Plastic scintillating optical fiber and method of manufacturing the same

Abstract

One aspect of the present invention comprises a plastic scintillation optical fiber having a core (2) comprising a transparent resin having scintillation properties and at least one phosphor that absorbs the scintillation light emitted by the transparent resin and converts it to a longer wavelength, a cladding (3) covering the outer peripheral surface of the core (2) and having a lower refractive index than the core (2), and an outermost peripheral layer (1) covering the outer peripheral surface of the cladding (3) and containing a compound of a heavy metal element. The core (2), cladding (3) and outermost peripheral layer (1) are integrally formed.

Description

Technical Field

[0001] This invention relates to plastic scintillation optical fibers and methods for manufacturing the same. Background Technology

[0002] Existing plastic scintillating fiber (PSF) is a plastic optical fiber in which the outer periphery of the core, which serves as the scintillator, is covered by a cladding with a refractive index lower than that of the core. It is primarily used for radiation detection. Typically, the core is composed of a polymer material obtained by adding an organic phosphor to a substrate with aromatic rings, such as polystyrene or polyvinyl toluene. The cladding is composed of a low-refractive-index polymer material, such as polymethyl methacrylate or fluorinated polymethyl methacrylate.

[0003] The principle of radiation detection using plastic scintillation optical fiber is explained. The core substrate of the scintillation optical fiber has an aromatic ring and the following characteristics: when irradiated radiation passes through the scintillation optical fiber, some energy is absorbed through re-emission by secondary particles within the core, and then emitted as ultraviolet light. If no phosphor is added to the core substrate, the ultraviolet light is absorbed by the core substrate itself and disappears within the core without being transmitted.

[0004] In plastic scintillating optical fibers, the ultraviolet light is absorbed by a phosphor added to the fiber core substrate, and then emitted as longer wavelength light. Therefore, by selecting an appropriate phosphor, light of a shorter wavelength, such as blue, that is less likely to be absorbed by the fiber core substrate can be converted and transmitted within the fiber. The light transmitted within the fiber is detected in a detector connected to one or both ends.

[0005] Thus, scintillation fiber combines the functions of emission and light transmission based on radiation detection, and is used in applications such as calculating the location and amount of radiation transmission. For such scintillation fiber, the key is how to efficiently convert the ultraviolet light emitted from the fiber core to a longer wavelength for long-distance transmission.

[0006] On the other hand, wavelength-shifting fiber (WLSF) is typically used in conjunction with scintillating fiber. Wavelength-shifting fiber is used, for example, in combination with a plastic scintillator that emits blue light. Grooves and holes are formed in a plate-shaped or rod-shaped plastic scintillator, and a wavelength-shifting fiber that absorbs blue light and converts it into green light is embedded therein.

[0007] For large and wide-area detectors, there are situations where light attenuation and space constraints make it difficult to transmit light from each scintillator to a distant external photodetector (such as a photomultiplier tube). In such cases, thin, flexible wavelength conversion fibers capable of long-distance transmission are preferred. Multiple wavelength conversion fibers can be freely configured up to the external photodetector.

[0008] The core of the wavelength-converting fiber is composed of polystyrene resin and polymethyl methacrylate resin, and contains dissolved wavelength-converting phosphors (hereinafter also referred to as "wavelength-converting phosphors"). The wavelength-converting fiber absorbs scintillation light incident from an external scintillator through the phosphor within the core and efficiently performs wavelength conversion, while simultaneously transmitting the light within the fiber. The scintillator used in conjunction with the wavelength-converting fiber is not limited to plastic scintillators; inorganic scintillators with high detection sensitivity to X-rays and gamma rays can also be used.

[0009] In this way, wavelength-converting optical fibers can be used to easily focus scintillation light emitted by large-area or long-sized scintillators used for detecting X-rays and gamma rays. Furthermore, wavelength-converting optical fibers can transmit light that has undergone wavelength conversion within the fiber core and freely connect to photodetectors.

[0010] Regarding the detection of X-rays and gamma rays, plastic scintillators composed solely of light elements have a low probability of interaction with X-rays and gamma rays, resulting in low detection sensitivity and difficulty in detection. Therefore, inorganic scintillators, for example, are used. BaF2, CsI, CaF2, CeF3, and Bi4Ge3O are known as inorganic scintillators. 12 Y2SiO5, Y3Al l5 O 12 Bi4Ge3O 12 , PbWO4, CdWO4, Gd2SiO5: Ce 3+ Lu2SiO5:Ce 3+ And many others.

[0011] However, inorganic scintillators have a decay length of only a few millimeters, low transparency, and cannot transmit emitted light (i.e., scintillating light) over long distances. In addition, due to the limitation of crystal size, it is difficult to use inorganic scintillators to transmit light to photodetectors.

[0012] Furthermore, as disclosed in Non-Patent Document 1, there are examples of improving the detection sensitivity of X-rays and gamma rays by adding compounds containing heavy metal elements such as bismuth compounds to plastic scintillators. However, as the concentration of the added heavy metal elements increases, the transmittance of the plastic scintillator decreases, making it unsuitable for large-size applications.

[0013] Therefore, in patent documents 1-3, wavelength-converting optical fibers are used to transmit light to a photodetector along the end face and surface of a scintillator. By using wavelength-converting optical fibers, the detection light can be transmitted over a longer distance.

[0014] In this regard, in patent documents 1 to 3, especially in image detection and other detections that emphasize spatial resolution disclosed in patent document 2, post-processing of combining scintillators with wavelength conversion optical fibers is often required.

