JPH053914B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a resin molded dosimeter that accurately and conveniently measures the absorbed dose due to ionizing radiation such as gamma rays, X-rays, electron beams, heavily charged particle beams, and neutron beams. This will expand the applications of the meter. 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 conditions of high temperature and humidity. The present invention exhibits excellent effects on dose measurements at these facilities, dose measurements for research and experiments using various types of radiation, and dose comparisons between irradiation facilities. Conventional solid-state radiation dosimeters aimed at high-level dose measurements from 10Gy to 100KGy include thermoluminescence dosimeters, liyoluminescence dosimeters, polymethyl methacrylate dosimeters, and radial chromic die film dosimeters. , cobalt glass dosimeters, etc. are well known. 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, and the irradiation dose is determined from this. 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 (excluding glass dosimeters); (2) the dose response after irradiation changes over time; It exhibits the so-called phaating phenomenon (excluding thermoluminescence dosimeters and radial chromic die-film dosimeters), (3) the effective dose measurement range is narrow, and (4) radial chromic die-film dosimeters and liyoluminescent 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). This dosimetry method does not have the drawbacks of the above-mentioned dosimeters. In other words, radicals are generated within the alanine crystals due to irradiation, so the radicals are stable, and therefore the radical concentration changes over time very little, and for the same reason, the radicals are relatively stable against heat and moisture. . Therefore, the accuracy of dose measurement is high;
Good reproducibility of measured values. Furthermore, the effective dose measurement range is from 10Gy to 100KGy, making it possible to measure a wider dose range at medium and high levels than other dosimeters. However, alanine crystal powder itself is
Because it is soluble in water, it is affected by water vapor and high humidity air, and because it is a fine powder, it is extremely inconvenient to handle.Furthermore, the powder quickly becomes charged with static electricity, making it difficult to accurately handle it. It is also difficult to weigh and insert into sample tubes. For these reasons, alanine crystal powder as it is has little value as a practical dosimeter. For this reason, research has been conducted to develop a dosimeter that takes advantage of the features of alanine crystal powder. Among the research results to date, paraffin or powdered cellulose is used as a solidifying agent, and after dispersing alanine crystal powder in this, compression molding is performed to create pellets, which are used as dosimeter elements. The method is known as standard (Inter.J.Appl.Radt.Isotope, 33 , 1101
(1982) Rad.Protection, EUR7448−EN Vo12,
489 (1982)). However, even with this method, the molded product using paraffin or cellulose as a solidifying agent is brittle, and even after molding, it can become deformed or chipped due to external force or vibration, making it impossible to accurately measure the dose.
In addition, since only compression molding (paraffin, cellulose) or casting method (paraffin) is used as the molding method, the molded bodies obtained are limited to pellet-like shapes or short cylindrical or prismatic shapes. and,
It is almost impossible to mass-produce molded articles using the above-mentioned method in which paraffin or cellulose, which easily loses its shape, is used as a solidifying agent. In addition to the above, when paraffin is used, even the one with the highest melting point has a
Since the temperature is 70°C, paraffin cannot be used in high temperature areas, such as when irradiating metal containers at high dose rates, as the paraffin will melt. On the other hand, when cellulose is used, the cellulose itself generates peroxide radicals upon irradiation, which overlap with the radicals generated in the alanine crystals, making it difficult to determine the accurate radical concentration of only the alanine crystals by ESR. This results in inaccurate dose measurements in the case of cellulose, and the measurable dose range is therefore limited to a narrower range than in the case of alanine alone. Also,
