Neutron shielding materials and their manufacturing methods

Abstract

This invention provides a neutron shielding material with good light transmittance and excellent shielding performance against thermal neutron lines, as well as a method for manufacturing the same. The neutron shielding material of this invention is characterized by being composed of a light-transmitting molded article comprising a light-transmitting material and a boron compound concentrated to a mass number of 10 boron isotopes. By using a boron compound containing boron isotopes concentrated to a mass number of 10, the shielding performance against thermal neutron lines can be improved. As a result, it can be widely applied to components requiring both visual visibility and neutron blocking capabilities.

Description

Neutron shielding materials and their manufacturing methods This invention relates to neutron shielding materials and their manufacturing methods, and more specifically, to neutron shielding materials and their manufacturing methods that have good light transmittance and excellent shielding performance against thermal neutron lines. Because the energy dependence of neutron beam conversion factors is very high, high-energy, high-speed neutron beam systems have a significant impact on external radiation exposure to the human body. Therefore, in nuclear energy facilities such as nuclear reactors or high-velocity bioreactors, nuclear fusion facilities, and neutron beam therapy facilities for medical treatment of affected areas, it is an important issue to protect workers from neutron beams. In particular, for monitoring devices (peepholes), safety management tools for operators, and cameras (such as those used to observe operators in emergency situations, emergency rescue facilities and vehicles, and patients undergoing treatment in neutron beam therapy facilities for medical purposes), it is desirable to develop molded protective products with excellent neutron beam shielding performance and excellent visual recognition. Generally, it is known to be effective to slow down high-speed neutron beams by elastic scattering them with lightweight atoms such as hydrogen atoms. Therefore, inexpensive and easy-to-use high-hydrogen-content materials are used as neutron shielding materials. Hydrocarbon compounds with a high hydrogen number are used as high-hydrogen-content materials, more specifically, such as acrylic resins, polyethylene resins, epoxy resins, and paraffin waxes. Furthermore, in order to shield thermal neutron lines slowed down by neutron-shielding materials, it is effective to use elements with large neutron-capturing cross-sectional areas to absorb the thermal neutron lines. Examples of elements with large neutron-capturing cross-sectional areas include... 3 He 6 Li and 10 B, etc. Patent Document 1 discloses a resin composition for a transparent neutron shielding material, which uses epoxy resin and an amine-based curing agent as essential components. Furthermore, Patent Document 1 uses an epoxy resin with an alicyclic backbone as the epoxy resin and an alicyclic diamine curing agent as the amine curing agent, setting the hydrogen atom number density to 6.78 × 10⁻⁶. 22 atoms / cm 3 The above improves the shielding performance against high-speed neutron lines. However, although the resin composition of the neutron shielding material disclosed in Patent Document 1 shows a certain effect in slowing down high-speed neutron lines, its shielding performance against thermal neutron lines cannot be said to be sufficient because it does not contain elements that can efficiently absorb slowed-down thermal neutron lines. Furthermore, Patent Document 2 discloses a neutron shielding material, which is formed by curing a mixture containing epoxy resin, polyethylene, and inorganic boron compounds using an amine-based curing agent. However, this neutron shielding material has poor visual visibility due to insufficient light transmittance. [Prior Art Documents] [Patent Documents] [Patent Document 1] WO2017 / 213265 Publication No. [Patent Document 2] Japanese Patent Publication No. 4-67160 [The problem that the invention aims to solve] This invention was made in view of the aforementioned problems, and its purpose is to provide a neutron shielding material with good light transmittance and excellent shielding performance against thermal neutron lines, as well as a method for manufacturing the same. [Means for Solving the Problem] The neutron shielding material of the present invention is designed to solve the aforementioned problems. It is characterized by being composed of a light-transmitting molded article comprising a light-transmitting material and a boron compound concentrated into a boron isotope of mass number 10. The boron compound in the aforementioned composition is concentrated to a naturally occurring boron content of 19.9% ​​by mass of 10. 10 B) Isotope compounds. Therefore, compared to compounds containing 80.1% naturally occurring compounds... 11 Compared to boron compounds of type B, excellent shielding performance against thermal neutron lines can be achieved while suppressing the boron (i.e., boron compound) content. Furthermore, by suppressing the boron compound content, the reduction in light transmittance caused by the presence of this boron compound can also be suppressed. As a result, according to the aforementioned configuration, a neutron shielding material with good light transmittance and excellent shielding performance against thermal neutron lines can be provided. In the aforementioned configuration, the concentration of boron isotopes of mass number 10 in the aforementioned boron compound is preferably 50% or higher. This reduces... 