JP7169183B2 - Method for measuring radioactivity of radioactive substances by plastic scintillator for radiation detection - Google Patents

Description

The present invention relates to a radiation detection method using a radiation detection plastic scintillator for radiation measurement, which is used in a wide range of scientific fields including the life science field.

Radiation, which is generally charged particles such as α-rays and β-rays, ionizes, excites, or dissociates atoms or molecules in a substance and loses energy when passing through the substance. The energy transferred to matter 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. This phenomenon is called scintillation, and the emitted light is called scintillation light.

Furthermore, in the case of uncharged radiation such as gamma rays and neutron rays, a similar phenomenon occurs due to the secondary charged particles emitted when the radiation interacts with matter. Radiation is detected using

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

Substances that cause the scintillation phenomenon are generally called scintillators. In the field of radiation measurement, inorganic scintillators including inorganic crystals such as NaI (Tl), organic crystals such as anthracene, and terphenyl emit fluorescence when radiation is incident. Liquid scintillators in which phosphors are dissolved in an organic solvent such as xylene, and organic scintillators including plastic scintillators in which phosphors are dissolved and dispersed in a styrene-based transparent resin are used.

In particular, plastic scintillators have been widely used for half a century due to their ease of handling and their ability to be molded into arbitrary and large-sized shapes.

A typical plastic scintillator is obtained by adding an organic scintillator to a styrene base resin. An organic scintillator has a first phosphor and a second phosphor, and it is usually recommended to combine the first phosphor and the second phosphor.
The first phosphor 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,
the second phosphor is 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) and the like.

It has long been common knowledge in the technical field that plastic scintillators require the addition of phosphors. The main reason for this is that the wavelength of the electromagnetic wave emitted by the styrene-based resin excited by irradiation of radiation has been reported to be as short as 150 to 300 nm. 2) Self-absorption by the base resin occurs, and the amount of light reaching the detecting portion is insufficient. In this regard, by adding a phosphor, the energy of the electromagnetic wave emitted by the base 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 high transmittance. It is said that it is possible to obtain scintillation light with a wavelength that is highly resistant to self-absorption.

Polyvinyltoluene (BC-400, manufactured by Saint-Gobain) and polystyrene (Luminade, manufactured by Tokyo Ink Co., Ltd.) are generally used as the styrene base resin for plastic scintillators.

As a method for measuring radioactive substances using a plastic scintillator, in Patent Document 1, a pellet-shaped solid scintillator made of a liquid containing a radioactive substance and a resin is placed in a vial and sealed, and the liquid is evaporated in the vial to emit radiation. It discloses how to measure

Further, in Patent Document 2, 5 μL of tritium aqueous solution 1 or carbon 14 aqueous solution 1 is dropped on a sheet-shaped plastic scintillator, and then the sheet-shaped plastic scintillator is left for 4 hours to evaporate and dry the water in the aqueous solution. , a method of placing another sheet-shaped plastic scintillator on top of a sheet-shaped plastic scintillator, sandwiching the scintillator, and placing the resulting sandwich in a vial to measure radiation. However, in the methods of Patent Documents 1 and 2, since the amount of sample water to be dropped is small, it is necessary to increase the concentration of radioactive substances in the sample water used for measurement.

On the other hand, as a method for accurately quantifying the amount of radioactive substances, a method of reducing the volume and concentration by evaporating a large amount of water containing a sample and applying it to a radiation measuring instrument is performed. However, with this method, it takes a lot of time and effort to reduce and concentrate a large amount of water containing radioactive substances, and reproducibility is difficult.

JP 2016-024133 A JP 2018-131476 A

A plastic scintillator that can accurately measure even samples with low concentrations of radioactive materials without the need for a lot of time and effort compared to the conventional radiation quantitative measurement method that involves reducing the volume of water containing a large amount of sample and then concentrating it. It is to find a radiation measurement method using

The present inventor put a plastic scintillator plate in a vial for radiation measurement, filled the vial with sample water, left it for a certain period of time, and then used a radioactivity measuring instrument while the vial was filled with sample water. or by discarding only the sample water in the vial while leaving the plastic scintillator plate in the vial and measuring the radioactivity using the vial containing the plastic scintillator, the radioactive substance concentration in the sample We found that accurate measurements are possible even for samples with low .

The invention according to claim 1,
A method for measuring the radioactivity of a low atomic number nuclide radioactive material,
A plate loading step of placing a plastic scintillator plate in the vial;
a pouring step of pouring the sample water into the vial containing the plastic scintillator plate so that the plastic scintillator plate is immersed;
an immersion step of allowing the vial to stand still for a certain period of time while the plastic scintillator plate is immersed in the sample water;
a draining step of draining the sample water from the vial and leaving the plastic scintillator plate in the vial;
a radioactivity measurement step of placing the vial containing the plastic scintillator plate from which the sample water has been discharged into a radiation measuring instrument and measuring radioactivity. .
The invention according to claim 2,
2. The method for measuring radioactivity of a low atomic number nuclide radioactive material according to claim 1, wherein said low atomic number nuclide is a low atomic number nuclide having an atomic number lower than that of phosphorus.