In the case of cellulose, since it is a mixture of alanine powder and cellulose powder, it is difficult to obtain a product with a uniform composition, and there are drawbacks such as large variations in the composition of each molded product. Problems to be Solved by the Invention An object of the present invention is to provide a novel and practical resin molded dosimeter using alanine crystal powder. In order to solve the above-mentioned problem of using alanine crystal powder as a practical dosimeter, the present invention aims to solve the problem of using alanine crystal powder as a practical dosimeter. A dosimeter is provided using a resin as a solidifying agent and comprising the same and alanine crystal powder. In addition, a resin composition in which a considerable amount of a radiation resistance imparting agent or an additive that increases the mobility of resin molecules and rapidly attenuates and eliminates radicals generated in the resin is used as a solidifying agent. , and an alanine crystal powder. Measures to solve the problem In order to accurately measure the dose, the amount of radicals generated in the resin by irradiation with ionizing radiation must be less than 1/10 of the amount of radicals generated in the alanine crystal by the same irradiation. There needs to be. In other words, when an alanine crystal is normally irradiated with 1×10 ³ Gy of radiation, 4.8×10 ¹⁷ spins/g of radicals are generated, but the amount of radicals generated in the synthetic resin contained in the dosimeter under the same irradiation is (4.8×
10 ¹⁷ spins/g) x (compositional weight of alanine contained in the dosimeter, g), dose measurement can be performed with high accuracy. 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
It is necessary that it decays within a short time of about 1 to 3 hours at around room temperature of 25°C and becomes less than 1/10 of the alanine (crystal) radical. Furthermore, in order to mix and mold alanine crystals and resin, it is desirable that the softening point and melting point of the resin be lower than the melting point of alanine crystals (293° C.). From this, the synthetic resins used in the present invention include polystyrene resins, acrylonitrile-styrene resins, hard acrylonitrile-butadiene-styrene resins, polybutylene terephthalate resins, polyethylene terephthalate resins, and polycarbonate resins that generate a small amount of radicals upon irradiation. Examples include resin,
In addition, low-density polyethylene (which also produces a small amount of radicals) is a resin that rapidly attenuates the generated radicals.
Examples include polypropylene and polyester resin. Furthermore, high-density polyethylene, nylon-12
In this case, a resin composition to which a considerable amount of N,N-diphenyl-paraphenylenediamine, propylfluoranthene, etc. is added as a radiation resistance imparting agent is effective. For vinyl chloride resins, resin compositions containing additives that increase the mobility of vinyl chloride molecules, such as phosphoric acid (trisisopropylphenyl) and octyl diphenyl phosphate, in addition to the above-mentioned compounds, are also effective. It goes without saying that these additives are even more effective when added to the already mentioned polystyrene, low density polyethylene, etc. The upper limit of the blending ratio of these resins and alanine crystal powder in the present invention depends on whether or not practical mechanical properties are maintained when handling these molded objects, and the lower limit is the amount of alanine that is effective as a dosimeter. It is determined depending on whether the alanine crystal powder contains 10 to 500 parts by weight of the alanine crystal powder per 100 parts by weight of the resin. Uniform mixing of the resin and alanine powder is carried out efficiently using a mixing roll or a Banbury mixer without applying too much force to the alanine crystals, and the mixing (kneading) temperature is kept from room temperature to below the melting point of the alanine crystals (293°C). Although it can be carried out at any suitable temperature, it is usually appropriate to carry out the process at a temperature in the range of 100 to 230°C, which is the kneading temperature of resins and the like. The homogeneous composition of resin and alanine thus obtained is similarly subjected to pressure molding, extrusion molding, etc., usually at a suitable temperature such as 100 to 250°C, to form various molded articles or films. In order to facilitate the production of molded bodies and films, or to improve the quality of products, the composition of the present invention may contain reinforcing materials, fillers, pigments, lubricants, or antioxidants that have little effect on the generation of alanine radicals. There is no problem in adding a heat stabilizer or the like.
Next, the configuration and effects of the present invention will be explained in more detail with reference to Examples. The blending amount is expressed in parts by weight (Phr) based on 100 resin amounts. Example 1 Low density polyethylene (Ube Industries, UBE-C400)
And polystyrene (Mitsubishi Monsanto, Dialex HH-102) was kneaded in small amounts on a mixing roll (two rolls) at 130°C.
200Phr DL-alanine crystal powder (Wako Pure Chemical Industries, Ltd.)
(Special grade) was added to make a uniform kneaded composition. After this,
The composition was pressurized (gauge pressure, 100 Kg/cm ² ) using a hot press at 130° C. to produce a polyethylene sheet molded body and a polystyrene sheet molded body each having a thickness of 2 mm. A small piece of 2 mm square and 3 cm long was cut out from the above sheet and exposed to 5 x 10 ² Gy of ⁶⁰ Co-γ rays at room temperature.
