WO2022059298A1 - プラスチックシンチレーションファイバ及びその製造方法 - Google Patents

プラスチックシンチレーションファイバ及びその製造方法 Download PDF

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Publication number
WO2022059298A1
WO2022059298A1 PCT/JP2021/025026 JP2021025026W WO2022059298A1 WO 2022059298 A1 WO2022059298 A1 WO 2022059298A1 JP 2021025026 W JP2021025026 W JP 2021025026W WO 2022059298 A1 WO2022059298 A1 WO 2022059298A1
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Prior art keywords
layer
core
plastic
fiber
clad layer
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PCT/JP2021/025026
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English (en)
French (fr)
Japanese (ja)
Inventor
勝洋 藤田
修 新治
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Kuraray Co Ltd
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Kuraray Co Ltd
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Priority to CN202180062925.7A priority Critical patent/CN116261677B/zh
Priority to EP21868985.9A priority patent/EP4215949A4/en
Priority to JP2022550362A priority patent/JP7645894B2/ja
Priority to US18/026,015 priority patent/US12270954B2/en
Publication of WO2022059298A1 publication Critical patent/WO2022059298A1/ja
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/20—Measuring radiation intensity with scintillation detectors
    • G01T1/201—Measuring radiation intensity with scintillation detectors using scintillating fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T3/00—Measuring neutron radiation
    • G01T3/06—Measuring neutron radiation with scintillation detectors

Definitions

  • the present invention relates to a plastic scintillation fiber and a method for manufacturing the same.
  • the conventional plastic scintillation fiber is a plastic fiber in which the outer peripheral surface of the core, which is a scintillator, is covered with a clad layer having a lower refractive index than the core, and is mainly used for radiation detection.
  • the core is composed of a polymer material obtained by adding an organic phosphor to a substrate having an aromatic ring such as polystyrene or polyvinyltoluene.
  • the clad layer is composed of a low refractive index polymer material such as polymethylmethacrylate or fluorine-containing polymethylmethacrylate.
  • the core base material of the scintillation fiber has an aromatic ring, and when the irradiated radiation crosses the scintillation fiber, it absorbs a part of the energy by re-radiation of secondary particles in the core and emits it as ultraviolet rays. It has the characteristic of doing. If no phosphor is added to the core substrate, this ultraviolet ray is self-absorbed by the core substrate itself and disappears without being transmitted in the core.
  • this ultraviolet ray is absorbed by the phosphor added to the core base material, and the light having a longer wavelength is re-emitted. Therefore, by selecting an appropriate phosphor, it is converted into light having a long wavelength such as blue, which is difficult to be self-absorbed by the core substrate, and transmitted in the fiber.
  • the light transmitted in the fiber is detected by a detector connected to one end or both ends.
  • the scintillation fiber has two functions of light emission by radiation detection and optical transmission, and is used for applications such as calculating the passing position and amount of radiation.
  • it is important how to efficiently convert the ultraviolet light emitted from the core into a long wavelength and transmit it over a long distance.
  • plastic wavelength conversion fiber (WLSF: Wavelength Shifting Fiber) is often used alongside scintillation fiber.
  • the wavelength conversion fiber is used in combination with, for example, a plastic scintillator that emits blue light. Grooves and holes are provided in a plate-shaped or rod-shaped plastic scintillator, and a wavelength conversion fiber that absorbs blue light and converts it into green light is embedded.
  • wavelength conversion fiber that is thin, easy to bend, and capable of long-distance transmission is preferably used.
  • a large number of wavelength conversion fibers can be freely laid out up to an external photoelectric detector.
  • the core of the wavelength conversion fiber is made of polystyrene resin or polymethylmethacrylate resin, and a fluorescent substance for wavelength conversion is dissolved in it.
  • the scintillation light incident from the external scintillator is absorbed by the phosphor in the core, and the wavelength is efficiently converted and transmitted in the fiber.
  • the scintillator to be combined with the wavelength conversion fiber is not limited to a plastic scintillator, but an inorganic scintillator having high sensitivity to neutrons and the like is used.
  • the wavelength conversion fiber can easily collect the scintillation light emitted from a large-area or long scintillator or a special scintillator for neutron detection.
  • the wavelength conversion fiber can transmit the wavelength-converted light in the core and freely connect to the photoelectric detector.
  • an inorganic scintillator is used.
  • the inorganic scintillator many known as those disclosed in Patent Document 1, LiF / ZnS: Ag, LiI: Eu 2+ , LiBaF 3 : Ce 3+ , LiCaAlF 6 : Ce 3+ , Li 2 B 4 O 7 : Cu + , etc. Has been done.