[0015] Existing technical documents

[0016] Patent documents

[0017] Patent Document 1: International Publication No. 2015 / 064588

[0018] Patent Document 2: Japanese Patent Application Publication No. 2011-141239

[0019] Patent Document 3: Japanese Patent Application Publication No. 2015-72227

[0020] Non-patent literature

[0021] Non-patent literature 1: Japanese Journal of Applied Physics 54, 102202 (2015) Summary of the Invention

[0022] The problem that the invention aims to solve

[0023] Existing plastic scintillation fibers require high core transparency because the light scintillation occurs within the fiber core itself and is transmitted to the photodetector. Therefore, it is not possible to obtain plastic scintillation fibers with improved X-ray and gamma-ray detection sensitivity by including compounds containing heavy metal elements in the core to increase the probability of interaction with X-rays and gamma rays.

[0024] On the other hand, existing scintillation detectors using wavelength conversion fibers require post-processing to combine the scintillator with the wavelength conversion fiber. Furthermore, in the case of image detection, the scintillator needs to be separated one by one and combined with each of the multiple wavelength conversion fibers, making the processing significantly more difficult.

[0025] The present invention was made in view of the following circumstances, and its object is to provide a plastic scintillation optical fiber capable of detecting X-rays and gamma rays with high sensitivity and excellent productivity.

[0026] Methods for solving problems

[0027] One embodiment of the plastic scintillation optical fiber of the present invention comprises:

[0028] A fiber core comprising a transparent resin with scintillating properties and at least one phosphor that absorbs the scintillating light emitted by the transparent resin and converts it to a longer wavelength;

[0029] A cladding layer covering the outer peripheral surface of the aforementioned fiber core and having a lower refractive index than the aforementioned fiber core; and

[0030] The outermost layer of a compound that covers the outer periphery of the aforementioned coating and contains heavy metal elements.

[0031] The aforementioned fiber core, cladding, and outermost peripheral layer are integrally formed.

[0032] When X-rays or gamma rays are irradiated onto a plastic scintillation optical fiber, charged particles such as electrons or positrons are generated due to interactions such as the photoelectric effect, Compton effect, and electron pair generation, resulting in scintillation emission.

[0033] In one aspect of the present invention, the outermost layer of a plastic scintillation fiber contains a compound of heavy metal elements, thereby increasing the probability of the aforementioned interactions and improving the detection sensitivity for X-rays and gamma rays compared to conventional plastic scintillation fibers. Here, the outermost layer does not require the high transparency necessary for light transmission like the fiber core, thus allowing for the addition of compounds of heavy metal elements at high concentrations.

[0034] In addition, the core, cladding and outermost layer are formed as a single unit, so no post-processing is required.

[0035] That is, it can provide plastic scintillation optical fibers with high detection sensitivity and excellent productivity for X-rays and gamma rays.

[0036] The outermost layer may contain a scintillating resin. This increases the scintillating light and further improves the detection sensitivity of X-rays and gamma rays.

[0037] Furthermore, the outermost peripheral layer may include at least one phosphor that absorbs the scintillation light emitted by the scintillation resin of the outermost peripheral layer and converts the wavelength to a longer wavelength. This suppresses the self-absorption of the scintillation light from the scintillation resin, further improving the detection sensitivity of X-rays and gamma rays.

[0038] The aforementioned heavy metal elements can be lead or bismuth.

[0039] In addition, in the outermost peripheral layer, the compounds of the aforementioned heavy metal elements can be copolymerized in the aforementioned scintillation resin.

[0040] The aforementioned core, cladding, and outermost layer can be integrally formed through a drawing process. This further improves productivity.

[0041] A protective layer can be integrally formed on the outermost side of the outermost layer to protect it. This improves durability and other properties.

[0042] Furthermore, the aforementioned cladding can have a multi-cladding structure containing 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. This results in a wider total internal reflection angle and higher luminescence.

[0043] A reflective layer may be provided on the outermost peripheral layer or even further out of the protective layer. The scintillation light emitted from the outermost peripheral layer and the fiber core is reflected by the reflective layer, thus preventing it from easily leaking to the outside from the side of the optical fiber, achieving high luminescence.

[0044] The aforementioned reflective film can be a metal film. Based on this configuration, high reflectivity can be achieved with a thin thickness. Furthermore, metal films have a high probability of interacting with X-rays and gamma rays; therefore, by increasing the thickness, the sensitivity to X-rays and gamma rays is improved, and the utilization efficiency of the scintillation light is also increased, achieving high luminescence.

[0045] One aspect of the present invention provides a method for manufacturing a plastic scintillation optical fiber comprising a core containing a transparent resin having scintillation properties and at least one phosphor that absorbs the scintillation light emitted by the transparent resin and converts it to a long wavelength, a cladding covering the outer peripheral surface of the core and having a lower refractive index than the core, and an outermost peripheral layer covering the outer peripheral surface of the cladding and containing a compound of a heavy metal element. The method includes: a step of inserting a second cylindrical body for the cladding into the interior of a first cylindrical body for the outermost peripheral layer, and inserting a rod for the core into the interior of the second cylindrical body to form a preform; and a step of heating the preform while simultaneously drawing it into a fiber.

[0046] One aspect of the present invention is a method for manufacturing a plastic scintillation fiber comprising a core containing a transparent resin having scintillation properties and at least one phosphor that absorbs the scintillation light emitted by the transparent resin and converts it to a long wavelength; a cladding covering the outer peripheral surface of the core and having a lower refractive index than the core; and an outermost peripheral layer covering the outer peripheral surface of the cladding and containing a compound of a heavy metal element, wherein the outermost peripheral layer is coated on the surface of the cladding covering the core.