When a plastic scintillator plate is immersed in sample water for a certain period of time, the amount of radioactive substances adsorbed to the surface of the plastic scintillator plate increases, the amount of radioactivity that can be detected by the radiation meter increases, and the radioactivity of the radioactive substance increases. quantification becomes easier. By immersing a plastic scintillator plate in sample water for a certain period of time, draining the sample water from the vial, and measuring the radioactivity with a radiation meter, even low-energy radiation that is absorbed by water can be detected. It can be reduced as much as possible, making it easier to measure the radioactivity of radioactive substances.

The invention according to claim 3 ,
3. The method for measuring the radioactivity of radioactive substances of low atomic number nuclides according to claim 2 , wherein the number of plastic scintillator plates to be put in the vial is 2 or more and 30 or less.

Putting as many plastic scintillator plates as possible in a vial for radiation measurement increases the apparent surface area of the plastic scintillator plates, increases the amount of radioactivity that can be detected by the radiation meter, and increases the radioactivity of radioactive substances. Easier to quantify. Specifically, it is preferable that the number of plastic scintillator plates contained in the vial is two or more. The larger the number of plates, the better, but if the number exceeds 30, the clearance between the plates becomes small, the apparent surface area becomes small, and the quantitative measurement of radioactivity becomes inefficient.

The invention according to claim 4 ,
4. The method for measuring the radioactivity of radioactive substances of low atomic number nuclides according to claim 3 , wherein the certain period of time is 1 day or more and 10 days or less.

A period of immersing the plastic scintillator plate in the sample water is preferably 1 day or more and 10 days or less. If the plastic scintillator plate is not immersed for at least one day, the radioactive substance will not sufficiently adhere to the surface of the plastic scintillator plate, and the radioactivity of the radioactive substance will not be sufficiently adsorbed for quantification. On the other hand, since there is no significant change in the measured values even after 10 days or more of soaking, there is little point in soaking for 10 days or more.

The invention according to claim 5 ,
5. The method for measuring radioactivity of low atomic number nuclides of radioactive substances according to claim 4 , wherein the vial is a vial made of glass or a vial made of plastic.

The vial used in the present invention is preferably a glass vial or a plastic vial. In the case of glass vials, low-potassium glass vials that do not contain much potassium are preferred.

The invention according to claim 6 ,
The vial has a volume of 5 mL or more and 25 mL or less,
6. The method for measuring radioactivity of low atomic number nuclides of radioactive substances according to claim 5 , wherein the plastic scintillator plate has a rectangular parallelepiped shape with short sides of 5 mm or more and 20 mm or less, long sides of 10 mm or more and 60 mm or less, and thicknesses of 0.1 mm or more and 1 mm or less. is.

A vial size of 15 mL or more and 25 mL or less is just right for the radiation meter. The size of the plastic scintillator plate suitable for such a vial is a rectangular parallelepiped shape having a short side of 8 mm or more and 20 mm or less, a long side of 40 mm or more and 60 mm or less, and a thickness of 0.1 mm or more and 1 mm or less. Radiation measurements of radioactive materials provide optimal radioactivity measurements.

The invention according to claim 7 ,
7. The method for measuring radioactivity of low atomic number nuclides of radioactive materials according to claim 6 , wherein said plastic scintillator plate is a polymer compound containing a benzene ring.

The invention according to claim 8 ,
8. The method for measuring the radioactivity of radioactive substances of low atomic number nuclides according to claim 7 , wherein the plastic scintillator plate is any one of a polyvinyl toluene plate, a polystyrene plate, an acrylic styrene plate, and a polystyrene terephthalate plate.

The invention according to claim 9 ,
9. The method for measuring the radioactivity of radioactive substances of low atomic number nuclides according to claim 8 , wherein the polystyrene plate is a plastic scintillator plate containing a polystyrene resin, an organic scintillator, and a soft styrene resin made of an elastomer containing styrene. is.

The invention according to claim 10 ,
The organic scintillator is
p-terphenyl (P-TP), 2,5-diphenyloxazole (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). be.

A plastic scintillator requires the addition of an organic scintillator (phosphor). This is because the wavelength of the electromagnetic wave emitted by the polystyrene resin excited by irradiation is as short as 150 to 300 nm, and it is necessary to convert it to the wavelength range of 300 to 400 nm, which is suitable for the measurement of the photomultiplier tube used for measurement. is. There are two types of organic scintillators (phosphors): the first phosphor and the second phosphor. Converted to ˜420 nm light and measured with a photomultiplier tube. For this reason, the first phosphor and the second phosphor are generally used in combination.

As the first phosphor, p-terphenyl (P-TP/), 2,5-diphenyloxazole (DPO), 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3 ,4-oxadiazole (Bu-PBD) and the like, and the second phosphor includes 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) and the like.