  • the inorganic scintillator has an attenuation length of several mm and is not highly transparent, and cannot transmit emitted light (that is, scintillation light) over a long distance.
  • emitted light that is, scintillation light
  • it is difficult to optically transmit to a photoelectric detector by an inorganic scintillator due to the limitation of crystal size.
  • Patent Documents 2 and 3 a sheet in which fine particles obtained by crushing an inorganic scintillator are dispersed in a transparent resin has been developed for detecting neutrons.
  • the difference in refractive index between the inorganic scintillator and the transparent resin is large, transparency cannot be ensured, and the sheet itself cannot efficiently transmit light to the photoelectric detector.
  • the wavelength conversion fiber is placed along the end face and the surface of the scintillator, and the wavelength conversion fiber is used for optical transmission to the photoelectric detector.
  • the detected light can be transmitted over a longer distance.
  • a large number of post-processings in which a scintillator and a wavelength conversion fiber are combined are required. Become.
  • the core itself is required to have high transparency because it emits scintillation light and also transmits light to the photoelectric detector. Therefore, it is not possible to obtain a plastic scintillation fiber for detecting a neutron beam by including a material that emits scintillation light by irradiation with a neutron beam in the core.
  • the scintillation light radiated from the external scintillator is wavelength-converted and transmitted in the core, so that the core is required to have high transparency. Therefore, it is not possible to obtain a plastic scintillation fiber for detecting a neutron beam by including a material that emits scintillation light by irradiation with a neutron beam in the core.
  • the present invention has been made in view of such circumstances, and an object of the present invention is to provide a plastic scintillation fiber capable of detecting a neutron beam and having excellent productivity.
  • the plastic scintillation fiber according to one aspect of the present invention is The outermost layer containing an organic compound containing an element having a neutron reaction cross section larger than that of hydrogen and containing a plastic material that emits scintillation light when irradiated with neutron rays.
  • a clad layer that covers the outer peripheral surface of the core and has a lower refractive index than the core is provided.
  • the wavelength conversion fiber including the core and the clad layer and the outermost peripheral layer covering the outer peripheral surface of the wavelength conversion fiber are integrally formed.
  • the outermost peripheral layer contains an organic compound containing an element having a neutron reaction cross section larger than that of hydrogen, and contains a plastic material that emits scintillation light by irradiation with neutron rays. Therefore, the sensitivity to neutrons is improved as compared with ordinary plastic scintillation fibers.
  • elements such as lithium 6, boron-10, and gadolinium, which have a neutron reaction cross section larger than hydrogen, emit much more radiation than the elements such as carbon, oxygen, and hydrogen that make up a normal plastic scintillator. Emit.
  • such radiation is generated in the plastic material constituting the outermost peripheral layer, and the scintillation light is generated by the radiation.
  • the organic compound can be added at a high concentration.
  • the internal core absorbs the scintillation light emitted from the outermost layer, converts the wavelength, and transmits the light. Therefore, it is possible to detect neutron rays, which are difficult to detect due to low sensitivity with conventional plastic scintillation fibers.
  • the wavelength conversion fiber including the core and the clad layer and the outermost peripheral layer covering the outer peripheral surface of the wavelength conversion fiber are integrally formed, post-processing for combining the scintillator and the wavelength conversion fiber, which has been conventionally required, is unnecessary. Will be. That is, it is possible to provide a plastic scintillation fiber capable of detecting a neutron beam and having excellent productivity.
  • the outermost layer may contain at least one kind of phosphor that absorbs the scintillation light and converts the wavelength into a long wavelength.
  • the organic compound may contain lithium 6.
  • the organic compound may contain boron-10.
  • the organic compound may be a carborane-based compound.
  • the carborane compound has a high ratio of boron to the molecular weight, and 10 atoms of boron can be efficiently added. Further, the ratio of boron to the molecular weight of the organic compound may be 50% or more. With such a configuration, the boron-10 can be contained at a high concentration, and the neutron reactivity becomes high.
  • the organic compound may contain gadolinium.
  • wavelength conversion fiber and the outermost peripheral layer may be integrally formed by drawing. Productivity is improved.
  • a protective layer that protects the outermost layer may be integrally formed on the outer side of the outermost layer. This improves durability and the like.
  • the clad layer may have a multi-clad structure including an inner clad layer and an outer clad layer that covers the outer peripheral surface of the inner clad layer and has a lower refractive index than the inner clad layer. .. The total reflection angle becomes wider and the light emission becomes higher.
