JP2011007510A - Radiation shield, radiation shield storage employing the same, and molded product of radiation shield - Google Patents

Abstract

In a radiation facility where both neutrons and gamma rays exist, it is possible to provide a work environment in which a medical worker can work with peace of mind even in a medical field where good shielding performance is expected and particularly low-level neutrons are expected. A radiation shielding material is provided.
The radiation shielding material is characterized in that a surface of spherical lead powder having a diameter of 0.2 to 2 mm is coated with a boride such as boron oxide or boric acid. This radiation shielding material can be put in a bag made of woven fabric, non-woven fabric or resin film, mixed with radiation shielding material and resin and formed into an arbitrary shape such as brick or plate, or radiation shielding material After mixing the resin and the resin, it may be accommodated in an injectable container. The resin used at this time is preferably an epoxy resin, a mixture of a silicone resin and an epoxy resin, a silicone resin, or the like.
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Description

  The present invention relates to a radiation shielding material that shields both neutrons and gamma rays in a field where both neutrons and gamma rays exist. Although secondary gamma rays are predicted to be generated by neutron capture reaction, the present invention relates to a radiation shielding material that shields such secondary gamma rays. The present invention also relates to a radiation shielding material container and a radiation shielding material molding using such a radiation shielding material.

  Generally, metallic materials with a large specific gravity are used for shielding gamma rays, and lead is frequently used from the viewpoint of cost. However, other metallic materials such as iron, tungsten, or compounds such as oxides thereof can also be used. . On the other hand, hydrogen or boron is effective for neutron shielding, polyethylene, paraffin or epoxy resin is used, and boron is added in some cases. Furthermore, in nuclear power plants and the like, water is used as a neutron absorber for cooling the furnace, and concrete containing a large amount of hydrogen is also used as a neutron absorber for the housing material. Various types of radiation shielding materials have been developed. Resins, rubber, concrete, etc., to which a material having a radiation shielding effect (for example, heavy metals such as lead and tungsten) is added, and heavy metals themselves have already been developed and some have been put into practical use. It is said that heavy metals for gamma rays and hydrogen and / or boron for neutrons have an effective shielding action.

  Next, when lead is used as a shielding material for gamma rays, lead may be activated and radiation may be emitted. This is not caused by lead, but antimony contained as an impurity in lead is activated. By having an easy nature. Therefore, activation is not caused when lead shot or the like is used as a shielding material using lead bullion, but it may be activated when recycled lead containing a large amount of antimony is used.

  For example, as shown in Patent Documents 1 to 5 below, there are many techniques that mainly focus on neutron absorption, but since they do not contain heavy metals, none of the secondary gamma ray shielding effects due to neutron capture can be expected. . Moreover, since iron powder is also added to the following Patent Document 6, it is possible to shield some secondary gamma rays, but it is considered to be inferior to heavy metals having a higher specific gravity because the specific gravity is 7.8. . Furthermore, in the following Patent Document 7, it is said that it is possible to shield both neutrons and gamma rays by adding lead powder and boric acid to an uncured resin and curing it after mixing. The mass ratio of the lead powder is 1: 2, and the volume ratio is 5: 1. Most of the structure is occupied by the resin, and it is estimated that the gamma ray shielding effect is limited. In addition, since lead powder and boric acid are simply added and mixed, lead with a large specific gravity settles when the resin hardens, so the upper part becomes like a supernatant, and a uniform dispersion of lead cannot be obtained. In addition, there is no denying the possibility of forming a portion where lead is not present.

Japanese Patent Publication No.62-49305 JP 52-106097 A JP-A-60-387 Japanese Examined Patent Publication No. 4-67160 JP 2001-310928 A Japanese Examined Patent Publication No. 4-47800 JP 2003-255081 A

In view of the present situation, the present inventors have invented a shielding material effective for both neutrons and gamma rays by appropriately combining lead and boride while intensively studying radiation shielding materials.
From the above, in the present invention, in a radiation facility where both neutrons and gamma rays exist such as a nuclear power plant and an accelerator facility, medical treatment is performed even in a medical field where good shielding performance is expected and particularly low-level neutrons are expected. It is intended to provide a radiation shielding material that can provide a work environment where workers can work with peace of mind.

