JPS63113382A - Resin-molded dosimeter element - Google Patents

Abstract

PURPOSE:To eliminate gradient of the base line in an ESR spectrum and distortion of an alanine spectrum while facilitating volume production, by molding a resin composition which has an alanine crystal powder and a lubricant contained in polystyrene. CONSTITUTION:Resin composition which has an alanine crystal powder and a lubricant contained in polystyrene is molded to form a resin-molded dosimeter element. Polystyrene is selected because of excellent in mixing and molding properties with respect to the alanine crystal powder. It is appropriate to select the alanine crystal powder in a range of 10-1,000pts.wt. per 100pts.wt. of polystyrene. It is also appropriate to select the lubricant in a range of 0.1-20pts.wt. per 100pts.wt. of polystyrene.

Description

[Detailed Description of the Invention] [Industrial Application Tn] The present invention accurately and easily measures the absorbed dose due to ionizing radiation such as gamma rays, X-rays, electron beams, heavily charged particle beams, and neutron beams. The present invention relates to a radiation dosimeter element for measurement.

[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 environments but also under environments such as high temperature and high humidity.

Conventional solid-state radiation dosimeters aimed at high-level dose measurements from 1OGy to 100kGy include thermoluminescence dosimeters, lyoluminescence dosimeters, polymethyl methacrylate dosimeters, radiachromic die-film dosimeters, and cobalt glass dosimeters. Dosimeters and the like are known. In both 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 of a specific wavelength are measured to determine the irradiation temperature.

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 widely (except for glass dosimeters).

(2) Exhibits the so-called fading phenomenon in which the dose response after irradiation changes over time (excluding thermoluminescence dosimeters and radiachromic gui film dosimeters).

(3) The effective dose measurement range is narrow.

(4) Radiachromic die-film dosimeters and liyoluminescence dosimeters have large variations in dose response 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 generates unique radicals (free radicals) that are stable in proportion to the absorbed dose. It is possible to measure the dose by determining it by (CEA-
R-3913, France 1970).

However, since the alanine crystal powder itself is soluble in water, it is affected by water and high humidity in water or in the 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 pellets, which are used as dosimeter elements. has been proposed (Int. J. Appl. Radiat.

l5ot, 33.1101 (1982), Radia
t.Protection.

EUR7448-EN Vo12,489 (198
2)).

However, molded objects made using media such as paraffin or cellulose are fragile, and even after molding, they can become deformed or chipped due to weak force or vibration, 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 cylindrical 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 exemplified. The highest melting point of paraffin is approximately 70°C, so when the temperature is high, for example, when measuring the dose of a sample in a metal container that is irradiated at a high dose rate, paraffin melts and cannot be used. When cellulose is used, since the cellulose itself generates peroxide radicals upon irradiation, 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 makes the dose measurement inaccurate and limits the measurable dose range to a narrower range than when using alanine alone. In addition, in the case of cellulose, it is a mixture of powders, so it is difficult to obtain a uniform composition, and there are large variations from one molded product to another.

In order to overcome the above drawbacks, an alanine dosimeter element using a polymer as a medium has been proposed (Kojima, et al.; No. 46
Proceedings of the Reaction Materials Lecture (1985, Autumn), Kojima.

3 others; Radiation Process Symposium Abstracts P9 (
1985, 11, 18)). 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, as mentioned above, the dosimeter element using alanine measures the dose by determining the radical concentration by ESR, and in reality it is read from the ESR spectrum, but by using a polymer as a medium, the ESR This caused a tilt in the baseline of the spectrum and distortion of the spectrum, which made it impossible to perform accurate measurements, resulting in the problem of large measurement variations between the line meter elements.
Manufacturing problems also occurred, such as the alanine composition of the resin sticking to the mold.

The present invention has been made based on the above, and aims 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. It is.

[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, the addition of the lubricant improves the baseline slope of the ESR spectrum and the alanine spectrum. It was discovered that the effects unique to resin molded dosimeter elements can be achieved, such as being able to eliminate the distortion of alanine and making the mixture of alanine and polymer uniform. This is expected to be due to the addition of the lubricant relaxing 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 determined by the accuracy of the dosimeter element. The lower limit is determined by whether or not the slope of the baseline of the ESR spectrum can be eliminated.
It is appropriate to select from a range of parts by weight.

