JP7588371B2 - Radiation detection film and method for producing same - Google Patents

Description

The present invention relates to a radiation detection film containing a scintillator that emits light when excited by radiation, a method for producing the same, and a radiation detection film laminate.

Liquid and pellet-shaped scintillators are known as scintillators for detecting radiation. Liquid scintillators have the problem that they are used in large quantities, and as a result, large quantities must be disposed of. On the other hand, an example of a pellet-type plastic scintillator for detecting radiation is disclosed in Patent Document 1. Such pellet-type plastic scintillators for detecting radiation are expensive.

In response to this, the inventors of the present application have developed particle-type scintillator-fixed silicic acid particles (Patent Document 2). These scintillator-fixed silicic acid particles are made by fixing, on the surface of silicic acid particles with an average particle size of 0.1 to 100 μm, a silica nanoparticle scintillator containing organic scintillator molecules, a binder, and a substance that enhances the fluorescence emitted by the scintillator, to the silicic acid particles via an adhesive. By obtaining a radiation detection material using these scintillator-fixed silicic acid particles as a material, it is possible to produce the material more cheaply and to increase the radiation detection sensitivity.

On the other hand, because such pellet-type and particle-type radiation detection sheets are difficult to handle, sheet-type radiation detection sheets have also been proposed (Patent Document 3). However, conventional radiation detection sheets have the problem of not being sufficiently flexible. Furthermore, currently, plate-shaped detection materials called imaging plates (IPs) and plastic scintillators are widely used as radiation detection materials. Both of these are very expensive, and in the event that radioactive material adheres to them, they must be thrown away, which causes problems such as difficulty in disposing of them. Furthermore, even the thinnest of these are thick, at around 0.5 mm, making them difficult to handle.

JP 2018-131476 A Patent No. 6590185 JP 2019-184281 A

The present invention has been made in view of this background. One of the objects of the present invention is to provide a radiation detection film that is more flexible and easier to handle, a method for producing the same, and a radiation detection film laminate.

Means for solving the problem and effects of the invention

The method for producing a radiation detection film according to the first embodiment of the present invention is a method for producing a radiation detection film containing a scintillator that is excited by radiation and emits light, and includes the steps of preparing a paper sheet containing scintillator-immobilized silicic acid particles, and overlapping the paper sheet with a film substrate, subjecting it to heat and pressure processing, and transferring the scintillator component to the film substrate. As a result, unlike conventional methods in which a scintillator layer is applied to a substrate, no binders are used for adhesion, making it easy to make the radiation detection film thin and easy to make it flexible.

In addition to the above, the method for producing a radiation detection film according to the second embodiment includes the step of preparing the paper sheet by forming a coating layer containing the scintillator-immobilized silicic acid particles on a sheet produced by a wet papermaking method or coating method in which silicic acid particles are aggregated on the surface of fibers and then paper-made, or by forming a sheet from a raw material containing fibers carrying the scintillator-immobilized silicic acid particles by a wet papermaking method.

In addition to any of the above, the method for producing a radiation detection film according to a third embodiment is such that the step of preparing the paper sheet is a step of forming a coating layer containing the scintillator-immobilized silicic acid particles on a sheet produced by a coating method in which a coating liquid is applied to a papermaking sheet, or a step of forming a sheet from a raw material containing fibers carrying the scintillator-immobilized silicic acid particles by a wet papermaking method.

Furthermore, in addition to any of the above, the manufacturing method of the radiation detection film according to the fourth embodiment includes the step of overlapping the paper sheet with the film substrate and subjecting it to thermal pressure processing, and transferring the scintillator component to the film substrate, comprising the steps of preparing two of the film substrates, overlapping them on both sides of the paper sheet, and subjecting them to thermal pressure processing. This makes it possible to form transfer surfaces on each of the two film substrates, and provides the advantage of being able to manufacture two radiation detection films from one paper sheet, thereby improving manufacturing efficiency.

Furthermore, in the method for producing a radiation detection film according to the fifth embodiment, in addition to any of the above, the film substrate has light-transmitting properties. This results in a light-transmitting radiation detection film, and by laminating multiple sheets of this film, it is possible to increase the luminescence intensity.

Furthermore, in the sixth embodiment of the method for producing a radiation detection film, in addition to any of the above, the film substrate is made of PET.

Furthermore, the method for producing a radiation detection film according to the seventh embodiment includes, in addition to any of the above, a step of stacking a plurality of radiation detection films onto which the scintillator component has been transferred. This results in a radiation detection film having translucency, and stacking a plurality of such films makes it possible to increase the luminescence intensity.