The organic scintillator that can be used for the invention is
p-terphenyl (P-TP/CAS number: 92-94-4), 2,5-diphenyloxazole (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)
is one or a plurality of phosphors selected from , and usually two phosphors are selected from this group and used in combination. In particular, p-terphenyl (P-TP) or 2,5-diphenyloxazole (DPO) as the first phosphor of the organic scintillator and 1,4-bis[2-(5-phenyloxazoly) as the second phosphor L)] benzene (POPOP) is preferably used in combination.

The invention according to claim 11 ,
The soft styrene resin is
SB (styrene-butadiene) copolymer, SBS (styrene-butadiene-styrene block) copolymer, MBS (methyl methacrylate-butadiene-styrene) copolymer, MABS (methyl methacrylate-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. It is a method for measuring the radioactivity of substances.

The soft styrene resin is an elastomer containing benzene rings, and preferably has good compatibility with polystyrene. Soft styrene resins 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, MABS ( methyl methacrylate-acrylonitrile-butadiene-styrene) copolymer, ASA (acrylonitrile-styrene-acrylic rubber) copolymer, AES (acrylonitrile-ethylene propylene rubber-styrene) copolymer, ABS (acrylonitrile-butadiene-styrene), copolymer polymers, AS (acrylonitrile-styrene) copolymers, MAS (methyl methacrylate-acrylic rubber-styrene) copolymers, methyl methacrylate-acrylic-butadiene rubber-styrene copolymers, and particularly preferred is SB ( styrene-butadiene) copolymer.

When measuring low-energy radiation emitted by radioactive materials with low atomic number nuclides, water has an attenuation effect on low-energy radiation. Better do. Hydrogen (deuterium, tritium), carbon, and the like are examples of low atomic number nuclides that should be measured after the sample water is drained. Radioactivity of nuclides with an atomic number higher than phosphorus may be measured without draining the sample water.

According to the present invention, according to the present invention, a plastic scintillator plate is placed in a vial for radiation measurement, the vial is filled with sample water, and after standing for a certain period of time, a radioactivity measuring instrument with the vial filled with sample water. or by discarding only the sample water in the vial while leaving the plastic scintillator plate in the vial and measuring the radioactivity using the vial containing the plastic scintillator. It can qualitatively and quantify the amount of radioactive material.

It is the figure which showed the procedure of the radioactivity measuring method (discharging sample water) of this invention. It is the figure which showed the procedure of the radiation measuring method (leaving sample water) of this invention.

Embodiments of the present invention will be described below. This embodiment is merely one form for carrying out the present invention, and the present invention is not limited by this embodiment, and various modifications and embodiments are possible without departing from the gist of the present invention. be.

The present invention uses a radiation measurement method using a plastic scintillator without requiring much labor and time, unlike the conventional radiation quantitative measurement method in which the volume of water containing a large amount of sample is reduced and concentrated. It is to carry out qualitative and quantitative measurements of radioactivity.

The present inventor put a plastic scintillator plate in a vial for radiation measurement, filled the vial with sample water, left it for a certain period of time, and then used a radioactivity measuring instrument with the vial filled with sample water. By measuring the radioactivity, or by discarding only the sample water in the vial while leaving the plastic scintillator plate in the vial and measuring the radioactivity using the vial containing the plastic scintillator, the amount of radioactive substances in the sample water It was found that the quantity can be qualitatively and quantitatively determined.

That is, the present invention
A plate loading step of placing a plastic scintillator plate in the vial;
a pouring step of pouring the sample water into the vial containing the plastic scintillator plate so that the plastic scintillator plate is immersed;
an immersion step of allowing the vial to stand still for a certain period of time while the plastic scintillator plate is immersed in the sample water;
and a radioactivity measurement step of placing the vial containing the plastic scintillator plate in a radiation meter and measuring the radioactivity.

As for the vial used in the present invention, it is preferable to use a general vial used for radiation measurement. Vials for radiation measurement include glass vials and plastic vials (mainly opaque plastic vials), but both can be used. Specifically, the glass vial is a low-potassium glass vial that does not contain a lot of potassium, and low-potassium ( ^40K 40K) ultra-clear glass scintillation vials manufactured by Meridian in the UK are suitable. is also applicable. As a plastic vial, a disposable polyethylene vial (20 mL) manufactured by PerkinElmer, USA is available, but it is suitable for quantification but not for qualitative analysis. A bottle with a capacity of about 5 mL or more and 25 mL or less is preferable, and a 7 mL bottle (small vial) or a 20 mL bottle (large vial) for a liquid scintillation counter is particularly convenient and suitable.

As a cap for plugging the vial, a polyethylene vial cap (uGV2-CAP manufactured by Meridian), a cork vial cap (Glass Vial Caps manufactured by PerkinElmer), and the like are suitable.

