JPH0511866B2 - - 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 widespread. 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, lyoluminescence 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 dose measurement 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 or 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. Furthermore, since the powder is fine and easily charged with static electricity, it is difficult to accurately weigh it 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 produce a pellet-like pellet, which is used as a dosimeter element. has been proposed (Int.J.Appl.
Radiat. Isot, 33, 1101 (1982), Radiat.
Protection, EUR7448−EN Vo12489 (1982)). However, molded products 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. Further, since only compression molding (paraffin, cellulose) or casting method (paraffin) can be used as a molding method, the molded bodies obtained are limited to pellet-like shapes or short cylinder or prismatic shapes. 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, an alanine dosimeter element using Polma as a medium has been proposed (Kojima et al.
3 others; Proceedings of the 46th Applied Physics Conference (Autumn 1985); Kojima, 3 others; Proceedings of the Radiation Process Symposium P9 (18 November 1985). The method using polymer as a medium has the advantage that various molding methods can be used, mass production is possible, and unlike paraffin, it 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, the ESR
It is read from the spectrum, but by using a polymer as a medium, the baseline of the ESR spectrum is tilted and the spectrum is distorted, which makes it impossible to measure with high precision, and there is a large variation in measurement between dosimeter elements. A problem arose. Also,
Manufacturing problems also occurred, such as the alanine composition of the resin sticking to the molding equipment and molding mold. The present invention has been made based on the above,
The purpose of this invention is to provide a resin molded dosimeter element that can eliminate the baseline slope of the ESR spectrum and the distortion of the alanine spectrum, and is uniform and easy to mass-produce. [Means for Solving the Problems] The resin molded dosimeter element of the present invention is characterized by being formed by molding a resin composition made of polystyrene containing alanine crystal powder and a lubricant. In the present invention, polystyrene is selected because it has excellent mixability with alanine crystal powder and moldability. The blending ratio of polystyrene 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 object, and the lower limit is the value that is effective as a dosimeter element. The amount of alanine crystal powder is determined depending on whether or not it contains a certain amount of alanine, and is suitably selected from the range of 10 to 1000 parts by weight of alanine crystal powder per 100 parts by weight of polystyrene. The lubricant may be mixed with polystyrene in advance, or may be added at the time of mixing polystyrene and alanine crystal powder. In the present invention, by adding a lubricant, the slope of the baseline of the ESR spectrum and the distortion of the alanine spectrum can be eliminated, and the mixing of alanine and polymer becomes uniform, which is an effect unique to resin molded dosimeter elements. It was found that It is assumed that such effects are achieved because the addition of the lubricant relieves the mechanical stress on the alanine powder during kneading and molding. The blending ratio of polystyrene and lubricant is not specified, but the upper limit is:
Depending on whether the accuracy of the dosimeter element can be maintained, the lower limit is determined depending on whether the slope of the baseline of the ESR spectrum can be eliminated, and the range is from 0.1 to 20 parts by weight of lubricant per 100 parts by weight of polystyrene. It is appropriate to be selected. 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 fatty 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, calcium 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, polystyrene (Asahi Kasei Corporation)
100 parts by weight of Styron 666, manufactured by Wako Pure Chemical Industries, Ltd., were kneaded with a mixing roll at 170°C, and 250 parts by weight of DL-α-alanine crystal powder (manufactured by Wako Pure Chemical Industries, Ltd., special grade) and 1 part by weight of a lubricant were added and kneaded. A uniform kneaded composition was obtained. In Comparative Example 1, a similar kneading composition was prepared without adding a lubricant. Next, the kneaded composition was extruded into a string shape at 150°C using a Brabender extruder.
Furthermore, a dosimeter element was produced by press-molding at 170°C into a small piece with a diameter of 3.0 mmφ and a length of 3 cm using a mold. The evaluation results of the kneading properties with a mixing roll, the extrudability with a Brabender extruder, and the adhesion with a mold when manufacturing the dosimeter elements of each example are shown in the first part.
Shown in the bottom column of the table. By adding a lubricant, the roll kneading properties and extrudability were improved compared to the comparative example. In addition, as a result of examining the ESR spectra of the prepared dosimeter elements, in Examples 1 to 5, the curve A in Fig. 1 was
As shown in , the baseline was smooth with almost no slope. On the other hand, in Comparative Example 1, the slope was extremely large as shown by curve B in FIG. When the peak-to-peak height in Comparative Example 1 is defined as H', the relative values of the peak-to-peak height in each Example were determined and were as shown in the lower column of Table 1. ESR measurement is at modulation frequency 100KHz, Mod.2G, Power
It was performed at 4 mW and room temperature. Next, the ESR spectrum after the dosimeter element of Example 4 was irradiated with 5×10 ² Gy of ⁶⁰ Co-γ rays at room temperature is as shown by the solid line in FIG. For comparison, the ESR spectrum of only alanine powder is shown in FIG. 2 by a chain line. Peak height h of the curve in Figure 2
is a value corresponding to the concentration of radicals generated by absorption of radiation, and the amount of radicals generated in materials other than alanine (polystyrene, lubricant) is extremely small. Also, the height per unit weight of the ESR peak of the dosimeter element of Example 4 (proportional to the concentration of generated radicals)
Figure 3 shows the relationship between the absorbed dose and the absorbed dose. The logarithm of the absorbed dose and the logarithm of the ESR peak height show a nearly linear relationship, indicating that it can be used as a dosimeter element. It has been confirmed that the dosimeter elements of other Examples have similar characteristics to those of Example 4. Examples 6 to 10, Comparative Example 2 Dosimeter elements were produced according to the formulations shown in each example in Table 2. In this case, polystyrene (Asahi Kasei Corporation)
While kneading 100 parts by weight of Styron 666, manufactured by Wako Pure Chemical Industries, Ltd., with a mixing roll at 170°C, 800 parts by weight of DL-α-alanine crystal powder (manufactured by Wako Pure Chemical Industries, Ltd., special grade) and a predetermined amount of lubricant were added and kneaded to form a uniform mixture. A kneaded composition was prepared. In Comparative Example 2, a similar kneading composition was prepared without adding a lubricant. Next, the kneaded composition was prepared in Example 1.
A dosimeter element was prepared by molding in the same manner as in 5. The evaluation results for kneading properties with a mixing roll and adhesion in a mold, and the relative value of the peak-to-peak height (the peak-to-peak height of Comparative Example 2) (based on) are shown in the lower column of Table 2.

【table】

【table】

[Table] [Effects of the invention] As explained above, according to the present invention, ESR
The slope of the baseline of the spectrum can be eliminated.
In addition, since the roll kneading property is improved, the polymer and alanine are mixed uniformly, and a uniform element can be manufactured, so that measurement accuracy can be improved. In addition, since extrudability is improved and adhesion in the mold is prevented, manufacturing efficiency can be improved and mass production becomes possible.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the difference in the baseline of the ESR spectra of the example and comparative example. Figure 2 is an explanatory diagram of the ESR spectrum after radiation irradiation.
The figure is an explanatory diagram of the relationship between the peak height per unit weight of the ESR spectrum of a dosimeter element and the absorbed dose.

Claims (1)

[Claims] 1. A resin molded dosimeter element, characterized in that it is formed by molding a resin composition of polystyrene containing alanine crystal powder and a lubricant.