Furthermore, in the eighth embodiment, in addition to any of the above, the method for producing a radiation detection film is such that the step of overlapping the paper sheet with a film substrate and subjecting them to heat and pressure processing, and transferring the scintillator component to the film substrate, is carried out at 80°C or higher.

Furthermore, in the method for producing a radiation detection film according to the ninth embodiment, in addition to any of the above, the step of overlapping the paper sheet with a film substrate and subjecting it to heat and pressure processing to transfer the scintillator component to the film substrate is a step of applying heat and pressure to a flat or roll-shaped film substrate to transfer the scintillator component to the film substrate.

Furthermore, in the method for producing a radiation detection film according to the tenth embodiment, in addition to any of the above, the scintillator is a complex of organic scintillator molecules and silica nanoparticles, and in the complex, the organic scintillator molecules encapsulated in an inclusion compound or the organic scintillator molecules and aromatic rings formed by a coupling agent are fixed to the inside or surface of the silica nanoparticles by a sol-gel method.

Furthermore, in the method for producing a radiation detection film according to the eleventh embodiment, in addition to any of the above, the step of preparing the paper sheet includes a first mixing step of adding an organic scintillator molecule and an inclusion compound to an organic solvent and heating the organic scintillator molecule or the organic scintillator molecule inclusive of the inclusion compound in the organic solvent; a second mixing step of adding a silicic acid source and a coupling agent to the first mixed liquid obtained in the first mixing step and heating and stirring the mixture to form silica nanoparticles in which the organic scintillator molecule is fixed to the inside or surface by a sol-gel method and the aromatic ring by the coupling agent is fixed to the inside or surface by a sol-gel method, thereby forming a composite of the organic scintillator molecule and the silica nanoparticle; a heating and drying step of heating and drying the second mixed liquid obtained in the second mixing step to obtain scintillator-immobilized silicic acid particles; and a step of forming a coating layer containing the scintillator-immobilized silicic acid particles on a sheet formed by a wet papermaking method, or forming a raw material including fibers carrying the scintillator-immobilized silicic acid particles into a sheet by a wet papermaking method to obtain a paper sheet.

Furthermore, in addition to any of the above, the method for producing a radiation detection film according to the twelfth embodiment is such that the scintillator-immobilized silicic acid particles contain silica particles and the scintillator immobilized on the surfaces of the particles, the silica particles have an average particle size of 1.5 to 20 μm, the scintillator is silica nanoparticles containing organic scintillator molecules, and the silica nanoparticles have an average particle size of 30 to 400 nm.

Furthermore, a radiation detection film according to a thirteenth embodiment is a radiation detection film comprising a film substrate having a scintillator-immobilized silicic acid particle-supporting layer on one side thereof, the film substrate having translucency, the film substrate having a luminescence excited by low-energy β-rays of tritium having a radioactivity concentration of 37 kBq/ml being 100 CPM or more as measured by a liquid scintillation counter . Unlike the conventional method of applying a scintillator layer to a substrate, the above-mentioned configuration does not use binders for adhesion, and therefore the radiation detection film can be easily thinned and made flexible. Furthermore, a translucent radiation detection film can be obtained, and the luminescence intensity can be increased by laminating a plurality of such films.

Furthermore, in addition to the above configuration, a radiation detection film according to a fourteenth embodiment has no binder layer between the scintillator-immobilized silicic acid particles and the film substrate on the one side.

Furthermore, in addition to any one of the above configurations, a radiation detection film according to a fifteenth embodiment has the scintillator-immobilized silicic acid particles covering the one surface of the film substrate in a striped or tiled pattern. With the above configuration, low-energy β rays of tritium can be efficiently detected.

Furthermore, in the radiation detection film according to the sixteenth embodiment, in addition to any of the above configurations, the scintillator-immobilized silicic acid particles are immobilized by carrying the organic molecules and organic scintillator used in the liquid scintillator.

Furthermore, in addition to any of the above configurations, the radiation detection film according to the seventeenth embodiment has a thickness of 50 μm or less.

Furthermore, in addition to any of the above configurations, the radiation detection film according to the eighteenth embodiment has the following features: the scintillator-immobilized silicic acid particles contain silica particles and the scintillator immobilized on the surfaces of the particles, the silica particles have an average particle size of 1.5 to 20 μm, the scintillator is silica nanoparticles containing organic scintillator molecules, and the silica nanoparticles have an average particle size of 30 to 400 nm.