The size of the plate of the plastic scintillator used in the present invention is preferably a rectangular parallelepiped having a short side of 8 mm or more and 20 mm or less, a long side of 40 mm or more and 60 mm or less, and a thickness of 0.1 mm or more and 1 mm or less. This plate size is just right for a 20 mL vial, and a plurality of plates can be placed in a 20 mL vial, enabling efficient radiation measurement.

Putting as many plastic scintillator plates as possible in a vial for radiation measurement increases the apparent surface area of the plastic scintillator plates, increases the amount of radioactivity that can be detected by the radiation meter, and increases the radioactivity of radioactive substances. Easier to quantify. In addition, when a plastic scintillator plate is soaked in sample water for a certain period of time, the amount of radioactive substances adsorbed to the surface of the plastic scintillator plate increases, the amount of radioactivity that can be detected by a radiation meter increases, and the radiation of radioactive substances increases. This makes it easier to quantify capacity. For substances that emit low-energy radiation (nuclides with a small atomic number), a plastic scintillator plate is soaked in sample water for a certain period of time, the sample water is drained from the vial, and the radioactivity is measured with a radiation meter. The amount of radiation absorbed by water can be reduced as much as possible, making it easier to quantify the radioactivity of radioactive substances.

The material of the plate of the plastic scintillator used in the present invention is preferably a polymer compound containing benzene rings. Among polymer compounds containing benzene rings, any one of polyvinyl toluene plates, polystyrene plates, acrylic styrene plates, and polystyrene terephthalate plates can be used. Examples of plastic scintillator plates made of polyvinyl toluene include BC-400 manufactured by Saint-Gobain. Polystyrene plastic scintillator plates include "Luminade" (registered trademark of Tokyo Ink Co., Ltd.) manufactured by Tokyo Ink Co., Ltd. Acrylic styrene plastic scintillator plates include those manufactured by Elgen. As a plastic scintillator plate made of polystyrene terephthalate, one manufactured by Teijin Limited can be mentioned.

The plastic scintillator used in the present invention is obtained by adding an organic scintillator to a styrene base resin such as polystyrene (PS) or polyvinyl toluene (PVT). The organic scintillator added to the base resin includes a first phosphor and a second phosphor, and usually the first phosphor and the second phosphor are used in combination.
The first phosphor 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,
the second phosphor is 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) and the like.
Especially preferred among these are
p-terphenyl (P-TP) or 2,5-diphenyloxazole (DPO) as the first phosphor;
This is a combination with 1,4-bis[2-(5-phenyloxazolyl)]benzene (POPOP) as the second phosphor.

The organic scintillator refers to a phosphor that absorbs radiation energy to cause excitation or ionization. Among these scintillators, since Kallman discovered the usefulness of naphthalene crystals as scintillators in 1947, crystal scintillators such as anthracene and stilbene have been discovered one after another. Many materials are now known as organic scintillators. Organic scintillators added to the plastic scintillator used in the present invention include p-terphenyl (P-TP), 2,5-diphenyloxazole (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) and the like, and these substances are used in the plastic scintillator used in the present invention. are appropriately added in combination of one type or a plurality of types.

A plastic scintillator requires the addition of a phosphor (organic scintillator). The main reason for this is that the wavelength of the electromagnetic wave emitted by the base resin excited by irradiation of radiation has been reported to be as short as 150 to 300 nm. 2) self-absorption by the base resin occurs, and the amount of light reaching the detecting portion is insufficient. In this regard, by adding a phosphor, the energy of the electromagnetic wave emitted by the base 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 high transmittance. It is said that it is possible to obtain scintillation light with a wavelength that is highly resistant to self-absorption.

The plastic scintillator using polystyrene (PS) as a base resin used in the present invention has a composition of 90% by weight or more of polystyrene resin, 1% by weight or less of organic scintillator, and 10% by weight or less of soft styrene resin based on the total amount. It consists of a resin composition. The soft styrene resin is an elastomer containing styrene.

Next, the radioactivity measuring method of the present invention will be described with reference to FIGS. 1 and 2. FIG.
The difference between the methods of FIGS. 1 and 2 is whether or not there is a step of draining the sample water at the stage before the vial is put into the radiation measuring device. and FIG. 2 is a method without a drainage step.

The radioactivity measuring method having the drainage step of FIG. 1 is effective for measuring low atomic number radionuclides. In other words, when measuring low-energy radiation emitted by radioactive materials with low atomic number nuclides, it is better to drain the sample water from the vial before measuring radioactivity with a radiation meter, because water has an attenuation effect. good. Hydrogen (deuterium, tritium), carbon, and the like are examples of low atomic number nuclides that should be measured after the sample water is drained.

On the other hand, the radioactivity measurement method without the drainage step of FIG. 2 is an effective method for atomic number nuclides with an atomic number of phosphorus (P) or higher.

