JP7048349B2 - High-dose field plastic scintillation fiber and its manufacturing method - Google Patents

Description

The present invention relates to a plastic scintillation fiber and a method for producing the same, and particularly to a plastic scintillation fiber suitable for radiation detection in a high dose field and a method for producing the same.

When energy such as pressure, heat, and light is applied to a substance from the outside, the electrons in the substance transition to an excited state with a certain probability. When the excited electrons return to the ground state, excess energy is emitted as heat or light. Among these, the light emission phenomenon in which excess energy is emitted as light by adding radiation (alpha rays, β rays, γ rays, X-rays, charged particle beams such as protons) as energy is called scintillation.

The scintillation fiber is an optical fiber for radiation detection using scintillation. The scintillation fiber is obtained by coating the outer peripheral surface of a core made of a transparent base material having scintillation property with a clad made of a transparent base material having a lower refractive index than that of the core. The light generated in the core by radiation propagates while repeating total internal reflection at the core / clad interface. Finally, this light is detected by a photodetector such as a photomultiplier (photomultiplier tube) or photodiode connected to the end of the fiber.

In the scintillation fiber, only the light generated in the core is confined in the core and propagates while repeating total internal reflection at the interface between the core and the cladding. This is because the light generated in the clad is easily dissipated to the outside of the fiber due to surface stains and scratches.

The core substrate is selected from those having high scintillation properties, that is, those that are easily electronically excited by radiation. Typical examples of electrons that are easily excited are outermost shell electrons in metal elements and π electrons with unsaturated bonds. However, the excitation light of the metal element is not suitable for fiber applications because it is rapidly extinguished by its own light absorption phenomenon. Further, as a transparent and scintillable material, a metal-doped multi-component glass or the like is known, but there are many problems in terms of transparency, processability, cost and the like.

From this point of view, an organic plastic scintillation fiber containing π electrons is generally used as the scintillation fiber. As the core base material, a resin having a benzene ring as a side chain, such as polystyrene or polyvinyltoluene, which has high transparency, contains a large amount of π electrons, and is stable to radiation, is used.

When radiation passes through the core of such a plastic scintillation fiber, the π electrons of the core substrate are excited, and scintillation light having a wavelength peculiar to the material is emitted. Polystyrene and polyvinyltoluene mainly emit scintillation light in the ultraviolet region. For example, the emission spectrum of polystyrene has a peak at 310 nm. However, since the light in such an ultraviolet short wavelength region is absorbed by the core base material itself, it disappears quickly and is not suitable for optical transmission.

Therefore, a general method is to add a fluorescent agent to the core substrate, convert it into light having a longer wavelength, and then transmit it in the fiber. Here, the fluorescent agent added to the core substrate absorbs the scintillation light emitted from the core substrate and re-emits the light having a longer wavelength. The fluorescent agent preferably has an absorption wavelength near the emission wavelength of the core substrate. Further, a plurality of fluorescent agents may be used to adjust the transmission wavelength. The light thus converted to a long wavelength propagates in the fiber and is detected by a detector connected to the end of the fiber.

Another reason for adding a fluorescent agent or the like into the core to convert the wavelength is to match the maximum wavelength sensitivity of a photodetector such as a photomultiplier. Generally, the wavelength at which the sensitivity of the photomultiplier is maximum is blue light around 430 nm, and in recent years, it is highly sensitive to green light having a longer wavelength such as a semiconductor photodetector (avalanche photodiode) corresponding to weak light. Things are also under development.

As a method for specifying the radiation passing position, a flight time difference measuring method, that is, a TOF (Time Of Flight) method is known (see Patent Documents 1 to 3). In the TOF method, detectors are provided at both ends of the scintillation fiber, and the passing position of the radiation is calculated by detecting the time difference until the optical pulse emitted by the radiation reaches both ends of the fiber.

By the way, scintillation by radiation is expressed by the interaction between radiation and atoms constituting a base material. That is, some break the bonds between atoms, some collide with the atoms and divide the atoms into protons, neutrons, electrons, etc., and some are bounced off and scattered, causing secondary particles in the substance. generate. These primary particles and secondary particles give energy to the atoms constituting the substance and the electrons around it, and some of the electrons are excited. Scintillation light is emitted when these excited electrons return to the ground state.