After irradiation, the relative radical concentration was determined using ESR (JEOR-FF3X) (for polyethylene molded bodies, within 2 hours after irradiation). Originally, the concentration of generated radicals can be determined from the area of the integral absorption peak of ESR, but here, the height between the peaks of the differential curve was used as a substitute for the convenience. The first ESR chart of each molded body dosimeter element
Shown in the figure (solid line). ESR measurement is modulation frequency 100K
Measured at Hz, Mod2G, Power 0.1mW, and room temperature.
A comparison with the ESR chart containing only alanine powder shown in Comparative Example 1 (dotted line a and chain line b in FIG. 1) reveals that the amount of radicals generated in each resin is extremely small. Example 2 FIG. 2 shows the relationship between the height per unit weight of the ESR peak (proportional to the concentration of generated radicals) and the absorbed dose of each molded wiremeter element produced by the method of Example 1. The ESR measurement conditions were the same as in Example 1, and irradiation was performed with ⁶⁰ Co-γ rays at room temperature, and the absorbed dose was calibrated using a Fritzke dosimeter as a standard dosimeter. In the figure, ○ and ● are polystyrene and polyethylene molded elements, respectively. Each molded element is
Logarithmic value of absorbed dose from 100Gy to 10KGy or more
The height of the ESR peak shows a linear relationship, indicating that it can be used as a dosimeter. Example 3 Various resin molded dosimeter elements were produced under the same conditions as in Example 1, and the ESR peak height (radical concentration) of each was determined. Table 1 shows the results. Each resin showed values similar to those of polystyrene and low-density polyethylene, and was found to be effective as a dosimeter. Example 4 An Izod impact test was conducted on each resin molded article of Example 3. The results are shown in Table 2. Compared to the case where paraffin and cellulose were used as solidifying agents (Comparative Example 2), the resin molded article
It showed excellent resin properties. This indicates that the resin molded dosimeter can withstand the forces, vibrations, and shocks that are likely to be applied during measurements or when mailing the dosimeter. Example 5 Polyvinyl chloride (Nippon Zeon Co., Ltd., PE-3002)
Propyl fluoranthene is mixed while kneading on a mixing roll at 120℃. was added, and furthermore, 200 Phr of DL alanine crystal powder was added little by little to obtain a uniform kneaded composition. Thereafter, the composition was pressed with a hot press at 120° C. (gauge pressure, 100 Kg/cm ² ) to produce a 2 mm thick polyvinyl chloride sheet molded body. 2 from this sheet
A small piece of mm square and 3 cm in length was cut out and irradiated with 5 x 10 ² Gy of ⁶⁰ Co-γ rays at room temperature, followed by ESR measurement. The ESR diagram was almost the same as that for the polyethylene molded element shown in FIG. 1b. Comparative example 1 DL alanine powder (Wako Pure Chemical, special grade) was added to ⁶⁰ Co−
An ESR chart in the case of 5×10 ² Gy irradiation with γ-rays is shown in FIG. 1 (dotted line a and chain line b). In addition, alanine powder and cellulose powder (Asahi Kasei, Avicel
PH102) at a weight ratio of 1:1 in a mortar post, and then cold molded into a shape with a diameter of 3 mmφ and a length of 3 cm.
Compression molding in a press (room temperature) (gauge pressure, 150
Kg/cm ² ). The ESR chart when this is irradiated with gamma rays similar to the above is also shown in Figure 1 (dotted line a).
Shown below. Elements using cellulose as a solidifying agent are extremely difficult to handle during mixing and compression molding, and they also need to be molded under high pressure to avoid deformation. Furthermore, as shown in the figure, the ESR peaks of cellulose peroxide radicals and alanine radicals overlap in the irradiated object, resulting in an asymmetrical shape, and because of the former radical, it shows changes over time, reducing the accuracy of dose measurement. Comparative Example 2 Alanine powder was mixed with paraffin (Wako Pure Chemical, mp68
The suspension was suspended in a molten state at 100°C in 100°C (70°C, first grade), stirred for several minutes, and then cooled (composition: paraffin:alanine = 1:1, weight ratio). This was compression molded using a cold press into a shape with a thickness of 2 mm, a width of 10 mm, and a length of 3 cm (gauge pressure 150
Kg/cm ² ). A mixture of cellulose and alanine was prepared in the same manner as in Comparative Example 1, with a thickness of 2 mm and a width of 10 mm.
A molded body with a length of 3 cm and a length of 3 cm was produced. The results of these Izod impact tests are shown in Table 2. As a result, it was found that these molded bodies were very brittle and easily deformed or chipped. Comparative Example 3 The ESR of a sample from Example 4 except for propylfluoranthene (irradiated with ⁶⁰ Co-γ rays, 5×10 ² Gy) was measured. In this case, polyvinyl chloride broad
The ESR absorption peak and the ESR absorption peak of alanine overlapped, and the peak height was 230 mm. this is,
This corresponds to 170% of the value of 135 mm in Example 4, indicating that the influence of polyvinyl chloride radicals is large.