11 The proportion of boron compounds in the boron isotope can be adjusted to further suppress the boron compound content, thereby improving light transmittance. Furthermore, it can further enhance the shielding performance against thermal neutron rays. In the aforementioned configuration, the content of the aforementioned boron compound, relative to the total mass of the aforementioned neutron shielding material, is preferably 0.001% by mass to 30% by mass (in boron atomic conversion). By making the content of the boron compound 0.001% by mass or more, good shielding performance against thermal neutron lines can be maintained. On the other hand, by making the content of the boron compound 30% by mass or less, good light transmittance can be maintained. In the aforementioned composition, the aforementioned boron compound is preferably selected from at least one group consisting of boron oxide, boric acid, borane, boroxine, boron trihalide, inorganic borates, boron fluorides, borides, boron hydride compounds, hetero compounds, boronite esters, organoborates, boron esters, dihydroboronic esters, boronite esters, organoboranes, carboranes, carboronic acids, and boron-containing complex compounds. In the aforementioned configuration, the light-transmitting material is preferably any one of a glassy substance, a thermoplastic resin, a thermosetting resin, or an elastomeric resin. Because these light-transmitting materials contain hydrogen atoms, they can slow down high-speed neutron rays through elastic scattering. As a result, according to the aforementioned configuration, good shielding performance can be achieved even against high-speed neutron rays. Furthermore, in the aforementioned composition, the aforementioned light-transmitting material is preferably selected from at least one of the group consisting of polyvinyl chloride resin, polystyrene resin, polyethylene resin, epoxy resin, urethane resin, cyclic polyolefin resin, polyimide resin, polycarbonate resin, polymethyl methacrylate resin, polyethylene terephthalate resin, acrylonitrile-butadiene-styrene copolymer resin, polyvinyl alcohol resin, polyolefin resin, and silicon-containing polymer compounds. The method for manufacturing neutron shielding material of the present invention is designed to solve the aforementioned problems. It is a method for manufacturing neutron shielding material composed of a light-transmitting molded article, characterized by comprising: a mixing step of mixing a light-transmitting material with a boron compound concentrated to a mass number of 10; and a curing step of curing the mixture of the light-transmitting material and the boron compound. Based on the aforementioned composition, the material used as the neutron shielding material, due to the use of a concentration of 19.9% ​​naturally occurring... 10 Boron compounds of the B isotope, therefore, compared with those using natural occurrences at 80.1%, 11 Compared to the case where boron compounds are present, neutron shielding materials can be manufactured by suppressing the content of boron (i.e., boron compounds). This allows for the creation of neutron shielding materials that simultaneously suppress the reduction in light transmittance caused by the presence of these boron compounds and exhibit excellent shielding performance against thermal neutron lines. In the aforementioned configuration, the concentration of boron isotopes of mass number 10 in the aforementioned boron compound is preferably 50% or higher. This reduces... 11 The proportion of boron compounds in the boron isotope allows for the manufacture of neutron-shielding materials with further suppressed boron compound content. As a result, neutron-shielding materials with superior light transmittance and thermal neutron line shielding performance can be produced. In the aforementioned configuration, the content of the boron compound, in terms of boron atoms, is preferably 0.001% by mass or more and 30% by mass or less, relative to the total mass of the aforementioned neutron shielding material. By making the boron compound content 0.001% by mass or more, a neutron shielding material that can maintain good shielding performance against thermal neutron lines can be manufactured. On the other hand, by making the boron compound content 30% by mass or less, a neutron shielding material that can maintain good light transmittance can be manufactured. In the aforementioned composition, the aforementioned boron compound is preferably selected from at least one group consisting of boranes, cycloboroxanes, boron trihalides, inorganic borates, boron fluorides, borides, boron hydrides, hetero compounds, borate esters, organoborates, borate esters, dialkylborates, borate esters, organoboranes, carboranes, carboronic acids, and boron-containing complex compounds. In the aforementioned configuration, the light-transmitting material is preferably any one of a glassy substance, a thermoplastic resin, a thermosetting resin, or an elastomeric resin. Because these light-transmitting materials contain hydrogen atoms, they can slow down high-speed neutron rays through elastic scattering. As a result, according to the aforementioned configuration, a neutron shielding material that exhibits good shielding performance even