Here, in the scintillation fiber used for the application of extremely weak radiation detection, it is necessary to use a resin having high scintillation property and transparency as the material of the core. Therefore, as described above, resins having an aromatic ring in the side chain, such as polystyrene and polyvinyltoluene, which are highly transparent and contain many π electrons which are easily electronically excited by radiation, have been generally used.

International Publication No. 2013/179970 Japanese Unexamined Patent Publication No. 5-249247 Japanese Unexamined Patent Publication No. 2014-25833 Japanese Unexamined Patent Publication No. 2000-137122

However, in a so-called high dose field with a high radiation dose, a plurality of radiations may pass through one core in a very short time. Here, if an optical pulse of the scintillation light due to the next radiation passage is generated before the optical pulse composed of the scintillation light reaches the detectors at both ends, the scintillation light before and after cannot be separated.

That is, in a high-dose field in which a plurality of radiations pass through the core at a frequency that cannot be ignored with respect to the time difference required for position identification in the TOF method, information on individual radiations cannot be separated. Therefore, the conventional scintillation fiber was useless. For example, in a high dose field where the particle fluence rate is 1 × 105 [ ¹ / (m ² · s)] or more, such a problem can occur. Here, the particle fluence rate is the number of particles (radiation) that pass through a unit area of an irradiation field per unit time.

The present invention has been made in view of the above, and an object of the present invention is to provide a plastic scintillation fiber having high resolution in a high dose field and excellent strength and handleability.

The plastic scintillation fiber according to one aspect of the present invention is
A plastic scintillation fiber having a core containing a fluorescent agent having ultraviolet light emission and a cladding having a clad having a refractive index lower than that of the core while covering the outer peripheral surface of the core.
The core is composed of a copolymer of a monomer having no aromatic ring in its structure and a vinyl aromatic monomer, and has a constant refractive index.

The plastic scintillation fiber according to one aspect of the present invention has fewer π electrons in the polymer as compared with the one in which the core is composed of a homopolymer of a vinyl aromatic monomer. Therefore, the emission probability of the scintillation light is not low even in a high dose field, and the resolution is higher than before. Moreover, since the core has a constant refractive index, it can be easily manufactured.

It is preferable that the clad has a multi-clad structure including an inner clad and an outer clad that covers the outer peripheral surface of the inner clad and has a refractive index lower than that of the inner clad. The numerical aperture can be increased.

Further, it is preferable that the outer clad contains a light-shielding agent. Noise caused by scintillation light generated in the cladding can be reduced.

The method for producing a plastic scintillation fiber according to one aspect of the present invention is
A method for producing a plastic scintillation fiber comprising a core containing a fluorescent agent having ultraviolet light emission and a clad covering the outer peripheral surface of the core.
A step of inserting a rod-shaped core rod made of a resin containing a fluorescent agent having ultraviolet light emission into a cylindrical clad pipe made of a resin having a refractive index lower than that of the core rod to prepare a preform. When,
The step of drawing a line while heating the preform is provided.
The core is composed of a copolymer of a monomer having no aromatic ring in its structure and a vinyl aromatic monomer, and has a constant refractive index.

The clad pipe may be composed of an inner clad pipe and an outer clad pipe made of a resin having a refractive index lower than that of the inner clad pipe while covering the outer peripheral surface of the inner clad pipe. preferable. The numerical aperture can be increased.

It is preferable that the outer clad pipe is made of a resin containing a light-shielding agent. Noise caused by scintillation light generated in the cladding can be reduced.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a plastic scintillation fiber having high resolution in a high dose field and excellent in strength and handleability.

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 Embodiment 2. FIG.

Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. Further, in order to clarify the explanation, the following description and drawings are appropriately simplified.

(Embodiment 1)
The plastic scintillation fiber according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of the plastic scintillation fiber according to the first embodiment.
As shown in FIG. 1, the plastic scintillation fiber according to the present embodiment includes a core 1 and a clad 2 that covers the outer peripheral surface of the core 1. This plastic scintillation fiber is particularly suitable for radiation detection in a high dose field.

The core 1 is made of a transparent resin which is a copolymer of a monomer having no aromatic ring in its structure and a vinyl aromatic monomer, and contains a fluorescent agent having ultraviolet light emission. Further, the core 1 has a constant refractive index. Details of the core base material constituting the core 1, the fluorescent agent, and the clad base material constituting the clad 2 will be described later.

