Transparent gamma ray, X-ray and neutron shielding material

Abstract

To provide a common transparent shielding material for neutrons, gamma rays, and x rays, which remains transparent even under high dose irradiation.SOLUTION: A common transparent shielding material for neutrons, gamma rays, and x rays is provided, formed of an epoxy resin molded product obtained by curing an epoxy resin composition mixed with nanoparticles of a single metal and / or metal compound using an acid anhydride.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This paper relates to a transparent gamma ray, X-ray and neutron shielding material made of an epoxy resin composition containing nanoparticles. [Background technology]

[0002] Radiation can be broadly divided into electromagnetic radiation and particle radiation. The main electromagnetic radiation is gamma rays and X-rays, while the main particle radiation is alpha rays (α rays = helium nuclei) and beta rays (β rays = electrons) that are produced by radioactive isotopes, and high-energy electrons, protons, neutrons, and heavy particles (heavy ions) that are produced in the space environment and accelerator facilities. Of these, electrically neutral neutron rays, gamma rays, and X-rays cannot be blocked by matter due to electromagnetic interactions, so in order to protect the human body and other things, shielding materials that are specifically tailored to their properties will be required.

[0003] Neutrons are produced by nuclear fission in nuclear reactors, and continue to be produced by spontaneous nuclear fission and (α,n) reactions in spent nuclear fuel. They are also produced by high-energy particle nuclear reactions in particle accelerators used for medical and research purposes, and by photonuclear reactions (nuclear reactions between photons and atomic nuclei) in medical X-ray linacs with energies exceeding 20 million electron volts (20MeV). In addition to being related to various fields such as energy and medicine, neutrons are also used in industry for non-destructive testing and in medicine, such as cancer treatment.

[0004] Gamma rays and X-rays, like neutrons, are generated from nuclear reactors and spent nuclear fuel, and are also used in various aspects of our lives and industry, such as medical diagnosis and treatment, industrial applications such as sterilization and polymer modification, agricultural applications such as breeding and pest eradication, and various non-destructive testing. They are also generated as secondary gamma rays when neutrons are absorbed and captured.

[0005] When the human body is exposed to radiation, even at a dose of 1 Sv or less, where no immediate effects are seen, there are cases where probabilistic effects such as the development of cancer can occur, and since the existence of a threshold for these effects has not been confirmed, in work where radiation exposure is considered possible, it is necessary to keep the exposure dose as low as reasonably possible (As Low As Reasonably Achievable: ALARA). The most effective means of reducing radiation exposure during a certain work period in a limited space is to provide shielding.

[0006] High-energy neutrons penetrate deep into the human body and impart large amounts of energy to the elements that compose the human body, resulting in a large dose conversion factor that indicates the radiation risk to the human body, and thus having a significant impact on external exposure to the human body. Neutrons from medical accelerators, nuclear reactors, spent nuclear fuel, etc. are mainly generated in the energy range called fast neutrons, with kinetic energy of about one million electron volts (MeV). Therefore, efficient shielding of fast neutrons is highly effective in reducing external exposure to neutron radiation. It is known that deceleration by elastic scattering with hydrogen atoms, which have almost the same mass as neutrons, is effective in shielding fast neutrons, and materials with a high hydrogen content have been used as fast neutron shielding materials. Since neutrons are electrically neutral, thick shielding, i.e., a large amount of shielding material, is required to shield them, and shielding materials that are inexpensive and easy to handle are desired. Among inexpensive materials, hydrocarbon compounds with a relatively large number of hydrogen atoms (for example, paraffins, polyethylene resins, epoxy resins, acrylic resins, etc.) are used and applied as neutron shielding structural members.

[0007] Gamma rays and X-rays are photons as particles, but to block photons, interactions with orbital electrons in atoms, such as the photoelectric effect (low energy photons), Compton scattering (high energy photons), and electron pair creation (even higher energy photons), are used, so heavy materials with high atomic numbers and high atomic density are used. In practice, inexpensive and easy-to-handle lead, iron, and concrete are used. In addition, the above-mentioned reactions with orbital electrons occur stochastically and energy is gradually lost, so the intensity of gamma rays and X-rays decreases exponentially in materials. Therefore, the dose of gamma rays and X-rays also decreases almost exponentially in materials, and the thickness at which the dose is halved is called the half-value layer (or half-value layer), and the half-value layer is usually inversely proportional to the density of the material. The half-value layer of cobalt-60 against gamma rays is 1 cm for lead and about 5 cm for concrete with a specific gravity of 2.3. The thickness at which the dose is reduced to 1 / 10 is called the 1 / 10 valence layer.