against high-speed neutron rays can be manufactured. Furthermore, in the aforementioned composition, the aforementioned light-transmitting material is preferably selected from at least one of the group consisting of polyvinyl chloride resin, polystyrene resin, polyethylene resin, epoxy resin, urethane resin, cyclic polyolefin resin, polyimide resin, polycarbonate resin, polymethyl methacrylate resin, polyethylene terephthalate resin, acrylonitrile-butadiene-styrene copolymer resin, polyvinyl alcohol resin, polyolefin resin, and silicon-containing polymer compounds. In the aforementioned configuration, the aforementioned mixing step is preferably a step of mixing at least one of the aforementioned boron compound in powder form, the aforementioned boron compound in solid form with a solvent to form a solution, the aforementioned boron compound in solid form with a dispersion liquid to form a dispersion medium, and the aforementioned boron compound in liquid form with the aforementioned light-transmitting material. Furthermore, in the aforementioned configuration, the preferred translucent material is a two-component thermosetting resin containing a main agent and a hardener, and the aforementioned mixing step is a step of further adding the main agent after mixing the aforementioned hardener and the aforementioned boron compound. [Effects of the Invention] According to the present invention, a neutron shielding material with good light transmittance and excellent shielding performance against thermal neutron lines and a method thereof are provided. [Form of Invention] (Neutron-Shielding Material) The following describes the neutron shielding material according to embodiments of the present invention. In this specification, the term "neutron" in neutron shielding material includes both high-speed neutrons and thermal neutrons. Therefore, when "neutron" is mentioned in this specification, it refers to either or both of "high-speed neutrons" and "thermal neutrons." Furthermore, the terms "high-speed neutron" and "high-speed neutron line" in this specification refer to neutrons (lines) with an energy level of 0.1 MeV or higher. Moreover, the terms "thermal neutron" and "thermal neutron line" in this specification refer to neutrons (lines) with an energy level below 0.1 MeV. The neutron shielding material of this embodiment is composed of a molded article comprising at least a light-transmitting material and a boron compound concentrated to a mass number of 10 boron isotopes. Furthermore, the neutron shielding material of this embodiment is light-transmitting. Moreover, the neutron shielding material of this embodiment may also be a molded article composed solely of a light-transmitting material and a boron compound. Here, the term "molded object" in this specification includes, in addition to plate-shaped objects, also particle-shaped or granular-shaped objects. Furthermore, the term "transmittance" in this specification refers to the property of allowing at least a portion of visible light to pass through. For example, for a neutron-shielding material, the transmittance in the wavelength range of 400 nm to 1000 nm is 80% or more, relative to the case where the neutron-shielding material is not present. Also, transmittance includes both colorless and colored cases, excluding cases where the neutron-shielding material is colorless. The boron compound in this embodiment is concentrated into 10 Boron compounds of the B isotope. 10 B-series neutron absorption profile is large (3840 barn). Therefore, after condensation... 10 Boron compounds of the boron isotope B function as thermal neutron absorbers in neutron-shielding materials. Furthermore, 11 The B isotope series does not react with neutrons. Here, the phrase "concentrated to a boron isotope of mass number 10" in this specification means that the boron isotope of mass number 10 is more concentrated than that found naturally. In boron atoms, naturally occurring boron atoms of mass number 10 and mass number 11 are... 10 B: 11 B exists in a ratio of 19.9% ​​to 80.1%. Therefore, the phrase "concentrated to a mass number of 10 boron isotopes" means that... 10 B is concentrated in a manner that is 19.9% ​​greater than its natural proportion. Boron compounds 10 The concentration of B isotope is preferably 50% or higher, more preferably 75% or higher, and exceptionally preferably 90% or higher. This is because... 10 By concentrating boron isotopes to 50% or higher, the content of boron compounds used to maintain good shielding performance against thermal neutron rays can be reduced. As a result, the decrease in light transmittance caused by the presence of boron compounds can be suppressed. Regarding the content of boron compounds, the lower limit is, relative to the total mass of the neutron shielding material, preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and particularly preferably 0.01% by mass or more. Furthermore, the upper limit is, relative to the total mass of the neutron shielding material, preferably 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 10% by mass or less. By setting the lower limit of the boron compound content to 0.001% by mass or more, good absorption performance of the thermal neutron lines can be maintained, thus maintaining excellent shielding effect. On the other hand, by setting the upper limit of the boron compound content to 30% by mass or less, the decrease in light transmittance caused by the presence of boron compounds can be