JP7019298B2 - Sheets or pellets for plastic scintillators - Google Patents

Description

The present invention relates to a plastic scintillator for radiation detection for radiation measurement, which is used in a wide range of scientific fields including science, engineering, and medicine.

Generally, radiation, which is a charged particle such as α ray or β ray, ionizes, excites or dissociates an atom or molecule in the substance when passing through the substance, and loses energy. The energy transmitted to the substance is further released as thermal kinetic energy or electromagnetic waves. When this substance is a substance that emits fluorescence, most of its energy is emitted as light in the visible region, and this phenomenon is called scintillation, and the emitted light is called scintillation light.

Furthermore, in the case of uncharged radiation such as γ-rays and neutron rays, the same phenomenon occurs due to the secondary charged particles emitted when the radiation interacts with a substance, so this scintillation phenomenon is described. Radiation is detected by using it.

A photomultiplier tube is used to measure scintillation light. A photomultiplier tube is a high-sensitivity photodetector with a current amplification (= electron multiplication) function based on a phototube that converts light energy into electrical energy using the photoelectric effect.

Substances that cause a scintillation phenomenon are generally collectively called scintillators, and in the field of radiation measurement, they emit fluorescence when exposed to radiation such as inorganic scintillators containing inorganic crystals represented by NaI (Tl), organic crystals such as anthracene, and turphenyl. A liquid scintillator in which a fluorescent substance is dissolved in an organic solvent such as xylene, and an organic scintillator including a plastic scintillator in which the fluorescent substance is dissolved and dispersed in a styrene-based transparent resin are used.

In particular, plastic scintillators have been used very often for half a century because of their ease of handling and their ability to be molded into arbitrary and large shapes.

The invention according to claim 1 is
A sheet or pellet for a plastic scintillator comprising a resin composition for a plastic scintillator containing a rigid general-purpose polystyrene resin (GPPS), an organic scintillator, and a soft styrene resin composed of an elastomer containing styrene.
The hard general-purpose polystyrene resin is contained in an amount of 80% by mass or more and the soft styrene resin is contained in an amount of 5% by mass or more and 10% by mass or less based on the total amount of the plastic scintillator sheet or the pellets.
The soft styrene resin is an SBS (styrene-butadiene-styrene block) copolymer.
The organic scintillator contains at least two types, a first fluorophore and a second fluorophore.
The first fluorophore is p-terphenyl (P-TP), 2,5-diphenyloxazole (DPO), 2- (4-tert-butylphenyl) -5- (4-biphenylyl) -1,3,4. -One or more phosphors selected from oxadiazole (Bu-PBD),
The second phosphor is 1,4-bis [2- (5-phenyloxazolyl)] benzene (POPOP) and 1,4-bis [2- (4-methyl-5-phenyloxazolyl)] benzene. A sheet or pellet for a plastic scintillator which is one or more phosphors selected from (DMPOPOP), 1,4-bis (2-methylstyryl) benzene (bis-MSB).

It has been a long-standing common sense in the technical field that plastic scintillators require the addition of phosphors. The main reason for this is that it has been reported that the wavelength of the electromagnetic wave emitted by the styrol resin excited by irradiation with radiation is as short as 150 to 300 nm. It does not match the suitable wavelength range of 300 to 400 nm. 2) The amount of light that reaches the detection part due to self-absorption by the parent resin is not sufficient. In this regard, by adding a phosphor, the energy of the electromagnetic wave emitted by the parent resin can be converted into light of ~ 350 nm by the first phosphor and ~ 420 nm by the second phosphor, which is suitable for measurement and has a transmittance of about 420 nm. It is said that it is possible to obtain scintillation light having a wavelength that is high and difficult to self-absorb.

Generally, polyvinyltoluene is used as the styrene-based base resin for plastic scintillators. Polypolytoluene (PVT) has 10% to 20% more fluorescence than polystyrene, which is a typical styrene resin. However, since polyvinyltoluene is not a general-purpose resin but a special resin, it has problems in terms of cost and convenience as compared with polystyrene. As a plastic scintillator using PVT, BC-400 manufactured by Saint-Gobain Co., Ltd. is commercially available.

