JPH0697264B2 - Polyethylene radiation dosimeter element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention accurately and simply measures absorbed doses of ionizing radiation such as γ-rays, X-rays, electron beams, heavy charged particle beams and neutron beams. The present invention relates to a polyethylene radiation dosimeter element for doing so.

[Prior Art] In recent years, large-scale facilities handling radioactive materials such as nuclear power plants and radiation waste treatment facilities, and various irradiation facilities such as particle beams and γ-rays have become widespread. In these facilities, it is required to accurately and simply evaluate the radiation dose over a wide dose range not only in the normal environment but also in the environment such as high temperature and high humidity.

Conventional solid-state radiation dosimeters for the purpose of high-level dosimetry from 10 Gy to 100 kGy include thermoluminescence dosimeters, lyoluminescence dosimeters, polymethylmethacrylate dosimeters, diachromic die film dosimeters, and cobalt glass. Dosimeters are known. All of these measures the irradiation dose by irradiating the solid element with radiation and then measuring the amount of light emitted from the solid element or the absorption of light of a specific wavelength, but there is a large variation in the dose response. There are problems such as large changes and narrow effective dose measurement range.

When an amino acid is irradiated in a crystalline state with radiation, a stable unique radical (free radical) is generated in proportion to its dose. Therefore, the concentration of produced radicals per unit weight is determined by an electron spin resonance (ESR) device to determine the dose. It is possible to measure. According to this method, a wide range of doses from 10 Gy to 100 kGy can be measured, and since the change (decay) in the number of radicals is extremely small at about 2% in two years, the change over time in the dose response is comparable to the above dosimeters. There are few differences.

However, since the amino acid crystal powder itself is soluble in water, it is affected by water and high humidity in water or air. Further, since the powder is fine and immediately charged with static electricity, accurate weighing and filling into a container are difficult, which is extremely inconvenient to handle. For this reason, a practical dosimeter device has been proposed in which amino acid crystal powder is molded and processed using a polymer as a binder (Kojima, 3 others; Proc.
85. Autumn), Kojima, and 3 others; Abstracts of Radiation Process Symposium P9 (1985.11.18)).

[Problems to be Solved by the Invention] In measurement with an amino acid dosimeter element using a polymer as a binder, when there are many radicals (hereinafter referred to as "predose") existing in the element before irradiation, or when irradiation occurs in the polymer It is preferable to select a polymer, such as low density polyethylene or polystyrene, which has a small predose and a small amount of radicals are generated by irradiation, because a large amount of radicals causes a measurement error.

However, even when such a polymer is used, there remains a problem that the measurement error in the dose range of 100 Gy or less becomes large. The measurement error can be reduced by increasing the content ratio of the amino acid crystal powder, but when the content ratio of the amino acid crystal powder is increased, the molding processability is deteriorated and the kneading cannot be performed uniformly, so that there is variation in characteristics between the elements. It has been pointed out that there is a problem that the product becomes large and the appearance of the product deteriorates.

The present invention has been made based on the above, and an object of the present invention is to provide a polyethylene radiation dose device element capable of highly filling amino acid crystal powder without lowering moldability and thus improving measurement accuracy. It is a thing.

[Means for Solving Problems] The polyethylene radiation dosimeter element of the present invention is produced by a medium- and low-pressure method such as the Phillips method and the Ziegler method, and is obtained by copolymerizing ethylene and an α-olefin having 4 or more carbon atoms. A linear low-density polyethylene having a density of 0.915 to 0.935 g / cm ³ and an amino acid crystal powder are contained in the composition to be molded. Examples of such linear low-density polyethylene commercially available include Ultzex (Mitsui Petrochemical Co., Ltd. product), NUC Polyethylene LL (Nippon Unicar Co., Ltd. product), and Yucaron L
-L (Mitsubishi Petrochemical Co., Ltd. product), Linirex (Nippon Petrochemical Co., Ltd. product), Sumikasen-L (Sumitomo Chemical Co., Ltd. product), Shorex L-PE (Showa Denko Co., Ltd. product), etc. can give.

As the amino acid crystal powder, glycine which is a monoaminomonocarboxylic acid, valine, leucine, serine which is an oxyamino acid, cysteine which is an amino acid containing sulfur,
Cystine, monoaminodicarboxylic acid lysine, arginine, aromatic ring amino acid phenylalanine, anthranilic acid and the like having relatively low molecular weight and high crystallinity are effective. As the amino acid crystal powder, a commercially available product may be used as it is, but it is also possible to use a product which is once dissolved in water and then recrystallized.

The mixing ratio of the linear low-density polyethylene and the amino acid crystal powder is not particularly specified, but the linear low-density polyethylene /
The weight ratio of the amino acid crystal powder is 10/90 to 90/10, preferably
It is appropriate to select from the range of 50 / 50-80 / 20.

In the present invention, an antioxidant and a lubricant may be appropriately contained in addition to the above components. By adding an antioxidant and a lubricant, it is possible to suppress an increase in predose during kneading and molding.