  • a reflective layer may be provided outside the outermost layer or the protective layer.
  • the scintillation light emitted from the outermost peripheral layer and the light wavelength-converted by the core are reflected by the reflective layer, so that the light is less likely to leak from the side surface of the fiber to the outside, resulting in high emission.
  • the reflective film may be a metal film. With this configuration, high reflectance can be obtained with a thin thickness.
  • the method for manufacturing a plastic scintillation fiber according to one aspect of the present invention is as follows.
  • the outermost layer containing an organic compound containing an element having a neutron reaction cross section larger than that of hydrogen and containing a plastic material that emits scintillation light when irradiated with neutron rays.
  • a core having a high refractive index which is provided inside the outermost layer and contains at least one kind of phosphor that absorbs the scintillation light and converts the wavelength into a long wavelength.
  • a method for manufacturing a plastic scintillation fiber comprising: a clad layer having a refractive index lower than that of the core while covering the outer peripheral surface of the core.
  • the present invention comprises a step of drawing a line while heating the preform.
  • the method for manufacturing a plastic scintillation fiber is as follows.
  • the outermost layer containing an organic compound containing an element having a neutron reaction cross section larger than that of hydrogen and containing a plastic material that emits scintillation light when irradiated with neutron rays.
  • a core having a high refractive index which is provided inside the outermost layer and contains at least one kind of phosphor that absorbs the scintillation light and converts the wavelength into a long wavelength.
  • a method for manufacturing a plastic scintillation fiber comprising: a clad layer having a refractive index lower than that of the core while covering the outer peripheral surface of the core. The outermost peripheral layer is coated on the surface of the wavelength conversion fiber including the core and the clad layer.
  • FIG. It is sectional drawing of the plastic scintillation fiber which concerns on Embodiment 1.
  • FIG. It is sectional drawing of the plastic scintillation fiber which concerns on the modification of Embodiment 1.
  • FIG. It is sectional drawing of the plastic scintillation fiber which concerns on other modification of Embodiment 1.
  • FIG. It is a perspective view which shows the manufacturing method of the plastic scintillation fiber which concerns on Embodiment 1.
  • FIG. It is a perspective view which shows the application example of the scintillation fiber which concerns on Embodiment 1.
  • FIG. It is the emission spectrum of the paraterphenyl added to the outermost layer and the absorption and emission spectra of the wavelength conversion phosphor BBOT.
  • FIG. 1 is a cross-sectional view of the plastic scintillation fiber according to the first embodiment.
  • the plastic scintillation fiber according to the first embodiment includes an outermost peripheral layer 1, a core 2, and a clad layer 3.
  • the outermost layer 1 is made of a plastic material that emits scintillation light by irradiation with neutron rays.
  • the plastic material contains an organic compound containing an element having a neutron reaction cross section larger than that of hydrogen. Further, the plastic material may contain, in addition to an organic compound containing an element having a neutron reaction cross section larger than that of hydrogen, a phosphor that absorbs scintillation light emitted from the plastic material and converts it into a long wavelength.
  • the outermost peripheral layer 1 may sufficiently emit light and be transparent to the extent that scintillation light penetrates the clad layer 3 and is incident on the core 2 in the center, and high transparency is not required, but it is as transparent as possible. It is desirable to have.
  • the thickness of the outermost layer may be increased in order to obtain the required sensitivity to neutrons. Even if the outermost layer 1 which is a scintillator layer has low transparency, long-distance transmission is possible if the core 2 at the center, which is responsible for optical transmission, has high transparency.
  • the core 2 is made of a transparent resin having a high refractive index, which is provided inside the outermost layer 1 and contains at least one kind of phosphor that absorbs the scintillation light generated in the outermost layer 1 and converts it into a longer wavelength. Become.
  • the refractive index of the transparent resin constituting the core 2 is preferably 1.5 or more.
  • the clad layer 3 covers the outer peripheral surface of the core 2 and is made of a transparent resin having a lower refractive index than the core 2.
  • the wavelength conversion fiber composed of the core 2 and the clad layer 3 and the outermost peripheral layer 1 covering the outer peripheral surface of the wavelength conversion fiber are integrally formed.
  • the transparency of the clad layer 3 is as important as the transparency of the core 2.
  • the transparency of the outermost layer 1 is not so important.
  • the thickness of the clad layer 3 is preferably 3 ⁇ m to 100 ⁇ m, which is sufficiently thicker than the depth of the evanescent wave from which the transmitted light seeps from the core 2 to the clad layer 3. If the thickness of the clad layer 3 is sufficiently thicker than the depth of the evanescent wave exuding into the clad layer 3, the refractive index of the clad layer 3 and the outermost peripheral layer 1 may be the same, or the same transparent resin may be used.