On the other hand, when the organic scintillator is added to polystyrene, which is a typical general-purpose resin of styrene resin, it is difficult to knead the two due to the characteristics of the resin, and the properties are hard and brittle, so that it can be sufficiently used as a plastic scintillator. It is not possible to make resin pellets or resin plates with physical characteristics. For this reason, despite the fact that polystyrene can be used as a plastic scintillator in various prior documents, no one has actually mass-produced and put it on the market.

Patent Document 1 discloses a technique for manufacturing a plastic scintillator using only a base resin without using an organic scintillator. However, the amount of fluorescent light is not sufficient with the parent resin alone, and it is not widely used.

Patent Document 2 discloses a method in which a glass vial is placed in a pellet-shaped solid scintillator composed of a liquid containing a radioactive substance and a resin, sealed, and the liquid is evaporated in the vial for radiation measurement. However, there is no detailed description of the components of the solid scintillator in the document.

Japanese Patent No. 5205681 Japanese Patent No. 5904511

It is an object of the present invention to provide a resin plate and a resin pellet of a plastic scintillator that does not become hard and brittle even when an organic scintillator is added to a general-purpose resin, polystyrene resin, and can sufficiently withstand use as a plastic scintillator.

The present inventor added a soft styrene resin made of an elastomer containing styrene to a polystyrene resin which is a general-purpose resin, so that even if an organic scintillator is added to the polystyrene resin, the properties do not become hard and brittle, and the plastic scintillator can be used as a plastic scintillator. It has been found that resin plates and resin pellets of plastic scintillators that can withstand use can be produced.

The invention according to claim 1 is
A resin composition for a plastic scintillator in which 80% by mass or more of rigid general-purpose polystyrene resin (GPPS) and 5% by mass or more and 20% by mass or less of a soft styrene resin composed of an organic scintillator and an elastomer containing styrene are melt-kneaded . And
The soft styrene resin is an SBS (styrene-butadiene-styrene block) copolymer.
The organic scintillator contains at least two types, a first fluorophore and a second fluorophore.
The first fluorophore is p-terphenyl (P-TP), 2,5-diphenyloxazole (DPO), 2- (4-tert-butylphenyl) -5- (4-biphenylyl) -1,3,4. -One or more phosphors selected from oxadiazole (Bu-PBD),
The second phosphor is 1,4-bis [2- (5-phenyloxazolyl)] benzene (POPOP) and 1,4-bis [2- (4-methyl-5-phenyloxazolyl)] benzene. A resin composition for a plastic scintillator which is one or more phosphors selected from (DMPOPOP), 1,4-bis (2-methylstyryl) benzene (bis-MSB) .

The present inventor adds an organic scintillator and a soft styrene resin composed of an elastomer containing styrene to a polystyrene resin which is a general-purpose resin, so that even if an organic scintillator is added to the polystyrene resin, the properties become hard and brittle. It was found that resin plates and resin pellets of plastic scintillators that can be sufficiently used as plastic scintillators can be produced.

It is necessary to add an organic scintillator (fluorescent substance) to the plastic scintillator. This is because the wavelength of the electromagnetic wave emitted by the polystyrene resin excited by irradiation with radiation is as short as 150 to 300 nm, and it is necessary to convert it to 300 to 400 n in the wavelength range suitable for measurement of the photomultiplier tube used for measurement. Is. There are two types of organic scintillators (fluorescent materials), the first phosphor and the second phosphor. The energy of the electromagnetic wave emitted by the polystyrene resin is converted into light of ~ 350 nm by the first phosphor, and further by the second phosphor. It is converted to light of ~ 420 nm and measured with a photoelectron double tube. Therefore, generally, the first fluorescent substance and the second fluorescent substance are used in combination.

The first phosphors include p-terphenyl (P-TP), 2,5-diphenyloxadiazole (DPO), 2- (4-tert-butylphenyl) -5- (4-biphenylyl) -1,3. Examples thereof include 4-oxadiazole (Bu-PBD), and examples of the second phosphor include 1,4-bis [2- (5-phenyloxazolyl)] benzene (POPOP) and 1,4-bis [. 2- (4-Methyl-5-phenyloxazolyl)] benzene (DMPOPOP), 1,4-bis (2-methylstyryl) benzene (bis-MSB) and the like can be mentioned.

