JPH0533754B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a radiation dosimeter element for accurately and conveniently measuring the absorbed dose due to ionizing radiation such as gamma rays, X-rays, electron beams, heavily charged particle beams, and neutron beams. It is related to. [Background Art] In recent years, large-scale facilities that handle radioactive materials, such as nuclear power plants and radioactive waste treatment facilities, and various irradiation facilities such as particle beams and gamma rays have become popular. These facilities are required to accurately and easily measure radiation doses over a wide dose range, not only under normal conditions, but also under environments such as high temperature and high humidity. As a solid-state radiation dosimeter aimed at high-level dose measurement between conventional 10Gy and 100KGy,
Known dosimeters include thermoluminescence dosimeters, lioluminescence dosimeters, polymethyl methacrylate dosimeters, radial chromic die film dosimeters, and cobalt glass dosimeters. In all of these methods, after irradiating a solid-state element with radiation, the amount of light emitted from the solid-state element and the absorption of light at a specific wavelength are measured to determine the irradiation dose. However, these dosimeters have the following drawbacks. (1) Even under the same irradiation and environmental conditions, the dose response (i.e., the amount of light emitted and the amount of light absorbed) varies greatly (excluding glass dosimeters). (2) Shows the so-called fading phenomenon in which the dose response after irradiation changes over time (excluding thermoluminescence dosimeters and radial chromic di-film dosimeters). (3) The effective dosimetry range is narrow. (4) For radiochromic di-film dosimeters and liyoluminescence dosimeters, the dose response varies greatly depending on the environment at the time of irradiation, such as temperature and humidity. When alanine, a type of amino acid, is irradiated with radiation in a crystalline state, it produces unique radicals (free radicals) that are stable in proportion to the absorbed dose. (CEA-R-3913, France 1970). However, alanine crystal powder itself is
Since it is soluble in water, it is affected by water and high humidity in water or air. In addition, since the powder is fine and easily charged with static electricity, it is difficult to accurately measure the basis weight and fill it into a test tube for measurement, making it extremely inconvenient to handle. For these reasons, alanine crystal powder as it is has little value as a practical dosimeter, and research has been conducted to develop a dosimeter that takes advantage of the characteristics of alanine crystal powder. Among the research results to date, there is a method in which paraffin or powdered cellulose is used as a medium, alanine crystal powder is dispersed in this, and then compression molded to make pellets, which are then used as dosimeter elements. Proposed (Int.J.Appl.
Radiat. Isot, 33, 1101 (1982), Radiat.
Protection, EUR7448−EN Vo12, 489
(1982)). However, molded objects made using media such as paraffin or cellulose are fragile, and even after molding, weak force or vibration can cause them to deform or chip, making accurate dose measurements impossible. In addition, compression molding (paraffin, cellulose) or casting method (paraffin) can be used as a molding method.
Therefore, the molded bodies obtained are limited to those in the form of pellets or short cylinders or prisms. Moreover, it is almost impossible to mass-produce molded bodies using the above method. In addition to the above, the following drawbacks are also listed. Paraffin has a melting point of approximately 70°C at its highest, so it cannot be used at high temperatures, for example when measuring the dose of a sample in a metal container that is irradiated at a high dose rate, as paraffin will melt. When cellulose is used, the cellulose itself generates peroxide radicals when irradiated, so the radicals generated in the alanine crystals and the ESR signal overlap, making it difficult to determine the accurate radical concentration of the alanine crystals alone. This leads to inaccurate dosimetry and
The measurable dose range is narrower than that for alanine alone. In addition, in the case of cellulose, it is difficult to obtain a uniform composition because it is a mixture of powders, and there are large variations among individual molded bodies. To overcome the above drawbacks, alanine dosimeter elements using polymers such as ethylene propylene rubber, low-density polyethylene, and polystyrene have been proposed (Kojima, 3 others; Proceedings of the 46th Applied Physics Conference). 1985, Autumn), Kojima, and 3 others; Radiation Process Symposium Abstracts P9 (1985, 11, 18)). Furthermore, Japanese Patent Application Laid-Open No. 61-57878 proposes an alanine dosimeter element using synthetic rubber and natural rubber as media. Furthermore, JP-A No. 61-97585 describes polymers that generate a small amount of radicals upon irradiation, such as polystyrene, acrylonitrile-styrene, and polybutylene terephthalate, and low-density polyethylene,
Alanine dosimeter elements using polymers such as polypropylene and polyester, which rapidly attenuate generated radicals, have been proposed. Methods using polymers and rubber as media have the advantage that various molding methods can be used, mass production is possible, and unlike paraffin, they can be used at temperatures above 70°C. Furthermore, since a uniform composition can be easily obtained, its practicality as a dosimeter element has been dramatically increased. [Problems to be Solved by the Invention] As a result of studying the mass production of dosimeter elements using polymer as a medium, the following problems became clear.