[0047] Invention Effects

[0048] According to the present invention, a plastic scintillation optical fiber capable of detecting X-rays and gamma rays with high sensitivity and excellent productivity can be provided. Attached Figure Description

[0049] Figure 1 This is a cross-sectional view of the plastic scintillation optical fiber according to Embodiment 1.

[0050] Figure 2 This is a cross-sectional view of a plastic scintillation optical fiber, a variation of Embodiment 1.

[0051] Figure 3 This is a cross-sectional view of a plastic scintillation optical fiber, which is another variation of Embodiment 1.

[0052] Figure 4A perspective view showing the manufacturing method of the plastic scintillation optical fiber according to Embodiment 1.

[0053] Figure 5 A perspective view showing an application example of the scintillation fiber of Embodiment 1. Detailed Implementation

[0054] The following detailed description of specific embodiments of the application of the present invention is provided with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. Furthermore, for clarity, the following description and drawings have been appropriately simplified.

[0055] (Implementation Method 1)

[0056] <Composition of Plastic Scintillation Optical Fiber>

[0057] Reference Figure 1 The plastic scintillation optical fiber of Embodiment 1 of the present invention will be described. Figure 1 This is a cross-sectional view of the plastic scintillation optical fiber according to Embodiment 1.

[0058] like Figure 1 As shown, the plastic scintillation optical fiber of Embodiment 1 has an outermost peripheral layer 1, a core 2, and a cladding 3.

[0059] The outermost layer 1 is composed of a transparent resin containing a compound of heavy metal elements. For example, the outermost layer 1 is composed of a transparent resin with scintillating properties, which, in addition to containing a compound of heavy metal elements, also contains a phosphor that absorbs the scintillating light emitted by the transparent resin and converts it to a longer wavelength. Here, heavy metal elements refer to metallic elements with a specific gravity of 4 or higher.

[0060] When the outermost peripheral layer 1 is composed of a transparent resin with scintillating properties, the scintillating light increases, further improving the detection sensitivity of X-rays and gamma rays. Furthermore, when the outermost peripheral layer 1 contains a wavelength-converting phosphor, the self-absorption of the scintillating light from the transparent resin can be suppressed, further improving the detection sensitivity of X-rays and gamma rays.

[0061] The outermost layer 1 only needs to be sufficiently luminescent and transparent to allow scintillation light to penetrate the cladding 3 and reach the core 2 at the center. While high transparency is not required, it is desirable to be as transparent and thin as possible. The thickness of the outermost layer 1 can be sufficient to achieve the required detection sensitivity for X-rays and gamma rays. Even if the transparency of the outermost layer 1, which serves as the scintillator layer, is low, long-distance transmission is still possible if the core 2 at the center, which is responsible for light transmission, has high transparency.

[0062] The fiber core 2 is disposed inside the outermost peripheral layer 1 and is composed of a transparent resin with a high refractive index that emits scintillation light by passing charged particles such as electrons and positrons generated in the outermost peripheral layer 1. Furthermore, this transparent resin contains at least one phosphor that absorbs the scintillation light and further converts it to a longer wavelength. The refractive index of the transparent resin constituting the fiber core 2 is preferably 1.5 or higher.

[0063] The cladding 3 covers the outer peripheral surface of the fiber core 2 and is made of a transparent resin with a refractive index lower than that of the fiber core 2. Here, the fiber core 2, the cladding 3, and the outermost peripheral layer 1 are integrally formed.

[0064] For long-distance transmission in the form of optical fibers, the transparency of cladding 3 is just as important as that of the core 2. For long-distance transmission, the transparency of the outermost layer 1 is less important.

[0065] For long-distance transmission in the form of optical fiber, the thickness of cladding 3 is preferably sufficient, ranging from 3 μm to 100 μm, compared to the depth to which the transmitted light permeates from the fiber core to the evanescent wave in cladding 3. If the thickness of cladding 3 is sufficient compared to the depth to which the evanescent wave permeates to cladding 3, then cladding 3 and the outermost peripheral layer 1 can have the same refractive index, and thus can be made of the same transparent resin.

[0066] As the wavelength-converting phosphor contained in the fiber core 2, it is desirable that the absorption spectrum matches the wavelength of the scintillation light generated by the scintillation-sensitive resin contained in the fiber core 2, and that the fluorescence spectrum performing wavelength conversion is as far away from the absorption spectrum as possible. Furthermore, in order to match the wavelength sensitivity of photodetectors such as photomultiplier tubes (PMTs) and avalanche photodiodes (APDs), the fiber core 2 may further contain a second phosphor that performs wavelength conversion. It should be noted that details of the phosphor will be explained later.

[0067] The plastic scintillation fiber of Embodiment 1 contains compounds of heavy metal elements with a high probability of interaction with X-rays and gamma rays in its outermost peripheral layer 1. Therefore, when irradiated by X-rays and gamma rays, more charged particles such as electrons and positrons are generated in the outermost peripheral layer 1 compared to existing fibers composed only of light elements such as carbon, hydrogen, and oxygen, due to the photoelectric effect, Compton effect, and electron pair generation. Consequently, more scintillation light is generated in the fiber core 2 located inside the outermost peripheral layer 1, and the scintillation light propagates within the fiber core 2. Therefore, compared to existing plastic scintillation fibers, it is possible to detect X-rays and gamma rays with high sensitivity.

[0068] Furthermore, the core 2, cladding 3, and outermost peripheral layer 1 are integrally formed. Therefore, the processing required for existing X-ray and gamma-ray detection, which involves combining a scintillator with a wavelength conversion fiber, is eliminated, resulting in a significant increase in productivity and a reduction in costs.

[0069] Additionally, a protective layer (not shown) can be integrally formed on the outermost periphery layer 1 to protect the outermost periphery layer. This protective layer improves the durability and other properties of the plastic scintillation optical fiber.