A radioactivity measurement method (“radiation measurement method <A> (method of discharging sample water) of the present invention”) having a drainage step will be described below with reference to FIG.
The first step, ie, the “plate loading step” (<1> in FIG. 1) is the step of loading a plurality of superimposed plastic scintillator plates into a vial. A plurality of plastic scintillator plates 3 are put into an empty vial 2 generally used for radiation measurement. The long side, short side, and height of the plate are preferably sizes that fit the vial 2 as much as possible, and the thickness is preferably adjusted so that a plurality of plates can fit in the vial. The reason why a plurality of plastic scintillator plates 3 are used is to increase the apparent surface area of the plastic scintillator plates 3, increase the amount of radioactivity that can be detected by the radiation measuring instrument, and facilitate the quantification of the radioactivity of radioactive substances. . The number of plastic scintillator plates 3 to be put in the vial 2 is preferably 2 to 15, and particularly preferably about 12. Also, it is better to provide a certain gap between the plastic scintillator plates 3. This is so that the sample water can enter between the plastic scintillator plates 3 when the vial 2 is filled with the sample water. is. A gap (clearance) between the plastic scintillator plates 3 is preferably about 0.1 mm to 1 mm. If the gap between the plastic scintillator plates 3 placed in the vial 2 is not at least 0.1 mm or more, the apparent surface area of the plastic scintillator plates 3 becomes small and the quantitative measurement of radioactivity becomes inefficient. If the thickness is 1 mm or more, the effect of retaining the radioactive substance adsorbed on the surface of the plastic scintillator plate 3 is lowered, which is not suitable for quantitative determination.

In the second step, the “pouring step” (<2> in FIG. 1), the sample water 1 is poured into a vial 2 containing a plurality of plastic scintillator plates 3 so that the plastic scintillator plates 3 are immersed, and the vial cap 4 is attached. This is the process of putting the lid on. After putting a plurality of plastic scintillator plates 3 into the vial 2 in the first step, the sample water 1 is poured into the vial 2 so that the plastic scintillator plates 3 are submerged. This is so that the entire plastic scintillator plate 3 is in contact with the sample water 1. When the sample water 1 and the plastic scintillator plate 3 are in contact with each other, the radioactive substances in the sample water adhere to the surface of the plastic scintillator plate 3, and the radiation measurement is performed. This is because the sensitivity increases when After the sample water 1 is poured into the vial 2, the vial cap 4 is used to cover the vial 2 to prevent the sample water 1 from spilling or evaporating.

The third step, ie, the “immersion step” (<3> in FIG. 1) is the step of leaving the vial 2 still for a certain period of time while the plastic scintillator plate 3 is immersed in the sample water 1 . If the plastic scintillator plate 3 is allowed to stand still for a certain period of time while being immersed in the sample water 1 in the vial 2, the amount of radioactive substances adhered to the surface of the plastic scintillator plate 3 in the sample water increases, and radiation It is preferable because the sensitivity is increased and the quantification is facilitated in the measurement. The certain period of time is preferably at least 1 day or more and 12 days or less at the longest. A sufficient amount of sensitivity cannot be expected in the radiation measurement unless it is left to stand for at least one day. Also, if the sample water is allowed to stand still for longer than 10 days, the possibility of negative effects such as the generation of impurities increases, depending on the sample water.

In the fourth step, ie, the “draining step” (<4> in FIG. 1), after leaving the vial 2 filled with the sample water 1 with the plastic scintillator plate 3 immersed in it for a certain period of time, only the sample water 1 is poured into the vial. 2 to leave the plastic scintillator plate 3 in the vial 2 . After the plastic scintillator plate 3 is immersed in the water sample 1 for a certain period of time, the sample water is discharged from the vial 2, and then the radioactivity is measured with a radiation meter, thereby reducing the amount of radiation absorbed by the water as much as possible. It becomes easier to quantify the radioactivity of radioactive substances.

In the fifth step, the “radioactivity measurement step” (<5> in FIG. 1), the vial 2 containing the plastic scintillator plate 3 after discharging only the sample water 1 is capped with the vial cap 4, and the radiation measuring device is This is the process of measuring the radioactivity by placing it in Any scintillation counter device can be used as a device for measuring the radioactivity of the vial 4 containing the plastic scintillator plate 3 after discharging only the sample water 1, but in particular, a liquid scintillation counter device 5 (LSC) ( PerkinElmer, product name: Tri-Carb 3110TR) is preferred.