[0008] There is no universal shielding material for all types of radiation. For example, polyethylene is effective as a neutron shielding material, but is not very effective against gamma rays and X-rays. On the other hand, lead and iron have a very high shielding capacity against gamma rays and X-rays, but a low shielding capacity against neutrons by themselves.

[0009] Concrete is the most commonly used shielding material for facilities that handle neutrons, gamma rays, and X-rays, and is also used as a structural material. In addition, spent fuel from nuclear power plants is shielded from neutrons and gamma rays by being submerged in a pool of water several meters deep. Concrete has a slightly lower shielding performance against neutrons than polyethylene or water, but has excellent shielding performance against gamma rays and X-rays. In addition, concrete's shielding performance against gamma rays and X-rays is inferior to that of lead, iron, and their compounds, but its shielding performance against neutrons is far superior to that of lead and elemental iron.

[0010] Solid materials that have the ability to shield against gamma rays and X-rays are generally opaque, such as concrete and lead blocks, with the exception of lead glass, and the shielding material obstructs visibility, significantly reducing work efficiency. Even in the case of transparent materials, care must be taken to prevent deterioration of visibility due to coloring caused by long-term exposure to radiation.

[0011] In hot cells that handle highly radioactive materials, the windows may be exposed to a radiation dose of about 10 Gy / h, which means that they will be exposed to a radiation dose of about 100 kGy over several years of use. It is said that commercially available lead glass becomes discolored and its transparency deteriorates when exposed to 1 kGy, so for high-dose-rate, long-term use, it is desirable for the window to maintain a practical level of transparency against radiation doses exceeding this, up to about 100 kGy or 1 MGy.

[0012] A patent document relating to neutron shielding materials is JP 2014-514587 A, however, the transparency of the neutron shielding material described in this document is not mentioned. Regarding transparent neutron shielding materials, Patent Document 1 (JP 2017-213256 A) discloses an epoxy resin neutron shielding material having a light transmittance of 80% or more in the wavelength range of 400 nm to 700 nm, and a thickness (1 / 10 valence layer) of 14 cm or less at which the dose of neutron rays generated from a Californium-252 point isotropic source is 1 / 10. Furthermore, Patent Document 2 (JP Patent Publication No. 2017-516991 A) discloses an optically transparent radiation shielding material containing a polymer component and about 10 to about 40 wt % of a heavy metal other than lead. Numerous polymers are given as the polymer component, but specifically, a method of producing a bismuth-containing monomer and then polymerizing it, and a method of mixing a bismuth source and a monomer and then polymerizing it are given. As these monomers, acrylic or methacrylic monomers are given. Furthermore, as another method, a method of coating nanoparticles of a heavy metal or a heavy metal oxide with a siloxane polymer having a vinyl functional group at the end and polymerizing it is given. Non-Patent Document 1 discusses the coloring of epoxy resins due to irradiation with cobalt-60, and suggests the possibility of using them as a dosimeter in the range of 1-50 kGy by quantifying the coloring. When used as a shielding material, it is necessary to devise a way to reduce the coloring of epoxy resins when used under radiation exposure.

[0013] The data on the attenuation of neutron and gamma ray doses in major shielding materials described in Non-Patent Document 2 is used to evaluate the neutron and gamma ray shielding performance in radiation handling facilities. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Special table 2014-514587 publication [Patent Document 2] Special table 2017-213256 publication [Patent Document 3] Special Publication No. 2017-516991 [Non-patent literature]

[0015] [Non-Patent Document 1] Nuclear Instruments and Methods in Physics Research B 311 (2013) 1-4 [Non-Patent Document 2] Nuclear Safety Technology Center, Public Interest Foundation, "Practical Shielding Calculation (Radiation) Data Collection for Radiation Facilities 2015" (October 2015)

[0016] In the accident at the Fukushima Daiichi Nuclear Power Plant, which was caused by the tsunami resulting from the Tohoku Pacific Ocean Earthquake that occurred on March 11, 2011, the fuel in the three reactors melted down and became "fuel debris" that exists inside and underground of the reactors. In order to safely proceed with the decommissioning of the Fukushima Daiichi Nuclear Power Plant, it is necessary to remove the fuel debris or analyze the removed debris. The fuel debris contains spontaneous fissionable nuclides such as 242Cm and 244Cm and alpha-ray emitting nuclides such as 238Pu, and neutrons generated by spontaneous fission and neutrons generated by the (alpha, n) reaction of alpha rays with light elements such as oxygen are emitted from the debris. When this fuel debris is removed from the reactor and analyzed, it is necessary to sufficiently reduce the external exposure of workers to neutrons. In addition, fuel debris contains fission product (FP) nuclides, such as 137Cs, which are produced by nuclear fission, and radioactive product nuclides, such as 60Co, many of which emit strong gamma rays. The intensity of these neutrons and gamma rays is at a level that can cause high doses of radiation that could be life-threatening to humans, and they must be shielded strictly. The shape and composition of the fuel debris to be removed are diverse, and after the debris is removed from the containment vessel, it is possible that workers will carry out the removal operations while directly observing the debris in a simple cell installed outside the containment vessel. If such a cell had a window made of a transparent shielding material that could adequately block neutrons and gamma rays, the work efficiency would be significantly improved.