[0070] The material of the protective layer is not particularly limited, but from a productivity point of view, a thermoplastic resin that can be integrally formed with the outermost peripheral layer 1 is preferred.

[0071] <Example of a modified plastic scintillation fiber>

[0072] Figure 2 This is a cross-sectional view of the plastic scintillation fiber in a modified example of Embodiment 1. Figure 2 As shown, a reflective layer 5 can be provided on the surface of the outermost peripheral layer 1 or the protective layer. The scintillation light emitted from the outermost peripheral layer 1 and the fiber core 2 is reflected by the reflective layer 5, thus preventing leakage from the side of the optical fiber to the outside and achieving high luminescence. Here, by making the reflective layer 5 a metal film, high reflectivity can be obtained with a thin thickness. On the other hand, metal films have a high probability of interacting with X-rays and gamma rays; therefore, by increasing the thickness, the sensitivity to X-rays and gamma rays can be improved, and the utilization efficiency of the scintillation light is also increased, achieving high luminescence.

[0073] Figure 3 This is a cross-sectional view of a plastic scintillation fiber according to another variation of Embodiment 1. The plastic scintillation fiber of this other variation has a cladding 3 as an inner cladding and a cladding 4 as an outer cladding. That is, the cladding has a multi-cladding structure containing an inner cladding (cladding 3) and an outer cladding (cladding 4). Cladding 4 covers the outer peripheral surface of cladding 3 and is made of a transparent resin with a refractive index lower than that of cladding 3.

[0074] Here, the scintillation light generated in the core 2 is isotropically emitted at the solid angle within the core 2. Therefore, only light within the total internal reflection angle based on the refractive index difference between the core 2 and the cladding 3 or cladding 4 can propagate in the fiber direction. Another variation of the plastic scintillation fiber, in addition to having cladding 3, also has a low-refractive-index cladding 4, thus... Figure 1 Compared to plastic scintillation fibers, the total internal reflection angle is wider (numerical aperture NA is larger), resulting in higher luminescence.

[0075] <Material of outermost layer 1>

[0076] The outermost layer 1 is composed of a transparent resin containing compounds of heavy metal elements.

[0077] The transparent resin constituting the outermost layer 1 is preferably thermoplastic so that it can be drawn into long, thin filaments by heating. As such a transparent resin, homopolymers or copolymers formed from any of the following groups are preferred: methyl methacrylate monomers, acrylate monomers, methyl acrylate monomers, and vinyl aromatic monomers, such as styrene.

[0078] From the viewpoint of light transmission performance, the refractive index of the transparent resin constituting the outermost layer 1 is not limited, but a material compatible with compounds of heavy metal elements is preferred. Here, the transparent resin can exhibit scintillation properties. By generating scintillation light not only in the fiber core 2 but also in the outermost layer 1, the detection sensitivity of X-rays and gamma rays is improved.

[0079] The transparent resin with scintillation properties contained in the outermost peripheral layer 1 is preferably a homopolymer or copolymer formed from any of the group of vinyl aromatic monomers, represented by styrene.

[0080] The heavy metal compound is preferably stable and has high solubility in monomers used as raw materials for transparent resins such as polymethyl methacrylate, polystyrene, and polyvinyl toluene, which constitute the outermost layer 1. High solubility results in a polymer with high transparency obtained by dissolving the heavy metal compound in the monomer and polymerizing it. Poor solubility prevents uniform dispersion in the outermost layer 1, leading to adverse effects such as deviations in the detection sensitivity to X-rays and gamma rays. Furthermore, when dispersed in powder form, fiber drawing via heating may become difficult.

[0081] Alternatively, the heavy metal compound can be a monomer that can copolymerize with the monomer used as a raw material for transparent resin.

[0082] As lead compounds, various carboxylates of lead, such as lead methacrylate (II), lead acetate (IV), lead citrate (II), lead naphthenate, lead octanoate (II), lead stearate (II), lead formate (II), lead tartrate (II), lead cyclohexanoate (II), and lead 2-ethylhexanoate (II), as well as lead acetylacetone (II), lead hexafluoroacetylacetone (II), bis(2,2,6,6-tetramethyl-3,5-heptadecanoic acid) lead, tetraphenyl lead, diphenyl dichloride, tetraphenyl(phenylethynyl) lead (IV), lead metavanadate (II), lead titanate (II), lead zirconate (II), lead arsenate (II), and lead hexafluorosilicate, are preferred.

[0083] Preferred bismuth compounds include carboxylates of bismuth such as basic bismuth gallate (III), basic bismuth salicylate (III), bismuth methacrylate (III), bismuth acrylate (III), bismuth neodecanoate (III), bismuth oxoacetate (III), bismuth benzoate (III), bismuth citrate (III), and bismuth tris(2-ethylhexanoate) (III); bismuth compounds such as triphenylbismuth, tri-p-tolylbismuth, and tris(2-methoxyphenyl)bismuth; bismuth alkoxides such as triisopropoxybismuth, triethoxybismuth, and tritert-pentoxybismuth; and bismuth chelates such as tris(2,2,6,6-tetramethyl-3,5-heptadecanoate). It should be noted that the carboxylic acid in the carboxylate and the alcohol in the alkoxide can be not a single substance, but a combination of two or more.