  • the core 2 may include a second phosphor for further wavelength conversion in order to match the wavelength sensitivity of a photoelectric detector such as a photomultiplier tube (PMT) or an avalanche photodiode (APD).
  • a photoelectric detector such as a photomultiplier tube (PMT) or an avalanche photodiode (APD). The details of the phosphor will be described later.
  • the plastic scintillation fiber according to the first embodiment scintillation light is generated in the outermost peripheral layer 1 by irradiation with neutron rays, and the scintillation light is absorbed by the internal core 2 to be wavelength-converted and optically transmitted. Therefore, the sensitivity is low with the conventional plastic scintillation fiber, and the neutron beam, which was difficult to detect, can be detected with high sensitivity. That is, the plastic scintillation fiber according to the first embodiment is a composite type plastic optical fiber having both a scintillation function for neutron rays and a wavelength conversion function.
  • the wavelength conversion fiber composed of the core 2 and the clad layer 3 and the outermost peripheral layer 1 covering the outer peripheral surface of the wavelength conversion fiber are integrally formed. Therefore, post-processing that combines a scintillator and a wavelength conversion fiber, which was conventionally required, is not required, and productivity can be dramatically improved and costs can be reduced as compared with the conventional case.
  • a protective layer (not shown) that protects the outermost peripheral layer may be integrally formed on the outermost side of the outermost peripheral layer 1. The protective layer improves the durability of the plastic scintillation fiber.
  • FIG. 2 is a cross-sectional view of a plastic scintillation fiber according to a modified example of the first embodiment.
  • the reflective layer 5 may be provided on the surface of the outermost peripheral layer 1 or the protective layer.
  • the scintillation light emitted by the outermost peripheral layer 1 and the light wavelength-converted by the core 2 are reflected by the reflection layer 5, so that the light is less likely to leak from the side surface of the fiber to the outside, resulting in high emission.
  • the reflective layer 5 as a metal film, a high reflectance can be obtained with a thin thickness, which is preferable.
  • FIG. 3 is a cross-sectional view of a plastic scintillation fiber according to another modification of the first embodiment.
  • the plastic scintillation fiber according to another modification includes a clad layer 3 as an inner clad layer and a clad layer 4 as an outer clad layer. That is, the clad layer has a multi-clad structure including an inner clad layer (clad layer 3) and an outer clad layer (clad layer 4).
  • the clad layer 4 covers the outer peripheral surface of the clad layer 3 and is made of a transparent resin having a lower refractive index than that of the clad layer 3.
  • the re-emitted light whose wavelength is converted in the core 2 is emitted isotropically in a solid angle in the core 2. Therefore, only light within the total reflection angle based on the difference in refractive index between the core 2 and the clad layer 3 or the clad layer 4 can be transmitted in the fiber direction. Since the plastic scintillation fiber according to the other modification includes the clad layer 4 having a low refractive index in addition to the clad layer 3, the total reflection angle is wider than that of the plastic scintillation fiber of FIG. 1 (numerical aperture NA is larger). , Higher emission.
  • the outermost layer 1 which is a scintillator layer is made of a transparent resin, that is, a plastic material which emits scintillation light by irradiation with neutron rays.
  • the transparent resin contains an organic compound containing an element having a neutron reaction cross section larger than that of hydrogen.
  • the transparent resin constituting the outermost peripheral layer 1 is preferably thermoplastic so that it can be drawn finely by heating.
  • a transparent resin any one of a methacrylic acid ester monomer group represented by methyl methacrylate, an acrylic acid ester monomer group represented by methyl acrylate, and an aromatic monomer group having a vinyl group represented by styrene.
  • a homopolymer composed of or a copolymer is preferable.
  • the transparent resin may contain a phosphor that emits scintillation light by radiation, or the transparent resin itself may emit scintillation light by radiation.
  • a homopolymer or a copolymer composed of any of a group of aromatic monomers having a vinyl group typified by styrene is suitable.
  • An organic compound containing an element having a neutron reaction cross section larger than that of hydrogen should be stable and highly soluble in an aromatic monomer having a vinyl group typified by styrene (that is, a monomer which is a raw material of a transparent resin). desirable.
  • an aromatic monomer having a vinyl group typified by styrene that is, a monomer which is a raw material of a transparent resin.