[0017] Space radiation, such as heavy ion particles and energetic protons (e.g., those trapped in the Van Allen belts and those from solar flares) contained in galactic cosmic rays (GCR), provides significant radiation exposure to workers, passengers, and equipment in the aerospace and other industries. For example, commercial high-altitude flights may expose flight crew and frequent flyers to radiation levels significantly higher than those permitted for the general public under legally recommended standards. High-energy heavy particles and protons react with the nuclei of atoms that make up the spacecraft's beam walls to generate neutron rays that are difficult to shield. Therefore, the aerospace industry also requires the development of more efficient neutron shielding materials. Transparent neutron shielding materials are particularly required for the windshields of high-altitude aircraft and the windows of spacecraft. Furthermore, in relatively low orbits such as those in which the International Space Station is located, there are high-energy electrons trapped in the Van Allen belts, and shielding against X-rays and other radiation generated by these electrons undergoing bremsstrahlung radiation is also required. For windows and other components closest to the crew, materials that are transparent and can block neutrons and X-rays are desirable.

[0018] Furthermore, in the medical field, "particle beam therapy" such as heavy ion cancer therapy and proton beam cancer therapy has become popular as a less invasive and highly effective cancer treatment method, but the use of these high-energy particles inevitably generates neutrons due to nuclear reactions between the particles and structural materials or the human body. X-ray linac therapy, which has been popular as a radiation cancer treatment method for a long time, has also developed to increase the energy of X-rays as the patient's body size increases, and the influence of neutrons generated by photonuclear reactions cannot be ignored. Furthermore, the technology of boron capture neutron therapy (BNCT), which directly uses neutrons to attack cancer cells, has also progressed significantly, such as by using neutrons from accelerators. For this reason, it is becoming increasingly necessary to simultaneously shield against both neutrons and gamma rays / X-rays in future radiation medicine. In particular, transparent shielding materials are desired to reduce the exposure of medical staff while monitoring patients.

[0019] From the above viewpoints, there is a demand for transparent shielding materials that are effective in environments where both neutrons and gamma rays coexist, rather than shielding materials that shield only neutrons or gamma rays.

[0020] Concrete has generally been used to simultaneously shield against neutrons, gamma rays, and X-rays, but no transparent material with shielding properties comparable to that of concrete has been found to shield against both neutrons and gamma rays and X-rays.

[0021] In addition, the inventors discovered a problem in that when the transparent neutron shielding material described in the above-mentioned patent document was exposed to an environment containing high doses of gamma rays, coloration occurred to such an extent that transparency was completely lost when the material was irradiated with a dose of about 1 MGy.

[0022] Therefore, the inventors have taken the following measures to develop an excellent, transparent gamma ray / X-ray and neutron shielding material that has shielding performance equal to or greater than that of ordinary concrete and whose transparency is not impaired even when irradiated with a dose of about 1 MGy.

[0023] An epoxy resin, which has excellent neutron shielding capability and excellent radiation resistance, is used as a curing agent and a hardened material cured with an acid anhydride is used as the matrix.

[0024] Compounds containing elements with large atomic numbers that have excellent gamma ray shielding capabilities are made into nanoparticles.

[0025] The resulting nanoparticles are dispersed in a matrix so as not to impair transparency.

[0026] However, the inventors unexpectedly discovered that the addition of nanoparticles not only contributes to improving the gamma ray shielding ability, but also contributes to preventing discoloration of the epoxy resin used as the matrix due to gamma ray irradiation, which led to the present invention. Summary of the Invention [Problem to be solved by the invention]

[0027] The objective of the present invention is to provide a transparent material that has shielding capacity for both neutrons, gamma rays, and X-rays equal to or greater than that of concrete used for radiation shielding, and that retains its transparency even under high-dose irradiation. [Means for solving the problem]

[0028] The gist of the present invention is 、 Epoxy resin made by mixing nanoparticles of metal element and / or metal compound into epoxy resin composition and curing it with acid anhydride Made of hardened material Neutrons and gamma rays, X Line for transparent It is a shielding material. And the metal element and metal elements and / or as metal compounds is Y It is preferable that the nanoparticles contain at least one element selected from the group consisting of Zr, Nb, Mo, Hf, Ta, W and lanthanides, and the average particle size of the nanoparticles is preferably 20 nm or less. Effect of the Invention