[0084] The wavelength-converting phosphor contained in the outermost peripheral layer 1 is an organic phosphor with an aromatic ring and a resonant structure, preferably dissolved as a single molecule in the core 2. Representative phosphors include 2-(4-tert-butylphenyl)-5-(4-biphenyl)-1,3,4- absorbing wavelengths in the 250–350 nm range. diazole (b-PBD), 2-(4-biphenyl)-5-phenyl-1,3,4- diazole (PBD), p-terphenyl (PTP), p-tetraphenyl (PQP), 2,5-diphenyl Pyrazolium (PPO), 1-phenyl-3-(2,4,6-trimethylphenyl)-2-pyrazoline (PMP), 3-hydroxyflavone (3HF), etc.

[0085] In addition, 4,4'-bis(2,5-dimethylstyryl)-biphenyl (BDB) and 2,5-bis(5-tert-butyl-benzo[3]) are preferred for absorption in the 350-400 nm range. (Azoxy)thiophene (BBOT), 1,4-bis(2-(5-phenyl) 1,4-bis-(4-methyl-5-phenyl-2-) (Azolyl)benzene (DMPOPOP), 1,4-diphenyl-1,3-butadiene (DPB), 1,6-diphenyl-1,3,5-hextriene (DPH), etc.

[0086] As an example of the outermost layer 1, a copolymer of methyl methacrylate and lead methacrylate can be cited. By including lead as a heavy metal element, the probability of generating charged particles such as positrons and electrons when irradiated with X-rays or gamma rays is increased due to the photoelectric effect, Compton effect, and electron pair generation. The charged particles generated here reach the core 2 disposed inside the outermost layer 1, causing the core 2 to shimmer and emit light.

[0087] Another example of the outermost layer 1 is an outermost layer in which triphenylbismuth is added to polystyrene, and which converts the scintillation light of polystyrene into a long-wavelength phosphor. By including bismuth, a heavy metal element, the probability of generating charged particles such as positrons and electrons when irradiated with X-rays or gamma rays is increased due to the photoelectric effect, Compton effect, and electron pair generation. The charged particles generated here cause the outermost layer 1 to emit light through the scintillation light of the polystyrene contained in the outermost layer 1, and also cause the fiber core 2, which is disposed inside the outermost layer 1, to scintillate.

[0088] It should be noted that the types of heavy metal compounds, transparent resins, and wavelength-converting phosphors are not limited to those mentioned above. Furthermore, the mixing ratios and concentrations of the above materials can be appropriately selected to consider factors such as ease of manufacturing, and are not limited to those described above.

[0089] <Materials of Core 2>

[0090] The material used in the fiber core 2 is not limited as long as it is a transparent resin with shimmering properties, wherein homopolymers or copolymers formed from any of the vinyl aromatic monomers represented by styrene are preferred.

[0091] Polymers formed from vinyl aromatic monomers are preferred and have a higher refractive index. The greater the refractive index difference between the core 2 and the cladding 3, the wider the total internal reflection angle. That is, it can transmit scintillation light generated within the core 2 and light from wavelength-converted light at larger angles, thus enabling the acquisition of scintillation fibers with higher luminescence.

[0092] The wavelength-converting phosphor contained in core 2 is an organic phosphor with an aromatic ring and a resonant structure, preferably dissolved as a single molecule in core 2. Representative phosphors include 2-(4-tert-butylphenyl)-5-(4-biphenyl)-1,3,4- absorbing wavelengths in the 250–350 nm range. diazole (b-PBD), 2-(4-biphenyl)-5-phenyl-1,3,4- diazole (PBD), p-terphenyl (PTP), p-tetraphenyl (PQP), 2,5-diphenyl Pyrazolium (PPO), 1-phenyl-3-(2,4,6-trimethylphenyl)-2-pyrazoline (PMP), 3-hydroxyflavone (3HF), etc.

[0093] In addition, 4,4'-bis(2,5-dimethylstyryl)-biphenyl (BDB) and 2,5-bis(5-tert-butyl-benzo[3]) are preferred for absorption in the 350-400 nm range. (Azoxy)thiophene (BBOT), 1,4-bis(2-(5-phenyl) 1,4-bis-(4-methyl-5-phenyl-2-) (Azolyl)benzene (DMPOPOP), 1,4-diphenyl-1,3-butadiene (DPB), 1,6-diphenyl-1,3,5-hextriene (DPH), etc.

[0094] Regarding the concentration of the wavelength-converting phosphor, whether alone or in combination, it is preferably 50–10,000 ppm by mass, and more preferably 100–1,000 ppm. If the concentration is too low, the core 2 cannot efficiently absorb the scintillation light from the outermost layer 1. Conversely, if the concentration is too high, the self-absorption effect of the phosphor itself increases, leading to a decrease in wavelength conversion efficiency or a decrease in the transmittance of the converted light, resulting in a poorer attenuation length.

[0095] <Materials of Cladding 3>

[0096] The material used for the cladding 3 is not limited as long as it is a transparent resin with a lower refractive index than the core 2. Preferably, it is a homopolymer or copolymer made from any of the following groups of monomers: methyl methacrylate (represented by methyl methacrylate) and fluorinated monomers such as perfluoroalkyl methacrylate; or acrylate monomers such as methyl acrylate and fluorinated monomers such as perfluoroalkyl acrylate.

[0097] <Materials of cladding 4>

[0098] The material used for coating 4 can be any transparent resin with a lower refractive index than coating 3. It can be selected from the monomer group of coating 3, etc. It is particularly preferred to select from the fluorine-containing monomer group with a low refractive index.

[0099] These monomer groups can be readily polymerized or copolymerized by heat or light irradiation, thus allowing for easy adjustment of the refractive index through composition and offering the advantage of ease of handling. During polymerization, organic peroxides or azo compounds can be added as polymerization initiators. Representative organic peroxides include 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, n-butyl 4,4-bis(tert-butylperoxy)valerate, and 1,1-bis(tert-butylperoxy)cyclohexane, but there are no particular limitations on any substance that generates free radicals through heat or light irradiation.