[Examples of the Invention] Example 1 Linear low-density polyethylene (manufactured by Nippon Petrochemical Co., Ltd., Linirex DF-3310, density 0.927, melt index)
2.0) 300 g of DL-α-alanine (manufactured by Wako Pure Chemical Industries, Ltd., special grade) was added while kneading 300 g with a 6-inch test roll at 140 ° C. Next, using a mold at 150 ° C, 3 mmφ (outer diameter) ×
A cylindrical dosimeter element was manufactured by press molding to 30 mm (length).

Example 2 As a linear low-density polyethylene, Nippon Petrochemical Co., Ltd.
A dosimeter element was produced in the same manner as in Example 1 except that Rinilex AF-3310 (Density: 0.922, Melt index: 1.0) was used.

Example 3 As a linear low-density polyethylene, Nippon Petrochemical Co., Ltd.
A dosimeter element was produced in the same manner as in Example 1 except that Ultzex 2021L (density 0.920, melt index 2.0) manufactured by Ultzex Co., Ltd. was used.

Example 4 Mitsubishi Yuka Co., Ltd. Yucaron LL-F30H (density 0.920, melt index 1.0) as linear low-density polyethylene
A dosimeter element was produced in the same manner as in Example 1 except that was used.

Comparative Example 1 A dosimeter element was produced in the same manner as in Example 1 except that low-density polyethylene (UBE-520, Ube Industries, Ltd., density 0.920, melt index 1.0) was used instead of linear low-density polyethylene. .

Comparative Example 2 A dosimeter element was produced in the same manner as in Example 1 except that medium density polyethylene (UBEZ-322, Ube Industries, Ltd., density 0.935, melt index 1.0) was used instead of linear low density polyethylene. .

Comparative Example 3 Instead of linear low density polyethylene, ethylene vinyl acetate copolymer (EV-17, Mitsui DuPont Chemical Co., Ltd.)
0, density 0.960, melt index 1.0, vinyl acetate amount 33%) were used, and a dosimeter element was produced in the same manner as in Example 1 except that the roll kneading temperature and the die molding temperature were 110 ° C.

Comparative Example 4 Instead of linear low density polyethylene, ethylene propylene rubber (EP-02P, Nippon Synthetic Rubber Co., Ltd., density 0.860, melt index 1.9, ethylene amount 80 mol%) was used, and roll kneading temperature and mold molding temperature were used. A dosimeter element was produced in the same manner as in Example 1 except that the temperature was set to 110 ° C.

Comparative Example 5 Example 1 was repeated except that ethylene butene terpolymer (Stylon X-75, Mitsui Petrochemical Co., Ltd.) was used in place of the linear low-density polyethylene, and the roll kneading temperature and the die molding temperature were 80 ° C. A dosimeter element was produced in the same manner.

Comparative Example 6 Instead of linear low-density polyethylene, polystyrene (Asahi Kasei Corp. Styron 475S, density 1.05, melt flow rate (200 ° C.) 1.7) was used, except that the roll kneading temperature and mold molding temperature were 160 ° C. A dosimeter element was manufactured in the same manner as in Example 1.

Comparative Example 7 Instead of linear low density polyethylene, ethylene ethyl acrylate copolymer (Japan Petrochemical Co., Ltd. A-170, density
Example 1 except that 0.930, melt index 0.82) was used, and the roll kneading temperature and die molding temperature were 100 ° C.
A dosimeter element was produced in the same manner as in.

Table 1 shows the results of evaluation of the formability and the dose variation of the dosimeter element in Examples and Comparative Examples. The evaluation was based on the following.

Moldability: Judging from the ease of molding and the appearance of the device. Predose (initial radical concentration): Measured from the peak height of the ESR spectrum. The microwave frequency is 9.5GHz,
Microwave output was 4mW, magnetic field modulation was 100kHz and 1mT, and the test was performed at 25 ℃. Comparative Example 1 was used as a reference (Δ), and when it was smaller than Comparative Example 1, it was evaluated as ◯, and when it was greater than Comparative Example 1, it was evaluated as x.

Variation in dose response: Using a ⁶⁰ Co radiation source, 20 elements were irradiated with 10 ⁴ R of γ rays, and then the peak height of the ESR spectrum was measured to obtain the variation. 2% or less variation is ○, 2
4% was evaluated as Δ and 4% or more was evaluated as x.

[Effects of the Invention] As described above, according to the present invention, the compounding ratio of the amino acid crystal powder can be increased to reduce the influence of the polymer on the dose measurement, so that the measurement accuracy can be improved and the molding processability is excellent. Therefore, there is no variation between elements and a polyethylene radiation dosimeter element having a good appearance can be obtained.

Claims (2)

[Claims] 1. A linear low-density polyethylene having a density of 0.915 to 0.935 g / cm ³ produced by copolymerizing ethylene and an α-olefin having 4 or more carbon atoms, which is produced by the medium- and low-pressure method, and an amino acid crystal powder. A polyethylene radiation dosimeter element, characterized by being formed by molding a composition containing it. 2. A polyethylene radiation dosimeter element according to claim 1, wherein the amino acid is alanine.