[0029] The molded article made of the epoxy resin composition of the present invention has a shielding ability equal to or greater than that of concrete not only in the case of neutrons or gamma rays alone but also in an environment where both exist together, and a transparent gamma ray, X-ray and neutron shielding material with little decrease in light transmittance due to radiation exposure under high dose rate radiation exposure has been provided. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 shows a comparison between the measured and calculated values ​​of attenuation of the dose of neutrons from an americium-beryllium neutron source per shielding thickness for a transparent shielding material (Example) made of an epoxy resin composition containing 46% by weight of zirconia.

[0031] [Diagram 2]This figure shows a comparison between the measured and calculated values ​​of attenuation of the dose of gamma rays from a cobalt-60 source per shielding thickness for a transparent shielding material (Example) made of an epoxy resin composition containing 46% by weight of zirconia.

[0032] [Diagram 3] FIG. 1 shows photographs comparing the coloration of a transparent shielding material (Example) made of an epoxy resin composition containing 46% by weight of zirconia with that of commercially available lead glass (LX-57B, manufactured by Nippon Electric Glass Co., Ltd.) after irradiation with gamma rays from a cobalt-60 source at doses of 100 kGy and 1 MGy. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The present invention will now be described in further detail. <Terminology explanation>

[0034] The term "transparent shielding material" as used in the present invention means that the presence or movement of an object can be observed through the shielding material.

[0035] According to JIST8141 sunshade protective equipment, Table JA.1-Usage standards are set for light transmission in various environments, from welding work to reflected light during outdoor work on snow. In addition, the light transmission rate of sunglasses for outdoor use is said to be 20-30%. <Epoxy resin raw material>

[0036] The epoxy resin used in the present invention is not particularly limited as long as it is a resin having an epoxy group. For example, aromatic epoxy resins having a skeleton such as bisphenol-A or bisphenol-F, and aliphatic epoxy resins having a skeleton such as alkylene glycol or cyclohexanediol, etc. are included. Among them, it is preferable to use an epoxy resin having an alicyclic skeleton.

[0037] The epoxy resin having an alicyclic skeleton is preferably selected from the group consisting of epoxy resins obtained by epoxidizing a cyclic olefin and epoxy resins obtained by hydrogenating an aromatic epoxy resin.

[0038] Examples of alicyclic epoxy resins obtained by epoxidizing cyclic olefins include 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 1,2-epoxy-vinylcyclohexene, bis(3,4-epoxycyclohexylmethyl)adipate, 1-epoxyethyl-3,4-epoxycyclohexane, limonene diepoxide, oligomeric alicyclic epoxy resins (Daicel Chemical Industries, Ltd. product names: Epolead GT300, Epolead GT400, EHPE-3150), etc. Among these, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate is preferred, and by blending this alicyclic epoxy resin, the viscosity of the epoxy resin composition can be reduced and the workability can be improved.

[0039] Examples of epoxy resins obtained by hydrogenating aromatic epoxy resins include biphenol type epoxy resins such as bisphenol A type epoxy resins, bisphenol F type epoxy resins, 3,3',5,5'-tetramethyl-4,4'-biphenol type epoxy resins, and 4,4'-biphenol type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, naphthalene diol type epoxy resins, trisphenylol methane type epoxy resins, tetrakisphenylol ethane type epoxy resins, and phenol dicyclopentadiene novolac type epoxy resins, and the like, which are obtained by hydrogenating the aromatic rings of aromatic epoxy resins. Among these, hydrogenated epoxy resins obtained by hydrogenating the aromatic rings of bisphenol A type epoxy resins, bisphenol F type epoxy resins, and biphenol type epoxy resins are particularly preferred in that they can provide epoxy resins with a high hydrogenation rate.

[0040] The hydrogenation rate of the hydrogenated epoxy resin obtained by hydrogenating such an aromatic epoxy resin is preferably in the range of 90 to 100%, more preferably in the range of 95 to 100%. If the hydrogenation rate is less than 90%, it is not preferable because it absorbs light of short wavelengths, causing deterioration of the resin over time and yellowing. This hydrogenation rate can be measured by measuring the change in absorbance (wavelength: 275 nm) using a spectrophotometer.

[0041] The above-mentioned alicyclic epoxy resins may be used alone or in combination of two or more. <Hardening agent>

[0042] The curing agent used in the present invention is an acid anhydride. As the curing agent for the epoxy resin, at least one selected from the group consisting of polyfunctional phenols, amine compounds, acid anhydride compounds, imidazole compounds, amide compounds, cationic polymerization initiators, and organic phosphines can be used, but the use of an acid anhydride is most preferable from the viewpoint of coloring.