In other words, the dosimeter element using alanine measures the dose by determining the radical concentration using ESR, as mentioned above, and in reality, ESR
As can be read from the spectrum, a considerable amount of radicals (hereinafter referred to as predose) is detected when ESR measurements are performed with a dosimeter element using a polymer as a medium in an unirradiated state. This can lead to a large measurement error in the measurement of absorbed doses in the low dose range. The results of previous studies have revealed that in the low dose range below 10 ⁴ R, the linear relationship between the absorbed dose and the amount of radicals determined by ESR measurement deviates. The present invention has been made based on the above,
The object of the present invention is to provide a resin molded dosimeter element that can significantly improve measurement accuracy by reducing predose. [Means for Solving the Problems] The resin molded dosimeter element of the present invention is characterized in that the amount of free radicals generated in the resin by irradiation with ionizing radiation is lower than the amount of radicals generated in the alanine crystal by the same irradiation. It is characterized in that it is formed by molding a resin composition that contains alanine crystal powder and an antioxidant in a synthetic resin that is 1/10 or less of the amount of synthetic resin. In addition, in the resin molded dosimeter element of the present invention, the radicals generated in the resin by irradiation with ionizing radiation are unstable and attenuate within a short time at room temperature, and the amount of radicals generated in the alanine crystal by the same irradiation is reduced. 1/10
It is characterized by being formed by molding a resin composition made of a synthetic resin as shown below containing alanine crystal powder and an antioxidant. In order to accurately measure the dose, the amount of radicals present in the resin must be less than 1/10 of that of alanine. For this purpose, either the amount of radicals generated in the resin due to irradiation is small, or the radicals generated in the resin are attenuated within a short time of about 1 to 3 hours at room temperature of 15 to 25°C, and one of the alanine crystal radicals is reduced. /10 or less. Furthermore, in order to mix and mold alanine crystals and resin, it is necessary to set the softening point and melting point of the resin to the melting point of alanine crystals (293℃).
The following is desirable. For this reason, the synthetic resins used in the present invention that generate a small amount of radicals upon irradiation include ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, acrylonitrile-styrene resin, hard acrylonitrile-butadiene-styrene resin, and polybutylene terephthalate resin. resin, polyethylene terephthalate resin, polycarbonate resin, etc.
Further, examples of resins that rapidly reduce the amount of generated radicals include low-density polyethylene (which also produces a small amount of radicals), polypropylene, and polyester resins. The blending ratio of these resins and alanine crystal powder is not particularly specified, but the upper limit depends on moldability and whether practical mechanical properties are maintained when handling the molded product, and the lower limit depends on the dosimeter element. It is determined by whether or not it contains an effective amount of alanine, and it is appropriate to select from the range of 10 to 100 parts by weight, preferably 100 to 600 parts by weight, of alanine crystal powder per 100 parts by weight of the resin. The antioxidant may be mixed with the resin in advance, or may be added at the time of mixing the resin and the alanine crystal powder. In the present invention, it has been found that the addition of an antioxidant can suppress the increase in predose caused by the resin, which is an effect unique to resin molded dosimeter elements. The reason why such effects are achieved is expected to be due to the fact that the addition of the antioxidant suppresses thermal deterioration of the resin during kneading and molding. The blending ratio of resin and antioxidant is not particularly specified, but the upper limit is:
Depending on whether the accuracy as a dosimeter element can be maintained, the lower limit is determined depending on whether there is an effect of suppressing the occurrence of pre-dose, and the antioxidant is 0.01 to 30 parts by weight, preferably 0.05 parts by weight, per 100 parts by weight of the resin. It is suitably selected from the range of ~15 parts by weight. Examples of antioxidants include naphthylamine-based phenyl-α-naphthylamine, phenyl-β-naphthylamine, aldol-α-naphthylamine, diphenylamine-based P-isopropoxy-
Diphenylamine, P-(P-toluene sulfonylamide)-diphenylamine, bis-(phenyl isopropylidene)-4,4'-diphenylamine, N,N'-diphenyl ethylenediamine,
Octylated diphenylamine, nonylated diphenylamine, alkylated diphenylamine, etc., P
-Phenyldiamine-based N,N'-diphenyl-
P-phenyldiamine, N-isopropyl-
N'-phenyl-P-phenylenediamine, N-
Cyclohexyl-N'-phenyl-P-phenylenediamine, N,N'-bis(1,4-dimethylpentyl)-P-phenylenediamine, N,N'-
Diallyl-P-phenylresinamine, hindered diallyl-P-phenylenediamine, etc., quinoline-based polymers of 2,2,4-trimethyl-1,2-dihydroquinoline, 6-dodecyl-2,
2,5-di-hydroquinone derivatives such as 2,4-trimethyl-1,2-dihydroquinoline
(Tertiary amyl)hydroquinone, 2,5-di-tert-butylhydroquinone, hydroquinone monomethyl ether, etc., monophenolic 1-oxy-3-methyl-4-isopropylbenzene, 2,
6-tert-butylphenol, derivative of 2,6-di-tert-butyl-3-methylphenol, 2,
6-di-tert-butyl-4-n-butylphenol, 4-hydroxymethyl-2,6-di-tert-butylphenol, butylhydroxyanisole, 2,4-dimethyl-6-tert-butyl Phenol, 2-methyl-4,6-dinonylphenol, 2,6-di-tert-butyl-α-dimethylamino-P-cresol, 6-(4-hydroxy-
3,5-di-tert-butylanilino)-2,-bis-octyl-thio-1,3,5-triazine,
n-octadecyl-3-(4'-hydroxy-3',
5'-di-tert-butyl phenyl) propionate, styrenated phenol, octylated phenol, alkylated P-cresol, butylated styrenated cresol, hindered phenol, phenolic phosphite, etc., bis, tris, polyphenol type as methylene bis(dimethyl-4-6-phenol), 2,2'-methylene-
Bis-(4-methyl-6-tert-butylphenol), 2,2-methylene-bis-(4-methyl-6
-cyclohexyl phenol), 2,2'-methylene-bis(4-ethyl-6-tert-butylphenol), 4,4'methylene-bis-(2,6-tert-butylphenol),
3-butylphenol), 2,2'-methylene-bis-(6-α-methyl-benzyl-P-cresol), 4,4'-butylidenebis-(3-methyl-6
-tert-butylphenol), 1,1-bis-(4
-hydroxyphenyl)-cyclohexane, 2,
2'-dihydroxy-3,3'-di-(α-methylcyclohexyl)5,5'-dimethyl diphenylmethane, alkylated bisphenol, hindered bisphenol, 1,3,5-trimethyl-2,
4,6-tris(3,5-di-tert-butyl-4
-hydroxybenzyl)benzene, tris-(2
-Methyl-4-hydroxy-5-tert-butylphenyl)butane, tetrakis-[methylene-3-
4,4'-thiobis-(6-tert-butyl-3-methylphenol) as a thiobisphenol, such as (3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]methane. ), 4,4'-thiobis(6-tert-butyl-4-methylphenol), dialkyl phenol sulfide, and the like. In the present invention, it is possible to use a lubricant, and the amount thereof is preferably in the range of 0.1 to 20 parts by weight per 100 parts by weight of the resin. It has been confirmed through experiments that the increase in pre-dose can be further suppressed by using an antioxidant and a lubricant in combination. Examples of lubricants include paraffin wax such as paraffin wax, hydrocarbon resin such as polyethylene wax, stearic acid, hydroxystearic acid, complex stearic acid, hydrogenated oil, palmitic acid, margaric acid, nonadecylic acid, arachidic acid, and oleic acid. Acids, fatty acids such as erucic acid, stearamide, oxy-stearoamide, oleyl amide, erucyl amide, ricinol amide, behen amide, methylol amide, methylene bis stearamide, methylene bis stearo behenamide, ethylene bis stearamide, etc. Fatty acid amide type, n-butyl stearate, methyl hydroxystearate, fatty acid ester type such as polyhydric alcohol fatty acid ester, saturated resin acid ester, ketone wax,
Fatty acid ketones such as symmetrical aliphatic ketones derived from lauric acid, fatty alcohols such as higher alcohols and higher alcohol esters, partial esters of fatty acids and polyhydric alcohols such as glycerin fatty acid esters, hydroxystearic acid triglycerides, and sorbitan fatty acid esters. cadmium stearate, zinc stearate, calcium behenate, calcium stearate, cadmium laurate, cadmium ricinoleate, cadmium naphthenate, cadmium diethylhexoate, barium stearate, barium laurate, barium ricinoleate, barium naphthenate, Barium 2-ethylhexoate, calcium stearate, calcium laurate, calcium ricinoleate, strontium stearate,
Examples include metal soaps such as zinc laurate, zinc ricinoleate, zinc 2-ethylhexoate, lead stearate, tin stearate, magnesium stearate, dibasic lead stearate, lead naphthenate, and aluminum stearate. [Examples of the Invention] Examples 1 to 5, Comparative Example 1 Dosimeter elements were produced according to the formulations shown in each example in Table 1. In this case, polyethylene (Ube Industries, Ltd.)