The organic scintillator that can be used in the present invention is
p-terphenyl (P-TP / CAS number: 92-94-4), 2,5-diphenyloxadiazole (DPO / CAS number: 92-71-7), 2- (4-tert-butylphenyl) -5 -(4-Biphenylyl) -1,3,4-oxadiazole (Bu-PBD / CAS number: 15082-28-7), 1,4-bis [2- (5-phenyloxazolyl)] benzene ( POPOP / CAS number: 1806-34-4), 1,4-bis [2- (4-methyl-5-phenyloxazolyl)] benzene (DMPOPOP / CAS number: 3073-87-8), 1,4 -Bis (2-methylstyryl) benzene (Bis-MSB / CAS number: 13280-61-0)
It is one or more fluorescent substances selected from the above, and usually two kinds of fluorescent substances are selected from this group and used in combination. In particular, p-terphenyl (P-TP) or 2,5-diphenyloxazole (DPO) as the first fluorophore of the organic scintillator and 1,4-bis [2- (5-phenyloxazoli) as the second fluorophore. L)] It is preferable to use in combination with benzene (POPOP).

The soft styrene resin is an elastomer containing a benzene ring, and a resin having good compatibility with polystyrene is particularly preferable. Examples of the soft styrene resin that can be used in the present invention include SB (styrene-butadiene) copolymer, SBS (styrene-butadiene-styrene block) copolymer, MBS (methyl methacrylate-butadiene-styrene) copolymer, and MABS ( Methyl methacrylate-acrylonitrile-butadiene-styrene) copolymer, ASA (acrylonitrile-styrene-acrylic rubber) copolymer, AES (acrylonitrile-ethylene propylene rubber-styrene) copolymer, ABS (acrylonitrile-butadiene-styrene), co-polymer Examples include polymers, AS (acrylonitrile-styrene) copolymers, MAS (methylmethacrylate-acrylic rubber-styrene) copolymers, and methylmethacrylate-acrylic-butadiene rubber-styrene copolymers, with SB (Styrene) being particularly suitable. Styrene-butadiene) copolymer.

The invention according to claim 2 is a sheet for a plastic scintillator made of the resin composition for a plastic scintillator according to claim 1.

The invention according to claim 3 is a pellet for a plastic scintillator comprising the resin composition for a plastic scintillator according to claim 1.

According to the present invention, by adding a soft styrene resin made of an elastomer containing styrene to a polystyrene resin which is a general-purpose resin, a plastic scintillator that can sufficiently withstand use as a plastic scintillator even if an organic scintillator is added to the polystyrene resin. Resin plates and resin pellets can be provided.

It is a procedure diagram of the radiation measurement method using a pellet-shaped plastic scintillator. It is a procedure diagram of the radiation measurement method using a sheet-shaped plastic scintillator.

Hereinafter, embodiments of the present invention will be described. The present embodiment is merely one embodiment for carrying out the present invention, and the present invention is not limited to the present embodiment, and various modified embodiments are possible without departing from the gist of the present invention. be.

It is an object of the present invention to provide a resin plate and resin pellet of a plastic scintillator that does not become hard and brittle even when an organic scintillator is added to polystyrene resin, which is a general-purpose resin, and can sufficiently withstand use as a plastic scintillator. And.

That is, the present invention is a resin composition for a plastic scintillator containing a polystyrene resin, an organic scintillator, and a soft styrene resin composed of an elastomer containing styrene.

In addition, the organic scintillator
p-terphenyl (P-TP), 2,5-diphenyloxadiazole (DPO), 2- (4-tert-butylphenyl) -5- (4-biphenylyl) -1,3,4-oxadiazole (Bu) -PBD), 1,4-bis [2- (5-phenyloxazolyl)] benzene (POPOP), 1,4-bis [2- (4-methyl-5-phenyloxazolyl)] benzene (DMPOPOP) ), 1,4-Bis (2-methylstyryl) benzene (bis-MSB), one or more phosphors.

Further, the soft styrene resin is
SB (styrene-butadiene) copolymer, SBS (styrene-butadiene-styrene block) polymer, MBS (methylmethacrylate-butadiene-styrene) polymer, MABS (methylmethacrylate-acrylonitrile-butadiene-styrene) copolymer , ASA (acrylonitrile-styrene-acrylic rubber) copolymer, AES (acrylonitrile-ethylene propylene rubber-styrene) copolymer, ABS (acrylonitrile-butadiene-styrene), copolymer, AS (acrylonitrile-styrene) copolymer , MAS (methyl methacrylate-acrylic rubber-styrene) copolymer, methyl methacrylate-acrylic-butadiene rubber-styrene copolymer, at least one soft styrene resin.

