one kind of neutron capture isotope to be selected from lithium 6 and boron 10; and wavelength conversion fibers at least a part of which is enclosed in the resin composition. The resin composition includes: a first cylindrical area for enclosing an outer periphery of the wavelength conversion fiber; and a second area positioned on an outer side of the first area. A density of the inorganic phosphor particles in the first area is lower than a density of the inorganic phosphor particles in the second area.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a neutron scintillator, a neutron detector, and a neutron detection method.

  Recently, neutron detectors using neutron scintillators are being developed. A neutron scintillator is a substance that emits fluorescence by the action of the neutron when it is incident. A neutron scintillator can be used as a neutron detector by combining a photodetector such as a photomultiplier tube.

  Although a neutron detector using a neutron scintillator has the advantage of high detection efficiency for neutrons, it is sensitive to γ rays and has a problem of low n / γ discrimination. Neutron detection efficiency is the ratio of the number of neutrons counted by the detector to the number of neutrons incident on the detector. When the detection efficiency is low, the absolute number of neutrons to be measured decreases, and the measurement accuracy Decreases. In addition, γ-rays exist as natural radiation, and are also generated when a neutron hits a component of a detection system for detecting neutrons or an object to be inspected, so the n / γ discrimination ability is low, If γ rays are counted as neutrons, the accuracy of neutron counting decreases.

  In Patent Document 1, a wavelength conversion fiber is encapsulated in a resin composition portion, and the wavelength conversion fiber is disposed at a specific position with respect to the outer wall surface of the resin composition portion, thereby improving n / γ discrimination ability. A scintillator is disclosed.

JP-A-2006-3854

In decommissioning work at the Fukushima Daiichi NPS, it is necessary to know the location of fuel debris that has accumulated in the reactor containment vessel. When investigating the internal space of the reactor containment vessel, since a worker cannot enter the reactor containment vessel where fuel debris has accumulated, a remotely operable investigation device is used. A neutron scintillator is attached to such an investigation device, and the position of the fuel debris is grasped based on the detection result of neutrons by the neutron scintillator. However, gamma ray count around the fuel debris predominance against neutrons (e.g. 10 ⁸ times). Therefore, in order to accurately grasp the position of the fuel debris, development of a neutron scintillator with further improved n / γ discrimination ability is required.

  The present invention has been made in view of the above-described problems, and a neutron scintillator, a neutron detector, and a neutron detection method capable of accurately measuring neutrons even in a field with a high dose of γ-rays serving as background noise The purpose is to provide.

  The neutron scintillator of the present invention includes a resin composition part including inorganic phosphor particles containing at least one neutron capture isotope selected from lithium 6 and boron 10, and at least a part of the resin composition part being encapsulated in the resin composition part. A neutron scintillator having a wavelength conversion fiber as a constituent element, wherein the resin composition portion includes a cylindrical first region including an outer periphery of the wavelength conversion fiber, and a first region located outside the first region. And the density of the inorganic phosphor particles in the first region is lower than the density of the inorganic phosphor particles in the second region.

  According to this structure, it has the inorganic fluorescent substance particle containing a neutron capture isotope in the resin composition part which covers a wavelength conversion fiber. When neutrons are incident on the neutron capture isotope, secondary particles (α rays and tritium or α rays and lithium 7) jump out. In addition, gamma rays eject orbital electrons of atoms in the material as secondary electrons. Since secondary particles resulting from the incidence of neutrons have a short range, most of the secondary particles consume energy in the inorganic phosphor particles and generate light having a substantially constant peak value. On the other hand, secondary electrons caused by the incidence of γ rays have a long range. By making the inorganic phosphor into a particulate form, secondary electrons quickly deviate from the inorganic phosphor particles, and the energy imparted to the inorganic phosphor decreases. That is, the peak value of light emission accompanying γ-ray incidence can be reduced. Therefore, it can be determined from the peak value that the light is caused by the incidence of neutrons, and the n / γ discrimination ability can be enhanced.

  In addition, according to this configuration, the inorganic phosphor particles in the vicinity of the wavelength conversion fiber are reduced by reducing the density (that is, the content per unit volume) of the inorganic phosphor particles in the vicinity (first region) of the wavelength conversion fiber. Can reduce light emission caused by γ-rays irradiated from. The peak value of the light reaching the wavelength conversion fiber depends on the distance from the emitted inorganic phosphor particles. Therefore, by reducing the light emission from the vicinity of the wavelength conversion fiber, it is possible to reduce the component having a large peak value in the light detected due to the γ rays. As described above, this neutron scintillator reduces the crest value of light caused by γ rays, and distinguishes light caused by neutrons from light caused by γ rays by the difference in crest values. By reducing the light caused by γ rays from the vicinity of the wavelength conversion fiber, it shows a high peak value among the light caused by γ rays and emits light in the region close to the peak value of light caused by neutrons. Can be suppressed, and the n / γ discrimination ability can be enhanced. Note that, by reducing the density of the inorganic phosphor particles in the vicinity of the wavelength conversion fiber, the peak value of light caused by neutrons irradiated from the inorganic phosphor particles in the vicinity of the wavelength conversion fiber is also reduced. However, the peak value of light caused by neutrons shows a specific peak value. For this reason, the effect of lowering the density of the inorganic phosphor particles in the vicinity of the wavelength conversion fiber extends to a region where the peak value is slightly higher than the peak value, and the effect on the peak value is small. Therefore, even when the density of the inorganic phosphor particles in the vicinity of the wavelength conversion fiber is lowered, sufficient neutron detection efficiency can be obtained.

  In the neutron scintillator, the first region of the resin composition part may not include the inorganic phosphor particles.

  According to this configuration, since the inorganic phosphor particles are not included in the vicinity of the wavelength conversion fiber, the above-described effects can be made more remarkable and the n / γ discrimination ability can be further enhanced.

  Said neutron scintillator WHEREIN: It is good also as a structure which has ratio of the distance of the center axis | shaft of a wavelength conversion fiber and the outer wall surface of a resin composition part with respect to the diameter of the said wavelength conversion fiber in the range of 1-10.

  In the neutron scintillator, the ratio of the refractive index of the inorganic phosphor particles to the refractive index of the resin may be in the range of 0.95 to 1.05 at the emission wavelength of the inorganic phosphor particles.

  According to this configuration, by setting the ratio of the refractive index of the transparent resin within such a range, light scattering at the interface between the inorganic phosphor particles and the resin can be suppressed, and the transparency of the resin composition portion is improved. Can do. As a result, it becomes possible to detect the light emission of the inorganic phosphor particles with high efficiency, and to improve the detection efficiency of neutrons.

  In the neutron scintillator described above, a neutron detector comprising the neutron scintillator and a photodetector.

  According to this configuration, a neutron detector with high n / γ discrimination capability can be provided.

  Further, the neutron detector as one embodiment of the present invention includes a resin composition part containing inorganic phosphor particles containing a neutron capture isotope, and a wavelength conversion fiber at least partially encapsulated in the resin composition part. And a neutron scintillator having a component, a photodetector for detecting light emitted from the neutron scintillator, and a determination unit for determining the presence or absence of neutron beams, the determination unit in the photodetector The logarithm of the detection frequency with respect to the detected peak value of the light is approximated to a linear function, and when the detection frequency of the peak value in the vicinity of 4.8 MeV or 2.3 MeV deviates from the linear function, judge.

  According to this configuration, it is possible to provide a neutron detector that can easily determine the presence of neutrons when deviating from a linear function approximated based on the detection result.

  Further, the method for detecting neutrons according to one embodiment of the present invention includes a resin composition part including inorganic phosphor particles containing a neutron capture isotope, and wavelength conversion in which at least a part is included in the resin composition part. Using a neutron scintillator comprising a fiber as a component and a photodetector for detecting light emitted from the neutron scintillator, the logarithm of the detection frequency with respect to the peak value of the light detected by the photodetector Is approximated to a linear function, and the presence of a neutron beam is determined when the detection frequency of the peak value near 4.8 MeV or 2.3 MeV deviates from the linear function.

  According to this configuration, the presence of neutrons can be easily determined when deviating from a linear function approximated based on the detection result.

  According to the present invention, it is possible to provide a neutron scintillator, a neutron detector, and a neutron detection method capable of accurately measuring neutrons even in a field where the dose of γ rays that become background noise is high.

It is a cross-sectional schematic diagram of the neutron scintillator of one Embodiment. 1 is a schematic longitudinal sectional view of a neutron scintillator according to an embodiment, and shows a schematic structure of a neutron detector including a neutron scintillator. It is a graph which shows an example of a detection result when γ-ray and neutron n are each irradiated to a neutron scintillator which has a resin composition part in which inorganic fluorescent substance particles are dispersed uniformly. It is the graph which modeled the detection result in the neutron detector of one embodiment. It is the schematic which shows the neutron detector of a modification. It is a cross-sectional view of the neutron scintillator modeled in the examples. In the model of an Example, it is the graph which plotted the number of photons which enter into a wavelength conversion fiber resulting from incidence | injection of a neutron, and the frequency | count of the occurrence of this event. In the model of the example, a graph plotting the number of photons irradiated from the inorganic phosphor particles at a position away from the wavelength conversion fiber and incident on the wavelength conversion fiber due to the incidence of neutrons, and the number of occurrences of this event It is. In the model of an Example, it is the graph which plotted the number of photons which injects into a wavelength conversion fiber resulting from incidence | injection of a gamma ray, and the frequency | count of the occurrence of this event. In the model of the example, the number of photons irradiated from the inorganic phosphor particles at a position away from the wavelength conversion fiber and incident on the wavelength conversion fiber due to the incidence of γ rays and the number of occurrences of this event are plotted. It is a graph. FIG. 10 is a graph in which FIG. 7 and FIG. 9 are superimposed, and is a graph obtained by taking a logarithm as the number of event occurrences. FIG. 11 is a graph obtained by superimposing FIGS. 8 and 10 and a logarithm of the number of event occurrences. FIG. 10 is a graph in which FIGS. 7 and 9 are overlapped and partially enlarged. FIG. FIG. 11 is a graph partially enlarged by overlapping FIG. 8 and FIG. 10.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

  FIG. 1 is a schematic cross-sectional view of a neutron scintillator 1 of the present embodiment. FIG. 2 is a schematic longitudinal sectional view of the neutron scintillator 1. In FIG. 2, the schematic structure of the neutron detector 2 including the neutron scintillator 1 is also shown.