Furthermore, in a radiation detection film according to a nineteenth embodiment, in addition to any one of the configurations described above, the film base is made of PET.

Furthermore, a radiation detection film laminate according to a twentieth embodiment is constructed by laminating a plurality of radiation detection films according to any one of the above. With the above construction, by laminating a plurality of light-transmitting radiation detection films, it is possible to increase the luminescence intensity and improve the radiation detection accuracy.

1 is a schematic cross-sectional view of a radiation detection film according to a first embodiment. 2A to 2C are schematic cross-sectional views showing a method for manufacturing the radiation detection film according to embodiment 1. 5A to 5C are schematic cross-sectional views illustrating a method for producing a radiation detection film according to a second embodiment. 5A to 5C are schematic cross-sectional views showing a method for producing a radiation detection film according to a third embodiment. 10A to 10C are schematic cross-sectional views showing a method for producing a radiation detection film according to a fourth embodiment. 1 is a graph showing XRD patterns of the radiation detection film in Example 1, the film substrate before thermal transfer, and silica powder. 1 is a graph showing the XRD patterns of a radiation detection film and a paper sheet after thermal transfer. 1 is a graph showing surface fluorescence upon excitation of the radiation detection film at 280 nm. Figure 9A is a low magnification SEM photograph of a paper sheet, Figure 9B is a high magnification SEM photograph, Figure 9C is an even higher magnification SEM photograph, Figure 9D is the qualitative spectrum within the green frame in Figure 9C, Figure 9E is the qualitative spectrum within the blue frame, Figure 9F is the qualitative spectrum within the red frame, Figure 9G is the qualitative spectrum within the purple frame, and Figure 9H is the result of elemental analysis of Figures 9D to 9G. FIG. 10A is an SEM photograph of the radiation detection film, FIG. 10B is an SEM photograph of the film substrate, FIG. 10C is an enlarged SEM photograph of FIG. 10A, FIG. 10D is a qualitative spectrum within the green frame in FIG. 10C, FIG. 10E is a qualitative spectrum within the blue frame, FIG. 10F is a qualitative spectrum within the red frame, FIG. 10G is a qualitative spectrum within the purple frame, and FIG. 10H is the result of elemental analysis of FIGS. 10D to 10G. (a) is a photograph of a glass vial with radiation detection film wrapped around the inside, and (b) is a photograph of a glass vial with a balloon that electrostatically adsorbs radon gas in the air and is wrapped in scintillation paper and placed inside. 12A is an SEM photograph of the radiation detection film, FIG. 12B is a qualitative spectrum within the green frame in FIG. 12A, FIG. 12C is a qualitative spectrum within the blue frame, and FIG. 12D is the result of elemental analysis of FIGS. 12B to 12C. This is a photograph of the mantle placed in a glass vial. FIG. 14A is a photograph of the mantle covered with radiation detection film, and FIG. 14B is an image in which a CCD image of scintillation light is overlaid. FIG. 15A is a schematic diagram showing the state in which the radiation detection film has been cut into five pieces, and FIG. 15B is a schematic diagram showing the state in which each cut piece is immersed in an aqueous tritium solution in a glass vial. 1 is a graph showing the results of count rate measurements. FIG. 2 is a schematic cross-sectional view showing a paper sheet according to one embodiment of the present invention. 4A and 4B are a schematic cross-sectional view and an enlarged cross-sectional view of a main part of a paper sheet according to another embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a paper sheet according to another embodiment of the present invention. 1 is a perspective view showing a manufacturing process of a paper sheet according to an embodiment of the present invention; 5 is a schematic process diagram showing a paper sheet manufacturing process according to another embodiment of the present invention. FIG. FIG. 2 is an enlarged cross-sectional view of a paper sheet according to another embodiment of the present invention. The photographs are optical microscope photographs of the surfaces of a radiation detection film and a film substrate on which thermal transfer has not been performed, with and without irradiation with ultraviolet LED light having a wavelength of 365 to 375 nm.