[0100] In addition, thiols can be added as chain transfer agents to adjust the molecular weight. Octylthiol is a representative thiol, but there are no particular restrictions on substances with an R-SH structure (where R represents an organic group).

[0101] <Materials of the Reflective Layer>

[0102] The material constituting the reflective layer 5 is not limited as long as it is capable of reflecting light emitted from the side of the optical fiber with high reflectivity. Among them, metal films are preferred because they can achieve high reflectivity with a thinner thickness compared to materials such as white reflective coatings, and their sensitivity to X-rays and gamma rays is further improved.

[0103] There are no particular limitations on the metal film, as long as it is a metal with high reflectivity in the required wavelength range, such as aluminum, gold, silver, or nickel. Aluminum and silver are preferred based on high reflectivity in the visible light region. Furthermore, from a cost perspective, aluminum is preferred.

[0104] It should be noted that the thickness of the metal film is not particularly limited, but it is preferable to obtain high reflectivity with the thinnest possible thickness in the visible light region. For example, in the case of aluminum, 10–100 nm is preferred, and more preferably 20–70 nm. In the case of silver, 35–150 nm is preferred, and more preferably 50–100 nm. On the other hand, when there is no limitation on the diameter of the optical fiber, the metal film can be made thicker within the possible range. By making the metal film thicker, the sensitivity to X-rays and gamma rays is further improved.

[0105] In addition, there are no particular restrictions on the film formation method, such as vapor deposition and sputtering.

[0106] <Manufacturing Method of Plastic Scintillation Optical Fiber>

[0107] Figure 4 A perspective view showing the manufacturing method of the plastic scintillation optical fiber according to Embodiment 1. Figure 4 Showing the manufacturing process Figure 1 The parent material (preform) of the plastic scintillation optical fiber is shown.

[0108] The first cylindrical body 11 is a cylindrical body formed from a thermoplastic resin containing compounds of heavy metal elements. The first cylindrical body 11 forms the outermost peripheral layer 1 after the wire drawing process.

[0109] Rod 12 is a cylinder formed from a transparent thermoplastic resin containing at least one phosphor that absorbs scintillation light and converts the wavelength to a longer wavelength. Rod 12 forms the fiber core 2 after the fiber drawing process.

[0110] The second cylindrical body 13 is a cylindrical body formed of a transparent thermoplastic resin with a lower refractive index than the rod 12. The second cylindrical body 13 forms the cladding 3 after the wire drawing process.

[0111] like Figure 4 As shown, a second cylindrical body 13 is inserted into the interior of the first cylindrical body 11, and a rod 12 is inserted into the interior of the second cylindrical body 13, thereby creating a preformed rod. Figure 4The diagram illustrates the process of inserting rod 12 into the interior of the second cylindrical body 13. While heating the tip of the preformed rod, it is drawn to an outer diameter of, for example, 1 mm, thereby obtaining the plastic scintillation optical fiber of Embodiment 1.

[0112] It should be noted that, as Figure 4 As shown, although there is a gap between the first cylindrical body 11, the second cylindrical body 13 and the rod 12, the fiber core 2, the cladding 3 and the outermost peripheral layer 1 are formed in a tight integral manner due to the drawing process under reduced pressure.

[0113] Figure 3 The plastic scintillation optical fiber shown in the modified example can also be manufactured using the same manufacturing method.

[0114] In the manufacturing method of the plastic scintillation fiber of Embodiment 1, the outermost peripheral layer 1 containing a compound of heavy metal elements is integrally formed with the outer peripheral surface of the cladding 3 covering the fiber core 2. Therefore, this plastic scintillation fiber can improve the detection sensitivity of X-rays and gamma rays without reducing the optical transmission performance of the fiber core 2, and can detect X-rays and gamma rays separately.

[0115] Therefore, the post-processing required for combining scintillators with wavelength conversion fibers, as was previously necessary for X-rays and gamma rays, is eliminated, resulting in increased productivity and reduced costs compared to previous methods. Particularly in image inspection applications, it is no longer necessary to separate each scintillator individually and combine it with each wavelength conversion fiber; simply placing the plastic scintillator fiber side-by-side is sufficient. This leads to a significant increase in productivity and a substantial reduction in costs compared to previous methods.

[0116] It should be noted that the core 2 and cladding 3 can be integrally formed by coating (including painting) the outermost peripheral layer 1 containing heavy metal elements on the surface of the cladding 3 covering the core 2.

[0117] <Examples of Applications of Plastic Scintillation Fiber Optics>

[0118] Next, refer to Figure 5 An example of the application of the plastic scintillation optical fiber in Implementation Method 1 is explained. Figure 5 A perspective view showing an application example of the plastic scintillation fiber of Embodiment 1. In this application example, the plastic scintillation fiber PSF of Embodiment 1 is arranged in an array on a substrate.

[0119] It should be noted that, Figure 5 The right-handed xyz orthogonal coordinate system shown is for the convenience of illustrating the positional relationships of the constituent elements. Typically, the positive z-axis is vertically upward, and the xy plane is horizontal.

[0120] Each plastic scintillation fiber PSF is connected to a photodetector (not shown) such as a photomultiplier tube, which can detect the transmitted light. With this configuration, for example, one-dimensional image detection (position detection) can be performed with a resolution of 1 mm. Here, the resolution is equal to the diameter of the plastic scintillation fiber PSF. Furthermore, if an array of two such plastic scintillation fiber PSFs is arranged in an orthogonal, overlapping configuration, two-dimensional image detection can also be achieved.