In the scintillation fiber according to the present embodiment, the core 1 is composed of a copolymer of a monomer having no aromatic ring in its structure and a vinyl aromatic monomer. Therefore, in the scintillation fiber according to the present embodiment, there are few π electrons in the polymer, which are easily excited by radiation, as compared with the one in which the core 1 is composed of a homopolymer of a vinyl aromatic monomer. As a result, the emission probability of scintillation light is low even in a high dose field, and the resolution in a high dose field is higher than in the past.
Further, since the core 1 has a constant refractive index, it can be easily manufactured as compared with a core having a refractive index distribution.

The content of the monomer having no aromatic ring in the structure in the core 1 is not particularly limited, but is preferably 10 to 90% by mass. If the content of the monomer containing no aromatic ring in the structure is less than 10% by mass, the emission probability of the scintillation light cannot be effectively reduced, and the resolution in a high dose field cannot be sufficiently improved. On the other hand, when the content of the monomer containing no aromatic ring in the structure exceeds 90% by mass, the content of the vinyl aromatic monomer becomes relatively small, and the refractive index of the core 1 becomes too low. Therefore, the difference in the refractive index between the core 1 and the clad 2 becomes small, and the performance as an optical fiber cannot be fully exhibited.

[Core base material]
As the core base material, as a monomer having no aromatic ring in the structure, any one of a group of monomers such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, cyclohexyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate. One or more and as vinyl aromatic monomers, benzyl methacrylate, phenyl methacrylate, chlorobenzyl methacrylate, 1-phenylethyl methacrylate, 1,2-diphenylethyl methacrylate, diphenylethyl methacrylate, 1-phenylcyclohexyl methacrylate, pentachlorophenyl methacrylate, penta A copolymer obtained by copolymerizing one or more of the monomers of any one of the monomers of bromophenyl methacrylate, 1-naphthyl methacrylate, 2-naphthyl methacrylate, styrene, α-methylstyrene, and vinyltoluene is suitable.

At the time of polymerization, a general polymerization initiator and a molecular weight adjusting agent may be added.
The molecular weight adjusting agent is not particularly limited as long as it suppresses the polymerization growth reaction. Examples of typical molecular weight modifiers include mercaptans. Specifically, examples of the mercaptan include normal octyl mercaptan and normal decanyl mercaptan.

[Clad base material]
As the clad substrate, a weight obtained by polymerizing or copolymerizing one or more of the monomer groups of methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, cyclohexyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate and butyl acrylate. Coalescence is suitable. Of these, a polymer of a methylmethylate monomer or a copolymer of methyl methacrylate and another monomer is desirable. Methyl methacrylate has the advantage of being highly transparent and easy to handle because it polymerizes easily. At the time of polymerization, a general polymerization initiator and a molecular weight adjusting agent may be added.

[Fluorescent agent]
The fluorescent agent added to the core substrate is selected from those that are ultraviolet-emitting, have a plurality of aromatic rings, and have a structure capable of resonance. Typical fluorescent agents include 2- (4-t-butylphenyl) -5- (4-biphenyl) -1,3,4-oxadiazole (b-PBD), 2- (4-biphenyl)-. 5-Phenyl-1,3,4-oxadiazole (PBD), paraterphenyl (PTP), paraquarterphenyl (PQP), 2,5-diphenyloxazole (PPO), 1-phenyl-3- (2,) 4,6-trimethylphenyl) -2-pyrazolin (PMP), 3-hydroxyflavon (3HF), 4,4'-bis- (2,5-dimethylstyryl) -diphenyl (BDB), 2,5-bis- (5-t-butyl-benzoxazoyl) thiophene (BBOT), 1,4-bis- (2- (5-phenyloxazolyl)) benzene (POPOP), 1,4-bis- (4-methyl-5-) Examples thereof include phenyl-2-oxazolyl benzene (DMPOPOP), 1,4-diphenyl-1,3-butadiene (DPB), 1,6-diphenyl-1,3,5-hexatriene (DPH) and the like.
These may be used alone or in combination of a plurality of fluorescent agents.

An example of a combination of fluorescent agents will be described below.
The effect of the fluorescent agent is to absorb the scintillation light emitted by the core substrate, convert it into light having a longer wavelength, and emit it. Therefore, it is desirable that the core substrate has light absorption near the emission wavelength. Examples of these fluorescent agents include b-PBD, PTP, PQP and the like. These are referred to as first fluorescent agents for convenience.