suppressed, thus maintaining good light transmittance of the neutron shielding material. As for boron compounds, there are no particular limitations as long as they do not excessively impair the light transmittance of the neutron-shielding material. Preferably, the boron compound is selected from at least one of the following groups: boranes, cycloboronic alkanes, boron trihalides, inorganic borates, boron fluorides, borides, boron hydrides, hetero compounds, borate esters, organoborates, borate esters, dialkylborates, borate esters, organoboranes, carboranes, carboronic acids, and boron-containing complexes. There are no particular limitations on the types of boron-containing inorganic compounds, such as boronanes like boron oxide, boric acid, monoborane, diborane, and ammoniaborane; boron trihalides like boron chloride, boron fluoride, and boron bromide; inorganic borates like sodium metaborate, sodium tetraborate, sodium polyborate, and sodium mercaptododecanoate; boron fluorides like lithium boron fluoride and potassium boron fluoride; boron compounds like aluminum diboride, iron tetraboride, boron carbide, boron nitride, and boron phosphide; boron hydride compounds like aluminum boron hydride and sodium boron hydride; and hetero compounds like boron fullerene and heterodiamond. Furthermore, there are no particular limitations on the boron-containing organic compounds among boron compounds. Examples include boronous acids such as borophenylalanine and fluoroboronic phenylalanine; organoborates such as lithium bis(oxalate)borate; borate esters such as trimethyl borate and triethyl borate; dialkylborates such as diphenyldialkylboronic acid, 2-aminoethyl(2-aminoethoxy)diphenylborane and dicyclohexyl(trifluoromethanesulfonyl)borane, and dicyclohexylborane trifluoromethanesulfonate; boronous esters such as 2-(2-iodophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxacyclopentaborane, 1-iodo-2-(4,4,5,5-tetramethyl-1,3,2-dioxacyclopentaborane-2-yl)benzene, and pinacol-2-iodophenylboronic acid; organoboranes such as triethylborane and trimethylborane; carboranes, carborane acids, etc. Furthermore, there are no particular limitations on the boron-containing organic and inorganic compounds among boron compounds. Examples of boron-containing complexes include triethylamine borane, dimethyl sulfide borane, boron trifluoride monoethylamine, and boron trifluoride piperidine. Furthermore, the boron compounds exemplified may be used alone or in combination of two or more. Furthermore, as boron compounds, those with surface treatments can also be used to improve dispersibility in transparent materials. This prevents the bias of boron compounds in the neutron-shielding material, thereby improving its light transmittance and uniformity. There are no particular limitations on the surface treatment method, but examples include surface treatments using silane coupling agents, titanate coupling agents, fatty acids, surfactants, and modified polymers. The preferred light-transmitting material is any one of a glassy substance, thermoplastic resin, thermosetting resin, or elastomeric resin. Because these light-transmitting materials contain hydrogen atoms, they can slow down high-speed neutron lines through elastic scattering. Furthermore, in the neutron shielding material of this embodiment, the boron compound has the property of absorbing the slowed-down high-speed neutron lines, i.e., thermal neutron lines. As a result, the neutron shielding material of this embodiment exhibits good shielding performance not only against thermal neutron lines but also against high-speed neutron lines. More specifically, translucent materials can be exemplified by materials made from quartz (SiO2). 2) At least one of the following groups: glass, borosilicate glass, polyvinyl chloride resin, polystyrene resin, polyethylene resin, epoxy resin, urethane resin, cyclic polyolefin resin, polyimide resin, polycarbonate resin, polymethyl methacrylate resin, polyethylene terephthalate resin, acrylonitrile-butadiene-styrene copolymer resin, polyvinyl alcohol resin, polyolefin resin, and silicon-containing polymers. These light-transmitting materials may be used in any combination with the boron compounds exemplified above. Regarding the content of light-transmitting material, its lower limit relative to the total mass of neutron shielding material is preferably 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more. By setting the lower limit of the light-transmitting material content to 70% by mass or more, good absorption performance against high-speed neutron rays can be maintained, thus maintaining excellent shielding effect. In the neutron shielding material of this embodiment, additives may be included to improve its mechanical strength, thermal conductivity, thermal expansion coefficient, or weather resistance, or to suppress degradation. There are no particular limitations on such additives, as long as they do not impair the effects of the present invention, such as neutron shielding performance and light transmittance. Specific examples of additives include fillers, diluents, plasticizers, resveratrols, moisture absorbers (storage stability improvers), adhesion promoters, hardening catalysts, ultraviolet absorbers, antioxidants, anti-aging agents, property modifiers, flame retardants, adhesion promoters, anti-sagging agents, colorants, and free radical polymerization initiators. The neutron shielding material in this embodiment is composed of a molded