  The neutron scintillator 1 includes a resin composition part 30, a wavelength conversion fiber 20 included in the resin composition part 30, and a reflector 35 surrounding the outer periphery of the resin composition part 30. In addition, the resin composition part 30 includes inorganic phosphor particles 31 containing at least one neutron capture isotope selected from lithium 6 and boron 10 and a resin part 32 as constituent elements.

  A neutron detector 2 shown in FIG. 2 includes a neutron scintillator 1, a photodetector 3 connected to the wavelength conversion fiber 20 of the neutron scintillator 1, and a determination unit 4 connected to the photodetector 3. The neutron detector 2 determines the presence of neutrons by causing the light generated when the neutrons are incident on the inorganic phosphor particles 31 to be incident on the wavelength conversion fiber 20 and detecting the light with the photodetector 3.

  In the present specification, “encapsulation” indicates a state in which the fiber surface along the body axis direction of the wavelength conversion fiber 20 is covered with the 360 ° resin composition portion 30. On the other hand, both ends or one end of the end face of the fiber protrudes from the resin composition portion 30. In order to extract the scintillation light, at least one end of the fiber needs to be out of the resin composition portion 30, but the remaining end may exist in the resin composition portion 30 or protrude from the resin composition portion 30. Also good.

<Resin part>
The resin part 32 is provided around the inorganic phosphor particles 31 and is interposed between the plurality of inorganic phosphor particles 31. That is, in the resin composition part 30, the inorganic phosphor particles 31 are dispersed in the resin part 32. As described above, the inorganic phosphor particles 31 of the present embodiment are smaller in size than commonly used inorganic phosphors. Therefore, since the single inorganic phosphor particle 31 has poor neutron detection efficiency, the neutron detection efficiency can be increased by dispersing the plurality of inorganic phosphor particles 31 in the resin portion 32.

  The resin part 32 is preferably a transparent resin in order to efficiently guide the fluorescence emitted from the inorganic phosphor particles 31 to the wavelength conversion fiber 20. Specifically, the internal transmittance of the resin at the emission wavelength of the inorganic phosphor particles 31 is preferably 80% / cm or more, and particularly preferably 90% / cm or more. Specific examples of such resins include silicone resins and fluororesins. Examples include poly (meth) acrylate, polycarbonate, polystyrene, polyvinyl toluene, and polyvinyl alcohol. A plurality of resins may be mixed and used for the purpose of adjusting the refractive index, strength, and the like. Among the transparent resins, it is preferable to use a transparent resin having a refractive index at the emission wavelength of the inorganic phosphor particles 31 close to the refractive index of the inorganic phosphor particles 31. Specifically, the ratio of the refractive index of the transparent resin to the refractive index of the inorganic phosphor particles 31 is preferably 0.95 to 1.05, and most preferably 0.98 to 1.02. By setting the ratio of the refractive index of the transparent resin within such a range, light scattering at the interface between the inorganic phosphor particles 31 and the resin can be suppressed, and the transparency of the resin composition portion 30 can be enhanced. In addition, the said refractive index is a refractive index in the temperature range which uses the neutron scintillator 1 of this embodiment. For example, when the neutron scintillator 1 of the present embodiment is used at 100 ° C., the refractive index ratio needs to be obtained at 100 ° C.

<Inorganic phosphor particles>
The inorganic phosphor particles 31 contain at least one neutron capture isotope selected from lithium 6 and boron 10. In the inorganic phosphor particle 31, neutron capture reaction between lithium 6 or boron 10 and neutron n generates α-ray and tritium or α-ray and lithium 7 (hereinafter also referred to as secondary particles), respectively. Thus, energy of 4.8 MeV or 2.3 MeV is applied to the inorganic phosphor particles 31. By applying the energy, the inorganic phosphor particles 31 are excited and emit fluorescence.

  The neutron scintillator 1 using the inorganic phosphor particles 31 has high neutron detection efficiency because of the high efficiency of the neutron capture reaction by the lithium 6 and the boron 10, and is given to the inorganic phosphor particles 31 after the neutron capture reaction. Since the generated energy is high, the intensity of fluorescence emitted when neutron n is detected is excellent.

  In the present embodiment, the inorganic phosphor particles 31 are particles made of an inorganic substance that contains a neutron capture isotope and emits fluorescence, and the inorganic substance itself is grasped as one chemical substance. Therefore, a mixture particle formed by mixing non-fluorescent particles containing a neutron capture isotope and phosphor particles not containing a neutron capture isotope is not included. More specifically, it is preferable not to include a mixture particle such as a mixture of non-fluorescent LiF containing a neutron capture isotope and ZnS: Ag which is a phosphor not containing a neutron capture isotope. In such mixture particles, a part of the energy of the secondary particles generated in the particles containing the neutron capture isotope is lost before reaching the fluorescent particles. The energy lost at this time varies depending on the range from the generation point of the secondary particles to the particles that emit fluorescence, and as a result, the fluorescence intensity of the particles that emit fluorescence varies greatly. Therefore, since the desired n / γ discrimination ability cannot be obtained, it is preferable that such mixture particles are not employed in the present embodiment.

In the present embodiment, the content of lithium 6 and boron 10 in the inorganic phosphor particles 31 (hereinafter also referred to as neutron capture isotope content) is 1 atom / nm ³ and 0.3 atom / nm ³ or more, respectively. It is particularly preferable that they are 6 atom / nm ³ and 2 atom / nm ³ or more, respectively. The neutron capture isotope content refers to the number of neutron capture isotopes contained per 1 nm ³ of the inorganic phosphor particles 31. By setting the neutron capture isotope content in the above range, the probability that the incident neutron n causes a neutron capture reaction is increased, and the neutron detection efficiency is improved.

The neutron capture isotope content is selected from the chemical composition of the inorganic phosphor particles 31 and lithium in lithium fluoride (LiF) or boron oxide (B ₂ O ₃ ) used as a raw material for the inorganic phosphor particles 31. It can be adjusted as appropriate by adjusting the isotope ratio of 6 and boron 10. Here, the isotope ratio is an element ratio of the lithium 6 isotope to the total lithium element and an element ratio of the boron 10 isotope to the total boron element. For natural lithium and boron, about 7.6% and about 19.9%.

  On the other hand, the upper limit of the neutron capture isotope content is not particularly limited, but is preferably as high as possible.

In addition, the content of lithium 6 (C _{Li, P} ) and the content of boron 10 (C _{B, P} ) in the inorganic phosphor particles 31 are determined in advance according to the density of the inorganic phosphor particles 31, the inorganic phosphor particles 31. The mass fractions of lithium and boron, and the isotope ratios of lithium 6 and boron 10 in the raw material can be obtained and substituted into the following formulas (1) and (2), respectively.

C _{Li, P} = ρ × W _Li × R _Li / (700−R _Li ) × A × 10 ⁻²³ (1)
C _{B, P} = ρ × W _B × R _B / (1100−R _B ) × A × 10 ⁻²³ (2)
(In the formula, C _{Li, P} and C _{B, P} are the contents of lithium 6 and boron 10 in the inorganic phosphor particles 31, respectively, ρ is the density [g / cm ³ ] of neutron scintillator, W _Li and W _B is lithium and the mass fraction of boron for each inorganic phosphor particles 31 _[wt%], isotopic ratio of lithium 6 and boron 10 in each _{R Li} and _{R B} material [%], a is Avogadro's number [ 6.02 × 10 ²³ ])

The inorganic phosphor particle 31 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: LiYF ₄ , Eu: LiI, Ce: Li ₆ Gd (BO ₃ ) ₃ , C Inorganic phosphor particles 31 made of crystals such as LiCs ₂ YCl ₆ , Ce: LiCs ₂ YBr ₆ , Ce: LiCs ₂ LaCl ₆ , Ce: LiCs ₂ LaBr ₆ , Ce: LiCs ₂ CeCl ₆ , Ce: LiRb ₂ LaBr _6, etc. _and, from the _{Li 2 O-MgO-Al 2} O 3 -SiO 2 -Ce 2 O 3 system glass Inorganic phosphor particles 31, and the like that.

  The wavelength at which the inorganic phosphor particles 31 emit light is preferably in the near-ultraviolet region to the visible light region, particularly in the visible light region, in that it is easy to obtain transparency when mixed with the resin portion 32 described later. preferable.

  The neutron capture isotope contained in the inorganic phosphor particles 31 is preferably lithium 6 only. By using only lithium 6 as the neutron capture isotope that contributes to the neutron capture reaction, a constant energy can always be imparted to the inorganic phosphor particles 31, and an extremely high energy of 4.8 MeV can be imparted. it can. Therefore, it is possible to obtain the neutron scintillator 1 with little variation in fluorescence intensity and particularly excellent in fluorescence intensity.

Among the inorganic phosphor particles 31 containing only lithium 6 as a neutron capture isotope, chemical formula LiM ¹ M ² X ₆ (where M ¹ is at least one alkaline earth metal selected from Mg, Ca, Sr and Ba) M ² is at least one metal element selected from Al, Ga and Sc, and X is at least one halogen element selected from F, Cl, Br and I). A corkyrite crystal containing at least one lanthanoid element and a corkylite crystal containing at least one alkali metal element are preferred.
If the corklite type crystal is specifically exemplified, the inorganic phosphor particles 31 composed of Eu: LiCaAlF ₆ , Eu, Na: LiCaAlF ₆ , Eu: LiSrAlF ₆ and Eu, Na: LiSrAlF ₆ have a high light emission amount, and Most preferred because it is deliquescent and chemically stable.