That is, the present invention is a radiation shielding material characterized in that boride is coated on the surface of a spherical lead powder having a diameter of 0.2 to 2 mm, preferably 0.25 to 1 mm. Examples of the boride include boron oxide and boric acid.
The present invention is also characterized in that, in the radiation shielding material having the above characteristics, the weight ratio of boron oxide or boric acid to the lead powder is 100: 1 to 100: 40.
Furthermore, the present invention relates to a structure in which the radiation shielding material is contained in a bag made of woven fabric, nonwoven fabric or resin film, or a container that can be injected (for example, caulking) in a state where the radiation shielding material and resin are mixed. The resin used in this case is also a radiation shielding material container, and a silicone resin is particularly preferable as the resin used in this case.
Further, the present invention is a radiation shielding material molded product obtained by molding the mixture of the radiation shielding material and the resin into an arbitrary shape such as a brick block or a plate-like body, or inserted between concrete blocks. . The resin that can be used in the present invention is not particularly limited as long as the dispersibility of the radiation shielding material is not impaired, but an epoxy resin, a mixture of a silicone resin and an epoxy resin or a silicone resin is preferable, and a brick block It is particularly preferable to use an epoxy resin or a mixture of a silicone resin and an epoxy resin when molding into a plate-like body or the like. In the present invention, the mixing ratio of the radiation shielding material and the above resin can be appropriately selected according to the type and application of the resin, but the general mixing ratio is 100: 1 to 100: 200 in weight ratio.

Since the radiation shielding material of the present invention has a relatively inexpensive lead shot as a main component, it can be used as an effective shielding material for both neutron and gamma rays, which is not only excellent shielding performance but also economically cost-effective. It becomes possible. Such radiation shielding materials play an important role in nuclear power plants and accelerator facilities. In radiation facilities dominated by high-energy epithermal neutrons, shielding performance is superior to shielding materials that have been developed so far. As a result, it is possible to reduce the size of the apparatus and the area of the radiation facility.
According to the present invention, not only such a main shielding material but also an auxiliary use such as a filler filling a gap in concrete can be used.

It is a graph which shows the shielding rate with respect to a thermal neutron area | region of various shielding materials. It is a graph which shows the shielding rate with respect to an epithermal neutron area | region of various shielding materials. It is a graph which shows the gamma ray transmitted radiation dose of various shielding materials. It is a graph which shows the neutron transmitted radiation dose of various shielding materials.

The present invention will be described in detail. In order to manufacture the radiation shielding material of the present invention, it is necessary to carry out the following procedure.
In the first step, boride is coated on the surface of spherical lead powder (hereinafter simply referred to as lead shot) having a diameter of 0.2 to 2 mm. As boride, boric acid, boron oxide, sodium borate (anhydrous), sodium borate decahydrate, potassium borate tetrahydrate, borax, lead borate, zinc borate, lithium borate, boric acid can be used those such as various barium, this time experimented with two boron oxide _(B 2 _{O 3)} and boric acid _(H 3 BO _3). Needless to say, similar effects can be obtained with other borides. Further, a rotary ball mill was used as a mixer. The lead shot and boride are weighed so as to achieve the specified blending ratio, then put into the ball mill and rotated at a low speed for a predetermined time, so that the lead shot can be coated on the surface without deformation. It was. In this case, the same surface coating is possible for a mixer such as a Henschel mixer, a rocking mixer, or a vibrating ball mill. However, in a rough machine, an attritor or the like, it is presumed that the pulverization proceeds and the lead shot is deformed. The boride-coated lead shot produced in the first step can be easily used as a radiation shielding material by placing it in an aluminum case or iron case, or in a bag made of woven fabric, nonwoven fabric or resin film. . Moreover, it is speculated that the adhesion mechanism of lead and boride is not merely causing a chemical reaction simply by being physically connected by the force at the time of mixing. Therefore, when coating is difficult, there is no problem even if a small amount of an adhesive such as ethyl cellulose, an adhesive, or a fat such as rapeseed oil is added as a binder.