[0043] Examples of the acid anhydride include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, trimellitic anhydride, dodecylsuccinic anhydride, chlorendic anhydride, trialkyltetrahydrophthalic anhydride, glycerol tris(anhydrotrimellitate), trialkyltetrahydrophthalic anhydride-maleic anhydride adduct, ethylene glycol bisanhydrotrimellitate, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, maleic anhydride, and condensates of maleic anhydride and unsaturated compounds. These may be used alone or in combination of two or more. Among them, alicyclic acid anhydrides are suitable for achieving high light transmittance. It is preferable to use the acid anhydride compound in the curing agent so that the equivalent ratio (acid anhydride groups of the acid anhydride compound in the curing agent relative to all epoxy groups in the epoxy compound-containing composition) is in the range of 0.6 to 1.0. <Accelerator>

[0044] It is intended to be used to increase the speed of the curing reaction. Specific examples include tertiary amines such as triethylamine and benzyldimethylamine, imidazoles such as 1-isobutyl-2-methylimidazole, 2-methylimidazole, 1-benzyl-2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and benzimidazole, organic phosphorus compounds such as tributylphosphine, methyldiphenylphosphine, triphenylphosphine, diphenylphosphine, phenylphosphine, and triphenyl phosphite, tetraphenylphosphonium tetraphenylborate, tetraphenylphosphonium tetra-p-tolylborate, tetra-n-butylphosphonium bromide, and tetra-n-butylphosphine. Examples of the latent curing accelerator include quaternary phosphonium salts such as sulfonium o,o-diethyl phosphorodithionate, tetraphenylphosphonium tetraphenylborate, tetraphenylphosphonium ethyltriphenylborate, and tetrabutylphosphonium tetrabutylborate, diazabicycloalkenes such as 1,8-diazabicyclo[5.4.0]undecene-7 and its organic acid salts, organometallic compounds such as zinc octylate, tin octylate, and aluminum acetylacetone complex, quaternary ammonium salts such as tetraethylammonium bromide and tetrabutylammonium bromide, boron compounds such as boron trifluoride and triphenylborate, and metal halide compounds such as zinc chloride and stannic chloride.Furthermore, latent curing accelerators such as high-melting point imidazole compounds, dicyandiamide, microcapsule-type latent accelerators in which the surface of phosphorus-based and phosphine-based accelerators is coated with a polymer, amine salt-type latent curing accelerators, Lewis acid salts, and Bronsted acid salts, which are high-temperature dissociation-type thermal cationic polymerization-type latent curing accelerators, can also be used. These curing accelerators can be used alone or in combination of two or more kinds. They are preferably used in an amount of 0.1 to 20 parts by weight per 100 parts by weight of the total epoxy compound components as solids. <Metal compound nanoparticles>

[0045] The metal element and / or metal compound nanoparticles used in the present invention preferably have the following characteristics. The elemental metal and / or metal compound nanoparticles preferably contain at least one element selected from the group consisting of Y, Zr, Nb, Mo, Hf, Ta, W and lanthanides. The metal compound nanoparticles are preferably at least one of an oxide, a nitride, a carbide, and a boride.

[0046] It is preferred that the nanoparticles have an average particle size of 20 nm or less. It is also desirable that the nanoparticles are dispersed in an organic solvent that is compatible with the epoxy resin. Examples of zirconia nanoparticle dispersions using methyl ethyl ketone as a dispersion medium include Nippon Shokubai Co., Ltd. (product name Zircostar, particle size: 11 nm (https: / / www.shokubai.co.jp / ja / particle / new / new3.html) and ITEC Co., Ltd. (product name Zirconeo-Ck, particle size: 10 nm: https: / / www.ipros.jp / catalog / detail / 351751). <Other additives>

[0047] In addition to the above-mentioned components, antioxidants, stabilizers, reactive or non-reactive diluents, plasticizers, release agents, flame retardants, pigments, colorants, fluorescent materials, etc. may be added to the curable epoxy resin composition of the present invention as necessary within the scope of the invention. In addition, fillers such as silica (fumed silica, colloidal silica, precipitated silica, etc.) and glass may be added for the purpose of improving various physical properties such as thermal expansion coefficient, hardness, and thixotropy. Glass can be used in any shape, including short fiber, long fiber, woven fabric, and nonwoven fabric. Types of glass that can be used include E glass, T glass, D glass, and NE glass. <Method of manufacturing molded body>

[0048] Air bubbles that cause a decrease in neutron shielding ability are trapped in the molded product, causing serious shielding defects and resulting in a molded product that cannot be used in practice. In view of this, the present invention solves this problem by taking a process in which the epoxy resin composition is degassed in advance when molding into a mold, the mixture is divided and poured intermittently into the mold, and the heat generated by curing is removed by cooling the outside of the mold while preventing the entrapment of bubbles at the bottom of the sprue of the mold.

