Low-transmission radiation detecting plastic scintillation fiber

Abstract

The present invention relates to a low-transmissive radiation detecting plastic scintillating optical fiber. A plastic scintillating optical fiber capable of detecting low-transmissive radiation is provided. A plastic scintillating optical fiber according to an embodiment of the present invention includes a plastic optical fiber having a core (1) containing one or more fluorescent agents, a cladding layer (2) having a lower refractive index than the core (1) disposed in a central portion, and an outermost layer (3) covering an outer peripheral surface of the cladding layer (2). The outermost layer (3) contains a base material that generates scintillating light and one or more fluorescent agents that convert the scintillating light to a longer wavelength side.

Description

[0001] This application is a divisional application of the application filed on January 8, 2020, with application number 202080008622.2 and invention title "Low Transmittance Radiation Detection Plastic Scintillation Fiber". Technical Field

[0002] This invention relates to plastic scintillation optical fibers, and more particularly to plastic scintillation optical fibers suitable for detecting low-transmittance radiation. Background Technology

[0003] Plastic scintillating fiber (PSF) is a type of plastic fiber consisting of a core that acts as a scintillator, with a cladding layer having a lower refractive index than the core. It is primarily used for radiation detection. Typically, the core is made of a polymer material containing organic fluorescent agents added to a substrate with aromatic rings, such as polystyrene or polyethylene toluene. The cladding is made of a low-refractive-index polymer material, such as polymethyl methacrylate or fluorinated polymethyl methacrylate.

[0004] The principle of radiation detection using scintillation fiber is explained. It has the following characteristics: the core of the scintillation fiber has an aromatic ring. If the irradiated radiation traverses the scintillation fiber, a portion of the energy is absorbed through re-radiation by secondary particles within the core, and released as ultraviolet light. If no fluorescent agent is added to the core, this ultraviolet light is absorbed by the core itself and cannot propagate within the core, thus disappearing.

[0005] In a scintillation fiber, the ultraviolet light is absorbed by a phosphor added to the core substrate, and then emitted as longer wavelength light. Therefore, by selecting an appropriate phosphor that is not easily absorbed by the core substrate, such as converting it into light of a shorter wavelength like blue, it can propagate within the fiber. The light propagating within the fiber is detected in a detector connected to one or both ends.

[0006] Thus, scintillation fiber combines the functions of radiation detection and light transmission, and is used in applications such as calculating the passage location of radiation. In such scintillation fiber, as disclosed in Patent Documents 1-3, it is important to efficiently convert the wavelength of ultraviolet light emitted from the core into a longer wavelength and to determine whether long-distance transmission is possible.

[0007] Here, Patent Document 1 discloses a method for efficient long-distance transmission by providing a reflective layer on the outside of the cladding.

[0008] Patent document 2 discloses a method for adding a fluorescent agent to the cladding layer, the purpose of which is to prevent the detection of a phenomenon known as crosstalk, which is caused by the emission of light from adjacent fibers.

[0009] Patent document 3 discloses a method for controlling the diameter of the core and cladding, the purpose of which is to prevent the detection of multiple radiation lines in a high radiation field.

[0010] Patent document 4 discloses a method that prevents a decrease in luminescence caused by the transverse position of radiation rays by controlling the concentration of phosphor in the core.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Publication No. 63-129304

[0014] Patent Document 2: Japanese Patent Application Publication No. 2000-137122

[0015] Patent Document 3: International Publication No. 2018 / 043383

[0016] Patent Document 4: International Publication No. 2018 / 110536 Summary of the Invention

[0017] The problem the invention aims to solve

[0018] The inventors have discovered the following problems with scintillation optical fibers.

[0019] In the conventional plastic scintillation optical fibers disclosed in Patent Documents 1-4, scintillation light generated by radiation rays reaching the core is detected.

[0020] However, some types of radiation, such as tritium beta rays, have significantly low transmittance to matter. With conventional plastic scintillation optical fibers, these low-transmittance rays cannot reach the core. Therefore, there is a problem where no scintillation light is generated in the core, making the radiation undetectable.

[0021] The purpose of this invention is to provide a plastic scintillation optical fiber capable of detecting low-transmittance radiation.