The polystyrene resin used in the present invention will be described. Polystyrene resin is a plastic resin made by polymerizing a styrene monomer made from crude oil and naphtha, and is widely used as one of the five major general-purpose resins along with polyethylene, polypropylene, and polyvinyl chloride. Polystyrene resins include general-purpose polystyrene (GPPS), which is highly transparent and hard, and milky white impact-resistant polystyrene (HIPS), which has improved impact resistance by adding a rubber component. In the latter half of the 1990s, polystyrene with a syndiotactic structure was synthesized and industrialized by metallocene-catalyzed polymerization. The polystyrene produced thereby is a crystalline polymer, which is opaque but has better heat resistance than the atactic polystyrene.

In the present invention, GPPS and atactic polystyrene having high transparency are suitable. In the present invention, polystyrene resin is the main component, and polystyrene resin is preferably contained in the plastic scintillator in an amount of 80 wt% or more, preferably 90 wt% or more, and more preferably 95 wt% or more.

Next, the organic scintillator used in the present invention will be described. A scintillator is a fluorophore that absorbs the energy of radiation and is excited or ionized. Among them, as organic scintillators, crystal scintillators such as anthracene and stilbene have been discovered one after another since Kallman discovered the usefulness of naphthalene crystals as scintillators in 1947. Many substances are now known as organic scintillators. The scintillators available in the present invention are p-terphenyl (P-TP), 2,5-diphenyloxadiazole (DPO), 2- (4-tert-butylphenyl) -5- (4-biphenylyl) -1, 3,4-Oxadiazole (Bu-PBD), 1,4-bis [2- (5-phenyloxazolyl)] benzene (POPOP), 1,4-bis [2- (4-methyl-5-) Phenyloxadiazole)] Benzene (DMPOPOP), 1,4-bis (2-methylstyryl) benzene (bis-MSB), etc., and these substances may be used alone or in combination in the present invention. Can be done.

Plastic scintillators require the addition of phosphors (organic scintillators). The main reason for this is that it has been reported that the wavelength of the electromagnetic wave emitted by the mother resin excited by irradiation with radiation is as short as 150 to 300 nm, so it is suitable for 1) measurement of photoelectron double tubes used for measurement. It does not match the wavelength range of 300 to 400 nm. 2) The amount of light that reaches the detection part due to self-absorption by the parent resin is not sufficient. In this regard, by adding a phosphor, the energy of the electromagnetic wave emitted by the parent resin can be converted into light of ~ 350 nm by the first phosphor and ~ 420 nm by the second phosphor, which is suitable for measurement and has a transmittance of about 420 nm. It is said that it is possible to obtain scintillation light having a wavelength that is high and difficult to self-absorb.

The plastic scintillator is obtained by adding the organic scintillator to a styrene-based parent resin such as polystyrene (PS) or polyvinyltoluene (PVT). The organic scintillator added to the base resin includes the first fluorescent substance and the second fluorescent substance described above, and usually, the first fluorescent substance and the second fluorescent substance are used in combination.
The first fluorophore is p-terphenyl (P-TP), 2,5-diphenyloxazole (DPO), 2- (4-tert-butylphenyl) -5- (4-biphenylyl) -1,3,4. -Oxadiazole (Bu-PBD) and the like can be mentioned.
The second fluorophore is 1,4-bis [2- (5-phenyloxazolyl)] benzene (POPOP),
Examples thereof include 1,4-bis [2- (4-methyl-5-phenyloxazolyl)] benzene (DMPOPOP) and 1,4-bis (2-methylstyryl) benzene (bis-MSB).
Of these, the most suitable
With p-terphenyl (P-TP) or 2,5-diphenyloxazole (DPO) as the first fluorophore,
It is a combination with 1,4-bis [2- (5-phenyloxazolyl)] benzene (POPOP) as a second phosphor.

Next, the soft styrene resin used in the present invention will be described. As the soft styrene resin in the present invention, it is preferable to use an elastomer containing styrene, and it is particularly preferable to use a thermoplastic elastomer.