[0049] Mixing of raw materials: Each compounding component is weighed and mixed. There are no particular restrictions on the mixer used for mixing, but it is preferable to use a mixer that can mix and degas at the same time. A typical example is a chemical mixer manufactured by Aikosha Seisakusho Co., Ltd.

[0050] Degassing: The resulting mixture is degassed using a dedicated degassing machine. Since the performance required for the molded product of the present invention is neutron shielding performance and light transmittance, it is essential to establish manufacturing technology that removes as many bubbles as possible from the molded product. The degassing machine may be a vacuum degassing device manufactured by Otsuka Seisakusho Co., Ltd. The degassing time is determined from the data on the rising tendency of reaction heat and the curing time for the selected mixture of epoxy resin and hardener. The time required for degassing is generally 1 to 120 minutes, and in practice it is preferably adjusted to 7 to 60 minutes.

[0051] Molding: There are no particular restrictions on the molding method, but a mold can be constructed according to the shape of the required parts, and a casting method can be used in which the degassed mixture is poured into the mold. After casting, the mold is left to stand at room temperature until it hardens sufficiently. The completion of hardening can be determined by measuring the temperature of the molded product. The time required for curing is generally 1 hour to 168 hours, and in practice it is preferably adjusted to 6 hours to 72 hours. <Evaluation of material shielding performance>

[0052] The energy of neutrons generated in these various industrial and medical procedures is generally around one million electron volts (MeV), and the neutron shielding performance of shielding materials can be evaluated using the energy spectrum of neutrons generated in nuclear fission reactions in nuclear reactors, etc.

[0053] When considering applications in nuclear facilities, the shielding performance of shielding materials against gamma rays and X-rays is evaluated for gamma rays emitted from radioactive nuclides such as cobalt-60 and cesium-137. Cobalt-60, which has higher energy and allows the performance of thicker shielding materials to be evaluated, is often used as the radiation source.

[0054] Non-Patent Document 2 shows the effective dose due to neutrons and secondary gamma rays per thickness of ordinary concrete when neutrons generated by spontaneous fission of Californium-252, a point isotropic radiation source, penetrate ordinary concrete.

[0055] To compare the neutron shielding performance of neutron shielding materials with ordinary concrete, the effective doses from neutrons and secondary gamma rays per thickness calculated under the same irradiation conditions as in Non-Patent Document 2 should be compared with the values ​​for ordinary concrete described in the literature.

[0056] The effective dose due to neutrons and secondary gamma rays in the shielding material can be calculated by solving the Boltzmann equation for neutrons and secondary gamma rays using a combination of an appropriate neutron-gamma ray coupling cross section library and a discrete ordinates (Sn) calculation code or a Monte Carlo calculation code to obtain the neutron flux and secondary gamma ray flux, which can then be multiplied by a conversion factor to the effective dose.

[0057] The accuracy and validity of neutron dose calculations can be evaluated by irradiating a neutron beam that has passed through a collimator from a Californium-252 or Americium-241-Beryllium neutron source onto a flat test specimen made of the shielding material in question, measuring the effective neutron dose for each shielding thickness, and comparing this with the analysis results obtained by simulating the experimental system. The thickness of the shielding material can be adjusted by preparing several test specimens of the same thickness and stacking them appropriately.

[0058] Neutron dose can be measured using a dosimeter for neutrons with energies below those of fission neutrons, such as a commercially available neutron rem counter.

[0059] Furthermore, Non-Patent Document 2 also shows the effective dose of gamma rays per thickness of ordinary concrete when gamma rays emitted from a point isotropic radiation source, cobalt 60, penetrate ordinary concrete.

[0060] To compare the gamma ray shielding performance of a gamma ray shielding material with that of ordinary concrete, the effective dose due to gamma rays per thickness calculated under the same irradiation conditions as in Non-Patent Document 2 should be compared with the value for ordinary concrete described in the literature.

[0061] The effective dose from gamma rays in a shielding material can be calculated by solving the Boltzmann equation for photons using a combination of an appropriate photon cross section library and a discrete ordinates (Sn) or Monte Carlo code to determine the gamma ray flux, and multiplying this by a conversion factor to the effective dose, or by using a gamma ray dose calculation method such as the point decay kernel method.