object, which can be in the form of a plate or other molded body, or in the form of particles or granules. In the case of particle-shaped or granular neutron shielding materials, they can be further used as raw materials for neutron shielding products. When the neutron shielding material is a molded body, it can be a composite body formed by joining a molded body containing a boron compound with another molded body made of a light-transmitting material that does not contain a boron compound. Alternatively, it can be a composite body formed by joining molded bodies containing different types of boron compounds. Furthermore, it can be a composite body containing the same type of boron compound, but with varying amounts of the boron compound and / or... 10 This refers to a composite body formed by joining together molded bodies with different concentrations of boron isotope. Such composite bodies can be constructed as a laminate, where each molded body is stacked at least one layer in any order. Alternatively, they can be constructed by placing each molded body in any position on the same surface. In the latter case, the composite body can be designed to achieve the effects of the present invention only in a specific area within the surface, offering a high degree of design freedom. Furthermore, there are no particular limitations on the method of joining the molded bodies; for example, methods such as heat fusion or adhesive bonding at the joint surfaces can be used. (Method for Manufacturing Neutron Shielding Material) Next, the method for manufacturing the neutron shielding material of this embodiment will be described below. The method for manufacturing the transparent neutron shielding material of this embodiment includes at least a mixing step of mixing a light-transmitting material and a boron compound, and a curing step of curing the mixture of the light-transmitting material and the boron compound. Regarding the form of the boron compound in the mixing step, examples include at least one of the following: a solution of a solid boron compound dissolved in a solvent, a dispersion of a solid boron compound dispersed in a dispersion medium, and a liquid boron compound. If the boron compound is in one of these forms, it can be uniformly present in the neutron shielding material, thereby improving neutron shielding performance and light transmittance, as well as achieving in-plane homogenization. Furthermore, the boron compound can also be in powder form. As a solvent for dissolving, dispersing, or miscible with solid boron compounds and liquid boron compounds, there are no particular limitations, as long as the effects of the present invention, such as neutron beam shielding performance and light transmittance, are not impaired. Specifically, examples include water, alcohols, and amines. There are no particular limitations on the method for mixing the transparent material and the boron compound in the mixing step, and various methods can be used. For example, when the transparent material is a glassy substance, a method can be used to heat and melt the mixture after mixing the solid glassy substance and the solid boron compound. The heating time and heating temperature can be appropriately set according to the type of solid glassy substance and solid boron compound. Furthermore, when the translucent material is a thermoplastic resin, methods such as using a two-roller, kneader, Bamboo mixer, or extruder to mix the thermoplastic resin with boron compounds can be cited. Furthermore, in cases where the translucent material is a two-component thermosetting resin containing a main agent and a hardener, a method can be employed where a solid boron compound is dissolved and mixed in the hardener, followed by the addition and mixing of the main agent. In such a mixing method, the boron compound can be uniformly present in the neutron-shielding material, thereby improving neutron shielding performance and translucentness, as well as achieving in-plane homogenization. Here, the hardener is added for the purpose of forming a cross-linked structure by adding epoxy groups to each other in the presence of a catalyst, or for forming a cross-linked structure by a compound having two or more epoxy groups and a compound having two or more active hydrogens. As a hardening agent, there are no particular limitations as long as it does not impair the effects of the present invention, such as neutron shielding performance and light transmittance. Specifically, examples include chain-like aliphatic polyamines, cyclic aliphatic polyamines, aliphatic aromatic amines, aromatic amines, polyamides, dicyandiamide, polythiols, acid anhydrides, and BF. 3. Complexes, imidazole compounds, phenolic varnishes, phenolic methylformaldehyde, etc. Furthermore, as catalysts, examples include cations or anions with high strain energy that release the strain energy of the epoxy groups in a 3-membered ring. The amount of hardener added can be appropriately set according to the type of hardener. The curing step is suitably performed according to the form of the mixture of the translucent material and the boron compound. For example, if the translucent material is a glassy substance, and it is mixed with a boron compound and melted by heat, the melted mixture is cooled during the curing step. Similarly, if the translucent material is a thermoplastic resin, and the thermoplastic resin and boron compound are mixed, the mixture is also cooled during the curing