However, since the emission wavelength of these fluorescent agents is generally lower than the optimum light receiving sensitivity of the detector, it is preferable to convert the light to a longer wavelength, and the fluorescence emitted by the first fluorescent agent is converted into light having a longer wavelength. Agents may be added. These are referred to as a second fluorescent agent for convenience. Examples of the second fluorescent agent include BBOT, BDB, POPOP and the like.

For example, a fluorescent agent such as 3HF whose absorption wavelength and emission wavelength are greatly separated can be used alone, but since such a fluorescent agent exists only in a limited number, the first fluorescent agent and the second fluorescence are used. Two types of fluorescent agents are often used.
The preferable amount of the first fluorescent agent added is 0.5 to 3.0% by mass, more preferably 0.8 to 2.2% by mass. The reason for the relatively high concentration is that the short wavelength scintillation light emitted from the core material must be converted to a longer wavelength within a short distance from the emission position without being absorbed by the core material itself. Is. If the amount of the first fluorescent agent added is small, the initial wavelength conversion efficiency deteriorates, so that the final light emission performance cannot be ensured. On the contrary, excessive addition is difficult in the solubility of the fluorescent agent in the core material, increases the cost, and causes deterioration of transmission loss.
The preferable amount of the second fluorescent agent added is 0.01 to 0.5% by mass, more preferably 0.02 to 0.3% by mass. If the amount added is too small, the light converted by the first fluorescent agent cannot be efficiently absorbed and the wavelength can be converted to a longer wavelength. On the contrary, if the addition amount is too large, not only the cost is increased, but also the transmission loss is deteriorated due to the light absorption loss of the fluorescent agent itself.

[Production method]
There are no particular restrictions on the method for manufacturing the scintillation fiber. For example, a so-called melt extrusion method can be used in which a plurality of thermoplastic resin pellets having different refractive indexes are simultaneously melt-extruded using a multi-die in which a circular shape and a tubular shape are combined to form a clad fiber. Alternatively, a so-called coating method can be used in which a low refractive index resin is applied to the surface of a monofilament-shaped transparent high refractive index resin to form a clad.

However, in the melt extrusion method, since the inside of the cylinder of the extruder is subjected to shear stress, the base material and the fluorescent agent are deteriorated, and the transparency is deteriorated. In addition, the coating method has low productivity in consideration of heat drying after coating.

Therefore, a transparent rod-shaped polymer for the core (rod for the core) made of the high refractive index substrate is inserted into the cylindrical transparent polymer for the clad (pipe for the clad) made of the low refractive index substrate to form a preform. The so-called preform heating wire drawing method, in which the material is heated from the surroundings with a tubular heater and drawn, is preferable.
Since the preform heating wire drawing method is not subjected to shear stress, the deterioration of the base material is small and the transparency is excellent. Further, since the core rod and the clad pipe are manufactured separately, the dimensional accuracy of the fiber obtained by the subsequent heating wire drawing is also excellent.

Here, it is desirable that the core rod is placed in a cylindrical polymerization container and thermally polymerized. The polymerization method is preferably spontaneous polymerization by heat, but a minimum amount of pyrolytic radical initiator may be added. Further, a photo-cleavable radical initiator may be used in combination. Further, if the molecular weight of the core rod is too low, a draw-down phenomenon that flows down due to its own weight and a draw resonance phenomenon in which the fiber diameter fluctuates periodically occurs at the time of heating and drawing, and it becomes difficult to maintain dimensional accuracy. On the contrary, if the molecular weight is too high, the viscosity becomes high, so that it is necessary to raise the heating temperature, which causes problems such as coloring and thermal decomposition due to thermal deterioration. Therefore, a molecular weight adjusting agent may be added as needed.

Further, the clad pipe can be produced by a method of polymerizing and solidifying while forming a hollow portion by pressing a monomer against the side surface of the cylindrical container by centrifugal force in a rotating cylindrical container. Alternatively, a method of forming a hollow portion by making a hole in the center of the shaft of the rod-shaped polymer with a drill or the like, or a method of extruding thermoplastic resin pellets from a melt extruder equipped with a circular die to form a pipe shape, etc. May be used.

