Coating type radiation-shielding material and radiation-shielding elastomer material

Abstract

An object of the invention is to provide a radiation-shielding material that has a high radiation-shielding capability and can be easily coated, molded and sheeted. Metals or the like having a radiation-shielding capability are blended with an elastomer precursor in a high concentration thereby providing a radiation-shielding material that has a higher radiation-shielding capability than ever before and can be easily coated, molded and sheeted in any desired configuration.

Claims

1. A coating type radiation-shielding material, comprising: a tungsten powder having an average particle diameter of 0.5-10 m; an elastomer precursor; and a lithium compound, wherein said elastomer precursor and said tungsten powder are blended in a blending rate of 5:95 to 20:80 as calculated on solid basis, said lithium compound is blended in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of a mixture of said elastomer precursor and said tungsten powder, and said elastomer precursor has a viscosity of 10 to 1,000 mPa.Math.s at room temperature and is able to be subjected to a curing reaction including cross-linking in such a way as to have a solid matter content of 50 to 100 wt %.

2. The coating type radiation-shielding material as recited in claim 1, wherein the coating type radiation-shielding material further comprises a strontium compound, a magnesium compound, a lanthanide element compound, or a mixture thereof.

3. The coating type radiation-shielding material as recited in claim 1, wherein the coating type radiation-shielding material further comprises (1) a boron powder or a boron compound powder, or (2) a ferrite powder.

4. The coating type radiation-shielding material as recited in claim 1, wherein the coating type radiation-shielding material further comprises (1) a boron powder or a boron compound powder, and (2) a ferrite powder.

5. A radiation-shielding elastomer material, comprising: a substrate; and the coating type radiation-shielding material as recited in claim 1 on a surface of the substrate.

6. The coating type radiation-shielding material as recited in claim 1, wherein the elastomer precursor is acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, chloro-sulfonated polyethylene rubber, epichlorohydrin rubber, chloroprene rubber, silicone rubber, styrene.Math.butadiene rubber, fluororubber, polyisobutylene rubber, styrene-based thermoplastic elastomer, olefin-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, urethane-based thermoplastic elastomer, ester-based thermoplastic elastomer, or amide-based thermoplastic elastomer.

Description

MODES FOR CARRYING OUT THE INVENTION

(1) This invention will now be explained in further details.

(2) This invention has features of blending a tungsten powder or the like with an elastomer precursor having a liquid property in high concentrations to make the density of a shielding material high and the radiation-shielding rate high. The shielding material may also be cured or otherwise crosslinked after coating operation into a coating film layer while it may still be coated, cast molded or sheeted. Addition of the lithium compound or the like to the shielding material makes sure a coating radiation-shielding material with or without being cured, which material is further improved in terms of radiation-shielding rate.

(3) The elastomer precursor that is cured as by cross-linking reactions after coating has a solid content (residues remaining after a 3-hour heating at 105 C.) of preferably 30 to 100% by weight, and more preferably 50 to 100% by weight. As the solid content is lower than 30% by weight, more volatile components are left in the shielding material to cause more voids to remain in the cured product after evaporation, resulting in a drop of shielding rate. In a lower solid content it is required to increase the amount of the elastomer precursor to be added for the purpose of making sure of the solid content necessary for high-concentration incorporation of tungsten powders with the result that the viscosity gets too low, leading possibly to sedimentation and separation of tungsten.

(4) The aforesaid elastomer precursor has a viscosity of preferably 1 to 2,000 mPa.Math.s, and more preferably 10 to 1,000 mPa.Math.s. In a viscosity of lower than 1 mPa.Math.s, the viscosity of the shielding material gets too low, leading possibly to sedimentation and separation of tungsten powders. In a viscosity of greater than 2,000 mPa.Math.s, on the other hand, high-concentration incorporation of the tungsten powders becomes difficult, and the viscosity of the shielding material grows too high for coating as well.

(5) In the invention, the mixing ratio of the elastomer precursor and tungsten powders is preferably 3:97 to 25:75, and more preferably 5:95 to 20:80 on weight basis. In a mixing ratio of lower than 3:97, it is difficult to form a sound film layer by coating, and the coating film layer run out of adhesion and strength. In a mixing ratio of greater than 25:75, on the other hand, the density of the shielding material gets low, failing to make sure of high radiation-shielding rates.

(6) The aforesaid elastomer precursor includes, but is not limited to, thermosetting elastomers such as natural or synthetic rubber before crosslinking reactions, for instance, acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, chloro-sulfonated polyethylene rubber, epichlorohydrin rubber, chloroprene rubber, silicone rubber, styrene.butadiene rubber, fluororubber, and polyisobutylene rubber. Thermoplastic elastomers such as those based on styrene, olefin, vinyl chloride, urethane, ester and amide may also be used.