step. If the translucent material is a two-component thermosetting resin containing a main agent and a hardener, the curing step is performed at room temperature or by heating (thermosetting). Furthermore, post-curing can be performed after curing to further promote the curing of the epoxy resin. Based on the above, if the method for manufacturing the neutron shielding material of this embodiment is adopted, a transparent neutron shielding material with good light transmittance and excellent shielding performance, at least for thermal neutron lines, can be easily manufactured. [Example] Hereinafter, suitable embodiments of the present invention will be described in detail by way of example. However, unless otherwise specified, the materials or amounts of admixtures described in the embodiments are not intended to limit the scope of the present invention to them. (Example 1) <Manufacturing of Neutron Shielding Material> In this example, a highly transparent epoxy resin (manufactured by ITW Corporation, trade name: Devcon (registered trademark) ET) is used as the light-transmitting material, and a concentrated... 10 Boric acid of B isotope (hereinafter referred to as "B-isotope") 10 "B Concentrated Boric Acid" (manufactured by Stella Chemifa Co., Ltd.) is a boron compound. 10 B Concentrated boric acid 10 The concentration of the B isotope is 96%. First, measure 45.0g of bisphenol A-based epoxy resin and 22.5g of aromatic polyamine-based curing agent, which are the main components of the high-transparency epoxy resin. Second, add... 10 B. Concentrate 0.0675g of boric acid and dissolve it. Then, dissolve... 10 B. A mixture is prepared by mixing concentrated boric acid with aromatic polyamine curing agent and bisphenol A epoxy resin (mixing step). Next, the mixture is poured into a 150mm × 150mm polysiloxane mold frame and left to harden at room temperature for 12 hours (curing step). This process manufactures... 10B is a neutron shielding material with a concentrated boric acid content of 1000 ppm (0.1% by mass) and a molded body of 150 mm (vertical) × 150 mm (horizontal) × 2.5 mm (thickness). (Example 2) In this example, 10 The amount of concentrated boric acid added (B) was changed to 0.3375g. Otherwise, the neutron shielding material of this embodiment was manufactured using the same method as in Example 1. Furthermore, the neutron shielding material contains... 10 B. The concentration of boric acid is 5000 ppm (0.5% by mass). (Comparative Example 1) In this comparative example, no additions are made. 10 B. Concentrated boric acid. The neutron shielding material of this comparative example was manufactured using the same method as in Example 1. (Comparative Example 2) In this comparative example, instead of 10 B. Concentrated boric acid, using boric acid in a naturally occurring ratio. The neutron shielding material of this comparative example was manufactured using the same method as in Example 2. Furthermore, the boric acid content in the neutron shielding material was 5000 ppm (0.5% by mass). (Determination of neutron shielding performance) Using a thermal neutron beam (thermal neutron beam: 4.0 × 10⁻⁶) 5 n / cm 2 A neutron line source (at 1 MW) is used as the neutron line source, and neutron shielding materials manufactured in each embodiment or comparative example are disposed between the neutron line source and the LiCaF scintillator. The disposed neutron shielding material is adjusted in such a way that several sheets of neutron shielding material are stacked together to make the whole material have a specified thickness. Next, a thermal neutron beam was directed at the LiCaF scintillator, and the number of events that penetrated the thermal neutron lines of the neutron-shielding material was measured. The neutron transmittance for each thickness of the thermal neutron line was then calculated. The results are shown in Figure 1. As can be seen from Figure 1, the results of evaluating the shielding performance of thermal neutron lines show that the neutron penetration of the thermal neutron lines of the neutron shielding materials in Examples 1 and 2 is lower than that in Comparative Examples 1 and 2, indicating that the thermal neutron lines are effectively shielded. (Evaluation of Light Transmittance) For the neutron shielding materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, the total light transmittance in the range of 400 nm to 1000 nm was measured using a UV-Vis-NIR spectrophotometer (manufactured by Japan Spectrophotometer Co., Ltd., trade name: V-670ODS) to evaluate the light transmittance. Furthermore, in the measurement of total light transmittance, as shown in Table 1, several sheets of neutron shielding material were stacked to adjust the overall thickness, and measurements were performed for each total thickness. The measurement results are shown in Table 1. As shown in Table 1, in both Examples 1 and 2, the total thickness of the neutron shielding materials exhibits a total light transmittance of over 80%, confirming excellent light transmittance. That is, even when containing... 