[0062] The accuracy and validity of the gamma ray dose calculation is evaluated by irradiating a photon beam from a cobalt-60 source through a collimator onto a flat test piece made of the shielding material, measuring the photon dose (effective dose) for each thickness of the shielding, and comparing this with the results of an analysis performed simulating the experimental system to evaluate the accuracy of the analysis. The thickness of the shielding material can be adjusted by preparing several test pieces of the same thickness and stacking them appropriately.

[0063] Gamma ray dose can be measured using a dosimeter that is sensitive to 1.17 MeV and 1.33 MeV gamma rays emitted from cobalt-60, such as a commercially available NaI survey meter. <Evaluation of changes in light transmittance due to radiation exposure>

[0064] The change in transmittance due to radiation exposure can be measured as follows. To simulate high-dose irradiation of 100 kGy or 1 MGy, which corresponds to several years of use in a high-dose-rate radiation facility, accelerated testing can be performed using a facility capable of long-term irradiation at a high dose rate of approximately 10 kGy per hour, with irradiation for 10 or 100 hours.

[0065] Facilities capable of such long-term, high-dose-rate irradiation include irradiation facilities that use cobalt-60 sources.

[0066] The visible light transmittance of a sample that has been subjected to accelerated irradiation testing and a sample before the accelerated irradiation testing are measured, and the results are compared to evaluate the change in light transmittance due to radiation exposure.

[0067] A tint meter that measures the light transmittance of car window glass can be used as a transmittance measuring device, such as KETECH Industry Instrument Store's WTM-1100 or Satotec's visible light transmittance measuring device tint meter TM2000. EXAMPLES

[0068] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to these examples.

[0069] <Example> In a 500 ml glass rotating container of a rotary evaporator, 818 g of Zircostar ZP-159A, 218 g of hydrogenated bisphenol A type epoxy resin (YX8000 manufactured by Mitsubishi Chemical Corporation), 157 g of methylhexahydrophthalic anhydride (RIKACID MH-700 manufactured by New Japan Chemical Co., Ltd.), and 2.2 g of methyl tributylphosphonium dimethyl phosphate (PX-4MP manufactured by Nippon Chemical Industry Co., Ltd.) were weighed, and a methyl ethyl ketone (MEK) removal operation was performed for 5.5 hours using a rotary evaporator to remove 78.5% of MEK. After casting into a 12 x 12 x 5 cm mold, the mixture was kept in a thermostatic chamber at an atmospheric temperature of 40 ° C for 24 hours. The mixture was kept in a thermostatic chamber at an atmospheric temperature of 80 ° C for 1 hour, then heated to 90 ° C and kept for 8 hours. After further holding at 110°C for 2 hours, the molded body was removed from the mold and held in a thermostatic chamber at an atmospheric temperature of 150°C for 1.5 hours, after which it was naturally cooled in the chamber. After removal, it was machined to obtain a test specimen for shielding test of 10 x 10 x 3 cm containing 46 mass% zirconia. In addition, a test specimen of 5 x 5 x 1.1 cm thickness was prepared and used for radiation resistance test. <Comparative Example 1>

[0070] Non-Patent Document 2 The effective dose transmittance of ordinary concrete for cobalt-60 gamma rays shown in Table 6.1(20) and the effective dose transmittance for Californium-252 neutrons shown in Table 10.1(2) are used as Comparative Example 1 for evaluating the shielding performance of the examples.

[0071] The gamma ray and neutron effective dose transmittance of Comparative Example 1 is used by those skilled in the art as a standard value of the shielding performance of ordinary concrete in the evaluation of radiation shielding for nuclear facilities or facilities using radiation. <Comparative Example 2>

[0072] A medical lead glass (LX-57B) manufactured by Nippon Electric Glass Co., Ltd., which is commercially available as a transparent X-ray shielding material and has a thickness of 5 x 5 x 1.1 cm, was subjected to a gamma ray irradiation test under the same conditions as in the example, to obtain Comparative Example 2 regarding radiation resistance. <Reference example>

[0073] A shielding material containing tungsten oxide (52 mass%) in the same volume ratio (14%) as the zirconia in the example is used as a reference example. Since the volume ratio to the epoxy resin is the same, it is considered possible to manufacture it by the manufacturing method used in the above example. <Shielding performance evaluation of the embodiment>

[0074] A neutron shielding experiment was carried out using five test specimens of the embodiment, using an americium-beryllium neutron source. The attenuation of the neutron dose rate in the shielding obtained in this experiment is shown in Figure 1, in comparison with the attenuation obtained by the experimental analysis using the continuous energy Monte Carlo method with the MCNP6.1 code. The actual measured value and the analytical value are in good agreement within the range of experimental error.