  • the higher the solubility the higher the transparency of the polymer obtained by dissolving the organic compound in the aromatic monomer and polymerizing it. If the solubility is low, the organic compound is not uniformly dispersed in the transparent resin, and problems such as variation in sensitivity to neutrons occur. Further, when dispersed as a powder, it may be difficult to draw a line by heating.
  • Examples of elements having a neutron reaction cross section larger than hydrogen include lithium 6, boron-10, and gadolinium.
  • organic compound containing lithium 6 lithium carboxylates such as lithium methacrylate, lithium phenylsalicylate, and lithium pivalite are preferably used.
  • carborane-based compounds such as o-carborane, m-carborane, p-carborane, and derivatives thereof are preferably used.
  • the carborane compound (B 10 C 2 H 12 ) has a high ratio of boron to the molecular weight, and 10 atoms of boron can be efficiently added.
  • the ratio of the total atomic weight of boron to the molecular weight is 50% by mass or more, the boron-10 can be contained at a high concentration, and the neutron reactivity becomes high.
  • gadolinium alkoxide such as gadolinium isopropoxide
  • gadolinium complex such as tris (2,2,6,6-tetramethyl-3,5-heptandionate) gadolinium and the like are preferably used.
  • the wavelength conversion phosphor contained in the outermost layer 1 is an organic phosphor having an aromatic ring and a structure capable of resonating, and it is preferable that a single molecule is dissolved in the core 2.
  • Typical phosphors include 2- (4-t-butylphenyl) -5- (4-biphenyl) -1,3,4-oxadiazole (b-PBD), 2- (2-PBD), which absorb 250 to 350 nm.
  • BDB 4,4'-bis- (2,5-dimethylstyryl) -diphenyl
  • BBOT 2,5-bis- (5-t-butyl-benzoxazoyl) thiophene
  • POPOP 4-Bis- (2- (5-Phenyloxazolyl)) Benzene
  • DMPOPOP 1,4-Bis- (4-Methyl-5-Phenyl-2-oxazolyl) Benzene
  • DMPOPOP 1,4- Diphenyl-1,3-butadiene
  • DPH 1,6-diphenyl-1,3,5-hexatriene
  • An example of the outermost layer 1 is a polystyrene containing lithium pivalite as an organic compound containing an element having a neutron reaction cross section larger than that of hydrogen, and a phosphor containing a phosphor that converts the scintillation light emitted by the polystyrene into a long wavelength. Be done. About 7.5% of the lithium contained in lithium pivalite is lithium 6. Lithium-6 produces alpha rays by neutron rays. This alpha ray causes polystyrene to emit scintillation light, and the phosphor absorbs the scintillation light to shift to a longer wavelength and emit light. The outermost layer 1 emits visible light having a diameter of 400 to 500 nm by a neutron beam.
  • a carborane-based compound containing a high proportion of boron as an organic compound containing an element having a neutron reaction cross-sectional area larger than that of hydrogen is contained, and fluorescence that converts polystyrene scintillation light into a long wavelength.
  • Polystyrene containing the body can be mentioned.
  • About 19.8% of the boron contained in the carborane-based compound is boron-10, which has a much larger neutron reaction cross section than hydrogen. Boron-10 produces alpha rays by neutron rays.
  • This alpha ray causes polystyrene to emit scintillation light, and the phosphor absorbs the scintillation light to shift to a longer wavelength and emit light.
  • the outermost layer 1 scintillates ultraviolet light of 350 to 400 nm by a neutron beam.
  • the types of organic compounds, plastic materials (transparent resins) and phosphors having a neutron reaction cross section larger than that of hydrogen are not limited to the above. Further, the blending ratio, concentration, etc. of the above materials are appropriately selected depending on the difficulty of production and the like, and are not limited to the above.
  • a polymer composed of an aromatic monomer having a vinyl group has a high refractive index and is preferable.
  • the difference in refractive index between the core 2 and the clad layer 3 becomes large, and the total reflection angle becomes wide. That is, among the wavelength-converted light in the core 2, the light having a wider angle can be transmitted, so that a scintillation fiber having higher light emission can be obtained.
  • the wavelength conversion phosphor contained in the core 2 is an organic phosphor having an aromatic ring and a structure capable of resonating, and it is preferable that a single molecule is dissolved in the core 2.
  • Typical phosphors are 2- (4-t-butylphenyl) -5- (4-biphenyl) -1,3,4-oxadiazole (b-PBD), 2- (2-PBD), which absorb 250 to 350 nm.
