JPH045360B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a uniform large area radiation source and a method for manufacturing the same. The radiation source of the present invention has a large area and is used as a radiation source for calibrating hand-foot monitors, survey meters for inspecting surface contamination, and the like.

Description of the Prior Art A plane radiation source having a large area has high utility value as a radiation source for calibrating a survey meter for inspecting surface contamination of a hand-foot monitor. However, until now, no material has been available that satisfies the above intended use in terms of radioactivity intensity, uniformity of radioactivity surface density, shape, etc. In particular, in the case of β-ray sources, they are used as a source for radiation control such as in the calibration of survey meters, and as a source for standard irradiation of β-rays.They are suitable for not only uniform radioactivity surface density, but also thin, low self-absorption and backscattering. The development of a shaped planar radiation source is awaited.

Conventional radiation source preparation methods include coating a thin film on the surface or immersing thin paper in a radioactive aqueous solution and then drying it, but it is important to improve the uniformity of the radioactive surface density. is extremely difficult. In addition, there are methods such as electrodeposition, mixing with metal powder, sintering, and spraying fine particles of ion exchange resin, but these methods are technically complicated and pose problems such as secondary contamination and self-absorption. There are many unresolved issues regarding how to reduce the size of . On the other hand, when a conventional ion-exchange membrane is used as a base material, reinforcement with packing material is required to improve dimensional stability in the membrane surface direction, which reduces the uniformity of radioactive surface density and self-absorption. Due to this problem, it is impossible to manufacture thin films with a thickness of about 1 micron to 30 microns.

Problems Solved by the Invention The present invention solves a technique for making uniform the radioactivity intensity and radioactivity area density and reducing self-absorption and backscattering when manufacturing a uniform large-area radiation source.

Specific Means for Solving the Problems The present invention for solving the above-mentioned problems consists of: (a) a method of imparting a radionuclide trapping function to a polymer membrane by a radiation graft polymerization method; It includes two methods for uniformly introducing radionuclides.

To describe method (a) in more detail, the polymer membrane is irradiated with ionizing radiation and then contacted with a polymerizable monomer that has a radionuclide capture function or a polymerizable monomer that has a functional group that can be converted into a cationic group. or by simultaneously irradiating the polymer membrane and the polymerizable monomer with ionizing radiation to produce a graft polymer film in which the monomer is graft-polymerized to the polymer membrane; It mainly consists of impregnating the water with a solution containing radionuclides.

The polymer membrane used in carrying out the present invention may be one that can be graft-polymerized with a monomer that has a radionuclide capture function or a functional group that can be converted into a cationic group by irradiation with radiation. Although the shape and material are not critical, preferred examples include polyethylene, polypropylene, ethylene-tetrafluoroethylene copolymer, and polyethylene terephthalate.

The polymerizable monomers having a radionuclide capture function or having a functional group that can be converted into a cationic group used in the present invention include vinyl sulfonic acid, styrene sulfonic acid, acrylic acid, and methacrylic acid. , paravinylphenol, fluorovinylsulfonic acid, fluorovinylcarboxylic acid, and metal salts thereof.

Ionizing radiation sources used in the graft polymerization of the present invention include α rays, β rays, γ rays, accelerated electron beams, and rays, but electron beams or γ rays are practically preferred.

The graft polymerization method of the present invention includes a simultaneous irradiation graft polymerization method in which the base material and the polymerizable monomer are irradiated with radiation while coexisting with each other, or a method in which only the base material is irradiated with radiation in advance and then the polymerizable monomer is irradiated with radiation. Any pre-irradiation graft polymerization method with contact with the body is possible.

As another method of the present invention, a method of introducing radionuclides into a radiation-grafted polymerized membrane can be easily achieved by immersing an ion exchange membrane in an aqueous solution containing radionuclides and adsorbing the radionuclides. It is a characteristic. However, in order to create a flat radiation source with excellent uniformity of radioactive surface density, it is necessary to avoid the effects of scratches and bends on the membrane surface, as well as the adhesion of air bubbles, when the membrane is immersed in an aqueous solution of radioactive nuclides. Easy to accept. Therefore, set the membrane in a holder as shown in Figure 1, use an immersion container as shown in Figure 2, and place the membrane at the center of the container with the membrane surface in equilibrium with the liquid level. Soaking is recommended. In FIG. 1, A and B are a plan view and an elevation view, respectively.