  In the neutron scintillator 1 of the present embodiment, the n / γ discrimination ability is improved by using the inorganic phosphor particles 31 in which the inorganic phosphor is particulate. Hereinafter, the action mechanism in which the n / γ discrimination ability is improved by using the inorganic phosphor particles 31 will be described.

  In general, when γ rays are incident on the neutron scintillator 1, secondary electrons e are generated inside the neutron scintillator 1, and the inorganic phosphor emits light by applying energy when the secondary electrons pass through the inorganic phosphor. To do. When the peak value output by such light emission is as high as the peak value due to the incidence of neutron n and both cannot be distinguished, γ-rays are counted as neutron n and an error occurs in the neutron count. In particular, when the dose of γ-rays is high, errors due to γ-rays increase and become a significant problem.

  The peak value output from the neutron detector by the incidence of γ rays depends on the energy imparted by the secondary electrons e. Therefore, by reducing the energy, the peak value outputted when the γ rays are incident on the neutron scintillator 1 is output. The peak value to be reduced can be reduced.

  Here, the range distance in which the secondary electrons e generated when γ rays are incident on the neutron scintillator 1 moves through the neutron scintillator 1 while applying energy to the neutron scintillator 1 is as long as several millimeters.

  On the other hand, when the neutron n is incident on the neutron scintillator 1, as described above, the neutron capture reaction between the lithium 6 and boron 10 contained in the inorganic phosphor in the neutron scintillator 1 and the neutron n occurs. When the secondary particles impart energy to the inorganic phosphor, the inorganic phosphor emits light, but the range distance of the secondary particles is several μm to several tens μm, which is shorter than the secondary electrons.

  According to this embodiment, by making the inorganic phosphor into a particulate form, the secondary electrons e can be quickly deviated from the inorganic phosphor particles 31, and the energy imparted by the secondary electrons e to the inorganic phosphor can be reduced. Can do. Since secondary particles resulting from the incidence of neutrons have a short range, most of the secondary particles consume energy in the inorganic phosphor particles 31 and generate light having a substantially constant peak value. On the other hand, secondary electrons e caused by the incidence of γ rays jump out of the inorganic phosphor particles 31 due to a long range distance, and do not consume all energy in the inorganic phosphor particles 31. The peak value accompanying light emission can be reduced. Therefore, it can be determined from the peak value that the light is caused by the incidence of neutron n, and the n / γ discrimination ability can be enhanced.

  In the present embodiment, the size of the inorganic phosphor particles 31 is such that almost all the energy of the secondary particles generated by the incidence of neutrons n is imparted to the inorganic phosphor, and the incidence of γ rays as much as possible. Therefore, the secondary electron e is preferably small enough to deviate.

According to the study by the present inventors, the shape of the inorganic phosphor particles 31 is preferably a shape having a specific surface area of 50 cm ² / cm ³ or more, and a shape having a specific surface area of 100 cm ² / cm ³ or more. It is particularly preferable that In the present specification, the specific surface area of the inorganic phosphor particles 31 refers to the surface area per unit volume of the inorganic phosphor particles 31.

  Since the specific surface area is a surface area per unit volume, (1) it tends to increase as the absolute volume of the inorganic phosphor particles 31 decreases, and (2) when the shape is spherical, the specific surface area is the largest. Conversely, the smaller the specific surface area of the inorganic phosphor particles 31, the more the inorganic phosphor particles 31 are separated from the true sphere. For example, when considering a cube having sides extending in the X-axis, Y-axis, and Z-axis directions, the specific surface area is the smallest in the case of a regular hexahedron with X = Y = Z, and the length in one of the axial directions is shortened. As a result, the specific surface area becomes larger even if the other axial side is made longer in the same volume.

More specifically, the specific surface area of a regular hexahedron having a side of 0.5 cm is 12 cm ² / cm ³ , but in the case of the regular hexahedron of 0.1 cm (0.001 cm ³ ), the ratio is The surface area is 60 cm ² / cm ³ . Furthermore, when the thickness is 0.025 cm with the same volume (0.001 cm ³ ), the vertical and horizontal dimensions are 0.2 cm × 0.2 cm, and the specific surface area is 100 cm ² / cm ³ .

  In other words, a large specific surface area indicates that at least one of the axial lengths has a very small portion. Since the secondary electrons e generated by the small axial direction and the γ rays running in the direction close to the axial direction deviate from the crystal as described above, the energy imparted to the inorganic phosphor particles 31 from the secondary electrons e. Can be reduced.

A suitable shape of the inorganic phosphor particles 31 based on the specific surface area is found by the above knowledge and consideration, and the specific surface area is imparted to the inorganic phosphor particles 31 from the secondary electrons e. In consideration of energy, it can be used as an index of a shape taking into account that the inorganic phosphor particles 31 have various particle forms. In practice, the specific surface area is preferably 50 cm ² / cm ³ or more, and more preferably, the specific surface area is 100 cm ² / cm ³ or more, thereby obtaining a neutron detector particularly excellent in n / γ discrimination. it can.

In the present embodiment, the upper limit of the specific surface area is not particularly limited, but is preferably 1000 cm ² / cm ³ or less. When the specific surface area exceeds 1000 cm ² / cm ³ , that is, when the axial length of at least one of the inorganic phosphor particles 31 is excessively small, neutrons of the lithium 6 and boron 10 and the neutron n There is a possibility that an event in which the secondary particles generated by the capture reaction deviate from the inorganic phosphor particles 31 before giving the total energy to the inorganic phosphor particles 31 may occur. In such an event, the energy given to the inorganic phosphor particles 31 due to the incidence of neutron n is reduced, so that the intensity of light emission of the inorganic phosphor is reduced. In order to reliably give the total energy of the secondary particles to the inorganic phosphor particles 31 and increase the light emission intensity of the inorganic phosphor, it is particularly preferable that the specific surface area of the inorganic phosphor particles 31 is 500 cm ² / cm ³ or less. preferable.

  Although the term “axis” is used in the above description, it is merely used for convenience to indicate the spatial coordinate positions of X, Y, and Z, and the inorganic phosphor particles 31 used in the present embodiment are arranged in these specific axial directions. Of course, it is not limited to a cube having sides.

  When the inorganic phosphor particles 31 are indefinite, the specific surface area can be easily obtained from the density and mass-based specific surface area obtained using a density meter and a BET specific surface area meter.

  In the present embodiment, the shape of the inorganic phosphor particles 31 that can be suitably used is specifically exemplified as a flat, prismatic, cylindrical, spherical, or irregular particle form, which is equivalent to a specific surface area sphere. The shape whose diameter is 50-1500 micrometers, Most preferably, it is 100-1000 micrometers is mentioned.

  The method for producing the inorganic phosphor particles 31 used in the present embodiment is not particularly limited, and a method for obtaining particles having a desired shape by pulverizing and classifying a bulk body having a shape larger than the particles having the suitable shape, Alternatively, a method of directly obtaining inorganic phosphor particles 31 having a suitable shape by a particle generation reaction using a solution as a starting material can be mentioned.

<Resin composition part>
As described above, the resin composition part 30 includes the resin part 32 and the inorganic phosphor particles 31 dispersed in the resin part 32.
As shown in FIG. 1, the resin composition portion 30 has a cylindrical first region A1 that encloses the outer periphery of the wavelength conversion fiber 20, and a second region A2 that is located outside the first region A1. The first region A1 does not contain the inorganic phosphor particles 31, and the second region A2 contains the inorganic phosphor particles 31.

Here, in order to explain the effect of configuring the first region A1 that does not include the inorganic phosphor particles 31, the detection result when the inorganic phosphor particles are uniformly dispersed in the resin composition portion will be described.
FIG. 3 is a graph showing an example of a detection result when γ-rays and neutrons n are each irradiated to a neutron scintillator having a resin composition part in which inorganic phosphor particles are uniformly dispersed.

As shown in FIG. 3, the detection result of the γ-ray extends at the point X beyond the peak value at which the neutron beam indicates the peak value P. The following two factors can be considered as the main factors that cause the peak value of light caused by γ rays to be in a wide range.
The first factor is that the range of secondary electrons e due to the incidence of γ rays is large, and the amount of energy consumed in the inorganic phosphor particles 31 depends on the reaction position and the emission direction of the secondary electrons e. It depends on how it changes.
The second factor is that the peak value of the light that is output by light emission caused by the incidence of γ rays and reaches the wavelength conversion fiber 20 depends on the distance between the inorganic phosphor particles 31 that emit light and the wavelength conversion fiber 20. by. The peak value of light reaching the wavelength conversion fiber 20 (which may be replaced with the number of photons) becomes larger when emitted from the vicinity.

  When the above two factors overlap, that is, when the secondary electrons e travel a long distance in the inorganic phosphor particles 31 located near the wavelength conversion fiber 20, the peak value due to γ rays is high. It is considered that the γ-ray detection result is overlapped with the neutron peak value P as indicated by a point X.

  On the other hand, when the neutron n is incident on the inorganic phosphor particle 31, the inorganic phosphor is excited by the secondary particles generated by the neutron capture reaction between the lithium 6 and boron 10 and the neutron n contained in the inorganic phosphor particle 31. Emit light L4. Since the secondary particles (α ray and tritium or α ray and lithium 7) generated when neutron n is incident have a short range, the energy is consumed in the inorganic phosphor particles 31, and the inorganic phosphor particles 31 are removed. Make it emit light. Therefore, the intensity (wave height value) of the light emission of the inorganic phosphor particles 31 due to the incidence of neutron n is almost constant. Note that only a small part of the secondary particles when neutron n is incident jump out of the inorganic phosphor particles 31. Therefore, in practice, part of the light emission becomes weak (region Y in FIG. 3).