  • BDB 4,4'-bis- (2,5-dimethylstyryl) -diphenyl
  • BBOT 2,5-bis- (5-t-butyl-benzoxazoyl) thiophene
  • POPOP 4-Bis- (2- (5-Phenyloxazolyl)) Benzene
  • DMPOPOP 1,4-Bis- (4-Methyl-5-Phenyl-2-oxazolyl) Benzene
  • DMPOPOP 1,4- Diphenyl-1,3-butadiene
  • DPH 1,6-diphenyl-1,3,5-hexatriene
  • the absorption spectrum of the wavelength conversion phosphor contained in the core 2 and the emission spectrum of the phosphor contained in the outermost layer 1 have a large overlap.
  • the above-mentioned wavelength conversion phosphor may be used alone, or a plurality of wavelength conversion phosphors may be used in combination.
  • the quantum yield is high and the overlap between the absorption spectrum and the emission spectrum is small (the Stokes shift is large).
  • a wavelength conversion phosphor that emits light at a longer wavelength is preferable, and two or more kinds may be used in combination as appropriate.
  • the wavelength conversion phosphor is preferably soluble in the transparent resin constituting the core 2.
  • the concentration of the wavelength conversion phosphor is preferably 50 to 10000 ppm, more preferably 100 to 1000 ppm, in terms of mass concentration, whether it is a single substance or a plurality of wavelength conversion phosphors. If the density is too low, the scintillation light from the outermost layer 1 cannot be efficiently absorbed by the core 2. On the contrary, if the concentration is too high, the influence of the self-absorption of the phosphor itself becomes large, the wavelength conversion efficiency is lowered, the transmittance for the converted light is lowered, and the attenuation length is deteriorated.
  • the material used for the clad layer 3 is not limited as long as it is a transparent resin having a lower refractive index than the core 2.
  • a homopolymer or a copolymer made from the above is preferable.
  • the material used for the clad layer 4 may be a transparent resin having a lower refractive index than that of the clad layer 3. It can be selected from the monomer group of the clad layer 3 and the like. In particular, it is preferable to select from the group of fluorine-containing monomers having a low refractive index.
  • an organic peroxide or an azo compound may be added as a polymerization initiator.
  • Typical organic peroxides include 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, n-butyl-4,4-bis (t-butylperoxy) valerate, 1, Examples thereof include 1-bis (t-butylperoxy) cyclohexane, but the present invention is not particularly limited as long as it generates radicals by heat or light irradiation.
  • mercaptan may be added as a chain transfer agent for adjusting the molecular weight.
  • a typical mercaptan is octyl mercaptan, but there is no particular limitation as long as it has an R-SH structure (where R represents an organic group).
  • the material constituting the reflective layer 5 is not limited as long as it can reflect the light emitted from the side surface of the fiber with high reflectance. Above all, the metal film is preferable in the case where a thinr thickness and higher reflectance can be obtained as compared with, for example, a white reflective paint, and a small diameter is required as a fiber.
  • the metal film is not particularly limited as long as it has a high reflectance in the required wavelength range such as aluminum, gold, silver, and nickel.
  • Aluminum and silver are suitable because of their high reflectance in the visible light region. Further, aluminum is preferable from the viewpoint of cost.
  • the thickness of the metal film is not particularly limited, it is preferable to obtain a high reflectance with a thickness as thin as possible in the visible light region.
  • a thickness as thin as possible in the visible light region For example, for aluminum, 10 to 100 nm is preferable, and 20 to 70 nm is more preferable.
  • silver 35 to 150 nm is preferable, and 50 to 100 nm is more preferable.
  • the film forming method is not particularly limited, such as a vapor deposition method and a sputtering method.
  • FIG. 4 is a perspective view showing a method for manufacturing a plastic scintillation fiber according to the first embodiment.
  • FIG. 4 shows a base material (preform) for manufacturing the plastic scintillation fiber shown in FIG.
  • the first cylinder 11 is a cylinder made of a thermoplastic resin that scintillates and emits light by neutron rays.
  • This thermoplastic resin contains an organic compound containing an element having a neutron reaction cross section larger than that of hydrogen.
  • the first cylindrical body 11 constitutes the outermost peripheral layer 1 after the drawing process. An example of a method for manufacturing the first cylindrical body 11 will be described later in Examples.
  • the rod 12 is a cylinder made of a transparent thermoplastic resin in which at least one kind of phosphor that absorbs scintillation light and converts the wavelength into a long wavelength is dissolved.
  • the rod 12 constitutes the core 2 after the wire drawing process.
  • the second cylinder 13 has a refractive index lower than that of the rod 12, and is a cylinder made of a transparent thermoplastic resin.
  • the second cylindrical body 13 constitutes the clad layer 3 after the drawing process.