(Embodiment 2)
Next, the plastic scintillation fiber according to the second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view of the plastic scintillation fiber according to the second embodiment.

As shown in FIG. 2, in the plastic scintillation fiber according to the first embodiment, the clad 2 has a multi-clad structure composed of a single layer. On the other hand, in the plastic scintillation fiber according to the second embodiment, the clad 2 has a multi-clad structure including at least two layers of an inner clad 21 and an outer clad 22.

The inner clad 21 is made of a transparent resin that covers the outer peripheral surface of the core 1 and has a lower refractive index than that of the core 1. Since the clad base material constituting the inner clad 21 is the same as the clad base material constituting the clad 2 in the first embodiment, the description thereof will be omitted.

The outer clad 22 is made of a resin that covers the outer peripheral surface of the inner clad 21 and has a lower refractive index than the inner clad 21. A resin containing a fluorine atom is mainly used. Details of the outer clad base material and the light-shielding agent constituting the outer clad 22 will be described later.

In the scintillation fiber according to the second embodiment, similarly to the scintillation fiber according to the first embodiment, the core 1 is composed of a copolymer of a monomer having no aromatic ring in its structure and a vinyl aromatic monomer. Therefore, the scintillation fiber according to the present embodiment also has less π electrons in the polymer than the core 1 composed of a homopolymer of a vinyl aromatic monomer. As a result, the emission probability of scintillation light is low even in a high dose field, and the resolution in a high dose field is higher than in the past.
Further, the clad 2 has a multi-clad structure including an inner clad 21 and an outer clad 22 having a refractive index lower than that of the inner clad 21. Therefore, the numerical aperture NA can be made larger than that of the scintillation fiber according to the first embodiment.

By the way, in a plastic scintillation fiber, σ electrons, which are the axes of molecular bonds, are excited by radiation, and scintillation light may be emitted when these electrons return to the ground state. This emission can occur in either the core 1 or the cladding 2. Here, the scintillation light emitted from the clad 2 may pass through the core 1 and the fluorescent agent of the core 1 may emit light. This light emission is irregular light emission other than the radiation that has reached the core 1, and is not preferable. This is because the light emission of the fluorescent agent of the core 1 due to the light emission of the clad 2 causes a time lag with respect to the light emission of the fluorescent agent of the core 1 due to the light emission of the core 1, and becomes noise. As a result, the accuracy of specifying the radiation passing position is lowered.

As described above, in the plastic scintillation fiber according to the second embodiment, the outer clad 22 may contain a light-shielding agent. When the outer clad 22 contains a light-shielding agent, the scintillation light generated in the outer clad 22 is less likely to reach the core 1, and the noise can be reduced. At that time, the thickness of the inner clad is preferably several times or more the transmission wavelength at which light can be confined, and is preferably as thin as possible, preferably 1 to 200 μm, and more preferably 5 to 30 μm.

[Outer clad base material]
As the outer clad substrate, methyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3,3-pentafluoropropyl methacrylate, 2 , 2,3,4,4,4-hexafluorobutyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, α-methyl fluoroacrylate, 2- (trifluoromethyl) ) A polymer obtained by polymerizing or copolymerizing one or more of the monomers of methyl propateate, and a mixture of the polymer and vinylidene fluoride are suitable. Of these, a mixture of 2,2,2-trifluoroethyl methacrylate polymer and polyvinylidene fluoride is desirable.
Further, when the core 1 has a large amount of monomer composition containing no aromatic ring in the structure (for example, when it is 50% by mass or more), the inner clad 21 is not provided in order to secure the difference in refractive index between the core and the clad. The clad may be only the outer clad 22.

[Shading agent]
As the light-shielding agent, either an organic dye or an inorganic pigment may be used as long as the transmittance measured in the form of being dissolved or dispersed in the outer clad substrate is 50% or less at an optical path length of 10 mm. Further, a plurality of light-shielding agents may be mixed and used. Examples of organic dyes include MACROLEX (registered trademark) Green G and Green 5B (manufactured by Lanxess), and examples of inorganic pigments include Mitsubishi carbon black (manufactured by Mitsubishi Chemical Corporation).

Hereinafter, examples according to the present invention will be described in more detail, but the present invention is not limited to the examples.