FIG. 3 shows the detection result when the number of γ-ray photons is significantly larger than the number of neutrons. In the vicinity of radioactive materials such as fuel debris, the number of photons of γ rays is said to be 10 ⁸ times the number of neutrons.

  In the present embodiment, the light L3 caused by γ rays and the light L4 caused by neutron rays are determined from the difference in peak values. However, as described above, when the inorganic phosphor particles 31 are located in the vicinity of the wavelength conversion fiber 20, the peak value of the light L3 caused by γ rays is detected to be high, and the light L4 caused by neutrons. There is a risk of being mistaken. According to this embodiment, the first region A1 surrounding the wavelength conversion fiber 20 does not include the inorganic phosphor particles 31, thereby suppressing the peak value of the light L4 caused by γ rays from being measured high. can do. As a result, the light L4 caused by neutrons can be detected separately from the light L3 caused by γ rays, and n / γ discrimination can be improved.

  Since the first region A1 does not include the inorganic phosphor particles 31, the neutron measurement result shown in FIG. 3 shows a peak although the base Z on the side where the peak value increases is smaller than the peak value P. The detection frequency of the value P is difficult to decrease. For this reason, according to the neutron scintillator, n / γ discrimination can be improved while suppressing a decrease in neutron detection efficiency due to the absence of the inorganic phosphor particles 31 in the first region A1.

  In the present embodiment, the case where the inorganic phosphor particles 31 are not included in the first region A1 is illustrated. However, if the density (that is, the content per unit volume) of the inorganic phosphor particles 31 in the first region A1 is lower than the density of the inorganic phosphor particles in the second region A2, a certain effect can be obtained. In 1st area | region A1 and 2nd area | region A2, the above-mentioned effect is easy to show | play, so that the difference in the density of the inorganic fluorescent substance particle 31 is large. Therefore, as shown in the above-described embodiment, the effect is most easily obtained when the inorganic phosphor particles 31 are not included in the first region A1.

In the present embodiment, the outer shape of the cross section of the first region A1 is a circular shape surrounding the wavelength conversion fiber 20. Further, the cross-sectional outline of the first region A1 is concentric with the cross-sectional outline of the wavelength conversion fiber 20. However, the cross-sectional outer shape of the first region A1 is not limited to this, and may be a rectangular shape or other polygonal shapes.
In the present embodiment, it is preferable that the first region A1 and the second region A2 have the resin portion 32 of the same material, but the material constituting the first region A1 is not necessarily the same material as the second region A2. Not necessarily. In addition, the first region A1 may be a void that is not filled with a material.

The neutron detection efficiency of the neutron scintillator 1 of the present embodiment depends on the content (ie, density) of the neutron capture isotope derived from the inorganic phosphor particles 31 in the second region A2 of the resin composition unit 30, and the content It can be improved by increasing. The neutron capture isotope content refers to the number of neutron capture isotopes derived from the inorganic phosphor particles 31 that are averagely included per 1 nm ³ in the second region A2 of the resin composition portion 30, and the lithium 6 For each of the content (C _{Li, C} ) and the content of boron 10 (C _{B, C} ), the content of lithium 6 (C _{Li, P} ) and the content of boron 10 in the inorganic phosphor particles 31 ( C _{B, P} ) and the volume fraction (V) of the inorganic phosphor particles 31 in the second region A2 can be obtained from the following equations (3) and (4).

C _{Li, C} = C _{Li, P} × (V / 100) (3)
C _{B, C} = C _{B, P} × (V / 100) (4)
(In the formula, C _{Li, C} and C _{B, C} are the contents of lithium 6 and boron 10 in the second region A2 of the resin composition part 30, respectively, C _{Li, P} and C _{B, P} are inorganic, respectively. The content of lithium 6 and the content of boron 10 in the phosphor particles 31, V indicates the volume fraction (V) [volume%] of the inorganic phosphor particles 31 in the resin composition portion 30)

  In the present embodiment, the content of the inorganic phosphor particles 31 in the resin composition portion 30 (the first region A1 and the second region A2) is not particularly limited, but as is apparent from the above formula, the resin composition portion. By increasing the volume fraction of the inorganic phosphor particles 31 in 30, the neutron detection efficiency can be improved. Therefore, the volume fraction of the inorganic phosphor particles 31 in the resin composition part 30 is preferably 5% by volume or more, particularly preferably 10% by volume or more, and most preferably 20% by volume or more. The upper limit of the volume fraction of the inorganic phosphor particles 31 with respect to the entire resin composition part 30 is not particularly limited, but is preferably less than 80% by volume and less than 50% by volume in consideration of the viscosity when the resin composition part 30 is manufactured. Is more preferable.

  On the other hand, in the present embodiment, in the resin composition part 30, it is desirable that the inorganic phosphor particles 31 are uniformly dispersed in the resin in the second region A2, and the interval between the adjacent inorganic phosphor particles 31 is wide. By widening the interval between the particles, secondary electrons deviating from a certain inorganic phosphor particle 31 are incident on other adjacent inorganic phosphor particles 31 to give energy to the inorganic phosphor particles 31 to emit light. Can be prevented from increasing.

  However, in general, since the specific gravity of the inorganic phosphor particles 31 is larger than the specific gravity of the resin, when the liquid or viscous resin and the inorganic phosphor particles 31 are mixed, the particles settle and agglomerate at the bottom. It may be difficult to maintain the interval. In such a case, a method of increasing the viscosity of the resin to impart thixotropic properties to the resin composition portion 30 and suppressing the sedimentation of the particles, further blending particles different from the inorganic phosphor particles 31, the particles are treated with inorganic fluorescence. A method of maintaining the spacing between the inorganic phosphor particles 31 by filling between the particles of the body, or the resin composition portion 30 thinner than the desired thickness, in which the particles settled and aggregated in the lower part, A method of maintaining a gap between macroscopic particles by preparing a plurality of resin composition portions 30 having a layer made only of a resin on the top and laminating them can be suitably employed.

  Although the manufacturing method of the said resin composition part 30 is not restrict | limited in particular, A specific manufacturing method is illustrated below.

  First, the first region A1 is formed on the outer periphery of the wavelength conversion fiber 20. An uncured resin material is prepared as a material for the resin portion 32. Further, the resin material is poured into a mold, and the resin material is cured in a state where the wavelength conversion fiber 20 is positioned at the approximate center, and then removed from the mold. Thus, the wavelength conversion fiber 20 is held at the center of the resin material, and the first region A1 is formed around the wavelength conversion fiber 20.

  Next, the second region A2 is formed outside the first region. In the case where the second region A2 of the resin composition portion 30 is the slurry-like or paste-like resin composition portion 30, first, the inorganic phosphor particles 31 and the liquid or viscous resin are mixed. In such a mixing operation, a known mixer such as a propeller mixer, a planetary mixer, or a butterfly mixer can be used without particular limitation.

  Next, it is preferable to defoam bubbles generated in the resin composition portion 30 in the mixing operation. In the defoaming operation, a defoamer such as a vacuum defoamer or a centrifugal defoamer can be used without any particular limitation. By performing such a defoaming operation, light scattering due to the bubbles can be suppressed, and the internal transmittance of the resin composition portion 30 can be increased.

  In the mixing operation and defoaming operation, an organic solvent may be added to the resin composition portion 30 for the purpose of reducing the viscosity of the resin composition portion 30 and efficiently mixing and defoaming.

  Moreover, when making 2nd area | region A2 of the resin composition part 30 into a solid state, it can manufacture easily with the following method. That is, a mixing operation and a defoaming operation are performed in the same manner as described above using a liquid or viscous resin precursor. Next, the obtained mixture of the inorganic phosphor particles 31 and the resin precursor is injected into a mold having a desired shape, and the resin precursor is cured. The curing method is not particularly limited, but a method of polymerizing the resin precursor by heating, ultraviolet irradiation, or addition of a catalyst is preferable.

  Here, the resin composition portion 30 of the present embodiment can be used in a slurry or paste form, and can be molded with a mold having a desired shape even when used in a solid form. Easy. Therefore, according to this embodiment, the neutron scintillator 1 having a rod shape, a hollow tube shape, or a large area can be provided according to the application.

<Wavelength conversion fiber>
The wavelength conversion fiber 20 functions as a light guide for guiding light emitted from the inorganic phosphor particles 31 in the resin composition portion 30 to the photodetector 3. The operation mechanism of the wavelength conversion fiber 20 will be described with reference to FIG. When the light L <b> 1 emitted from the inorganic phosphor particles 31 reaches the wavelength conversion fiber 20, it is absorbed by the wavelength conversion fiber 20. Further, the wavelength conversion fiber 20 re-emits light at a wavelength different from the original wavelength and emits light L2. The light L2 isotropically generated, but the light emitted at an angle with respect to the outer surface of the wavelength conversion fiber 20 propagates while totally reflecting the inside of the wavelength conversion fiber 20, and ends the wavelength conversion fiber 20. To reach. Then, by installing the photodetector 3 at the end of the wavelength conversion fiber 20, the light L <b> 2 generated from the inorganic phosphor particles 31 can be collected via the wavelength conversion fiber 20.