Hereinafter, a radioactivity measurement method (“radiation measurement method <B> of the present invention (method in which sample water is not discharged)”) having a drainage step will be described with reference to FIG.
The first step, ie, the “plate loading step” (<1> in FIG. 2) is the step of loading a plurality of superimposed plastic scintillator plates into a vial. A plurality of plastic scintillator plates 3 are put into an empty vial 2 generally used for radiation measurement. The long side, short side, and height of the plate are preferably sizes that fit the vial 2 as much as possible, and the thickness is preferably adjusted so that a plurality of plates can fit in the vial. The reason why a plurality of plastic scintillator plates 3 are used is to increase the apparent surface area of the plastic scintillator plates 3, increase the amount of radioactivity that can be detected by the radiation measuring instrument, and facilitate the quantification of the radioactivity of radioactive substances. . The number of plastic scintillator plates 3 to be put in the vial 2 is preferably 2 to 15, and particularly preferably about 12. Also, it is better to provide a certain gap between the plastic scintillator plates 3. This is so that the sample water can enter between the plastic scintillator plates 3 when the vial 2 is filled with the sample water. is. A gap (clearance) between the plastic scintillator plates 3 is preferably about 0.1 mm to 1 mm. If the gap between the plastic scintillator plates 3 placed in the vial 2 is not at least 0.1 mm or more, the apparent surface area of the plastic scintillator plates 3 becomes small and the quantitative measurement of radioactivity becomes inefficient. If the thickness is 1 mm or more, the effect of retaining the radioactive substance adsorbed on the surface of the plastic scintillator plate 3 is lowered, which is not suitable for quantitative determination.

In the second step, the “pouring step” (<2> in FIG. 2), the sample water 1 is poured into a vial 2 containing a plurality of plastic scintillator plates 3 so that the plastic scintillator plates 3 are immersed, and the vial cap 4 is attached. This is the process of putting the lid on. After putting a plurality of plastic scintillator plates 3 into the vial 2 in the first step, the sample water 1 is poured into the vial 2 so that the plastic scintillator plates 3 are submerged. This is so that the entire plastic scintillator plate 3 is in contact with the sample water 1. When the sample water 1 and the plastic scintillator plate 3 are in contact with each other, the radioactive substances in the sample water adhere to the surface of the plastic scintillator plate 3, and the radiation measurement is performed. This is because the sensitivity increases when After the sample water 1 is poured into the vial 2, the vial cap 4 is used to cover the vial 2 to prevent the sample water 1 from spilling or evaporating.

The third step, ie, the “immersion step” (<3> in FIG. 2) is the step of leaving the vial 2 still for a certain period of time while the plastic scintillator plate 3 is immersed in the sample water 1 . If the plastic scintillator plate 3 is allowed to stand still for a certain period of time while being immersed in the sample water 1 in the vial 2, the amount of radioactive substances adhered to the surface of the plastic scintillator plate 3 in the sample water increases, and radiation It is preferable because the sensitivity is increased and the quantification is facilitated in the measurement. The certain period of time is preferably at least 1 day or more and 12 days or less at the longest. A sufficient amount of sensitivity cannot be expected in the radiation measurement unless it is left to stand for at least one day. Also, if the sample water is allowed to stand still for longer than 10 days, the possibility of negative effects such as the generation of impurities increases, depending on the sample water.

The fourth step, ie, the “radioactivity measurement step” (<4> in FIG. 2), is the step of placing the vial in a radiation meter while leaving the plastic scintillator plate and sample water in the vial and measuring the radioactivity. Any scintillation counter device can be used as a device for measuring radioactivity, but liquid scintillation counter device 5 (LSC) (PerkinElmer, product name: Tri-Carb 3110TR) is particularly preferred.

Examples and comparative examples will be given below, but the present invention is not limited to these.

As the plastic scintillator plate used in this example, "Luminade" (registered trademark of Tokyo Ink Co., Ltd.) manufactured by Tokyo Ink Co., Ltd. was used. The composition of “Luminade” (registered trademark of Tokyo Ink Co., Ltd.) is composed of polystyrene resin, soft styrene resin, 2,5-diphenyloxazole (DPO) as an organic scintillator, 1,4-bis[2-(5-phenyloxa solyl)]benzene (POPOP).

1) Radiation measurement method <A> of the present invention (method of discharging sample water)
The radiation measurement of the present invention was carried out according to the procedure of the following 1st to 5th steps shown in FIG.
As the first step "plate input step"(<1> in FIG. 1), a plurality of plastic scintillator plates (width 13 mm, length 50 mm, thickness 0.5 mm) (the number of sheets is shown in Table 1) plate-like shape) was placed in a glass vial (20 mL bottle (low potassium ( ⁴⁰ K40K) ultra clear glass scintillation vial manufactured by Meridian, UK)).
As the second step, the “pouring step” (<2> in FIG. 1), a radiation source is placed in a glass vial containing a plurality of plastic scintillator plates (the number of which is shown in Table 1) so that the plastic scintillator plates are immersed. An aqueous solution (sample water) containing the vial was poured and capped with a vial cap (polyethylene uGV2-CAP manufactured by Meridian).
As the third step, the “immersion step” (<3> in FIG. 1), the glass vial is placed in an aqueous solution (sample water) containing a radiation source for a certain period of time (the stationary period is shown in Table 1) while the plastic scintillator plate is immersed in the aqueous solution (sample water) containing the radiation source. ) was left undisturbed.
As the fourth step "drainage step"(<4> in FIG. 1), after leaving the glass vial in which the plastic scintillator plate is immersed filled with the aqueous solution (sample water) containing the radiation source for a certain period of time, the vial The cap was opened, and only the aqueous solution (sample water) containing the radiation source was discharged from the glass vial, leaving the plastic scintillator plate in the glass vial.
As the fifth step "radioactivity measurement step"(<5> in Fig. 1), the glass vial containing the plastic scintillator plate after discharging only the aqueous solution (sample water) containing the radiation source is capped with a vial cap. The cells were placed in a liquid scintillation counter device 5 (LSC) (PerkinElmer, product name: Tri-Carb 3110TR), and radioactivity cpm (counts per minute) was measured.