In Figures 1 and 2, the ring cross section is U.
A graft polymer membrane 3 is stretched over a groove-shaped retaining ring 1, and a fixing ring 2 having a U-shaped cross section is pushed in from above the membrane to stretch the membrane onto the retaining ring. 4 is a fixing tape used when dipping these rings and the like.

The structure and effects of the present invention will be specifically explained below with reference to Examples.

Example 1 A 25 μm thick low density polyethylene film was irradiated with 100 KGy in a nitrogen atmosphere using an electron accelerator (acceleration voltage 1.5 meV, electron beam current 1 mA).
It was immersed in a 50 wt% aqueous acrylic acid solution (containing 0.25 wt% Mohr's salt) with a concentration of 0.1 ppm or less, and reacted at 25°C for 5 hours. As a result, a membrane with a grafting rate of 49% was obtained.

This graft polymerized membrane is immersed in a 1N hydrochloric acid solution for 5 hours, and then thoroughly washed with purified water. After washing, immediately set the membrane uniformly on the holder shown in FIG. 1 to prevent it from drying. Pour ¹⁴⁷ Pm hydrochloric acid aqueous solution (0.1N, PH-6) into the container shown in Figure 2, fix the holder shown in Figure 1 so that the membrane surface is horizontal, and leave it for 50 hours. Remove the membrane from the container, rinse thoroughly with water, and air dry. The degree of blackening of this film was measured by autoradiography using linear film, and the standard deviation of radioactivity intensity was 5.6.
% or less, the uniformity of the radioactive surface density was extremely good, and it was excellent as a flat standard radiation source. FIG. 3 is a radioactivity intensity distribution map of the obtained film.

Example 2 ²⁰⁴ Tl was applied to the membrane of Example 1 in the same manner as in Example 1.
As a result of creating a radiation source and measuring its radioactivity distribution using radiation autoradiography, as shown in Figure 4, the variation in radioactivity intensity was less than 4%, indicating that it is a highly uniform β-ray source. It was confirmed that there is.
To inspect the radioactive surface contamination of this radiation source, we conducted a wiping test using Sumiyaro paper and measured the degree of contamination using a GM counter. It was confirmed that there was no

Example 3 Example 1 was applied to a 25 μm thick high-density polyethylene film.
The result of graft polymerization using the same method as 69%
The grafting rate was obtained. After introducing ⁶⁰ Co nuclide into this film in the same manner as in Example 1, the distribution of radioactivity intensity was determined by autoradiography, and the result was 4.5%.
It was possible to obtain a γ-ray source with excellent uniformity.

[Brief explanation of drawings]

FIG. 1 shows a holder used to hold a membrane in the present invention. Figure 2 shows a container for immersing the membrane. FIG. 3 is a radioactivity intensity distribution diagram of the radiation source manufactured according to the present invention.
FIG. 4 is a deviation diagram of radioactivity intensity, and FIG. 5 is a diagram showing the results of a test for removing flakes from the surface of the radiation source.

Claims (1)

[Claims] 1. After irradiating the polymer membrane with ionizing radiation, it is brought into contact with a polymerizable monomer having a radionuclide capture function or a polymerizable monomer having a functional group that can be converted into a cationic group. or by simultaneously irradiating the polymer membrane and the nuclear polymerizable monomer with ionizing radiation to produce a graft polymer membrane in which the monomer is graft-polymerized to the polymer membrane, and then to the graft polymer membrane, In a method of manufacturing a uniform large-area radiation source by impregnating a solution containing a radionuclide, (a) a ring having a size appropriate to obtain a radioactive radiation source of a desired size and a ring cross section having a U-shaped groove; The graft polymerized membrane is stretched over a membrane retaining ring having the shape of: (b) a cross section U that fits into the U-shaped groove of the retaining ring;
(c) Fix the membrane to the retaining ring by pushing a letter-shaped fixing ring over the graft polymer membrane stretched over the retaining ring; A method characterized by allowing the solution to stand still in equilibrium and immersing it in a solution containing a radionuclide. 2. Polymerizable monomer having a radionuclide capture function,
Or, the polymerizable monomer having a functional group that can be converted into a cationic group is vinylsulfonic acid, styrenesulfonic acid, acrylic acid, methacrylic acid, paravinylphenol, fluorovinylsulfonic acid, fluorovinylcarboxylic acid, and these metals. 2. A method according to claim 1, wherein the salt is selected from salts.