[0121] Thus, by using the plastic scintillation fiber of this embodiment, it is also possible to achieve high spatial resolution X-ray and gamma-ray imaging detection easily and at low cost.

[0122] Example

[0123] The present invention will be further described in detail below through embodiments, but the present invention is not limited to the embodiments described.

[0124] <Example 1>

[0125] Adding 20% ​​by mass of lead methacrylate (II) to methyl methacrylate and copolymerizing it produces an outermost cylindrical body with an outer diameter of 95 mm and an inner diameter of 71 mm. Figure 4 The first cylindrical body 11).

[0126] Prepare a core rod with a diameter of 65 mm made of polystyrene (refractive index 1.59). Figure 4 The rod 12) and a cladding cylinder with an outer diameter of 70 mm and an inner diameter of 66 mm, made of polymethyl methacrylate (refractive index 1.49). Figure 4 The second cylindrical body 13). In the core rod, the 2-(4-tert-butylphenyl)-5-(4-biphenyl)-1,3,4- fluorophore, which serves as the wavelength conversion phosphor, is... The diazole (b-PBD) was dissolved at a concentration of 1% by mass and 2,5-bis-(5-tert-butyl-benzo[]) was added. (BBOT) azole thiophene was dissolved at a concentration of 200 ppm by mass.

[0127] like Figure 4 As shown, a cladding cylinder is inserted into the inner part of the outermost cylindrical body, and a core rod is inserted into the inner part of the cladding cylinder to fabricate a preform. While heating the tip of the preform, it is integrally drawn under reduced pressure to achieve an outer diameter of 1 mm, thereby obtaining the plastic scintillating fiber of Example 1. This plastic scintillating fiber has… Figure 1 The cross-section shown is as follows. The outer diameter is 1 mm, the diameter of the cladding 3 is 0.72 mm, the diameter of the fiber core 2 is 0.68 mm, the thickness of the outermost circumferential layer 1 is 0.14 mm, and the thickness of the cladding 3 is 0.02 mm.

[0128] The plastic scintillation fiber of Example 1 contains lead, an element with a higher probability of interaction with X-rays and gamma rays compared to light elements such as carbon, hydrogen, and oxygen, in its outermost peripheral layer 1. Therefore, compared to existing plastic scintillation fibers, the plastic scintillation fiber of Example 1 has improved detection sensitivity for X-rays and gamma rays.

[0129] <Example 2>

[0130] The outermost cylindrical body with an outer diameter of 95 mm and an inner diameter of 76 mm was formed in the same manner as in Example 1. Figure 4 The first cylindrical body 11). Additionally, a core rod with a diameter of 65 mm made of polystyrene (refractive index 1.59) was prepared in the same manner as in Example 1. Figure 4 The rod 12) and an inner cladding cylinder with an outer diameter of 70 mm and an inner diameter of 66 mm, made of polymethyl methacrylate (refractive index 1.49). Figure 4 The second cylindrical body 13). In the core rod, the 2-(4-tert-butylphenyl)-5-(4-biphenyl)-1,3,4- fluorophore, which serves as the wavelength conversion phosphor, is... The diazole (b-PBD) was dissolved at a concentration of 1% by mass and 2,5-bis-(5-tert-butyl-benzo[]) was added. (BBOT) azole thiophene was dissolved at a concentration of 200 ppm by mass.

[0131] Furthermore, in Example 2, an outer cladding cylinder (not shown) with an outer diameter of 75 mm and an inner diameter of 71 mm was prepared, consisting of a copolymer of fluorinated monomers such as perfluoroalkyl acrylate (refractive index 1.42). The outer cladding cylinder was formed after wire drawing. Figure 3 4.

[0132] Then, an outer cladding cylinder is inserted into the inner cladding cylinder, and a core rod is inserted into the inner cladding cylinder, thereby producing a preform.

[0133] While heating the tip of the preform, the fiber was integrally drawn under reduced pressure to achieve an outer diameter of 1 mm, thereby obtaining the plastic scintillation fiber of Example 2. This plastic scintillation fiber has... Figure 3 The cross-section shown is as follows. The outer diameter is 1 mm, the outer diameter of cladding 4 is 0.76 mm, the outer diameter of cladding 3 is 0.72 mm, the diameter of core 2 is 0.68 mm, the thickness of outermost layer 1 is 0.12 mm, the thickness of cladding 4 is 0.02 mm, and the thickness of cladding 3 is 0.02 mm.

[0134] When X-rays were incident on the plastic scintillation fiber of Example 2, approximately 30% higher light intensity was observed at the front end at a distance of 10 m compared to Example 1. It can be considered that although the diameter of the fiber core 2 is smaller than that of Example 1, the higher light emission is achieved by widening the total internal reflection angle through the use of a cladding 4 with lower refraction.

[0135] <Example 3>

[0136] Adding 5% by mass of triphenylbismuth and 2-(4-tert-butylphenyl)-5-(4-biphenyl)-1,3,4- to the styrene monomer Diazole (b-PBD) 1% by mass was polymerized and shaped into an outermost cylindrical body with an outer diameter of 95 mm and an inner diameter of 71 mm. Figure 4 The first cylindrical body 11).

[0137] Prepare a core rod with a diameter of 65 mm made of polystyrene (refractive index 1.59). Figure 4 The rod 12) and a cladding cylinder with an outer diameter of 70 mm and an inner diameter of 66 mm, made of polymethyl methacrylate (refractive index 1.49). Figure 4 The second cylindrical body 13). In the core rod, 2,5-bis-(5-tert-butyl-benzo[a]) is dissolved at a concentration of 200 ppm by mass as a wavelength-converting phosphor. BBOT (azolyl)thiophene.