2) Radiation measurement method <B> of the present invention (method without discharging sample water)
The radiation measurement of the present invention was carried out according to the procedure of the following 1st to 4th steps shown in FIG.
As the first step "plate input step"(<1> in FIG. 2), a plurality of plastic scintillator plates (width 13 mm, length 50 mm, thickness 0.5 mm) (the number of sheets is shown in Table 1) plate-like shape) was placed in a glass vial (20 mL bottle (low potassium ( ⁴⁰ K40K) ultra clear glass scintillation vial manufactured by Meridian, UK)).
As the second step “pouring step” (<2> in FIG. 2), a radiation source is placed in a glass vial containing a plurality of plastic scintillator plates (the number of which is shown in Table 1) so that the plastic scintillator plates are immersed. An aqueous solution (sample water) containing the vial was poured and capped with a vial cap (polyethylene uGV2-CAP manufactured by Meridian).
As the third step, the “immersion step” (<3> in FIG. 2), the glass vial is placed in an aqueous solution (sample water) containing a radiation source for a certain period of time (the standing period is shown in Table 1) while the plastic scintillator plate is immersed in the aqueous solution (sample water) containing the radiation source. ) was left undisturbed.
As the fourth step “radioactivity measurement step” (<5> in FIG. 2), an aqueous solution (sample water) containing a radiation source and a glass vial containing a plastic scintillator plate are placed in a liquid scintillation counter device 5 (LSC) (Perkin Elmer Co., product name: Tri-Carb 3110TR), and the radioactivity cpm (count rate, count per minute) was measured.

3) Radioactivity measurement method of comparative example (method using liquid scintillator)
The radiation measurement method of the comparative example is radioactivity measurement using a conventional liquid scintillator. Specifically, 1 mL of sample water and 10 mL of a liquid scintillation cocktail (NATIONAL DIAGNOSTICS, USA, "Ecoscint H") were placed in a glass vial (20 mL bottle (low potassium ( ^40K ) ultra-clear glass scintillation vial manufactured by Meridian, UK)). , capped with a vial cap (polyethylene, uGV2-CAP manufactured by Meridian), placed in a liquid scintillation counter 5 (LSC) (PerkinElmer, product name: Tri-Carb3110TR), and radioactivity cpm (counting rate , counts per minute) was measured.

The above operation (“1) Radiation measurement method <A> of the present invention (method of discharging sample water)” or “2) Radiation measurement method of the present invention <B> (method of not discharging sample water)” or “3) The counting efficiency Eff. (%) was calculated using the following formula

Eff. (%) = cpm/dpm x 100

That is, counting efficiency Eff. (%) is obtained by calculating disintegration per minute rate dpm (disintegration per minute) from the adjusted sample water, dividing it by counting rate cpm per minute, and showing it as a percentage.

Examples 1 to 8 and Comparative Example 1 describe experimental examples using tritiated water (HTO). The tritiated water used in Examples 1 to 8 and Comparative Example 1 was ³ H-Water (23 GBq/mL) manufactured by Moravek, diluted with distilled water to a predetermined ³ H concentration, and used after adjusting the concentration. . Experimental results for tritiated water (HTO) are shown in Table 1.

Examples 9 to 27 and Comparative Example 2 describe experimental examples using an aqueous ³ H-methionine solution. The ³ H-methionine aqueous solution used in Examples 9 to 27 and Comparative Example 2 is commonly used in the field of life sciences and is manufactured by American Radiolabeled Chemicals Inc. ³ H-methionine (1.85 MBq/mL) manufactured by Co., Ltd. was diluted with distilled water to a predetermined ³ H concentration and used after adjusting the concentration. Table 2 shows the experimental results for the ³ H-methionine aqueous solution.

Examples 28 to 55 describe experimental examples using ¹⁴ C-methionine aqueous solution. The ¹⁴ C-methionine aqueous solution used in Examples 28 to 55 is commonly used in the field of life science and is available from American Radiolabeled Chemicals Inc. ¹⁴ C-methionine (1.85 MBq/mL) manufactured by Co., Ltd. was diluted with distilled water so as to obtain a predetermined ¹⁴ C concentration, and the concentration was adjusted before use. Table 3 shows the experimental results of the ¹⁴ C-methionine aqueous solution.