  In the wavelength conversion fiber 20 in the present embodiment, the ratio of the refractive index of the wavelength conversion fiber 20 to the refractive index of the resin part 32 in the resin composition part 30 is 0.95 or more at the emission wavelength of the inorganic phosphor particles 31. Those are preferred. Light emitted from the inorganic phosphor particles 31 is incident on the wavelength conversion fiber 20 via the resin portion 32, but light L 1 that is about to enter the wavelength conversion fiber 20 at an incident angle exceeding a certain critical angle is the resin portion 32. And is totally reflected at the interface between the wavelength conversion fiber 20 and cannot enter. By setting the refractive index ratio to 0.95 or more, the critical angle can be set to about 70 degrees or more, and the efficiency of incidence from the resin composition portion 30 onto the wavelength conversion fiber 20 can be increased. By setting the refractive index ratio to 1 or more, total reflection of the light L1 does not occur at the interface between the resin portion 32 and the wavelength conversion fiber 20, which is particularly preferable. Further, by setting the refractive index ratio to 1.05 or more, the light L2 re-emitted by the wavelength conversion fiber 20 is totally reflected at the interface between the wavelength conversion fiber 20 and the resin composition portion 30, and the wavelength conversion fiber 20 The efficiency of propagating inside can be increased, and is most preferable.

The material of the wavelength conversion fiber 20 is not particularly limited, but generally, a material in which an organic phosphor having various absorption wavelengths is contained in a plastic base material such as polystyrene, polymethyl methacrylate and polyvinyl toluene is commercially available. The refractive index (n _D ) of these sodium D lines is about 1.5 to 1.6. Therefore, as the resin part 32 included in the resin composition part 30, it is preferable to use a low-refractive index resin having a lower refractive index than these in order to satisfy the above-described requirement of the refractive index ratio. Such a low refractive index resin, silicone resin, fluorinated silicone resins, phenyl silicone resin and fluorine resin can be preferably used, n _D is commercially available in about 1.3 to 1.5.

Further, as described above, the refractive index of the inorganic phosphor particles 31 is preferably as low as that of the low refractive index resin. The inorganic phosphor particles 31 are represented by the chemical formula LiM ¹ AlF ₆ (wherein M ¹ is at least one alkaline earth metal element selected from Mg, Ca, Sr and Ba), and at least one kind Of these, a corkylite-type crystal containing the lanthanoid element, and a corkylite-type crystal containing at least one alkali metal element are preferred. The n _{D of the} cordierite crystal is about 1.4, and it is easy to satisfy the refractive index ratio requirement. In addition, although demonstrated here taking the refractive index in sodium D line as an example for convenience, it is the same also about the light emission wavelength of inorganic fluorescent substance.

In the present embodiment, the wavelength conversion fiber 20 is preferably included in the resin composition portion 30.
In general, when light emitted from the resin composition unit 30 is collected by the wavelength conversion fiber 20, there is a problem that the light collection efficiency is poor. That is, (1) a loss caused by quenching a part of the light emitted from the resin composition unit 30 without reaching the wavelength conversion fiber 20, and (2) the wavelength conversion fiber 20 absorbing the light emission from the resin composition unit 30. Loss caused by re-emission, and (3) loss caused by the light emitted from the wavelength conversion fiber 20 being dissipated without propagating through the wavelength conversion fiber 20, etc. In general, the amount of light reaching the light detector 3 is only a few percent of the amount of light emitted from the inorganic phosphor particles 31.

  As described above, when the amount of light reaching the photodetector 3 is small, the variation in the amount of light inevitably increases. Therefore, as described above, a threshold is provided for the peak value, and neutrons and γ rays are discriminated by the threshold. And the counting error due to γ rays becomes remarkable.

  In the present embodiment, by including the wavelength conversion fiber 20 in the resin composition portion 30, (1) a part of the light emitted from the resin composition portion 30 is quenched without reaching the wavelength conversion fiber 20. Loss can be greatly reduced, and light collection efficiency is improved. That is, when the wavelength conversion fiber 20 is disposed outside the resin composition unit 30, the light generated in the resin composition unit 30 once exits from the resin composition unit 30, and then again through the intermediate phase. It is necessary to be incident on. Conventionally, various studies have been made to reduce the loss in this process, but there is still room for improvement. On the other hand, when the wavelength conversion fiber 20 is included in the resin composition portion 30, light emitted from the resin composition portion 30 enters the wavelength conversion fiber 20 without going through an intermediate phase, so that the loss is greatly reduced. it can.

In addition, by including the wavelength conversion fiber 20 in the resin composition portion 30, the amount of the wavelength conversion fiber 20 used can be reduced, and the structure of the resin composite can be simplified.
In the case of a structure in which the wavelength conversion fiber is arranged outside the resin composition part, in order to efficiently enter the light emitted from the resin composition part into the wavelength conversion fiber, the surface from which the light is emitted from the resin composition part is disposed on the wavelength conversion fiber. It is necessary that the light emitted from the resin composition portion is collected on the wavelength conversion fiber by using a reflective material having a complicated shape or covering with no gap.
As shown in the present embodiment, when the wavelength conversion fiber 20 is encapsulated in the resin composition part 30, the resin composition part is irradiated with light by a conventionally known simple method such as covering the outer periphery of the resin composition part 30 with a reflective material 35. Since the light traveling longitudinally and horizontally inside the resin composition part 30 will eventually reach the wavelength conversion part only by being enclosed in the inside of the resin composition part 30, the light emitted from the resin composition part 30 may be efficiently incident on the wavelength conversion fiber 20. it can. In order to contain the light inside the resin composition portion 30, the surface of the resin composition portion 30 may be covered with a reflecting material 35. The reflecting material 35 may be a white pigment such as unbaked polytetrafluoroethylene or barium sulfate. The one consisting of is preferred.

  In the neutron scintillator 1 of the present embodiment, when the wavelength conversion fiber 20 is encapsulated in the resin composition part 30, the wavelength conversion fiber 20 is arranged at a specific position with respect to the outer wall surface of the resin composition part 30. One. According to the study by the present inventors, the wavelength conversion fiber 20 is disposed at a specific position with respect to the outer wall surface of the resin composition portion 30, and the wavelength conversion fiber 20 is included in the resin composition portion 30 as narrow as possible. Improves n / γ discrimination. Specifically, the ratio (D / d) of the distance (D) between the center axis of the fiber and the outer wall surface of the resin composition portion 30 to the diameter (d) of the wavelength conversion fiber 20 is in the range of 1 to 10. The wavelength conversion fiber 20 is installed in

  When D / d is in the range of 1 to 10, the position of the outer wall surface closest to the central axis of the wavelength conversion fiber 20 is at least one time the diameter of the wavelength conversion fiber 20 and the outermost wall surface It means that the position is at most 10 times the diameter of the wavelength conversion fiber 20 at the maximum. D / d is preferably 2 to 5.

  In addition, when a plurality of wavelength conversion fibers 20 are included in the resin composition unit 30, the D / d that each wavelength conversion fiber 20 can take is calculated, and the maximum value and the minimum value among them are calculated for the plurality of fibers. It is set as the value of D / d which the resin composition part 30 to include can take.

1 ≦ D / d ≦ 10 (5)
By encapsulating the wavelength conversion fiber 20 in the resin composition portion 30 in the narrowest possible region so as to satisfy such an index, the distance that the secondary electrons e generated by γ rays travel through the inorganic phosphor particles 31 can be reduced. As a result, the peak value output when γ rays enter the neutron scintillator 1 can be reduced.

  In the present embodiment, the cross-sectional shape of the wavelength conversion fiber 20 is not particularly limited. As for the diameter (d) of the wavelength conversion fiber 20, the equivalent cross-sectional circle equivalent diameter of the wavelength conversion fiber 20 is regarded as the diameter of the wavelength conversion fiber 20 when the fiber cross section is not a circle.

  Further, if the wavelength of the wavelength conversion fiber 20 is too large, the optical path length of the light traveling through the fiber may increase and cause a decrease in the amount of light. Therefore, in this embodiment, the fiber having a diameter of 0.1 to 5 mm is used. It is preferable to do this.

  According to the present embodiment, the amount of use of the wavelength conversion fiber 20 can be reduced by the above-described effect. However, when the amount of use is excessively small, there is a risk that the loss of light amount may increase. It is preferable to use it. An appropriate usage amount can be defined by the ratio of the cross-sectional area of the wavelength conversion fiber 20 to the cross-sectional area of the resin composition portion 30 in a cross section perpendicular to the body axis of the wavelength conversion fiber 20. In order to make the light emitted from the resin composition portion 30 efficiently enter the resin composition portion 30, the ratio of the cross-sectional areas is preferably 0.0025 or more, and particularly preferably 0.01 or more. On the other hand, in order to reduce the amount of the wavelength conversion fiber 20 used and to simplify the structure of the resin composite and reduce the manufacturing cost, the ratio of the cross-sectional areas is preferably 1 or less. It is particularly preferable to set it to 1 or less.

<Neutron detector>
As shown in FIG. 2, the neutron detector 2 can be obtained by combining the neutron scintillator 1 with the photodetector 3 and the determination unit 4.
The light emitted from the resin composition part 30 by the incidence of neutrons is guided to the photodetector 3 through the wavelength conversion fiber 20. The light that reaches the photodetector 3 is converted into an electrical signal by the photodetector 3, and the incidence of neutrons is measured as an electrical signal, so that it can be used for neutron counting and the like. The photodetector 3 is not particularly limited, and a conventionally known photodetector 3 such as a photomultiplier tube, a photodiode, an avalanche photodiode, a Geiger mode avalanche photodiode, or a micro PMT can be used without any limitation.
In addition, in the wavelength conversion fiber 20, it is preferable that the end surface facing the photodetector 3 is a light emitting surface, and the light emitting surface is a smooth surface. By having such a light emitting surface, the light generated by the neutron scintillator 1 can be efficiently incident on the photodetector 3.

  The method for combining the neutron scintillator 1 and the photodetector 3 is not particularly limited. For example, the light emitting surface of the wavelength conversion fiber 20 is optically bonded to the light detecting surface of the photodetector 3 with optical grease or optical cement. A neutron detector can be manufactured by connecting a power source and a signal readout circuit to the photodetector 3. The signal readout circuit is generally composed of a preamplifier, a shaping amplifier, a multiple wave height analyzer, and the like.