[0022] Solution for solving the problem

[0023] One aspect of the present invention is a plastic scintillation fiber comprising plastic optical fibers.

[0024] It possesses:

[0025] The core contains one or more fluorescent agents;

[0026] The cladding has a lower refractive index than the aforementioned core located at the center; and,

[0027] The outermost layer, which covers the outer periphery of the aforementioned cladding layer.

[0028] The aforementioned outermost layer contains: a substrate that generates scintillation light, and one or more fluorescent agents that convert the scintillation light to a longer wavelength side.

[0029] The phosphor contained in the aforementioned core can further convert the light generated in the outermost layer to a longer wavelength. Before the low-transmittance radiation disappears, it can be converted into longer wavelength light emission that is difficult for the core substrate to absorb.

[0030] The aforementioned cladding may have a multi-cladding structure, which includes: an inner cladding layer and an outer cladding layer covering the outer peripheral surface of the aforementioned inner cladding layer and having a refractive index lower than that of the aforementioned inner cladding layer.

[0031] The fluorescent agent contained in the aforementioned core can convert ultraviolet light wavelengths into blue light. Alternatively, the fluorescent agent contained in the aforementioned core can convert blue light wavelengths into green light. Blue and green light are wavelengths considered to have good detection sensitivity in scintillation detectors.

[0032] The effects of the invention

[0033] According to the present invention, a plastic scintillation optical fiber capable of detecting low-transmittance radiation can be provided. Attached Figure Description

[0034] Figure 1 This is a cross-sectional view of the plastic scintillation fiber of Embodiment 1.

[0035] Figure 2 This is a cross-sectional view of a plastic scintillation fiber used as a comparative example. Detailed Implementation

[0036] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a cross-sectional view of the plastic scintillation fiber of Embodiment 1.

[0037] like Figure 1 As shown, the plastic scintillation optical fiber of this embodiment is a plastic optical fiber having a core 1 disposed at the center, a cladding 2 covering the outer peripheral surface of the core 1, and an outermost layer 3 covering the outer peripheral surface of the cladding 2.

[0038] Here, Figure 2 This is a cross-sectional view of a comparative example of a plastic scintillation fiber, and is corresponding to... Figure 1 The image. (As shown) Figure 2 As shown, the comparative example of plastic scintillation fiber has a core 1 disposed at the center and a cladding 2 covering the outer peripheral surface of the core 1, but does not have an outermost layer 3.

[0039] The core 1 and the outermost layer 3 contain one or more fluorescent agents that further convert light emitted from radiation to a longer wavelength. Examples of fluorescent agents that can be used include: fluorescent agents that convert ultraviolet light wavelengths to blue light; and fluorescent agents that convert blue light wavelengths to green light.

[0040] Cladding 2 has a lower refractive index than core 1. Here, cladding 2 may have a multi-cladding structure, which includes: an inner cladding layer and an outer cladding layer covering the outer peripheral surface of the inner cladding layer and having a lower refractive index than the inner cladding layer.

[0041] In the plastic scintillation fiber of this embodiment, the outermost layer 3 contains: a substrate that exhibits scintillation properties to radiation, and a phosphor that converts the scintillation light to a longer wavelength side. Therefore, even low-transmittance radiation can be detected.

[0042] Reference Figure 1 , 2 The principle behind it will be explained below.

[0043] first, Figure 2 In the comparative example of the plastic scintillation fiber shown, under the condition of low-transmittance radiation, the radiation cannot reach core 1. Therefore, no scintillation light originating from the radiation is generated, and thus, the detector cannot detect anything.

[0044] then, Figure 1 In the plastic scintillation optical fiber of this embodiment, the outermost layer 3 of the fiber has an aromatic ring in its substrate, which absorbs radiation and emits long-wavelength ultraviolet light. The emitted ultraviolet light is converted into long-wavelength light by a phosphor contained in the outermost layer 3. In this way, low-transmittance radiation is converted into long-wavelength light that is not easily self-absorbed within the fiber, allowing it to reach all the way to the core 1.

[0045] Light generated in the outermost layer 3 reaches core 1 through cladding 2. The light reaching core 1 is further converted into longer wavelengths by the phosphor contained within core 1. A portion of this light undergoes total internal reflection at the interface between core 1 and cladding 2 due to the refractive index difference, becoming confined within core 1 and propagating thereafter. The light propagating within core 1 is detected in a detector connected to one or both ends. Therefore, even low-transmittance radiation can be detected by the detector.