<Example 1>
[Core rod]
As the core rod, styrene and methyl methacrylate (MMA) to which 1% by mass of the fluorescent agent paraterphenyl (PTP) and 0.02% by mass of 2,5-bis- (5-t-butyl-benzoxazoyl) thiophene (BBOT) were added. ) Was copolymerized at a mass ratio of 60:40 to form a rod having an outer diameter of 66 mm. The refractive index of this copolymer was constant, 1.55 at 25 ° C.

[Clad pipe]
Polymerization initiator (NOF Corporation Perocta O (registered trademark) (PO-O): 0.05% by mass, NOF Corporation Perhexa V (registered trademark) (PH-V): 0.05% by mass) on methyl methacrylate monomer %) And the chain transfer agent n-octyl mercaptan (n-OM: 0.25% by mass) for adjusting the molecular weight were added. This was placed in a cylindrical container having an inner diameter of 70 mm, heated and polymerized while rotating in a heat medium in the axial direction to obtain a polymethylmethacrylate (PMMA) clad pipe having an outer diameter of 70 mm and an inner diameter of 68 mm. The refractive index of this PMMA clad pipe was constant and was 1.49 at 25 ° C.

[Preform preparation and heating line drawing]
A preform was prepared by combining a polystyrene core rod and a PMMA clad pipe. This preform was heated and drawn to obtain a scintillation fiber having an outer diameter of 1 mm. The core diameter was 0.97 mm.

<Example 2>
[Core rod]
As the core rod, 60% by mass of the fluorescent agent paraterphenyl (PTP) and 0.02% by mass of 2,5-bis- (5-t-butyl-benzoxazoyl) thiophene (BBOT) were added to the styrene and methyl methacrylate. A rod-shaped material having an outer diameter of 66 mm was used by copolymerizing with a mass ratio of 40 to 40. The refractive index of this copolymer was constant, 1.55 at 25 ° C.

[Pipe for inner clad]
A polymerization initiator (PO-O: 0.05% by mass, PH-V: 0.05% by mass) and a chain transfer agent n-octyl mercaptan (n-OM: 0.25) for adjusting the molecular weight of the methyl methacrylate monomer. Mass%) was added. This was placed in a cylindrical container having an inner diameter of 70 mm, heated and polymerized while rotating in a heat medium in the axial direction to obtain a polymethylmethacrylate (PMMA) clad pipe having an outer diameter of 70 mm and an inner diameter of 68 mm. The refractive index of this PMMA clad pipe was constant and was 1.49 at 25 ° C.

[Pipe for outer clad]
Trifluoroethyl methacrylate (3FMA) monomer, polymerization initiator (PO-O: 0.05% by mass, PH-V: 0.05% by mass) and chain transfer agent n-octyl mercaptan (n-) for adjusting the molecular weight. OM: 0.025% by mass) was added. This was placed in a cylindrical container having an inner diameter of 74 mm, heated and polymerized while rotating in a heat medium in the axial direction to obtain an outer pipe made of polytrifluoroethyl methacrylate having an outer diameter of 74 mm and an inner diameter of 72 mm. The refractive index of this polytrifluoroethyl methacrylate outer pipe was constant and was 1.42 at 25 ° C.

[Preform preparation and heating line drawing]
A preform was prepared by combining a polystyrene core rod, a PMMA inner pipe, and a polytrifluoroethyl methacrylate outer pipe. This preform was heated and drawn to obtain a scintillation fiber having an outer diameter of 1 mm. The core diameter was 0.97 mm.

<Example 3>
The same procedure as in Example 2 was carried out except that the dye MACROLEX Green G having light absorption as a light-shielding agent was added to the outer clad made of polytrifluoroethyl methacrylate in the same manner as in Example 2, and the polystyrene core rod, PMMA inner pipe and polytri were carried out. An outer pipe made of fluoroethyl methacrylate was obtained. The light transmittance of the outer pipe made of polytrifluoroethyl methacrylate was 1% at a thickness of 10 mm.

[Preform preparation and heating line drawing]
A preform was prepared by combining a polystyrene core rod, a PMMA inner pipe, and a polytrifluoroethyl methacrylate outer pipe. This preform was heated and drawn to obtain a scintillation fiber having an outer diameter of 1 mm. The core diameter was 0.97 mm.