More specifically, SB (styrene-butadiene) copolymer, SBS (styrene-butadiene-styrene block) copolymer, MBS (methylmethacrylate-butadiene-styrene) copolymer, MABS (methylmethacrylate-acrylonitrile-butadiene). -Sterethane) copolymer, ASA (acrylonitrile-styrene-acrylic rubber) copolymer, AES (acrylonitrile-ethylene propylene rubber-styrene) copolymer, ABS (acrylonitrile-butadiene-styrene), copolymer, AS (acrylonitrile) -Polymer) copolymer, MAS (methyl methacrylate-acrylic rubber-styrene) copolymer, methyl methacrylate-acrylic-butadiene rubber-styrene copolymer and the like can be used.

Among these soft styrene resins, SB (styrene-butadiene) copolymers are preferably selected from the viewpoint of transparency. The SB (styrene-butadiene) copolymer preferably has a styrene content of 50% by mass or more, and the mass ratio of styrene / butadiene of the SB (styrene-butadiene) copolymer is 90/10 to 60/40. It is preferably 90/10 to 70/30, and more preferably 90/10 to 70/30.
As specific examples of the above SBS, for example, Asahi Kasei Chemicals Co., Ltd .: Asaflex series, Denki Kagaku Kogyo Co., Ltd .: Clearen series, Chevron Phillips Co., Ltd .: K resin, BASF Co., Ltd .: Stylolux, Atofina Co., Ltd .: Fina Clear and the like are listed as commercial products.

The content of the soft styrene resin is preferably 5 to 20% by weight based on the total amount of the plastic scintillator. When the content is less than 5% by weight, the moldability is lowered. On the other hand, if it exceeds 20% by weight, the compatibility with the polystyrene resin is lowered, the moldability is deteriorated, and the obtained molded product is inferior in transparency. Further, by containing the above-mentioned predetermined amount of the soft styrene resin, the tensile properties such as the tensile elongation of the obtained polystyrene resin can be improved.

The resin composition for a plastic scintillator of the present invention preferably has a composition of 90% by weight or more for polystyrene resin, 1% by weight or less for an organic scintillator, and 10% by weight or less for a soft styrene resin with respect to the total amount.

The resin composition for a plastic scintillator of the present invention is produced by premixing each component with a high-speed mixer, a tumbler, or the like, and then melt-kneading. The melt-kneading step is performed by a single-screw extruder, a twin-screw extruder, or the like.

Examples and comparative examples will be described below, but the present invention is not limited thereto.
In Example 1, polystyrene, SB (styrene-butadiene) copolymer as a soft styrene resin, 2,5-diphenyloxazole (DPO / first phosphor) and 1,4-bis [2-] as an organic scintillator. (5-Phenyloxazolyl)] An example using benzene (POPOP / second phosphor) is shown.
In Examples 2 and 3, polystyrene, SB (styrene-butadiene) copolymer as a soft styrene resin, p-terphenyl (P-TP / first phosphor) and 1,4-bis (P-TP / first phosphor) as an organic scintillator ( An example using 5-phenyl-2-oxazolyl) benzene (POPOP / second phosphor) is shown.
Comparative Example 1 shows polystyrene and 2,5-diphenyloxazole (DPO / first fluorophore) and 1,4-bis [2- (5-phenyloxazolyl)] benzene (POPOP / second fluorescence) as organic scintillators. The body) was used, and an example in which the soft styrene resin was not added was shown.

As the polystyrene resin, Toyo Styrol GP manufactured by Toyo Polystyrene Co., Ltd. was used. Table 1 shows the grade and physical properties (catalog values) of the polystyrene resin used.

As the SB (styrene-butadiene) copolymer as the soft styrene resin, Clearene manufactured by Denka Co., Ltd. was used. Table 2 shows the grade and physical properties (catalog values) of the SB (styrene-butadiene) copolymer used.