[0046] [raw materials]

[0047] <Core Substrate>

[0048] There are no restrictions on the raw materials used in the core 1 of the plastic scintillating optical fiber, as long as they are transparent. Suitable materials include copolymers formed from any of the following groups: methyl methacrylate monomers (represented by methyl methacrylate), acrylate monomers (represented by methyl acrylate), and vinyl aromatic monomers (represented by styrene). Copolymers formed from vinyl aromatic monomers are preferred. There are no restrictions on the number of monomers used in the copolymerization, as long as there are two or more.

[0049] <Coated Substrate>

[0050] There are no restrictions on the raw materials used in the cladding 2 of the plastic scintillating optical fiber, as long as they have a lower refractive index than the material forming the core and are transparent. Among them, polymers or copolymers using any of the following as raw materials are suitable: methyl methacrylate monomers and fluorinated monomers such as perfluoroalkyl methacrylate; acrylate monomers and fluorinated monomers such as perfluoroalkyl acrylate.

[0051] <Outermost substrate>

[0052] There are no restrictions on the raw materials used in the outermost layer 3 of the plastic scintillating optical fiber, as long as they are transparent and absorb radiation while emitting ultraviolet light. Suitable candidates include copolymers formed from any of the following groups: methyl methacrylate monomers (represented by methyl methacrylate), acrylate monomers (represented by methyl acrylate), and vinyl aromatic monomers (represented by styrene). Copolymers formed from vinyl aromatic monomers are preferred. There are no restrictions on the number of monomers used in the copolymerization, as long as two or more monomers are used.

[0053] These monomer groups can be readily polymerized or copolymerized by heat or light irradiation, thus offering the advantages of precise compositional distribution and ease of operation. During polymerization, organic peroxides or azo compounds can be added as polymerization initiators. Representative organic peroxides include 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, n-butyl-4,4-bis(tert-butylperoxy)valerate, and 1,1-bis(tert-butylperoxy)cyclohexane, but there are no particular limitations as long as free radicals are generated through heat or light irradiation.

[0054] Furthermore, thiols can be added as chain transfer agents to adjust the molecular weight. Octylthiol is a representative thiol, but there are no particular restrictions as long as it has an R-SH structure (where R represents an organic group).

[0055] <Fluorescent Agent>

[0056] Fluorescent agents can be selected from those with a structure possessing multiple aromatic rings that can resonate. Representative fluorescent agents include 2-(4-tert-butylphenyl)-5-(4-biphenyl)-1,3,4-oxadiazole (b-PBD), 2-(4-biphenyl)-5-phenyl-1,3,4-oxadiazole (PBD), p-terphenyl (PTP), p-tetraphenyl (PQP), 2,5-diphenyloxazole (PPO), 4,4'-bis-(2,5-dimethylstyryl)-biphenyl (BDB), and 2,5-bis-(5-tert-butyl-benzoxazole). Phosphorus fluorocarbons include 1,4-bis-(2-(5-phenyloxazolyl))benzene (POPOP), 1,4-bis-(4-methyl-5-phenyl-2-oxazolyl)benzene (DMPOPOP), 1,4-diphenyl-1,3-butadiene (DPB), 1,6-diphenyl-1,3,5-hexanetriene (DPH), 1-phenyl-3-(2,4,6-trimethylphenyl)-2-pyrazoline (PMP), and 3-hydroxyflavone (3HF). These can be used alone or in combination with other fluorophores. Preferably, the fluorophore exhibiting radioluminescence is soluble in polymerizable monomers and the polymers constituting the core and outermost layers.

[0057] <First Fluorescent Agent>

[0058] One function of a fluorescent agent is to absorb the ultraviolet fluorescence emitted by a substrate that has absorbed radiation, convert it into longer wavelength light, and then release it. Therefore, the fluorescent agent contained in the outermost layer 3 is expected to have light absorption near the emission wavelength of the outermost substrate. Examples of such fluorescent agents include b-PBD, PTP, and PQP. For convenience, these are referred to as the first fluorescent agent. The first fluorescent agent preferably absorbs light with a wavelength of 250–350 nm and preferably emits light with a wavelength of 300–400 nm.