10 Concentrated boric acid (B) does not significantly reduce the original light transmittance of epoxy resin, which is a light-transmitting material. (Observation of camera images after thermal neutron beam irradiation) Next, regarding the shielding performance of the neutron shielding materials of each embodiment and comparative example against thermal neutron beams, the changes in images captured by the camera were observed and evaluated. First, the method for observing changes in the camera's image will be explained with reference to Figure 2. Figure 2 is a schematic diagram illustrating the camera used for observing camera images after thermal neutron beam irradiation. As shown in Figure 2(a), when observing changes in images captured by the camera, a network camera 1 (manufactured by Axis Communications AB, trade name: P1214E, image sensor: CCD) was used as the observation camera. Also, as shown in Figure 2(b), a polyethylene cover 2 was used to cover the network camera 1 to prevent irradiation from thermal neutron rays from the left and right sides, or from above and below. The polyethylene cover 2 contained 50% by mass of lithium fluoride relative to its total mass. Furthermore, a piece of neutron shielding material 3, prepared according to each embodiment or comparative example, was disposed in front of the camera to shield the front of the camera. Secondly, a thermal neutron beam was used as the neutron source to irradiate the front of the camera with 3.7 × 10⁻⁶ neutrons. 11 pcs / cm 2 A neutron beam. Figures 3 through 6 show the camera images after illumination. Furthermore, the number of dots (dots) in the entire captured area is measured, and the number of dots per unit area (dots / cm²) is calculated. 2 The results are shown in Table 2. In camera images without thermal neutron irradiation, no dots are visible on the screen. However, in camera images after thermal neutron irradiation, dots are confirmed to appear on the screen (see Figures 3-6). This is believed to be due to damage to the camera element of network camera 1 caused by the irradiated thermal neutrons. However, in the images of cameras covered by the neutron shielding materials of Examples 1 and 2, the number of dots is less compared to the images of cameras covered by the neutron shielding materials of Comparative Examples 1 and 2 (see Figures 3-6 and Table 2). This confirms that the neutron shielding materials of Examples 1 and 2 have excellent shielding performance against thermal neutrons. As a result, the neutron shielding materials of Examples 1 and 2, for example, are protective components for cameras used in neutron generating facilities, indicating that they can prevent camera image degradation caused by thermal neutron irradiation. Similarly, regarding the shielding performance of neutron shielding materials against thermal neutron lines, the camera used was changed, and the changes in the captured images were observed and evaluated. Regarding the observation method for changes in camera images, the observation camera used was changed to a video camera (manufactured by Panasonic Corporation, trade name: HC-V480MS, image sensor: CMOS). Furthermore, as shown in Figure 2(b), a piece of neutron shielding material 3 prepared in Example 2 or Comparative Example 1 was placed in front of the camera to shield the front of the camera. Secondly, a thermal neutron beam was used as the neutron source to irradiate the front of the camera with 3.7 × 10⁻⁶ neutrons. 11 pcs / cm 2 A neutron beam. After irradiation, in the camera covered by the neutron shielding material of Comparative Example 1, noise was immediately introduced into the camera image, causing the image to darken. This is because the imaging element was damaged by the irradiated thermal neutron rays. This image distortion occurred much faster than when using the aforementioned network camera. On the other hand, in the camera covered by the neutron shielding material of Example 2, even when irradiated with thermal neutron rays, no noise was generated in the camera image, and the image did not darken. Therefore, it is confirmed that the neutron shielding material of Example 2 has excellent shielding performance against thermal neutron rays. As a result, the neutron shielding material of Example 2, for example, is used as a protective component for cameras used in neutron generating facilities, indicating that it can prevent camera image degradation caused by thermal neutron irradiation. In particular, this effect is significant in cameras where the control system of the imaging element is more delicate and damage occurs rapidly. [Industrial Application Possibilities] The neutron shielding material of this invention has good light transmittance and excellent shielding performance, at least against thermal neutron lines, making it widely applicable to components requiring both visual visibility and neutron blocking. Therefore, the industrial applicability of this invention is extremely high. 1: Network camera; 2: Polyethylene cover; 3: Neutron shielding material [Figure 1] is a graph showing the relationship between the total thickness of the neutron shielding material and the neutron transmittance in Examples 1 and 2, and Comparative Examples 1 and 2. [Figure 2] is an explanatory diagram of a camera used for observing camera images after thermal neutron beam irradiation. [Figure 3] is a diagram showing a camera image of the neutron shielding material of Example 1 after thermal neutron irradiation. [Figure 4] is a diagram showing a camera image of the neutron shielding material of Example 2 after thermal neutron irradiation. [Figure 5] is a diagram showing a camera image of the neutron shielding material of Comparative Example 1 after thermal neutron irradiation. [Figure 6] is a diagram showing a camera image of the neutron shielding material of Comparative Example 2 after thermal neutron irradiation.