Examples 56 to 63 and Comparative Example 3 are experimental examples using ³² P-phosphoric acid aqueous solution. The ³² P-phosphoric acid aqueous solution used in Examples 56 to 63 and Comparative Example 3 was prepared by dissolving ¹³² P-H ₃ PO ₄ aqueous solution (185 MBq/mL) manufactured by PerkinElmer in distilled water so as to obtain a predetermined ³² P concentration. It was used after diluting and adjusting the concentration. Table 4 shows the experimental results of the ³² P-phosphoric acid aqueous solution.

Examples 64 to 78 describe experimental examples using a ⁹⁰ Sr aqueous solution. The ⁹⁰ Sr aqueous solution used in Examples 64 to 78 was a ⁹⁰ Sr aqueous solution (1.185 MBq/10 mL) of the standard solution manufactured by the Isotope Association of Japan, and adjusted to a predetermined ⁹⁰ Sr concentration. 0.05 mg/g of strontium chloride and 0.05 mg/g of yttrium chloride dissolved in )) to adjust the concentration. Table 5 shows the experimental results of the ⁹⁰ Sr aqueous solution.

In Examples 79-83 and Comparative Examples 4-5, experimental examples using ²²⁶ Ra- ²²² Rn aqueous solutions are described. The ²²⁶ Ra- ²²² Rn aqueous solution used in Examples 79 to 83 and Comparative Examples 4 to 5 was "Doll stone" (terracotta made from rocks and earth containing a small amount of natural uranium collected around Ningyo-toge, Okayama Prefecture ( A ²²⁶ Ra- ²²² Rn aqueous solution was used by submerging an unglazed tile in Italian, a registered trademark of Ningyotoge Nuclear Industry Co., Ltd., in 150 mL of distilled water for 3 months. Table 6 shows the experimental results of the ²²⁶ Ra- ²²² Rn aqueous solution.

According to the present invention, according to the present invention, a plastic scintillator plate is placed in a vial for radiation measurement, the vial is filled with sample water, and after standing for a certain period of time, a radioactivity measuring instrument with the vial filled with sample water. or by discarding only the sample water in the vial while leaving the plastic scintillator plate in the vial and measuring the radioactivity using the vial containing the plastic scintillator. It is possible to measure the radioactivity of water containing

1 sample water containing radioactive substance 2 vial 3 plastic scintillator plate 4 vial cap 5 liquid scintillation counter device (LSC)
6 Sample water supply container

Claims (11)

A method for measuring the radioactivity of a low atomic number nuclide radioactive material,
A plate loading step of placing a plastic scintillator plate in the vial;
a pouring step of pouring the sample water into the vial containing the plastic scintillator plate so that the plastic scintillator plate is immersed;
an immersion step of allowing the vial to stand still for a certain period of time while the plastic scintillator plate is immersed in the sample water;
a draining step of draining the sample water from the vial and leaving the plastic scintillator plate in the vial;
a radioactivity measurement step of placing the vial containing the plastic scintillator plate from which the sample water has been discharged into a radiation measuring instrument and measuring radioactivity. 2. The method for measuring the radioactivity of a low atomic number nuclide radioactive material according to claim 1, wherein said low atomic number nuclide is a low atomic number nuclide having an atomic number lower than that of phosphorus. 3. The method for measuring the radioactivity of radioactive substances of low atomic number nuclides according to claim 2, wherein the number of plastic scintillator plates to be put in the vial is 2 or more and 30 or less. 4. The method for measuring the radioactivity of a low atomic number nuclide radioactive material according to claim 3, wherein the certain period of time is 1 day or more and 10 days or less. 5. The method for measuring the radioactivity of low atomic number nuclides of radioactive substances according to claim 4, wherein the vial is a vial made of glass or a vial made of plastic. The vial has a volume of 5 mL or more and 25 mL or less,
6. The method for measuring radioactivity of low atomic number nuclides of radioactive substances according to claim 5, wherein the plastic scintillator plate has a rectangular parallelepiped shape with short sides of 5 mm or more and 20 mm or less, long sides of 10 mm or more and 60 mm or less, and thicknesses of 0.1 mm or more and 1 mm or less. . 7. The method for measuring radioactivity of low atomic number nuclides of radioactive materials according to claim 6, wherein said plastic scintillator plate is a polymer compound containing a benzene ring. 8. The method for measuring the radioactivity of radioactive substances of low atomic number nuclides according to claim 7, wherein the plastic scintillator plate is one of a polyvinyl toluene plate, a polystyrene plate, an acrylic styrene plate, and a polystyrene terephthalate plate. 9. The method for measuring the radioactivity of radioactive substances of low atomic number nuclides according to claim 8, wherein the polystyrene plate is a plastic scintillator plate containing a polystyrene resin, an organic scintillator, and a soft styrene resin made of an elastomer containing styrene. . The organic scintillator is
p-terphenyl (P-TP), 2,5-diphenyloxazole (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). The soft styrene resin is
SB (styrene-butadiene) copolymer, SBS (styrene-butadiene-styrene block) copolymer, MBS (methyl methacrylate-butadiene-styrene) copolymer, MABS (methyl methacrylate-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. A method of measuring the radioactivity of a substance.

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