FIG. 4 is a graph schematically showing a detection result in the neutron detector 2 of the present embodiment. In FIG. 4, the crest value of the light detected by the photodetector 3 is shown on the horizontal axis, and the logarithm of the number of detections (frequency) is shown on the vertical axis.
In the photodetector 3, light caused by γ rays and light caused by neutrons are detected in an overlapping state. Therefore, in the measurement in an environment where γ rays and neutrons are mixed, it is difficult to confirm the presence of neutrons by simply observing the number of detections.

  According to the study by the present inventors, as shown in FIG. 4, in the detection result in the photodetector 3, the logarithm of the detection frequency with respect to the peak value is approximated to a linear function (primary function LF).

  Focusing only on the detection result of light caused by γ rays, the logarithm of the detection frequency converges to a linear function of the crest value. When γ rays are incident, secondary electrons e are generated. Since the secondary electrons have a long range, it is difficult to consume energy only in the inorganic phosphor particles 31. For this reason, the light emission of the inorganic phosphor particles 31 due to the incidence of γ rays is not constant in intensity and converges to a linear function stochastically.

  On the other hand, secondary particles (α-ray and tritium in the case of lithium 6 and α-ray and lithium 7 in the case of boron 10) generated when neutrons are incident on the neutron capture isotope of the inorganic phosphor particles have a range. The distance is short. For this reason, the secondary particles consume energy in the inorganic phosphor particles 31 to cause the inorganic phosphor particles 31 to emit light with a specific intensity, and show a specific peak value. Therefore, in the detection result of the light by the neutron beam, a peak is observed at the peak value depending on the neutron capture isotope contained in the inorganic phosphor particle 31. More specifically, when lithium 6 is included as a neutron capture isotope, a peak is observed at a peak value corresponding to 4.8 MeV, and when boron 10 is included as a neutron capture isotope, the peak is 2.3 MeV. A peak is observed at the corresponding peak value.

As shown in FIG. 4, by taking the logarithm as the detection frequency, the detection result due to the γ rays can be determined as the linear function LF, and the detection result due to the neutron is detected as a peak. Therefore, the peak of the detection result caused by the neutron can be observed as a value E deviating from the linear function LF, and the presence of neutron can be determined.
According to the determination method of the present embodiment, even if the irradiation amount of neutrons incident on the neutron scintillator 1 is smaller than the irradiation amount of γ rays, the detection result caused by the γ rays is represented by a straight line (primary function). By approximating to (LF), the peak of the detection result caused by neutrons can be easily confirmed, and an accurate determination can be made.

  In the present embodiment, the determination unit 4 determines the presence of neutrons based on the determination method described above. That is, the determination unit 4 approximates the logarithm of the detection frequency with respect to the peak value of the light detected by the photodetector 3 to the linear function LF, and near 4.8 MeV or 2.3 MeV with respect to the approximated primary function LF. The presence of neutrons is determined when the detection frequency of the crest values deviates. More specifically, the ratio (E / σ) of the actually detected detection frequency (E) to the standard deviation (σ) of the detection frequency obtained from the linear function LF at a peak value in the vicinity of 4.8 MeV or 2.3 MeV. ) As the degree of divergence, and the presence of neutrons is determined based on the degree of divergence. The determination criteria for the presence of neutrons are not particularly limited and may be determined according to the required determination accuracy. However, it is preferable to determine the presence of neutrons when the degree of divergence exceeds 1, and the degree of divergence exceeds 2. In some cases, it is more preferable to determine the presence of neutrons, and it is most preferable to determine the presence of neutrons when the degree of deviation exceeds 3. It has been confirmed that 99.7% of the measured value falls within 3σ from the linear function LF in an environment where neutrons do not exist.

<Modification of neutron detector>
FIG. 5 is a schematic view showing a modified neutron detector 2A.
The modified neutron detector 2A includes a plurality of neutron scintillators 1 arranged, a plurality of photodetectors 3 connected to the wavelength conversion fibers 20 of the neutron scintillators 1, and a determination unit connected to the photodetector 3. 4A. A plurality of neutron scintillators 1 arranged are referred to as a neutron detection unit 8.
The neutron detector 2A provides a neutron detector with good neutron detection efficiency and good n / γ discrimination by arranging a plurality of neutron scintillators 1 in the normal direction of the spherical surface of the sphere centered on the neutron source. be able to.
Further, the neutron detector 2A has a sensitive area by arranging a plurality of neutron scintillators 1 so that the neutron sensitive part of the neutron detection unit 8 has a large solid angle extending on a sphere centered on the neutron source. A large neutron detector can be provided.

  In the present modification shown in FIG. 5, in the neutron detector 2 </ b> A, a plurality of photodetectors 3 are combined with each of the neutron scintillators 1 constituting the neutron detection unit 8. However, a configuration in which one photodetector 3 is combined with the neutron detection unit 8 may be adopted.

<Other variations>
Additional aspects for carrying out the invention are described below.
In addition to the inorganic phosphor particles 31 and the resin, a phosphor that does not contain a neutron capture isotope (hereinafter also referred to as a neutron-insensitive phosphor) is further mixed into the resin composition unit 30 constituting the neutron scintillator 1 in the above-described embodiment. It is also possible to do.

  In such an embodiment, secondary electrons generated by the incidence of γ rays reach the neutron-insensitive phosphor after being deviated from the inorganic phosphor particles 31 and impart energy, and the neutron-insensitive phosphor emits fluorescence. That is, when γ rays are incident, both the inorganic phosphor particles 31 and the neutron-insensitive phosphor give energy and emit fluorescence. On the other hand, when neutrons are incident, secondary particles generated in the inorganic phosphor particles 31 do not deviate from the inorganic phosphor particles 31, so that only the inorganic phosphor particles 31 emit fluorescence.

  Here, if a neutron-insensitive phosphor having a fluorescence property such as a fluorescence lifetime or a light emission wavelength is different from that of the inorganic phosphor particle 31, neutrons and γ-rays can be discriminated using the difference in the fluorescence property. That is, a mechanism capable of discriminating the difference in fluorescence characteristics is provided in the neutron detector, and when both the fluorescence derived from the inorganic phosphor particles 31 and the fluorescence derived from the neutron insensitive phosphor are detected, γ rays are incident. When only the fluorescence derived from the inorganic phosphor particles 31 is detected, it can be processed as an event in which neutrons are incident. By taking such a process, a neutron detector that is particularly excellent in n / γ discrimination ability can be obtained.

  A specific example of a mechanism capable of identifying a difference in fluorescence characteristics is a waveform analysis mechanism capable of identifying a difference in fluorescence lifetime between the inorganic phosphor particles 31 and the neutron-insensitive phosphor, and the inorganic phosphor particles 31 and the neutron-insensitive fluorescence. A wavelength analysis mechanism that can identify the light emission wavelength of the body is included.

  Hereinafter, the waveform analysis mechanism will be illustrated more specifically. The waveform analysis mechanism includes a preamplifier, a main amplifier, a waveform analyzer, and a time amplitude converter.

  In the neutron detector of the present embodiment formed by combining the neutron scintillator 1 and the photodetector 3, the signal output from the photodetector 3 is input to the main amplifier via the preamplifier, and is amplified and shaped. Here, the intensity of the signal amplified and shaped by the main amplifier and output from the main amplifier increases with time. The time required for the increase (hereinafter also referred to as rise time) is the inorganic phosphor particle 31. Alternatively, it reflects the fluorescence lifetime of the neutron-insensitive phosphor, and the shorter the fluorescence lifetime, the shorter the rise time.

  In order to analyze the rise time, the signal amplified and shaped by the main amplifier is input to the waveform analyzer. The waveform analyzer time-integrates the signal input from the main amplifier, and outputs a logic signal when the time-integrated signal intensity exceeds a predetermined threshold. Here, the waveform analyzer is provided with two-stage threshold values, and the first logic signal and the second logic signal are output at a certain time interval.

  Next, the two logic signals output from the waveform analyzer are input to a time amplitude converter (TAC), and the time difference between the two logic signals output from the waveform analyzer is converted into a pulse amplitude. Output. The pulse amplitude reflects the time interval between the first logic signal and the second logic signal output from the waveform analyzer, that is, the rise time.

  As understood from the above description, the smaller the pulse amplitude output from the time-amplitude converter, the shorter the rise time, and thus the shorter the fluorescence lifetime of the inorganic phosphor particle 31 or neutron-insensitive phosphor. .

  Hereinafter, the wavelength analysis mechanism will be illustrated more specifically. The wavelength analysis mechanism includes an optical filter, a second photodetector connected to the neutron scintillator 1 through the optical filter, and a discrimination circuit.

  In this embodiment, a part of the light emitted from the neutron scintillator 1 is guided to the first photodetector without going through the optical filter, and the other part is sent to the second photodetector through the optical filter. Led.

  Here, the inorganic phosphor particles 31 emit light at a wavelength of Anm, and the neutron-insensitive phosphor emits light at a wavelength of Bnm different from Anm. Then, as described above, when γ rays are incident, both the inorganic phosphor particles 31 and the neutron-insensitive phosphor emit fluorescence, so that the neutron scintillator 1 emits light of Anm and Bnm, and neutrons are emitted. When incident, only the inorganic phosphor particles 31 emit fluorescence, so only the light of Annm is emitted.

  In this aspect, the optical filter is a filter that blocks light having a wavelength of Anm and transmits light having a wavelength of Bnm. Therefore, the Anm light emitted from the neutron scintillator 1 when irradiated with neutrons reaches the first photodetector, but does not reach the second photodetector because it is blocked by the optical filter. On the other hand, among the light emitted from the scintillator when irradiated with γ-rays, the light of Anm is the same as the case of irradiating the neutron, but the light of Bnm reaches the first photodetector. And also reaches the second photodetector for transmission through the optical filter.