[0059] <Second fluorescent agent>

[0060] The emission wavelength of the first fluorescent agent is usually below 430 nm, which is near the detector's optimal photosensitivity. Therefore, it is preferable to further convert it to a longer wavelength by adding a fluorescent agent that converts the light emitted by the first fluorescent agent into longer wavelength light. For convenience, these are referred to as the second fluorescent agent. For example, the outermost layer 3 contains the first fluorescent agent, and the core 1 contains the second fluorescent agent.

[0061] Examples of second fluorescent agents include BBOT, BDB, and POPOP, among the fluorescent agents mentioned above. The second fluorescent agent preferably absorbs light with a wavelength of 300-400 nm and preferably emits light with a wavelength of 350-600 nm. Depending on the desired emitted wavelength, the second fluorescent agent can be used alone or in combination with multiple fluorescent agents. When using multiple fluorescent agents, they can be separated into an outermost layer 3 and a core layer 1.

[0062] [Wire diameter and manufacturing method]

[0063] The outer diameter of the plastic scintillation fiber of the present invention is, for example, 0.1 to 3 mm. The layer thickness ratio in the diameter direction of the outermost layer / cladding / core / cladding / outermost layer is, for example, 1 / 1 / 96 / 1 / 1 to 10 / 10 / 60 / 10 / 10. As described above, the cladding can be a multi-cladding formed by multiple layers with different refractive indices.

[0064] The plastic scintillation fiber of the present invention can be manufactured, for example, based on the manufacturing method described in Patent Document 3.

[0065] The present invention is not limited to the above embodiments, and appropriate modifications can be made without departing from the spirit of the invention.

[0066] This application claims priority based on Japanese Application Special Hoc 2019-002289, filed on January 10, 2019, the entire disclosure of which is incorporated herein by reference.

[0067] Explanation of reference numerals in the attached figures

[0068] 1 core

[0069] 2. Cladding

[0070] 3 Outermost layer

Claims

1. A low-transmittance radiation line detection plastic scintillation fiber, which is a plastic scintillation fiber containing plastic optical fibers. It possesses: The core contains one or more secondary fluorescent agents; A cladding layer having a lower refractive index than the core disposed at the center; and, The outermost layer, which covers the outer peripheral surface of the cladding. The outermost layer comprises: a substrate that absorbs radiation to generate scintillation light, and one or more first fluorescent agents that convert the scintillation light to a longer wavelength side; the substrate emits long-wavelength ultraviolet light; and the substrate that absorbs radiation to generate scintillation light comprises a copolymer formed from aromatic monomers having vinyl groups. The first fluorescent agent absorbs ultraviolet light with a wavelength of 250-350 nm and emits light with a wavelength of 300-400 nm. The second fluorescent agent absorbs the light emitted by the first fluorescent agent and converts it into light with a wavelength of 350–600 nm on the long wavelength side. The first fluorescent agent is soluble in the polymer constituting the outermost layer and is one or more fluorescent agents selected from the group consisting of 2-(4-tert-butylphenyl)-5-(4-biphenyl)-1,3,4-oxadiazole (b-PBD), 2-(4-biphenyl)-5-phenyl-1,3,4-oxadiazole (PBD), p-terphenyl (PTP), p-tetraphenyl (PQP), 2,5-diphenyloxazole (PPO), and 4,4'-bis-(2,5-dimethylstyryl)-biphenyl (BDB).

2. The plastic scintillation optical fiber according to claim 1, wherein, The cladding layer has a multi-cladding structure, the multi-cladding structure comprising: Inner cladding, and An outer cladding layer that covers the outer peripheral surface of the inner cladding layer and has a refractive index lower than that of the inner cladding layer.

3. The plastic scintillation optical fiber according to claim 1 or 2, wherein, The second fluorescent agent converts ultraviolet light wavelengths into blue light.

4. The plastic scintillation optical fiber according to claim 1 or 2, wherein, The second fluorescent agent converts blue light wavelengths into green light.

5. The plastic scintillation optical fiber according to claim 1 or 2, wherein, The low-transmittance radiation is tritium beta rays.

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