  • FIG. 4 shows a state in which the rod 12 is being inserted into the second cylindrical body 13.
  • the plastic scintillation fiber according to the first embodiment can be obtained by drawing a line to, for example, an outer diameter of 1 mm while heating the tip of the produced preform.
  • a gap is formed between the first cylindrical body 11, the second cylindrical body 13, and the rod 12, but the core 2 and the clad layer are to be drawn under reduced pressure. 3 and the outermost outermost layer 1 are in close contact with each other and integrally formed.
  • the plastic scintillation fiber according to the modified example shown in FIG. 3 can also be manufactured by the same manufacturing method.
  • a scintillator layer (outermost peripheral layer 1) that emits light by neutron rays is integrally formed on the outer peripheral surface of a wavelength conversion fiber (core 2 and clad layer 3). Therefore, the plastic scintillation fiber can detect neutron rays and can transmit light. That is, the plastic scintillation fiber alone has the functions of a conventional scintillator and a wavelength conversion fiber.
  • the scintillator layer (outermost peripheral layer 1) may be integrally formed by coating (including coating) on the surface of the wavelength conversion fiber.
  • the productivity is further improved.
  • FIG. 5 is a perspective view showing an application example of the plastic scintillation fiber according to the first embodiment.
  • the plastic scintillation fiber PSF according to the first embodiment is arranged in an array on the substrate.
  • the right-handed xyz orthogonal coordinates shown in FIG. 5 are for convenience in explaining the positional relationship of the components. Normally, the z-axis positive direction is vertically upward, and the xy plane is a horizontal plane.
  • a photoelectric detector such as a photomultiplier tube is connected to each plastic scintillation fiber PSF (not shown), and the transmitted light can be detected.
  • one-dimensional image detection position detection
  • the resolution is equal to the diameter of the plastic scintillation fiber PSF.
  • such an array of plastic scintillation fiber PSFs is provided in two stages and arranged so as to be orthogonal to each other and stacked one above the other, two-dimensional image detection can be realized.
  • Example 1 5% by mass of m-carborane, which is an organic compound containing boron-10, which has a neutron reaction cross section larger than that of hydrogen, and polymer 2- (4-t-butylphenyl) -5- (4-biphenyl) -1,3. 1% by mass of 4-oxadiazole (b-PBD) is added to a styrene monomer to polymerize the polymer, and the polymer is a cylindrical body for the outermost layer having an outer diameter of 50 mm and an inner diameter of 40 mm (first cylindrical body 11 in FIG. 4). Was molded.
  • b-PBD 4-oxadiazole
  • a core rod (rod 12 in FIG. 4) having a diameter of 32 mm made of polystyrene (refractive index 1.59) and a cylinder for a clad layer having an outer diameter of 38 mm and an inner diameter of 34 mm made of polymethylmethacrylate (refractive index 1.49).
  • the second cylinder 13) of FIG. 4 was prepared. 2,5-Bis- (5-t-butyl-benzoxazoyl) thiophene (BBOT) as a wavelength conversion phosphor was dissolved in the core rod at a concentration of 200 mass ppm.
  • BBOT 2,5-Bis- (5-t-butyl-benzoxazoyl) thiophene
  • the cylinder for the clad layer was inserted inside the cylinder for the outermost peripheral layer, and the rod for the core was inserted inside the cylinder for the clad layer to prepare a preform. While heating the tip of this preform, an integral wire was drawn so that the outer diameter was 1 mm under reduced pressure to obtain a plastic scintillation fiber according to Example 1.
  • This plastic scintillation fiber has the cross-sectional configuration shown in FIG. The outer diameter was 1000 ⁇ m, the diameter of the clad layer 3 was 770 ⁇ m, the diameter of the core 2 was 680 ⁇ m, the thickness of the outermost peripheral layer 1 was 115 ⁇ m, and the thickness of the clad layer 3 was 45 ⁇ m.
  • FIG. 6 shows the emission spectra of the fluorophore 2- (4-t-butylphenyl) -5- (4-biphenyl) -1,3,4-oxadiazole (b-PBD) added to the outermost layer 1. It is a graph which shows the absorption and emission spectrum of the wavelength conversion phosphor BBOT added to the core 2. As shown in FIG. 6, the overlap between the emission spectrum of b-PBD added to the outermost layer 1 and the absorption spectrum of BBOT added to the core 2 is large. Since the plastic scintillation fiber according to Example 1 contains an organic compound having a neutron reaction cross section larger than that of hydrogen, the neutron sensitivity is improved as compared with the conventional plastic scintillation fiber.