  Therefore, when Anm light is incident on the first photodetector and a signal is output from the photodetector, if no signal is output from the second photodetector, an event due to neutrons occurs, and Bnm light Is incident on the second photodetector and a signal is output from the photodetector, it can be identified as an event caused by γ rays.

  In this embodiment, a discrimination circuit is provided to discriminate neutrons and γ rays as described above. The discrimination circuit operates in synchronization with the signal from the first photodetector, and determines whether or not there is a signal from the second photodetector when the signal from the photodetector is output. Circuit. Specific examples of the discrimination circuit include an anti coincidence circuit and a gate circuit.

  Specific examples of such organic phosphors include 2,5-Diphenyloxazole, 1,4-Bis (5-phenyl-2-oxazole) benzene, 1,4-Bis (2-methylstyryl) benzene, anthracene, stilbene and Organic phosphors such as naphthalene and derivatives thereof may be mentioned. Such an organic phosphor generally has a shorter fluorescence lifetime than that of the inorganic phosphor particles 31, and therefore can be suitably used to improve n / γ discrimination using the difference in fluorescence lifetime.

  The content of the neutron-insensitive phosphor can be appropriately set within a range in which the effect of the present embodiment is exerted, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more with respect to the resin. Is particularly preferred. By setting the content to 0.01% by mass or more, the neutron-insensitive phosphor is efficiently excited by the energy imparted from the secondary electrons, and the intensity of light emitted from the neutron-insensitive phosphor increases. Further, the upper limit of the content of the neutron-insensitive phosphor is not particularly limited, but should be 5% by mass or less based on the resin for the purpose of preventing the intensity of light emitted from the neutron-insensitive phosphor from being attenuated by concentration quenching. Is preferable, and it is especially preferable to set it as 2 mass% or less. By setting the content of the neutron-insensitive phosphor in such a range, the intensity of light emitted from the neutron-insensitive phosphor increases, and neutrons and γ-rays are utilized by utilizing the difference in fluorescence characteristics from the inorganic phosphor particles 31. Can be easily discriminated.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In addition, not all combinations of features described in the embodiments are essential to the solution means of the present invention.

  In the present embodiment, the effect obtained by not including the inorganic phosphor particles 31 in the cylindrical first region including the outer periphery of the wavelength conversion fiber 20 is confirmed by assuming the modeled neutron scintillator 1S.

  FIG. 6 is a cross-sectional view of the modeled neutron scintillator 1S. In this model, the optical path of light in the neutron scintillator 1S will be described with respect to a cross section viewed from the longitudinal direction of the neutron scintillator 1S. However, the longitudinal direction of the neutron scintillator 1S in FIG. This is the same even when the optical path of (direction) is taken into account.

  The neutron scintillator 1S includes a wavelength conversion fiber 20S and a resin composition portion 30S surrounding the wavelength conversion fiber 20S. The neutron scintillator 1S has a uniform cross section and is formed in a rod shape. The neutron scintillator 1S has a circular cross section with a diameter of 5 mm.

  The wavelength conversion fiber 20S has a circular cross section with a diameter of 1 mm. The resin composition part 30S has a resin part 32S, one first inorganic phosphor particle 31Sa, and twenty second inorganic phosphor particles 31Sb. The first inorganic phosphor particles 31Sa are located on the surface 20a of the wavelength conversion fiber 20S. The second inorganic phosphor particles 31Sb are disposed at a distance of 1 mm from the surface 20a of the wavelength conversion fiber.

The first and second inorganic phosphor particles 31Sa and 31Sb emit light isotropically by the incidence of γ rays or neutrons.
The first inorganic phosphor particles 31Sa are located on the surface 20a of the wavelength conversion fiber 20S. For this reason, 180 degree light injects into the wavelength conversion fiber 20S among the light radiate | emitted from the 1st inorganic fluorescent substance particle 31Sa to 360 degree omnidirectional in a cross section.
On the other hand, since the second inorganic phosphor particles 31Sb are separated from the surface 20a of the wavelength conversion fiber 20S by a distance equal to the radius of the wavelength conversion fiber 20S, the light emitted in all 360 ° directions in the cross section Geometrically 60 ° light enters the wavelength conversion fiber 20S.

  An irregular reflection material 35S is provided on the outer peripheral surface 30a of the resin composition portion 30S. The irregularly reflecting material 35S reflects light emitted from the first and second inorganic phosphor particles 31Sa and 31Sb and reaching the outer peripheral surface 30a of the resin composition portion 30S with a reflectance of 90%. The outer peripheral surface 30a is separated from the surface 20a of the wavelength conversion fiber 20S by a distance that is four times the radius of the wavelength conversion fiber 20S. Accordingly, among the light that is reflected by the irregularly reflecting material 35S and diffused and emitted in the direction of 180 °, the geometrically 22 ° light is incident on the wavelength conversion fiber 20S.

In the model of FIG. 6, the ratio of the light incident on the wavelength conversion fiber 20 </ b> S out of the light emitted from each of the first and second inorganic phosphor particles 31 Sa and 31 Sb is calculated.
(Expression M1) is an expression for calculating the ratio Ra of light incident on the wavelength conversion fiber 20S out of the light emitted from the first inorganic phosphor particles 31Sa.
Similarly, (Expression M2) is an expression for calculating a ratio Rb of light incident on the wavelength conversion fiber 20S out of the light emitted from the second inorganic phosphor particles 31Sb.

The first term on the right side of (Formula M1) and (Formula M2) is the ratio of the light directly incident on the wavelength conversion fiber 20S out of the light emitted from the first or second inorganic phosphor particles 31Sa and 31Sb. Represents.
Further, the second term on the right side of (Formula M1) and (Formula M2) is after the light emitted from the first or second inorganic phosphor particles 31Sa and 31Sb is reflected by the irregular reflection material 35S only once. Represents the ratio of light incident on the wavelength conversion fiber 20S. Further, the third and subsequent terms on the right side are the ratio of light incident on the wavelength conversion fiber 20S after being reflected by the irregularly reflecting material 35S, such as twice, three times, and so on.
(Formula M1) and (Formula M2) can be calculated by converting into the following (Formula M3) and (Formula M4), respectively.

  From (Expression M3), in this model, the ratio Ra of the light incident on the wavelength conversion fiber 20S out of the light emitted from the first inorganic phosphor particles 31Sa is 0.76 (that is, 76%). In addition, from (Equation M4), the ratio Rb of light incident on the wavelength conversion fiber 20S out of the light emitted from the second inorganic phosphor particles 31Sb is 0.60 (that is, 60%).

  Next, in the model of FIG. 6, when neutrons N and γ rays are incident on the neutron scintillator 1S, they are emitted from the first and second inorganic phosphor particles 31Sa and 31Sb due to the neutrons and γ rays. The probability that m photons are incident on the wavelength conversion fiber 20S is calculated.

Here, in this model, the number of reactions when neutron N is incident on one inorganic phosphor particle 31Sa, 31Sb is 1 × 10 ³ . The number of reactions here means the number of times of excitation of the inorganic phosphor by the secondary particles generated when the neutron N is incident on the inorganic phosphor particles 31Sa and 31Sb. Therefore, when the neutron N is incident on one inorganic phosphor particle 31Sa, 31Sb, 1 × 10 ³ excitations occur.
In this model, the number of reactions when γ rays are incident on one inorganic phosphor particle 31Sa, 31Sb is 1 × 10 ¹¹ . The number of reactions here means the number of times of excitation of the inorganic phosphor by secondary electrons generated by the incidence of γ rays on the inorganic phosphor particles 31Sa and 31Sb. Therefore, when γ rays are incident on one inorganic phosphor particle 31Sa, 31Sb, 1 × 10 ¹¹ excitations occur.

In this model, the number of photons emitted from the inorganic phosphor particles 31Sa and 32Sb per reaction caused by the incidence of neutrons is 200 photon (actually referred to as 20,000 photon). To do. Similarly, in this model, the number of photons emitted from the inorganic phosphor particles 31Sa and 32Sb per reaction caused by the incidence of γ rays is 125 photon (actually, it is said to be 0 to 15,000 photon). ).
In an actual neutron scintillator, it is said that the value is in the above parentheses. However, in this model, the above value is used to simplify the calculation.

First, the number of photons that enter the wavelength conversion fiber 20S when neutrons enter the inorganic phosphor particles 31Sa and 32Sb will be examined.
When neutrons are incident on the first inorganic phosphor particles 31Sa, the probability Pna that only m photons emitted due to the incident neutrons enter the wavelength conversion fiber is expressed by the following (formula M5). expressed. In (Formula M5), Ra is 0.76 as determined above.

  Similarly, when a neutron is incident on the second inorganic phosphor particle 31Sb, the probability Pnb that only m photons emitted due to the incident neutron are incident on the wavelength conversion fiber 20S has the following ( It is represented by Formula M6). In (Formula M6), Rb is 0.60 as determined above.

Further, in one inorganic phosphor particle 31Sa, 31Sb, there is a point where the reaction occurs 1 × 10 ³ times by the incidence of neutron N, and one first inorganic phosphor particle 31Sa exists, and the second inorganic fluorescence particle Taking into account the fact that 20 body particles 31Sb are present, in the neutron scintillator of FIG. 6, when neutron n is incident on the first and second inorganic phosphor particles 31Sa and 31Sb, photons that are incident on the wavelength conversion fiber 20S The number of occurrences Cnab of the event having the number m is expressed by the following (formula M7).
Cnab = (1 × 10 ³ × 1 × Pna) + (1 × 10 ³ × 20 × Pnb)
(Formula M7)

  FIG. 7 shows a graph in which the number of photons incident on the wavelength conversion fiber 20S and the number of occurrences Cnab of this event are plotted based on the above-described (Expression M7).