<Comparison example>
[Core rod]
As the core rod, styrene to which 1% by mass of the fluorescent agent paraterphenyl (PTP) and 0.02% by mass of 2,5-bis- (5-t-butyl-benzoxazoyl) thiophene (BBOT) were added was thermally polymerized. Polystyrene was used in the form of a rod having an outer diameter of 66 mm. The refractive index of this polystyrene was constant and was 1.59 at 25 ° C.

[Clad pipe]
A polymerization initiator (PO-O: 0.05% by mass, PH-V: 0.05% by mass) and a chain transfer agent n-octyl mercaptan (n-OM: 0.25) for adjusting the molecular weight of the methyl methacrylate monomer. Mass%) is added. This was placed in a cylindrical container having an inner diameter of 70 mm, heated and polymerized while rotating in a heat medium in the axial direction to obtain a polymethylmethacrylate (PMMA) clad pipe having an outer diameter of 70 mm and an inner diameter of 68 mm. The refractive index of this PMMA clad pipe was constant and was 1.49 at 25 ° C.

[Preform preparation and heating line drawing]
A preform was prepared by combining a polystyrene core rod and a PMMA clad pipe. This preform was heated and drawn to obtain a scintillation fiber having an outer diameter of 1 mm. The core diameter was 0.97 mm.

Table 1 summarizes the above conditions.

For example, the emission frequency of scintillation light of a homopolymer of methyl methacrylate is about 1/10 of that of polystyrene. Therefore, the emission frequency of the scintillation light in the scintillation fiber according to Example 1 made of a copolymer having a monomer ratio of styrene and methyl methacrylate of 60:40 is the emission frequency of the scintillation light in the scintillation fiber according to the comparative example made of polystyrene. Is 1, then 1 × 0.6 + 1/10 × 0.4 = 0.64. That is, the scintillation fiber according to the first embodiment has a lower emission frequency of the scintillation light of about 60% than the scintillation fiber according to the comparative example. Moreover, since the structure such as the outer diameter is the same, it has the same strength and handleability.

Similarly, the scintillation fiber according to the second embodiment also emits less frequently than the scintillation fiber according to the comparative example at about 60%. Moreover, since the structure such as the outer diameter is the same, it has the same strength and handleability. Further, since the outer clad has a multi-clad structure in which a resin containing a fluorine atom having a lower refractive index than the inner clad is used, the opening ratio is large.

In the scintillation fiber according to the third embodiment, the emission frequency of the scintillation light in the core is as low as about 60% as compared with the comparative example. Moreover, since the structure such as the outer diameter is the same, it has the same strength and handleability. Further, since the outer clad has a multi-clad structure in which a resin containing a fluorine atom having a lower refractive index than the inner clad is used, the opening ratio is large. Moreover, since the outer clad contains a light-shielding agent, noise due to scintillation light generated in the clad is reduced.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit.

1 core 2 clad 21 inner clad 22 outer clad

Claims (6)

A plastic scintillation fiber having a core containing a fluorescent agent having ultraviolet light emission and a cladding having a clad having a refractive index lower than that of the core while covering the outer peripheral surface of the core.
The core is composed of a copolymer of a monomer containing no aromatic ring in the structure and a vinyl aromatic monomer, and the entire core has a constant refractive index.
Plastic scintillation fiber. The clad has a multi-clad structure including an inner clad and an outer clad that covers the outer peripheral surface of the inner clad and has a lower refractive index than the inner clad.
The plastic scintillation fiber according to claim 1. The outer clad contains a light-shielding agent.
The plastic scintillation fiber according to claim 2. A method for producing a plastic scintillation fiber comprising a core containing a fluorescent agent having ultraviolet light emission and a clad covering the outer peripheral surface of the core.
A step of inserting a rod-shaped core rod made of a resin containing a fluorescent agent having ultraviolet light emission into a cylindrical clad pipe made of a resin having a refractive index lower than that of the core rod to prepare a preform. When,
The step of drawing a line while heating the preform is provided.
The core is composed of a copolymer of a monomer containing no aromatic ring in the structure and a vinyl aromatic monomer, and has a constant refractive index.
How to make plastic scintillation fibers. The clad pipe is composed of an inner clad pipe and an outer clad pipe made of a resin having a refractive index lower than that of the inner clad pipe while covering the outer peripheral surface of the inner clad pipe.
The method for producing a plastic scintillation fiber according to claim 4. The outer clad pipe is made of a resin containing a light-shielding agent.
The method for producing a plastic scintillation fiber according to claim 5.

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