[0138] like Figure 4 As shown, a cladding cylinder is inserted into the inner part of the outermost cylindrical body, and a core rod is inserted into the inner part of the cladding cylinder to fabricate a preform. While heating the tip of the preform, it is integrally drawn under reduced pressure to achieve an outer diameter of 1 mm, thereby obtaining the plastic scintillating fiber of Example 3. This plastic scintillating fiber has… Figure 1 The cross-section shown is as follows. The outer diameter is 1 mm, the diameter of the cladding 3 is 0.72 mm, the diameter of the fiber core 2 is 0.68 mm, the thickness of the outermost circumferential layer 1 is 0.14 mm, and the thickness of the cladding 3 is 0.02 mm.

[0139] The plastic scintillation fiber of Example 3 contains bismuth, a heavy metal element that has a higher probability of interacting with X-rays and gamma rays compared to light elements such as carbon, hydrogen, and oxygen. Therefore, compared to existing plastic scintillation fibers, the plastic scintillation fiber of Example 3 has improved detection sensitivity for X-rays and gamma rays.

[0140] <Example 4>

[0141] An aluminum film with a thickness of about 50 nm was formed on the surface of the plastic scintillation fiber in Example 1 by vapor deposition.

[0142] The scintillation light emitted by the outermost peripheral layer 1 and the fiber core 2 is reflected by the reflective layer 5, thus making it less likely to leak from the side of the optical fiber to the outside, achieving high luminescence.

[0143] This invention is not limited to the above-described embodiments, and can be appropriately modified without departing from its spirit.

[0144] This application claims priority based on Japanese Patent Application No. 2020-173825, filed on October 15, 2020, the entire contents of which are incorporated herein by reference.

[0145] Symbol Explanation

[0146] 1. Outermost layer

[0147] 2 Fiber Core

[0148] 3. Cladding (inner cladding)

[0149] 4. Cladding (outer cladding)

[0150] 5. Reflective layer

[0151] 11 First cylindrical body

[0152] 12 sticks

[0153] 13 Second cylindrical body

[0154] PSF plastic scintillation fiber

Claims

1. A plastic scintillation optical fiber, It possesses: A fiber core comprising a transparent resin with scintillating properties and at least one phosphor that absorbs the scintillating light emitted by the transparent resin and converts it to a longer wavelength; A cladding layer covering the outer peripheral surface of the fiber core and having a lower refractive index than the fiber core; and The outermost layer of a compound that covers the outer periphery of the coating and contains heavy metal elements. The fiber core, the cladding, and the outermost peripheral layer are integrally formed. The outermost peripheral layer contains a transparent resin with shimmering properties. The outermost peripheral layer contains at least one phosphor that absorbs the scintillation light emitted by the transparent resin in the outermost peripheral layer and converts the wavelength to a longer wavelength.

2. The plastic scintillation optical fiber according to claim 1, wherein, The heavy metal element is lead.

3. The plastic scintillation optical fiber according to claim 1 or 2, wherein, The heavy metal element is bismuth.

4. The plastic scintillation optical fiber according to claim 1 or 2, wherein, In the outermost peripheral layer, the compounds of the heavy metal elements are copolymerized in the transparent resin with scintillation properties.

5. The plastic scintillation optical fiber according to claim 1 or 2, wherein, The core, the cladding, and the outermost peripheral layer are integrally formed by a drawing process.

6. The plastic scintillation optical fiber according to claim 1 or 2, wherein, A protective layer is integrally formed on the outermost periphery layer to protect the outermost periphery layer.

7. The plastic scintillation optical fiber according to claim 1 or 2, wherein, The cladding has a multi-cladding structure, which includes an inner cladding and an outer cladding that covers the outer peripheral surface of the inner cladding and has a lower refractive index than the inner cladding.

8. The plastic scintillation optical fiber according to claim 1 or 2, wherein, A reflective layer is located on the outermost periphery.

9. The plastic scintillation optical fiber according to claim 8, wherein, The reflective layer is a metal film.

10. A method for manufacturing a plastic scintillation optical fiber, The plastic scintillation fiber comprises a core containing a transparent resin with scintillation properties and at least one phosphor that absorbs the scintillation light emitted by the transparent resin and converts it to a longer wavelength, a cladding covering the outer peripheral surface of the core and having a lower refractive index than the core, and an outermost peripheral layer covering the outer peripheral surface of the cladding and containing a compound of heavy metal elements. The manufacturing method comprises: The process of manufacturing a preform by inserting a second cylinder for the cladding into the interior of a first cylinder for the outermost peripheral layer, and inserting a rod for the fiber core into the interior of the second cylinder; and The process of heating the preform while simultaneously drawing it into wires. The outermost peripheral layer contains a transparent resin with shimmering properties. The outermost peripheral layer contains at least one phosphor that absorbs the scintillation light emitted by the transparent resin in the outermost peripheral layer and converts the wavelength to a longer wavelength.

11. A method for manufacturing a plastic scintillation optical fiber, The plastic scintillation fiber comprises a core containing a transparent resin with scintillation properties and at least one phosphor that absorbs the scintillation light emitted by the transparent resin and converts it to a longer wavelength, a cladding covering the outer peripheral surface of the core and having a lower refractive index than the core, and an outermost peripheral layer covering the outer peripheral surface of the cladding and containing a compound of heavy metal elements. In the manufacturing method described above The outermost peripheral layer is coated on the surface of the cladding that covers the fiber core. The outermost peripheral layer contains a transparent resin with shimmering properties. The outermost peripheral layer contains at least one phosphor that absorbs the scintillation light emitted by the transparent resin in the outermost peripheral layer and converts the wavelength to a longer wavelength.

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