  The reason why the diameter of the lead shot is set to 0.2 to 2 mm, preferably 0.25 to 1 mm is that if it is less than 0.2 mm, coating becomes difficult and the boride cannot be uniformly dispersed on the lead shot. is there. Further, when the diameter exceeds 2 mm, the specific surface area becomes small, so that the mass of boride that can be coated on the surface is remarkably reduced. In order to reduce the activation of the lead material by gamma ray irradiation, the amount of antimony contained as an impurity needs to be 500 ppm or less, but the amount of antimony in the lead shot used in this example is about several ppm. There is no problem.

  Next, the weight ratio of boron oxide and boric acid to lead was set to 100: 1 to 100: 40. When the coating ratio was less than 100: 1, the coating thickness could be reduced and the effect of neutron shielding could be expected. This is because it disappears. On the other hand, if the ratio exceeds 100: 40, coating on lead shots becomes difficult even with the use of a bonding aid (adhesive, adhesive or oil), and there is a significant amount of boride alone without coating. become.

  As the second step, the lead shot coated with the boride obtained in the first step can be formed into any of various shapes such as bricks and plates by curing with an adhesive. Moreover, since the lead shot and boride are not simply mixed but physically coated on the surface, segregation hardly occurs and a stable effect can be obtained. In the following examples, an epoxy resin, a mixture of a silicone resin and an epoxy resin, or a silicone resin was used as an adhesive in this case, but other adhesives (vinyl acetate resin, rubber, poval, The same effect can be obtained with acrylic, urethane, cyanoacrylate, starch, water glass, and phenol). In particular, when silicone resin is blended in slightly more eyes, it leaks from the gaps, for example, by applying as a sealant between joints or cracks of concrete walls, or between the ventilation ducts or electrical wiring ducts and the concrete walls. It is possible to shield radiation.

  The present invention will be described in detail with reference to the following examples, but is not limited thereto.

Example 1
Boron oxide (B ₂ O ₃ ; manufactured by Kanto Chemical Co., Inc.) or boric acid (H ₃ BO ₃ ; manufactured by Kanto Chemical Co., Inc.) with a lead shot (Shinsho Lead Industry Co., Ltd.) having a diameter of 0.5 mm After mixing at a mass blending ratio shown in Table 1, the boride was uniformly coated on the surface of the lead shot by rotating and mixing with a ball mill for 3 hours. However, in S5 and S6, rapeseed oil was added in an amount of 0.5% by weight (based on lead shot). When this was put in an aluminum case (void thickness: 2 mm, 5 mm, 10 mm) and the shielding performance of relatively weak power thermal neutrons and strong epithermal neutrons was examined, the results shown in FIGS. 1 and 2 were obtained. In both cases, both thermal neutrons and epithermal neutrons were found to have a shielding effect. Similarly, the same shielding effect can be observed even if the shielding material shown in Table 1 is put into a bag made of non-woven fabric (ester / polyethylene blend EV50gS; manufactured by Daiichi Hotaya Co., Ltd.). It was found that bags can be used for filling gaps in concrete walls, or bags with shielding materials can be stacked and used as emergency shielding walls. The measurement of the shielding performance against neutrons was performed using an electron linear accelerator photoneutron source in the Kyoto University Reactor Laboratory.

Comparative Example 1
When the lead shot with a diameter of 0.5 mm (manufactured by Shinsho Lead Industry Co., Ltd.) was placed in an aluminum case (void thickness: 2 mm, 5 mm, 10 mm) and the neutron shielding performance was examined, the results shown in FIGS. (Illustrated as S0) was obtained, and it was found that the shielding ability against thermal neutrons and epithermal neutrons was remarkably inferior when boron (and hydrogen) was not present.