(7) The aforesaid tungsten powders have an average particle diameter of preferably 0.5 to 10 m, and more preferably 1 to 5 m. In an average particle diameter of less than 0.5 m, a greater amount of the elastomer precursor must be used in order to obtain a coating type shielding material, rendering high-concentration incorporation of tungsten difficult. In an average particle diameter of greater than 10 m, on the other hand, tungsten powders are likely to settle down, rendering the resultant shielding material less fit for a coating type one.

(8) The aforesaid lithium compound includes, but is not limited to, lithium chloride, lithium fluoride, lithium bromide, lithium iodide, lithium hydroxide, lithium hexafluorophosphate, lithium niobate, n-butyl lithium, lithium carbonate, lithium acetate and lithium citrate.

(9) These lithium compounds are used in an amount of preferably 0.1 to 3.0 parts by weight, and more preferably 0.2 to 1.0 parts by weight per a total of 100 parts by weight of the elastomer precursor and tungsten powders. In an amount of less than 0.1 part by weight, they do not contribute to improvements in the radiation-shielding rate, and in an amount of greater than 3.0 parts by weight, there is an increase in the amount of a solvent used for dissolution of the lithium compound. This in turn causes the liquid viscosity of the radiation-shielding material to drop, resulting possibly in sedimentation and separation of tungsten powders, and evaporation of a large amount of the solvent which in turn causes pinholes to occur in the coating film layer, leading to uneven radiation shielding.

(10) In addition to the aforesaid components, a strontium compound, a magnesium compound, and a lanthanide element compound such as a europium compound, an erbium compound and a dysprosium compound may be used alone or in mixed combinations of two or more to improve the radiation-shielding rate. Specifically, strontium carbonate, magnesium oxide, europium oxide, erbium oxide and dysprosium oxide may be used alone or in mixed combinations of two or more.

(11) These compounds may be used in an amount of preferably 0.5 to 5.0 parts by weight, and more preferably 1.0 to 3.0 parts by weight per a total of 100 parts by weight of the elastomer precursor and tungsten powders. In an amount of less than 0.5 parts by weight, there is no improvement in the radiation-shielding rate, and in an amount of greater than 5.0 parts by weight, there is no or little effect on improvements in the radiation-shielding rate due to an increased amount.

(12) Furthermore, other compounds capable of shielding off radiations such as boron, boron compounds, molybdenum and silver may be used not only in powdery or spherical form but also in scaly, acicular or fibrous form.

(13) With the coating or cast molding type radiation-shielding material according to the invention, it is possible to prepare cured radiation-shielding materials in various forms and thicknesses. They may be used in radiation-shielding chambers for making sure of a working space in radiation environments, for storage and delivery vessels for waste materials containing radioactive substances, for protective clothing or equipments for prevention of exposure in radiation environments including medical sites.

How to Provide a Solution to Problems with Shielding Panels and Prefabricated Type Container Material

(14) The radiation-shielding material of the invention is coated on rectangular flat and/or channel steels to make shielding panels, which may then be assembled to a prefabricated container or shielding wall capable of making sure of high radiation-shielding rates. The container may also be designed to have a double structure in which the shielding material is cast between its inside and an outer container to make a shielding container or panel having any desired shielding rate. The shielding material may further be sheeted and cut in any desired configuration for application to a steel or other substrate to make a shielding wall or the like.

EXAMPLES

(15) The invention is now explained more specifically with reference to examples.

(16) Raw Materials Used

(17) Elastomer Precursor

(18) One-pack type RTV rubber: Room temperature curing type silicone rubber KE-4895-T made by the Shin-Etsu (hereinafter called KE4895) and having a viscosity of 500 mPa.Math.s
Tungsten Powders Tungsten powders C20 made by Allied Material Co., Ltd. (hereinafter called C20)
Lithium Compounds Lithium acetate: Lithium acetate made by Wako Pure Chemical Industries, Ltd. (hereinafter called lithium acetate) Lithium citrate: Lithium citrate made by Wako Pure Chemical Industries, Ltd. (hereinafter called lithium citrate) Strontium Carbonate, Europium Oxide, Erbium Oxide, Dysprosium Oxide Strontium carbonate, europium oxide, erbium oxide, dysprosium oxide, all made by Wuxi Decorative Products, Co., Ltd. (hereinafter called strontium carbonate, europium oxide, erbium oxide, and dysprosium oxide)
Estimation Testing

(19) The radiation-shielding material prepared according to the invention was cast into an acrylic box having a constant-height side wall and a bottom plate of 5 mm in thickness and allowed to stand alone at normal temperature for 24 hours to obtain a cured radiation-shielding material having varying thicknesses. The -ray shielding rate of the cured material was measured using a cesium 137 radiation source No. 8101.10MBq.