[0075] Based on the results of this experiment, the effective dose transmission (Ft) of the neutrons and secondary gamma rays in the embodiment was calculated from the attenuation of the neutron dose rate from Californium-252 and the effective dose rate of the secondary gamma rays calculated by continuous energy Monte Carlo calculation, and is shown in Table 1 in comparison with the comparative example and reference example.

[0076] [Table 1]

[0077] The effective dose transmission rate (Ft) at a thickness of 30 cm was 53.5% for the ordinary concrete of the comparative example, whereas it was only 7.27% for the example, demonstrating extremely high neutron shielding performance.

[0078] A gamma-ray shielding experiment using a cobalt-60 source was carried out using five test specimens of the embodiment. The attenuation of the gamma-ray dose rate in the shielding obtained in this experiment is compared with the attenuation obtained by experimental analysis using the continuous energy Monte Carlo method with the MCNP6.1 code, and is shown in Figure 2. The analytical value is a value that ignores the shielding effect of the zirconia particle surface treatment agent included in the embodiment, so the actual measured value shows a lower dose rate than the analytical value, but it was shown that the shielding performance is higher than that obtained by analysis.

[0079] The gamma ray effective dose transmittance (Fa) of the shielding material of the embodiment was calculated from the attenuation of the gamma ray dose rate from cobalt 60 obtained based on the experimental results, and is shown in Table 2 in comparison with the comparative example and reference example.

[0080] [Table 2]

[0081] The gamma ray shielding performance of the working example is almost the same as that of ordinary concrete. If the type of nanoparticles is replaced with heavier tungsten oxide as in the reference example, the gamma ray shielding performance is greater than that of ordinary concrete. <Evaluation of Radiation Resistance in Examples>

[0082] A commercially available medical lead glass (LX-57B, Comparative Example 2) manufactured by Nippon Electric Glass Co., Ltd. and the epoxy resin composition of the Example, both measuring 5 x 5 x 1.1 cm, were simultaneously irradiated for 10 hours and 100 hours at a dose rate of 10 kGy / h using a cobalt-60 gamma ray source, giving doses of 100 kGy and 1 MGy.

[0083] Using a tint meter WTM-1100, the transmittance of visible light (wavelength 550 nm) was measured before and after irradiation for Example and Comparative Example 2. The measurement results are shown in Table 3, and photographs of the 5 x 5 x 1.1 cm thick samples of Example and Comparative Example 2 before and after irradiation are shown in Figure 3.

[0084] [Table 3]

[0085] In the examples, there was no change within the measurement error between before and after gamma ray irradiation at 100 kGy, and even after irradiation with 1 MGy, the transmittance was maintained at 50%, with the transmittance ratio compared to unirradiated being 0.5 or more.

[0086] The medical lead glass (LX-57B) of Comparative Example 2 had transmittance of 3.2% and 1.7% after irradiation with 100 kGy and 1 MGy, and was hardly recognized as being transparent. [Industrial Applicability]

[0087] From the above results, it can be seen that the gamma ray and neutron shielding material of the present invention, despite being a transparent material, has extremely excellent neutron shielding performance and equivalent gamma ray shielding performance compared to ordinary concrete, which is the most common shielding material, and is extremely less discolored by gamma ray irradiation compared to lead glass, which is widely used as a gamma ray shielding material, and contributes to radiation protection and efficiency in handling radioactive materials in various industries such as atomic energy and medical care.

Claims

1. A transparent shielding material for both neutrons and gamma rays / X-rays, comprising an epoxy resin cured product obtained by curing an epoxy resin composition containing a mixture of metal elemental substance and / or metal compound nanoparticles having an average particle size of 20 nm or less with an acid anhydride.

2. A transparent shielding material for both neutrons and gamma rays / X-rays, comprising the cured epoxy resin of claim 1, wherein the epoxy resin has an alicyclic skeleton.

3. 3. The transparent shielding material for shielding both neutrons and gamma rays / X-rays according to claim 2, wherein the alicyclic skeleton is an epoxy resin obtained by epoxidizing a cyclic olefin.

4. 3. The transparent shielding material for shielding both neutrons and gamma rays / X-rays according to claim 2, wherein the alicyclic skeleton is an epoxy resin obtained by hydrogenating an aromatic hydrocarbon.

5. The metal element and / or metal compound according to claim 1 is a transparent shielding material for shielding neutrons, gamma rays and X-rays, which is at least one element selected from the group consisting of Y, Zr, Nb, Mo, Hf, Ta, W and lanthanoids.

6. A transparent shielding material for both neutrons, gamma rays, and X-rays as claimed in claim 1, which has shielding performance equal to or greater than that of ordinary concrete against both neutrons produced by nuclear fission and gamma rays generated from cobalt 60, and has a light transmittance of 30% or more at a wavelength of 500 nm before radiation exposure.

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