While kneading 100 parts by weight of DL-α-alanine crystal powder (manufactured by Wako Pure Chemical Industries, Ltd., special grade) with a mixing roll at 135°C, 220 parts by weight of DL-α-alanine crystal powder (manufactured by Wako Pure Chemical Industries, Ltd., special grade) and a predetermined amount of antioxidant were kneaded. A uniform kneaded composition was obtained. In addition, in Comparative Example 1, a similar kneading composition was prepared without adding an antioxidant. Next, the kneaded composition was extruded into a string shape at 130°C using a Brabender extruder, and then press-molded at 150°C into small pieces with a diameter of 3.0 mmφ and a length of 3 cm using a mold to produce a dosimeter element. . The predose amount of the fabricated dosimeter element was measured using an ESR device. Measurement is at room temperature, frequency 9.4G
Hz, Power4mM, central magnetic field 3354G, Mod.10G,
I went with Amp.1000. The predose amount in each example is as shown in the lower column of Table 1, but the predose amount in Examples is also shown as a relative value when the predose amount in Comparative Example 1 is taken as 100. Examples 6 to 12, Comparative Example 2 Dosimeter elements were produced according to the formulations shown in each example in Table 2. In this case, ethylene vinyl acetate copolymer (manufactured by Mitsui DuPont Chemical Co., Ltd., EV170)
Using a mixing roll, the kneading temperature was set to 100℃.
Dosimeter elements were produced in the same manner as in Examples 1 to 5 except for the following. Note that in Examples 11 and 12, an antioxidant was used in combination. The predose amount in each example is as shown in the lower column of Table 2, but the predose amount in Examples is also shown as a relative value when the predose amount in Comparative Example 2 is taken as 100. Examples 13 to 17, Comparative Example 3 Dosimeter elements were produced according to the formulations shown in each example in Table 3. In this case, 80 parts by weight of 100 parts by weight of ethylene propylene rubber (manufactured by Japan Synthetic Rubber Co., Ltd., EP-02P)
While kneading with a mixing roll at .degree. C., 800 parts by weight of DL-.alpha.-alanine crystal powder (manufactured by Wako Pure Chemical Industries, Ltd., special grade) and a predetermined amount of an antioxidant were added and kneaded to obtain a uniform kneaded composition. Note that in Comparative Example 3, no antioxidant was used, and in Example 16, a lubricant was used in combination. Next, the kneaded composition was molded in the same manner as in Examples 1 to 5 to produce a dosimeter element, and the pre-dose amount was measured using an ESR device. The predose amount in each example is as shown in the lower column of Table 3, but the predose amount in Examples 13 to 17 is also shown as a relative value when the predose amount in Comparative Example 3 is set as 100. .

【table】

【table】

【table】

[Table] As is clear from Tables 1 and 3, in all of Examples 1 to 17 within the scope of the present invention, the addition of an antioxidant significantly reduces the pre-dose. [Effects of the Invention] As described above, according to the present invention, it is possible to significantly suppress an increase in pre-dose during manufacturing of dosimeter elements, and it is possible to improve measurement accuracy.

Claims (1)

[Claims] 1. Alanine crystal powder is added to a synthetic resin in which the amount of free radicals generated in the resin by irradiation with ionizing radiation is 1/10 or less of the amount of radicals generated in alanine crystals by the same irradiation. and a resin molded dosimeter element, characterized in that it is formed by molding a resin composition containing an antioxidant. 2. Alanine is added to a synthetic resin in which the radicals generated in the resin by irradiation with ionizing radiation are unstable and decay within a short time at room temperature, resulting in less than 1/10 of the amount of radicals generated in alanine crystals by equivalent irradiation. A resin molded dosimeter element, characterized in that it is formed by molding a resin composition containing crystal powder and an antioxidant.