【table】

【table】

[Table] No tsuchi.
Effects of the Invention (1) In the resin molded dosimeter according to the present invention, the amount of radicals produced in the resin is less than 1/10 of the amount of alanine radicals produced, so that accurate dose measurement can be performed. In addition, the measurable dose range is 10Gy to 10Gy, similar to the alanine crystal itself.
It is a wide range of 100Gy. (2) Resin molded dosimeters are less affected by the environment during irradiation, and therefore have high dose measurement accuracy and good reproducibility of measured values. That is, the upper limit of the measurable temperature range is as high as about 150°C, where alanine radicals are affected by temperature. In this case, the resin is not a factor regulating the upper limit temperature. Furthermore, most of these resins have no affinity for water, and the solidifying agent of these resins serves to protect against the drawback of alanine's solubility in water. Therefore, the resin molded dosimeter can perform measurements with good reproducibility even in environments with atmospheric humidity or water vapor at the time of measurement. (3) Resin molded dosimeters are very easy to handle, just like ordinary resin molded products, and because they are strong, they do not deform or break even if a certain amount of strong force is applied. Therefore, dose measurement can be performed simply and accurately. Furthermore, since this dose can be produced by extrusion molding into a long belt-shaped, sheet-shaped, or long linear shaped body, it is possible to measure the dose distribution inside a complex-shaped irradiated body. (4) Many molding methods such as pressure molding and extrusion molding are possible for resin molded dosimeters, and it is easy to mass-produce uniform resin molded dosimeters using these molding methods. (5) Resin molded dosimeters can withstand some strong forces, vibrations, and shocks, so the resin molded dosimeters irradiated at each facility are mailed to standards organizations that have ESR equipment with correct dose calibration. , and it is possible to uniformly perform dose evaluation and dose comparison. It has many features such as By combining it with the various resins mentioned above, the drawbacks of alanine crystal powder as a dosimetry method can be almost completely eliminated.

[Brief explanation of drawings]

FIGS. 1a and 1b are ESR charts of molded dosimeter elements manufactured in Examples and Comparative Examples of the present invention. FIG. 2 is a graph showing the relationship between the ESR peak height and absorbed dose of the molded body dosimeter elements manufactured in Examples.

Claims (1)

[Claims] 1. A synthetic resin in which the amount of 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 alanine crystal powder is blended and molded. A resin molded dosimeter made of 2. The dosimeter according to claim 1, wherein the alanine crystal powder is blended in an amount of 10 to 500 parts by weight per 100 parts by weight of the synthetic resin. 3 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 equivalent irradiation is less than 1/10. A resin molded dosimeter made by blending and molding powder. 4. The dosimeter according to claim 3, wherein the alanine crystal powder is blended in an amount of 10 to 500 parts by weight per 100 parts by weight of the synthetic resin. 5 By adding a radiation resistance imparting agent to the resin, the amount of radicals generated in the resin by irradiation with ionizing radiation is reduced to 1/1 of the amount of radicals generated in the alanine crystal.
A resin molded dosimeter made by blending alanine crystal powder into a resin composition with a concentration of 10 or less and molding the mixture. 6 Radiation resistance imparting agent per 100 parts by weight of resin
6. The dosimeter according to claim 5, wherein 0.5 to 30 parts by weight are added. 7. The dosimeter according to claim 5, wherein the alanine crystal powder is blended in an amount of 10 to 500 parts by weight based on 100 parts by weight of the resin composition. 8 By adding additives to the resin that promote the attenuation of radicals in the resin, the amount of radicals present in the resin due to ionizing radiation irradiation is reduced to 1/10 or less of the amount of radicals generated in alanine crystals by the same irradiation. A resin molded dosimeter made by blending alanine crystal powder into a resin composition and molding it. 9. The dosimeter according to claim 8, wherein 0.5 to 30 parts by weight of an additive that promotes attenuation of radicals in the resin is added to 100 parts by weight of the resin. 10. The dosimeter according to claim 8, wherein the alanine crystal powder is blended in an amount of 10 to 500 parts by weight based on 100 parts by weight of the resin composition.