Examples of lubricants include paraffin-based such as paraffin wax, hydrocarbon resin-based such as polyethylene wax, stearic acid, hydroxystearic acid, complex stearic acid, hardened oil, palmitic acid, margaric acid, nonadecylic acid, araxic acid, oleic acid, Fatty acids such as erucic acid, stearamide, oxy-stearamide, oleyl amide, erucyl amide, ricinol amide,
Behen amide, methylol amide, methylene bis
Fatty acid amide types such as stearamide, methylene bis stearo behenamide, ethylene bis stearamide, fatty acid ester types such as n-butyl stearate 1-, methyl hydroxystearate, polyhydric alcohol fatty acid ester, saturated fatty acid ester, ketone wax , fatty acid ketone systems such as symmetric aliphatic ketones derived from lauric acid, fatty alcohol systems such as higher alcohols, higher alcohol esters, fatty acid and polyhydric alcohol moieties such as glycerin fatty acid esters, hydroxystearic acid triglycerides, and sorbitan fatty acid esters. Ester type, cadmium stearate, zinc stearate, calcium behenate, calcium stearate,
Cadmium laurate, cadmium ricinoleate, cadmium naphthenate, cadmium 2-ethylhexoate,
Barium stearate, barium laurate, barium ricinoleate, barium naphthenate, barium 2-ethylhexoate, calcium stearate, calcium laurate, calcium ricinoleate, strontium stearate, zinc laurate, zinc ricinoleate, 2-ethylhexoate Examples include metal soaps such as zinc, 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 on each side of Table 1. In this case, while kneading 100 parts by weight of polystyrene (Asahi Kasei Co., Ltd., Styron 666) with a mixing roll at 170°C, 250 parts by weight of DL-α-alanine crystal powder (Wako Tsumugi (Yokosuri, special grade)) and 1 part by weight of a lubricant were added. Parts by weight were added and kneaded to obtain a uniform kneaded composition.In Comparative Example 1, a similar kneaded composition was prepared without adding a lubricant.Next, the kneaded composition was heated at 150°C using a Brabender extruder. A dosimeter element was produced by extrusion molding into a string shape and further press molding into a small piece with a diameter of 3.0 mmφ and a length of 3 cm at 170° C. using a mold.

The evaluation results regarding kneading performance with a mixing roll, extrusion quality with a Brabender extruder, and tackiness with a mold when manufacturing dosimeter elements on each side are shown in the lower column of Table 1. By adding a lubricant, roll kneading properties and extrudability are improved compared to the comparative example.

Further, as a result of examining the ESR spectra of the prepared dosimeter elements, it was found that in Examples 1 to 5, the baseline slope was smooth with almost no slope, as shown by curve A in FIG. On the other hand, in Comparative Example 1, the slope was extremely large as shown by curve B in FIG. The peak-to-peak height in Comparative Example 1 is H'
When the relative values of the peak-to-peak heights in each example were determined, the results were as shown in the lower column of Table 1. E.S.
Measurement of R is at modulation frequency 100KHz, Mod, 2G
Testing was carried out using XPower 4mW at room temperature.

Next, Co-γ rays were applied to the dosimeter element of Example 4 for 55 minutes at room temperature.
The ESR spectrum after irradiation with X102 Gy 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. The peak height h of the curve in FIG. 2 corresponds 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.

Further, FIG. 3 shows the relationship between the height of the ESR peak (proportional to the concentration of generated radicals per unit weight) of the dosimeter element of Example 4 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.

Example 6 - lO1 Comparative Example 2 Dosimeter elements were prepared according to the formulations shown on each side of Table 2. In this case, polystyrene (manufactured by Asahi Kasei ■, Styron 6)
66) While kneading 100 parts by weight with a mixing roll at 170°C, add DL-α-alanine crystal powder (Wako Tsumugi Pharmaceutical Co., Ltd.
800 parts by weight of 800 parts by weight (manufactured by M. Co., Ltd., special grade) and a predetermined amount of a lubricant were added and kneaded to obtain a uniform kneaded composition. In Comparative Example 2, a similar kneading composition was prepared without adding a lubricant. Next, the kneaded composition was molded in the same manner as in Examples 1 to 5 to produce a dosimeter element, and the evaluation results of kneading properties with a mixing roll, tackiness with a mold, and the relative peak-to-peak height were obtained. The values (based on the peak-to-peak height of Comparative Example 2) are shown in the lower column of Table 2.

[Effects of the Invention] As explained above, according to the present invention, it is possible to eliminate the slope of the baseline of the ESR spectrum, and the roll kneading properties are improved, so that the polymer and alanine are uniformly mixed. Since the device can be manufactured, 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, and Figure 3 is an explanatory diagram of the ES of the dosimeter element.
FIG. 2 is an explanatory diagram of the relationship between the height per unit weight of the peak of the R spectrum and the absorbed dose. Sai 11VI ゝ, \, ゝ, Sai 2 Illustration 3 Mouth

Claims (1)

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