Example 1

(20) Using T.K. Homodisper Model 12.5 made by PRIMIX Co., Ltd. (commonly named as Labodisper), 2.0 parts by weight of a lithium acetate solution obtained by dissolving 0.4 part by weight of lithium acetate in 1.6 parts by weight of methanol and 4.0 parts by weight of toluene were added to 8.0 parts by weight of KE4895, and agitated at 1,000 rpm for about 15 minutes. Then, the Labodisper vessel was placed in a water bath held at 70 C., and 92.0 parts by weight of C20 were slowly added to the vessel and agitated at an agitation speed increased up to 3,000 rpm for about 30 minutes while the solution temperature was held at 70 C. Then, the solution was cooled down near to normal temperature. Then, 0.2 parts by weight of pure water were added to the solution and they were mixed and agitated for 5 minute to prepare a radiation-shielding material. The radiation-shielding material was found to have a viscosity of 6,000 mPa.Math.s, and the cured radiation-shielding material obtained from this shielding material was found to have a density of 7.8 g/cm.sup.3. The results of estimation of the -ray shielding rate of this cured radiation-shield material are set out in Table 1.

(21) TABLE-US-00001 TABLE 1 Thickness of the Cured Material (mm) -Ray Shielding Rate (%) 1 10.0 2 16.6 5 25.7 10 45.0 15 57.7 20 66.5 25 75.7 30 81.7 40 89.1 50 93.7 -Ray Shielding Rate (%) Thickness of the Cured Reported in Prior Art Material (mm) Iron Lead 1 2 15.4 5 6.6 35.0 10 14.2 59.5 15 20 32.2 85.4 25 30 95.0 40 96.3 50 75.2 99.4

Example 2

(22) Example 1 was repeated with the exception that lithium citrate was used as the lithium compound to obtain a cured shielding material (having a density of 7.8 g/cm.sup.3). This cured shielding material was used to carry out the same estimation testing as in Example 1. The results are set out in Table 2.

(23) TABLE-US-00002 TABLE 2 Thickness of the Cured Material (mm) 10 20 30 40 -Ray Shielding Rate (%) 44.8 66.6 81.5 89.2

Example 3

(24) Example 1 was repeated with the exception that the lithium compound was not added to obtain a cured shielding material (having a density of 7.8 g/cm.sup.3). This cured shielding material was used to carry out the same estimation testing as in Example 1. The results are set out in Table 3.

(25) TABLE-US-00003 TABLE 3 Thickness of the Cured Material (mm) 10 20 30 40 -Ray Shielding Rate (%) 18.8 42.2 59.6 71.0

Example 4

(26) Example 1 was repeated with the exception that the addition of 2.0 parts by weight of lithium acetate in a methanol solution was followed by the addition of strontium carbonate, europium oxide, erbium oxide and dysprosium oxide to obtain a cured shielding material of 5 mm in thickness. This cured shielding material was used to carry out the same estimation testing as in Example 1. The results are set out in Table 4 together with the results of measurement of -ray shielding rate using cobalt 60 radiation source No. 2225.

(27) TABLE-US-00004 TABLE 4 Additives (% by weight) Example SrCO.sub.3 Eu.sub.2O.sub.3 Er.sub.2O.sub.3 Dy.sub.2O.sub.3 Total 4-0 0 0 0 0 0 4-1 1.0 0 0 0 1.0 4-2 0 1.0 0 0 1.0 4-3 0 0 1.0 0 1.0 4-4 0 0 0.5 0 0.5 4-5 0 0 0 1.0 1.0 4-6 0 1.0 0 1.0 2.0 4-7 0 1.5 0 1.5 3.0 Shielding Rate Example Cs-137 Radiation Source Co-60 Radiation Source 4-0 25.7 12.0 4-1 25.0 12.5 4-2 25.7 17.0 4-3 26.2 14.6 4-4 26.2 15.6 4-5 25.6 13.0 4-6 25.8 20.7 4-7 25.7 21.4

Example 5

(28) A radiation-shielding material prepared as in Example 1 was cast molded in a steel box having a constant-height side wall and a bottom plate of 12 mm in thickness, and the same estimation testing as in Example 1 was carried out. The results are set out in Table 5.

(29) TABLE-US-00005 TABLE 5 -Ray Shielding Rate Thickness of the -Ray Shielding Reported in Prior Art Cured Material (mm) Rate (%) Iron Lead 15 77.9 20 82.9 32.2 8.54 25 86.8 30 90.0 95.0