  In the above (Formula M7), the first term on the right side corresponds to the number of photons emitted from the first inorganic phosphor particle 31Sa, and the second term is emitted from the second inorganic phosphor particle 31Sb. Corresponds to the number of photons produced.

Here, as shown in the present embodiment, when the inorganic phosphor particles are not included in the vicinity of the wavelength conversion fiber 20S (that is, in FIG. 1, the first region A1 of the resin composition portion 30 does not include the inorganic phosphor particles 31). In this case, when the neutron N is incident on the second inorganic phosphor particle 31Sb, the number of occurrences Cnb of the event that the number of photons incident on the wavelength conversion fiber 20S becomes m is expressed by the following (formula M8). Is done.
Cnb = (1 × 10 ³ × 20 × Pnb) (Formula M8)

  FIG. 8 is a graph in which the number of photons incident on the wavelength conversion fiber 20S and the number of occurrences Cnb of this event are plotted based on the above-described (Expression M8).

Next, the number of photons that enter the wavelength conversion fiber 20S when γ rays enter the inorganic phosphor particles 31Sa and 32Sb will be discussed.
When γ rays are incident on the first inorganic phosphor particles 31Sa, the probability Pγa that only m photons emitted due to the incidence of the γ rays are incident on the wavelength conversion fiber is expressed by the following equation (M9). ).

  Similarly, when γ rays are incident on the second inorganic phosphor particles 31Sb, the probability Pγb that only m photons emitted due to the incidence of the γ rays are incident on the wavelength conversion fiber 20S is as follows. (Expression M10).

Further, in one inorganic phosphor particle 31Sa, 31Sb, there is a point where 1 × 10 ¹¹ reactions occur due to the incidence of γ rays, and there is one first inorganic phosphor particle 31Sa, and the second inorganic fluorescence particle In consideration of the fact that 20 body particles 31Sb are present, in the neutron scintillator of FIG. 6, the number of photons incident on the wavelength conversion fiber 20S becomes m for the incidence of γ rays on the inorganic phosphor particles 31S. The number of occurrences Cγab is expressed by the following (formula M11).
Cγab = (1 × 10 ¹¹ × 1 × Pγa) + (1 × 10 ¹¹ × 20 × Pγb)
(Formula M11)

  Based on (Formula M11) described above, when γ rays are incident on the first and second inorganic phosphor particles 31Sa and 31Sb, the number m of photons incident on the wavelength conversion fiber 20S and the number of occurrences of this event Cγab FIG. 9 shows a graph obtained by plotting.

In addition, when the inorganic phosphor particles are not included in the vicinity of the wavelength conversion fiber 20S (that is, when the inorganic phosphor particles 31 are not included in the first region A1 of the resin composition portion 30 in FIG. 1), The number of occurrences Cγb of the event that the number of photons incident on the wavelength conversion fiber 20S becomes m when entering the second inorganic phosphor particle 31Sb is expressed by the following (formula M12).
Cγb = (1 × 10 ¹¹ × 20 × Pγb) (Formula M12)

  Based on (Formula M12) described above, when γ rays are incident on the second inorganic phosphor particles 31Sb, the number of photons m incident on the wavelength conversion fiber 20S and the number of occurrences Cγb of this event are plotted. A graph is shown in FIG.

FIG. 11 shows the number m of photons incident on the wavelength conversion fiber 20S when neutron N and γ rays are incident on the first and second inorganic phosphor particles 31Sa and 31Sb, respectively, in this model. It is a graph which shows the relationship of the frequency | count of generation | occurrence | production. That is, FIG. 11 is a graph obtained by superimposing the graph shown in FIG. 7 and the graph shown in FIG.
FIG. 13 shows the number m of photons incident on the wavelength conversion fiber 20S due to neutrons N and γ rays in the model having the first and second inorganic phosphor particles 31Sa and 31Sb, respectively, and the occurrence of this event. It is a graph which shows the sum total of the relationship of frequency | count. That is, FIG. 13 is a graph in which the numbers of occurrences shown in FIGS. 7 and 9 are added together.
In FIG. 11, the vertical axis (number of occurrences) is logarithmic, and in FIG. 13, the vertical axis is linear.

FIG. 12 shows that when the first inorganic phosphor particles 31Sa of this model are omitted (when the inorganic phosphor particles are not included in the vicinity of the wavelength conversion fiber 20S), the neutron N and the γ-ray are respectively the first and first neutrons. 2 is a graph showing the relationship between the number of photons m incident on the wavelength conversion fiber 20S and the number of occurrences of this event when they are incident on two inorganic phosphor particles 31Sa and 31Sb. That is, FIG. 12 is a graph obtained by superimposing the graph shown in FIG. 8 and the graph shown in FIG.
FIG. 14 shows the sum of the relationship between the number of photons m incident on the wavelength conversion fiber 20S due to neutrons N and γ rays and the number of occurrences of this event in a model having only the second inorganic phosphor particles 31Sb. It is a graph which shows. That is, FIG. 14 is a graph in which the numbers of occurrences shown in FIGS. 8 and 10 are added together.
In FIG. 12, the vertical axis (number of occurrences) is logarithmic, and in FIG. 14, the vertical axis is linear.

As shown in FIG. 11, when inorganic phosphor particles are present in the vicinity of the wavelength conversion fiber 20S (that is, when the first inorganic phosphor particles 31Sa are present), an output result derived from γ rays, The output results depending on the neutron N are greatly overlapped. Moreover, one of the peaks of the output result depending on the neutron N overlaps with the output result derived from γ rays.
FIG. 13 can be regarded as a detection result of the neutron scintillator 1S when inorganic phosphor particles are present in the vicinity of the wavelength conversion fiber 20S. As shown in FIG. 13, when inorganic phosphor particles are present in the vicinity of the wavelength conversion fiber 20 </ b> S, one of the peak output results depending on the neutron N overlaps the output result derived from γ rays. The detection results of neutrons are difficult to confirm due to the presence of γ rays.

On the other hand, as shown in FIG. 12, when the inorganic phosphor particles are not present in the vicinity of the wavelength conversion fiber 20S (that is, when the first inorganic phosphor particles 31Sa are not present), the detection depends on the neutron N. The resulting peak is not buried in the graph due to gamma rays.
FIG. 14 can be regarded as a detection result of the neutron scintillator 1S when the inorganic phosphor particles are not present in the vicinity of the wavelength conversion fiber 20S. As shown in FIG. 14, in this detection result, since the peak of the detection result depending on the neutron N is not buried in the γ-ray, the number of event occurrences of a specific number of photons (converted to a peak value) is confirmed. can do.

  That is, when FIG. 13 and FIG. 14 are compared, when the inorganic phosphor particles are not disposed in the vicinity of the wavelength conversion fiber 20S (in the case of FIG. 14), the peak of the detection result depending on the neutron N is easily recognized. be able to. Therefore, in the actual measurement, only the peak caused by the neutron can be easily identified in the measurement result measured by the neutron scintillator. As a result, in the modeled neutron scintillator 1S, it was confirmed that the n / γ discrimination ability can be enhanced by disposing the inorganic phosphor particles in the vicinity of the wavelength conversion fiber 20S.

DESCRIPTION OF SYMBOLS 1 ... Neutron scintillator, 2 ... Neutron detector, 3 ... Photo detector, 4 ... Determination part, 20 ... Wavelength conversion fiber, 30 ... Resin composition part, 31 ... Inorganic fluorescent substance particle, 32 ... Resin part, A1 ... 1st Area, A2 ... second area

Claims (7)

A resin composition part comprising inorganic phosphor particles containing at least one neutron capture isotope selected from lithium 6 and boron 10, and a wavelength conversion fiber at least partially encapsulated in the resin composition part. A neutron scintillator as a component,
The resin composition part has a cylindrical first region including an outer periphery of the wavelength conversion fiber, and a second region located outside the first region, and the inorganic phosphor in the first region The density of the particles is lower than the density of the inorganic phosphor particles in the second region,
Neutron scintillator. The first region of the resin composition part does not contain the inorganic phosphor particles,
The neutron scintillator according to claim 1. The ratio of the distance between the central axis of the wavelength conversion fiber and the outer wall surface of the resin composition portion with respect to the diameter of the wavelength conversion fiber is in the range of 1 to 10.
The neutron scintillator according to claim 1 or 2. At the emission wavelength of the inorganic phosphor particles, the ratio of the refractive index of the inorganic phosphor particles to the refractive index of the resin is in the range of 0.95 to 1.05.
The neutron scintillator according to any one of claims 1 to 3. The neutron scintillator according to any one of claims 1 to 4 and a photodetector.
Neutron detector. A neutron scintillator comprising a resin composition part comprising inorganic phosphor particles containing a neutron capture isotope and a wavelength conversion fiber at least partially encapsulated in the resin composition part,
A photodetector for detecting light emitted from the neutron scintillator;
A determination unit for determining the presence or absence of neutron beams is provided.
The determination unit approximates the logarithm of the detection frequency with respect to the peak value of the light detected by the photodetector to a linear function, and the detection frequency of the peak value in the vicinity of 4.8 MeV or 2.3 MeV is obtained from the linear function. When there is a divergence, determine the presence of neutrons,
Neutron detector. A neutron scintillator comprising a resin composition part comprising inorganic phosphor particles containing a neutron capture isotope and a wavelength conversion fiber at least partially encapsulated in the resin composition part,
Using a photodetector that detects light emitted from the neutron scintillator,
When the logarithm of the detection frequency with respect to the peak value of the light detected by the photodetector is approximated to a linear function, the detection frequency of the peak value near 4.8 MeV or 2.3 MeV deviates from the linear function. Determine the presence of neutrons,
Neutron detection method.

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