In this example / comparative example, among the organic scintillators, 2,5-diphenyloxazole (DPO) and p-terphenyl (P-TP) are used as the first phosphor, and 1,4-bis [2-bis] is used as the second phosphor. (5-Phenyloxazolyl)] Benzene (POPOP) was used.
2,5-Diphenyloxazole (DPO) is a white crystalline powder at room temperature, having a molecular weight of 221.3 and a melting point of 71-74 ° C. (CAS No .: 92-71-7).
p-Terphenyl (p-Terphenyl, or 1,4-Diphenylbenezene / P-TP) is a white to pale yellow crystalline powder at room temperature with a molecular weight of 230.3 and a melting point of 211 ° C. (CAS No .: 92-). 94-4).
1,4-Bis [2- (5-phenyloxazolyl)] benzene (1,4-Bis [2- (5-phenyloxyzollyl)] benzene, or 1,4-Di (5-phenyl-2-oxazolyl) Benzene) / POPOP) is a pale yellow to pale yellow-green needle-like crystal at room temperature, has a molecular weight of 364.4, and has a melting point of 245 ° C. (CAS number: 1806-34-4).
All of the above organic scintillators were purchased from Tokyo Chemical Industry Co., Ltd.

Table 3 shows the compositions of the resin compositions for plastic scintillators of Examples, Comparative Examples and Reference Examples. In Reference Example 1, a pellet-shaped plastic scintillator (product name: EJ-200) made of polyvinyltoluene resin manufactured by G-Tech Co., Ltd. was used. Reference Example 2 used a plate-shaped plastic scintillator (product name: BC-400, 0.5 mm thick) made of polyvinyltoluene resin manufactured by Saint-Gobain.

The resin compositions for plastic scintillators having the compositions of Examples and Comparative Examples shown in Table 3 were prepared through the following steps. The mixture having the composition shown in each table was mixed with a Henschel mixer (Mitsui FM mixer manufactured by Mitsui Mining Co., Ltd.) to prepare a mixture. The mixture is melt-kneaded using a twin-screw extruder (30 mmΦ, PCM-30 manufactured by Ikegai Corp., the set temperature of the maximum temperature setting unit is shown in each table), strands are formed, and then cold-cut. Resin pellets were prepared.

The obtained resin pellets were evaluated as follows.
1) Pelletization The process of masterbatching with a twin-screw extruder was visually determined.
○: Strands are formed normally and there are no problems such as cutting in the middle. △: Strands are not stable due to their crisp appearance and cut in the middle. ×: Discharge from the extruder is unstable and cannot be pelletized.

2) Sheet formation A 0.5 mm thick sheet was prepared by using a T-die extruder capable of sheet molding the pellets.
○: Sheet molding is possible
△: The sheet is hard and brittle and does not form well ×: The sheet cannot be made

3) Measurement of bending strength of sheet-shaped plastic scintillator The bending strength (maximum point stress) of the sheet produced in 2) was measured. The measurement method was based on JIS K7171. The test conditions are a bending speed of 2 mm / sec and a distance between fulcrums of 50 mm.

4) Radiation measurement To measure the radiation detection performance of a plastic scintillator, prepare a vial for radiation measurement to which an aqueous solution containing a certain amount of tritium (triple hydrogen ( ³ H)) and carbon-14 ( ¹⁴ C) as a radiation source is added. Then, a liquid scintillation counter device (LSC) (Perkin Elmer Co., Ltd., product name: Tri-Carb3110TR) was used.
The concentration of the tritium (tritium ( ^3H )) aqueous solution was adjusted to 140 kHz / 5 μL by diluting the tritiated water with pure water.
The carbon-14 ( ^14C ) aqueous solution was prepared by dissolving L-arginine (L-Arginine [14C (U)], manufactured by Moravek Biochemicals, USA) in pure water and adjusting the concentration to 140 Bq / 5 μL.
Since the shape of the plastic scintillator differs depending on whether the shape of the plastic scintillator is the pellet shape or the sheet shape, the method for producing the vial is described separately below.

a) In the case of pellet shape The procedure of the radiation measurement method using a pellet-shaped plastic scintillator is shown in FIG. The procedure will be described with reference to FIG. The method is almost the same as the method described in Patent Document 2.
In a vial 2 (low potassium glass, 20 mL bottle), 15.5 g (average 15.47 g ± 0.22 g) of pellet-shaped plastic scintillator 3a (pellet diameter 3 mm) is placed, and the tritium aqueous solution 1 or the carbon-14 aqueous solution 1 is added. 5 μL was added dropwise. The vial was capped with a cap 4 (polyethylene, Meridian uGV2-CAP). The closed vial was placed in a constant temperature bath 5 preheated to 60 ° C. for 45 minutes, and the aqueous solution (trithium aqueous solution or carbon-14 aqueous solution) in the vial was evaporated into the vial. .. A vial in which the aqueous solution was evaporated was placed in LSC6, and the radiation dose cpm (count rate, count per minute) was measured.