Example 2
Of the lead shots S1 to S6 that showed better shielding performance than the lead shot S0 that is not coated with boron oxide or boric acid, the lead shot S5 coated with boric acid was used to further mix with the resin. A sealing material was created.
As the resin in this case, an epoxy resin (Bond E set L; manufactured by Konishi Co., Ltd.) and a modified silicone resin (Bond MOS10L; manufactured by Konishi Co., Ltd.) were used. For test piece A, 120 g of modified silicone, 60 g of epoxy resin, and 30 g of the same curing agent were stirred and mixed with respect to 4 kg of S5, and then poured into a mold to form a brick block of 100 × 200 × 50 mm. In the test piece B, 65 g of epoxy resin and 65 g of the same curing agent were stirred and mixed with respect to 4 kg of S54, and then poured into a mold to prepare a brick block of 100 × 200 × 50 mm. When 1 to 6 brick-like blocks with a thickness of 5 cm are installed side by side and their shielding performance is confirmed by measuring the amount of transmitted radiation, the results shown in FIGS. 3 and 4 are obtained. Good gamma and neutron shielding effects were observed. As shown in FIGS. 3 and 4, the radiation field used in this measurement has a gamma ray dose rate of 27 μSv / h and a neutron dose rate of 74 μSv / h at a shield thickness of 0 cm, and the neutron dose rate occupies the total dose rate. A neutron with a ratio of about 73% is the dominant field. In addition, the transmission radioactivity for neutrons and gamma rays was measured using an electron linear accelerator photoneutron source in the Kyoto University Reactor Laboratory.

Comparative Example 2
Brick blocks of 100x200x50mm were made using commercially available lead metal and commercially available polyethylene containing boric acid, respectively. Similar to Example 2, 1 to 6 brick-like blocks having a thickness of 5 cm were placed side by side and their shielding performance was confirmed by measuring the amount of transmitted radiation. The results shown in FIGS. Obtained. That is, polyethylene containing boric acid has sufficient shielding ability against neutrons, but has insufficient shielding ability against gamma rays. On the other hand, the lead block has sufficient shielding ability against gamma rays, but has insufficient shielding ability against neutrons. In addition, in FIG. 3, when the transmitted radiation amount of the boric acid containing polyethylene with respect to a gamma ray is seen, it turns out that it is inferior compared with this invention product in the area of 5 cm and 10 cm. This is presumably because the secondary gamma rays generated by the neutron beam capture reaction could not be shielded, resulting in an increase in the amount of transmitted radiation.

Example 3
Of the lead shots S1 to S6 that showed better shielding performance than the lead shot S0 that is not coated with boron oxide or boric acid, the lead shot S5 coated with boric acid was used to further mix with the resin. A sealing material was created.
As the resin in this case, a modified silicone resin (Bond MOS10L; manufactured by Konishi Co., Ltd.) was used. After adding 100 g of modified silicone to 100 g of S5 and stirring, it was put into an injection container and injected into the gap (interval: 1 cm) of the concrete block, but the workability was good. Regarding the shielding ability, the concrete block injected with the above mixture had a sufficient shielding ability against gamma rays and neutrons.

Claims (8)

A radiation shielding material, wherein a boride is coated on the surface of a spherical lead powder having a diameter of 0.2 to 2 mm. The radiation shielding material according to claim 1, wherein the boride is boron oxide, and a weight ratio of the boron oxide to the lead powder is 100: 1 to 100: 40. The radiation shielding material according to claim 1, wherein the boride is boric acid, and a weight ratio of the boric acid to the lead powder is 100: 1 to 100: 40. A radiation shielding material container, wherein the radiation shielding material according to any one of claims 1 to 3 is housed in a bag-like body made of a woven fabric, a nonwoven fabric, or a resin film. The radiation shielding material according to any one of claims 1 to 3, wherein the radiation shielding material and the resin are mixed and housed in a container having a structure that can be taken out by injection. Container. 6. The radiation shielding material container according to claim 5, wherein the resin is selected from the group consisting of an epoxy resin, a silicone resin, and a mixture of an epoxy resin and a silicone resin. A radiation shielding material molded product comprising a mixture of the radiation shielding material according to any one of claims 1 to 3 and a resin, and having a shape of a molded body formed into an arbitrary shape. The radiation shielding material molded article according to claim 7, wherein the resin is selected from the group consisting of an epoxy resin, a silicone resin, and a mixture of an epoxy resin and a silicone resin.

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