Claims

1. A neutron shielding material comprising a light-transmitting molded article comprising a light-transmitting material and a boron compound concentrated into a boron isotope of mass 10, wherein the content of the boron compound, in boron atom conversion, is 0.001% to 30% by mass relative to the total mass of the aforementioned neutron shielding material.

2. The neutron shielding material as claimed in claim 1, wherein the concentration of boron isotopes of mass number 10 in the aforementioned boron compound is 50% or more.

3. The neutron-shielding material as claimed in claim 1, wherein the aforementioned boron compound is at least one selected from the group consisting of boron oxide, boric acid, borane, boroxine, boron trihalide, inorganic borates, boron fluorides, borides, boron hydride compounds, hetero compounds, boronite esters, organoborates, boron esters, dihydroboronic esters, boronite esters, organoboranes, carboranes, carboronic acids, and boron-containing complex compounds.

4. The neutron shielding material as claimed in claim 1, wherein the aforementioned light-transmitting material is any one of a glassy substance, a thermoplastic resin, a thermosetting resin, or an elastomer resin.

5. The neutron-shielding material as claimed in claim 4, wherein the aforementioned light-transmitting material is at least one selected from the group consisting of polyvinyl chloride resin, polystyrene resin, polyethylene resin, epoxy resin, urethane resin, cyclic polyolefin resin, polyimide resin, polycarbonate resin, polymethyl methacrylate resin, polyethylene terephthalate resin, acrylonitrile-butadiene-styrene copolymer resin, polyvinyl alcohol resin, polyolefin resin, and silicon-containing polymers.

6. A method for manufacturing a neutron shielding material, comprising a method for manufacturing a neutron shielding material composed of a light-transmitting molded article, comprising: a mixing step of mixing a light-transmitting material with a boron compound concentrated to a mass number of 10 boron isotopes, and a curing step of curing the mixture of the light-transmitting material and the boron compound, wherein the content of the boron compound, in boron atom conversion, is 0.001% by mass or more and 30% by mass or less relative to the total mass of the neutron shielding material.

7. The method for manufacturing the neutron shielding material as claimed in claim 6, wherein the concentration of boron isotopes of mass number 10 in the aforementioned boron compound is 50% or more.

8. The method for manufacturing the neutron shielding material as claimed in claim 6, wherein the aforementioned boron compound is at least one selected from the group consisting of boranes, cycloboranes, boron trihalides, inorganic borates, boron fluorides, borides, boron hydrides, hetero compounds, borate esters, organoborates, borate esters, dialkylborates, borate esters, organoboranes, carboranes, carboronic acids, and boron-containing complex compounds.

9. The method for manufacturing a neutron shielding material as claimed in claim 6, wherein the aforementioned light-transmitting material is any one of a glassy substance, a thermoplastic resin, a thermosetting resin, or an elastomer resin.

10. The method for manufacturing the neutron shielding material as claimed in claim 9, wherein the aforementioned light-transmitting material is at least one selected from the group consisting of polyvinyl chloride resin, polystyrene resin, polyethylene resin, epoxy resin, urethane resin, cyclic polyolefin resin, polyimide resin, polycarbonate resin, polymethyl methacrylate resin, polyethylene terephthalate resin, acrylonitrile-butadiene-styrene copolymer resin, polyvinyl alcohol resin, polyolefin resin, and silicon-containing polymer compounds.

11. The method for manufacturing a neutron-shielding material as claimed in claim 6, wherein the aforementioned mixing step is a step of mixing at least one of the aforementioned boron compound in powder form, the aforementioned boron compound in solid form with a solvent to form a solution, the aforementioned boron compound in solid form with a dispersion liquid to form a dispersion medium, and the aforementioned boron compound in liquid form with the aforementioned light-transmitting material.

12. The method for manufacturing a neutron shielding material as claimed in claim 6, wherein the aforementioned light-transmitting material is a two-liquid thermosetting resin containing a main agent and a hardener, and the aforementioned mixing step is a step of mixing the aforementioned hardener and the aforementioned boron compound by further adding the aforementioned main agent.

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