The following describes the embodiments of the present invention based on the drawings. However, the embodiments shown below are examples of radiation detection powder and its manufacturing method, and paper sheets containing radiation detection powder and its manufacturing method for embodying the technical ideas of the present invention, and the present invention does not specify the radiation detection powder and its manufacturing method, and paper sheets containing radiation detection powder and its manufacturing method to the following. Furthermore, this specification does not specify the members shown in the claims to the members of the embodiments. In particular, the dimensions, materials, shapes, and relative positions of the components described in the embodiments are merely explanatory examples, and are not intended to limit the scope of the present invention unless otherwise specified. Note that the size and positional relationship of the members shown in each drawing may be exaggerated to clarify the explanation. Furthermore, in the following explanation, the same names and symbols indicate the same or similar members, and detailed explanations will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured in such a manner that multiple elements are composed of the same member, and one member can serve multiple elements, or conversely, the function of one member can be shared by multiple members.

The radiation detection film according to the first embodiment is a type of radiation detection material that contains a scintillator that emits light when excited by radiation, and is also called a scintillation film. Currently, plate-shaped detection materials called imaging plates and plastic scintillators are widely used as radiation detection materials. Both of these are very expensive, and have the problem that they must be thrown away if radioactive material adheres to them, and are difficult to dispose of. Furthermore, even the thinnest of these are about 0.5 mm thick, and until now there have been no products that are thin and flexible while also having sufficient detection performance.

In the radiation detection film according to this embodiment, the scintillator-fixed silicic acid particles 16 are made into a sheet by a papermaking method or the like, and this paper sheet 10 is then layered on a film substrate 8 such as a film and subjected to heat and pressure processing, thereby transferring the scintillator components to the film substrate 8 side, thereby obtaining a transparent radiation detection film.

Unlike conventional scintillator layer coating methods, this radiation detection film does not use binders to adhere the scintillator layer to the film substrate 8, making it easy to make it thin and flexible. Furthermore, particles containing the scintillator are exposed on the substrate surface. This allows the scintillator to emit light in response to low-energy beta rays from tritium, which can be detected by a liquid scintillation counter. In particular, since a film of 50 μm or less can be given radiation detection capabilities, its high flexibility makes it easy to deform its outer shape, and it can be used to wrap the object to be measured, or it can be laid out on a desk to check the distribution of radioactivity, or it can be wound into a roll for use.

Furthermore, the thin film also has the effect of reducing the amount of waste. In other words, by making it thinner, only a small amount of waste is generated.

Furthermore, in the radiation detection film according to this embodiment, the organic scintillator can be fixed to the film substrate 8 in a very simple manner. The film substrate 8 to which the organic scintillator is fixed is not limited to a transparent film, but can also be an opaque sheet such as paper, or a three-dimensional shape such as a container, further enhancing convenience. In particular, the organic scintillator is not limited to a sheet-shaped substrate, and if it can be fixed to the surface of a container, the container itself can also be used as the detection material.

Furthermore, by using a translucent substrate for the film substrate 8, it is possible to provide translucency. By using a radiation detection film with high transparency, the film substrate 8 does not impede the propagation of light emission. Therefore, for example, when immersed in tritium water in a glass vial, it is possible to add and immerse many radiation detection films at the same time, and the contact area with tritium increases, thereby increasing the light emission intensity. This is shown in Figure 16. In this figure, the horizontal axis corresponds to the number of radiation detection films when there is 1, 2, 3, 4, or 5.

In addition, pale yellow-white scintillator silica powder can be pressed onto a transparent film. The scintillation film formed by pressing in this way can detect tritium beta rays. Tritium has a short range, and is only detected on the surface of a plastic scintillator. In the radiation detection film according to this embodiment, the silica particles that serve as the scintillator are attached in stripes, and the surface of this scintillator silica powder is hydrophilic, so that more tritium can come into contact with the vicinity of the scintillator, causing the scintillator to emit light and produce scintillation light.

In addition, because the particles containing the scintillator are exposed on the surface of the substrate, the scintillator emits light in response to the low-energy beta rays of tritium, making it possible to detect this.

An additional benefit is that it can easily detect alpha rays from radon gas attached to the mantle or dust in the air.
(Radiation detection film)

The radiation detection film is shown in the schematic cross-sectional view of FIG. 1. The radiation detection film shown in this figure is composed of a film substrate 8. One surface of the film substrate 8 (the upper surface in FIG. 1) is a transfer surface onto which the scintillator-fixed silicic acid particles 16 are thermally transferred. There is no binder layer such as an adhesive between the scintillator-fixed silicic acid particles 16 and the film substrate 8. In this way, the flexibility of the radiation detection film can be exhibited by fixing the scintillator-fixed silicic acid particles 16 to the transfer surface by thermal transfer without using a binder layer such as an organic resin adhesive. The radiation detection film can also be made thinner. By making the film thinner, the flexibility is further improved, and the shape change and followability are also improved. For example, the radiation detection film can be wrapped around a balloon to which radon gas in the air electrostatically adheres, and used to detect radon gas. In addition, a scintillation vial can be easily constructed by covering the inner wall of a glass vial with the radiation detection film. These luminescence (scintillation light) can be easily measured using a scintillation counter. Furthermore, the thin radiation detection film can be used as a fabric to create wearable detectors for detecting beta and alpha rays.

