JPH0565116B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for accurately and easily measuring 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 thin film radiation dosimeter element for use in radiation dosimetry.

[Background Art] In recent years, large-scale facilities that handle radioactive materials, such as nuclear power plants and radioactive waste treatment facilities, and facilities that utilize various types of irradiation, such as particle beams and gamma rays, have become widespread. These facilities are required to accurately and easily evaluate 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 between 10Gy and 100kGy include thermoluminescence dosimeters, liyoluminescence dosimeters, polymethyl methacrylate dosimeters, and radial chromic di-film dosimeters. , cobalt glass dosimeters, etc. are known. In both of these methods, the dose is determined by irradiating a solid-state element with radiation and then measuring the amount of light emitted from the solid-state element and the absorption of light at a specific wavelength. It has problems such as large size and narrow effective dose measurement range.

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 dose, so the concentration of generated radicals per unit weight can be measured using an electron spin resonance (ESR) device It is possible to measure the dose by calculating According to this method, it is possible to measure a wide range of doses from 10 Gy to 100 kGy, and the change (attenuation) in the number of radicals is extremely small at about 2% over two years, so the change in dose response over time is smaller than that of the above dosimeters. There are far fewer.

However, since alanine powder itself is soluble in water, it is affected by water and 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 container, making it extremely inconvenient to handle. For this reason, a practical dosimeter element has been proposed in which alanine powder is molded using a polymer as a binder (Kojima and 3 others; Proceedings of the 46th Applied Physics Conference (Autumn 1985), Kojima and 3 others). ; Radiation Process Symposium Abstracts P9 (1985.11.18)).

The dosimeter element has a cylindrical shape with dimensions of 5 mmφ (outer diameter) x 10 mm (length) and 3 mmφ (outer diameter) x 30 mm (length).

[Problems to be solved by the invention] However, when measuring the dose of low-energy radiation or radiation species with weak penetrating power, the dose differs depending on the depth in the material, so the dose of a thick cylindrical shape is It has been pointed out that when measuring elements are used, only the average value of the dose can be measured for a thickness greater than the range of the radiation, making accurate dose evaluation impossible. Furthermore, it is not possible to measure the dose of parts placed in narrow areas, such as gaskets at pipe connections.

The present invention has been made based on the above,
Even if the dose differs depending on the depth in the material, the reliability of the dose measurement value is improved because the difference can be clearly evaluated with less error, and the thin film radiation dosimeter element also makes it possible to measure the dose in narrow areas. The purpose is to provide the following.

[Means for Solving the Problems] The radiation dosimeter element of the present invention has a composition in which a binder contains amino acid crystal powder, and a composition having a thickness of 1 mm.
It is characterized by being formed into a sheet or film-like thin film as shown below.

As the binder, natural rubber, synthetic rubber, or synthetic resin can be used, and it is particularly preferable to use a binder that produces a small amount of radicals due to radiation, or a binder that rapidly attenuates the generated radicals.

Examples of synthetic rubber include ethylene propylene (-diene) copolymer, ethylene-vinyl acetate copolymer, chloroprene rubber, nitrile rubber, butyl rubber, synthetic isoprene rubber, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, Examples include butadiene rubber, acrylic rubber, urethane rubber, silicone rubber, chlorosulfonated polyethylene, polyisobutylene, polyester rubber, epichlorohydrin rubber, tetrafluoroethylene-propylene alternating copolymer, and the like.

Examples of synthetic resins include paraffin, polystyrene, acrylonitrile-styrene resin, hard acrylonitrile-butadiene-styrene resin, polyethylene terephthalate resin, polyethylene terephthalate resin, polyarbonate resin, polyethylene, polypropylene, polyester resin, and nylon 12. .

Amino acid crystal powder includes monoamino monocarboxylic acids glycine, valine, and leucine, oxyamino acids serine, sulfur-containing amino acids cysteine and cystine, monoamino dicarboxylic acids lysine, arginine, and aromatic ring-containing amino acids. Those with relatively low molecular weight and high crystallinity, such as amino ring phenylalanine and anthranilic acid, are effective.

The blending ratio of the binder and the amino acid crystal powder is not particularly specified, but the upper limit depends on the forming processability and whether practical mechanical properties are maintained when handling the molded product, and the lower limit is the value that is effective as a dosimeter element. Amino acid crystal powder containing 100 parts by weight of Vyda
It is appropriate to select from the range of 10 to 1000 parts by weight, preferably 100 to 600 parts by weight.

In the present invention, an antioxidant and a lubricant may be appropriately contained in addition to the above-mentioned components. Antioxidant,
Addition of a lubricant can suppress an increase in predose (radicals present in the element before irradiation) during kneading and molding, and can improve measurement accuracy.

[Embodiments of the invention] Polyethylene (manufactured by Ube Industries, Ltd., UBEC-400)
400g and DL-α-alanine (manufactured by Wako Pure Chemical Industries, Ltd.)
600g of special grade) was kneaded with a 6-inch test roll at 140℃, and then press-molded into 1.0mm thick and
A 0.3 mm film dosimeter element (5 mm x 30 mm) was manufactured.

Using an electron beam accelerator, several of the above dosimeter elements are stacked to generate electron beams with different energies (0.5 MeV,
1.0MeV, 1.5MeV, 2.0MeV) at a dose equivalent to 10 ⁴ Gy (irradiation conditions were adjusted in advance using a calorimeter). The absorbed dose of the irradiated dosimeter element is
Measured using ESR.

Figure 1 shows the dose distribution (calculated values) to the thickness of the material for each energy. Figures 2 and 3 show, as an example, the results of measurements using the present dosimeter elements with thicknesses of 1.0 mm and 0.3 mm when using a 1.0 MeV electron beam. Thickness 1.0mm
(1.6 g/cm ² ) element has three levels of resolution, but if a 0.3 mm element is used, distribution measurement can be performed with nine levels of resolution. When a rod-shaped element with an outer diameter of 3 mmφ is used, such resolution cannot be expected, and only the average value of the distribution as shown in the figure or the average value of the thickness beyond the range of the radiation can be measured.

From this point of view, it is clear that the thinner the element, the more precisely the dose distribution in the depth direction in the substance can be measured, and the more accurate the dose evaluation becomes.

Furthermore, if the dosimeter element is thin in the form of a sheet or film as in the present invention, it can be installed in a narrow place, such as a connection part of a styrene pipe, and it can be used in a connection part exposed to gamma rays. It also becomes possible to measure the dose of rubber gaskets.

[Effects of the Invention] As explained above, according to the present invention, reliability can be improved because errors in dose evaluation that vary depending on material depth can be reduced, and dose measurement can be performed in a narrow place. It becomes possible.

[Brief explanation of the drawing]

Figure 1 is a graph of calculated values of the dose distribution curve, Figure 2 is a graph of calculated values of the dose distribution curve.
The figure is a graph showing the dose distribution measured with a 1 mm thick element, and Figure 3 is a graph showing the dose distribution measured with a 0.3 mm thick element.

Claims (1)

[Scope of Claims] 1. A thin film radiation dosimeter element, characterized in that it is formed by forming a composition in which a binder contains amino acid crystal powder into a sheet or film having a thickness of 1 mm or less. 2. The thin film radiation dosimeter element according to claim 1, wherein the amino acid is alanine.