b) In the case of sheet shape The procedure of the radiation measurement method using the sheet-shaped plastic scintillator is shown in FIG. The procedure will be described with reference to FIG.
5 μL of the tritium aqueous solution 1 or the carbon-14 aqueous solution 1 was dropped onto the sheet-shaped plastic scintillator 3b (plate shape having a width of 13 mm, a length of 50 mm, and a thickness of 0.5 mm). The sheet-shaped plastic scintillator was left to stand for 4 hours to evaporate and dry the water content of the aqueous solution. After confirming evaporation, another sheet-shaped plastic scintillator 3c (plate-shaped with a width of 13 mm, a length of 50 mm, and a thickness of 0.5 mm) is placed on the sheet-shaped plastic scintillator, and the plastic scintillator / radiation source is placed. / A three-layered sample 3d, such as a sandwich of plastic scintillators, was prepared. The sample 3d was placed in a vial 2 (low potassium glass, 20 mL bottle), plugged with a vial cap 4 (polyethylene, Meridian uGV2-CAP), the vial was placed in LSC6, and the radiation dose cpm. (Counting rate, count per minute) was measured.

From the count per minute cpm (count per minute) obtained from the above operation, the counting efficiency Eff. (%) Was calculated.

Eff. (%) = Cpm / dpm x 100

That is, the counting efficiency Eff. (%) Is obtained by calculating the decay rate dpm (disintegrations per minitus) per minute from the prepared sample (tritium aqueous solution: 140 Bq, carbon-14 aqueous solution: 140 Bq), dividing by the count rate cpm per minute, and indicating the percentage. ..

The test results of the pellet-shaped plastic scintillator are shown in Table 4. From the examples, it was confirmed that the measurement efficiency was about the same as that of the plastic scintillator using polyvinyltoluene as the base resin of Reference Example 1.

The test results of the sheet-shaped plastic scintillator are shown in Table 5. From the examples, it was confirmed that the measurement efficiency was about the same as that of the plastic scintillator using polyvinyltoluene (PVT) as the base resin of Reference Example 2.

By using the polystyrene resin of the present invention, an organic scintillator, and a plastic scintillator for radiation detection made of a soft styrene resin made of an elastomer containing styrene, a high-priced plastic scintillator that does not use a conventional general-purpose resin as a base resin can be obtained. Radiation detection inspection can be performed more easily than using it.

1 Aqueous solution containing radioactive substances 2 Vials 3a Pellet-shaped plastic scintillator 3b Sheet-shaped plastic scintillator 3c Sheet-shaped plastic scintillator (placed on 3b)
3d 3 layer sample of plastic scintillator / radiation source / plastic scintillator 4 Vial cap 5 Constant temperature bath 6 Liquid scintillation counter device (LSC)

Claims (1)

A sheet or pellet for a plastic scintillator comprising a resin composition for a plastic scintillator containing a rigid general-purpose polystyrene resin (GPPS), an organic scintillator, and a soft styrene resin composed of an elastomer containing styrene.
The hard general-purpose polystyrene resin is contained in an amount of 80% by mass or more and the soft styrene resin is contained in an amount of 5% by mass or more and 10% by mass or less based on the total amount of the plastic scintillator sheet or the pellets.
The soft styrene resin is an SBS (styrene-butadiene-styrene block) copolymer.
The organic scintillator contains at least two types, a first fluorophore and a second fluorophore.
The first fluorophore is p-terphenyl (P-TP), 2,5-diphenyloxazole (DPO), 2- (4-tert-butylphenyl) -5- (4-biphenylyl) -1,3,4. -One or more phosphors selected from oxadiazole (Bu-PBD),
The second phosphor is 1,4-bis [2- (5-phenyloxazolyl)] benzene (POPOP) and 1,4-bis [2- (4-methyl-5-phenyloxazolyl)] benzene. A sheet or pellet for a plastic scintillator that is one or more phosphors selected from (DMPOPOP), 1,4-bis (2-methylstyryl) benzene (bis-MSB).

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