  • Example 2 In the same manner as in Example 1, a cylinder for the outermost peripheral layer (first cylinder 11 in FIG. 4) having an outer diameter of 50 mm and an inner diameter of 40 mm was molded. Further, as in Example 1, a core rod (rod 12 in FIG. 4) having a diameter of 28 mm made of polystyrene (refractive index 1.59) and an outer diameter 33 mm made of polymethylmethacrylate (refractive index 1.49). A cylinder for an inner clad layer having an inner diameter of 30 mm (second cylinder 13 in FIG. 4) was prepared. BBOT was dissolved in the core rod as a wavelength conversion phosphor at a concentration of 300 mass ppm.
  • Example 2 a cylindrical body (not shown) for an outer clad layer having an outer diameter of 38 mm and an inner diameter of 35 mm made of a copolymer of a fluorinated monomer such as perfluoroalkyl acrylate (refractive index 1.42) was prepared.
  • the cylinder for the outer clad layer constitutes the clad layer 4 shown in FIG. 3 after the line drawing process.
  • a preform is produced by inserting the cylinder for the outer clad layer inside the cylinder for the outermost layer, inserting the cylinder for the inner clad layer inside the cylinder, and inserting the rod for the core inside the cylinder. did.
  • This plastic scintillation fiber has the cross-sectional configuration shown in FIG.
  • the outer diameter is 1000 ⁇ m
  • the outer diameter of the clad layer 4 is 754 ⁇ m
  • the outer diameter of the clad layer 3 is 682 ⁇ m
  • the diameter of the core 2 is 612 ⁇ m
  • the thickness of the outermost peripheral layer 1 is 123 ⁇ m
  • the thickness of the clad layer 4 is 36 ⁇ m
  • the clad layer 3 The thickness of was 35 ⁇ m.
  • Example 2 When a neutron beam was incident on the plastic scintillation fiber according to Example 2, a light amount about 30% higher than that of Example 1 could be observed at the tip 10 m away. Although the diameter of the core 2 was smaller than that of the first embodiment, it is considered that the total reflection angle was widened and the light emission was higher due to the provision of the clad layer 4 having a lower refraction.
  • Lithium pivalite which is an organic compound containing lithium 6 having a neutron reaction cross section larger than that of hydrogen, is 1.9% by mass, and the phosphor 2- (4-t-butylphenyl) -5- (4-biphenyl) -1, 3,4-Oxadiazole (b-PBD) mass% is added to a styrene monomer to polymerize it, and a cylindrical body for the outermost layer having an outer diameter of 50 mm and an inner diameter of 40 mm (first cylindrical body 11 in FIG. 4) is formed. Molded.
  • a core rod (rod 12 in FIG. 4) having a diameter of 32 mm made of polystyrene (refractive index 1.59) and a cylinder for a clad layer having an outer diameter of 38 mm and an inner diameter of 34 mm made of polymethylmethacrylate (refractive index 1.49).
  • the second cylinder 13) of FIG. 4 was prepared. 2,5-Bis- (5-t-butyl-benzoxazoyl) thiophene (BBOT) as a wavelength conversion phosphor was dissolved in the core rod at a concentration of 200 mass ppm.
  • BBOT 2,5-Bis- (5-t-butyl-benzoxazoyl) thiophene
  • the cylinder for the clad layer was inserted inside the cylinder for the outermost peripheral layer, and the rod for the core was inserted inside the cylinder for the clad layer to prepare a preform. While heating the tip of this preform, an integral wire was drawn so that the outer diameter was 1 mm under reduced pressure to obtain a plastic scintillation fiber according to Example 1.
  • This plastic scintillation fiber has the cross-sectional configuration shown in FIG. The outer diameter was 1000 ⁇ m, the diameter of the clad layer 3 was 770 ⁇ m, the diameter of the core 2 was 680 ⁇ m, the thickness of the outermost peripheral layer 1 was 115 ⁇ m, and the thickness of the clad layer 3 was 45 ⁇ m. Since the plastic scintillation fiber according to Example 3 contains an organic compound having a neutron reaction cross section larger than that of hydrogen, the neutron sensitivity is improved as compared with the conventional plastic scintillation fiber.
  • Example 4 An aluminum film was formed on the surface of the plastic scintillation fiber according to Example 1 by a thin-film deposition method to a thickness of about 50 nm. The scintillation light emitted by the outermost peripheral layer 1 and the light wavelength-converted by the core 2 are reflected by the reflection layer 5, so that the light is less likely to leak from the side surface of the fiber to the outside, resulting in high emission.

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