On the transfer surface, the scintillator-fixed silicic acid particles 16 do not cover one surface of the film substrate 8 in the form of a uniform layer, but are partially present as shown in FIG. 1. The scintillator-fixed silicic acid particles 16 are partially covering one surface of the film substrate 8 in a striped or tiled pattern. In other words, the scintillator-fixed silicic acid particles 16 do not completely cover one surface of the film substrate 8, but are partially exposed to the film substrate 8. By making it in such a state, the flexibility of the film substrate 8 can be fully exerted, and it is possible to avoid a situation in which the flexibility is reduced by a binder such as an adhesive. In addition, since the scintillator-fixed silicic acid particles 16 are present on most of the transfer surface, the function of detecting radiation and emitting light is not hindered. In addition, since the particles containing the scintillator are exposed on the substrate surface, the scintillator emits light due to the low-energy beta rays of tritium, which has the effect of being detected by a liquid scintillation counter.
(Film substrate 8)

The film substrate 8 is preferably light-transmitting. This allows a light-transmitting radiation detection film to be obtained. In addition, by laminating a plurality of light-transmitting radiation detection films to form a radiation detection film laminate, it is possible to increase the amount of excitation light and increase the luminescence intensity during radiation detection. That is, by making the film transparent, even if the radiation detection films are stacked, the luminescence of radiation detected by each radiation detection film can be transmitted. This allows high sensitivity detection. For example, when detecting tritium ( ³ H) water, it is possible to increase the detection efficiency according to the number of sheets by increasing the contact area with the tritium water. Conventionally, a liquid scintillator was used to detect tritium water, which caused a problem of generating a large amount of liquid scintillator waste liquid. In addition, there was also a problem that the scintillator could only contain a maximum of 50% tritium water when used. In response to this, the radiation detection film according to this embodiment can be directly immersed in tritium water to measure β rays from tritium. In addition, in conventional liquid scintillators, organic molecules such as toluene are used as a solvent. In contrast, in this embodiment, benzoic acid is used instead of toluene to support and immobilize silica particles.

In addition, the transparency allows the inside of the film to be visually confirmed. At the same time, a scintillation light image can be obtained using an image sensor such as a CCD camera.

The material of the film substrate 8 is not particularly limited as long as it is transparent to the scintillation light, and examples that can be used include PET, PE, PP, PVA, PC, PVC, PS, PAN, EVA, EVOH, EMAA, PA, glass, metal, regenerated cellulose, cellulose derivatives, glassine paper, etc. Among these, PET is preferred because it is highly transparent, has excellent flexibility, is inexpensive, and is easily available.

The thickness of the film substrate 8 is approximately the same as the thickness of the radiation detection film. The thickness of the film substrate 8 is 10 μm to 0.1 mm. Preferably, it is 50 μm or less.

Furthermore, the luminescence excited by low-energy β rays from tritium (maximum β-ray energy is 18.6 keV) with a radioactivity concentration of 37 kBq/ml per sheet of radiation detection film is 100 CPM or more when measured with a liquid scintillation counter.
(Scintillator-immobilized silicic acid particles 16)

The scintillator-immobilized silicic acid particles 16 contain silica particles and a scintillator immobilized on the surface of the particles. The average particle size of the silica particles is 1.5 to 20 μm. The scintillator is silica nanoparticles containing organic scintillator molecules. The average particle size of the silica nanoparticles is 30 to 400 nm.

In addition, because the radiation detection film contains hydrogen atoms, it can also be used to detect neutron radiation by adding boron (B) atoms to the film, which allows it to be used to detect neutron radiation in neutron capture therapy.
(Method of manufacturing radiation detection film)

Here, an example of a method for manufacturing a radiation detection film will be described with reference to Figures 2A to 2C. First, a paper sheet 10 is prepared in which scintillator-immobilized silicic acid particles 16 are supported on fibers. The paper sheet 10 can be made into a sheet by a papermaking method. In particular, a wet papermaking method is preferred. The wet papermaking method is a method in which silicic acid particles are aggregated on the surface of fibers to make paper, and is called an internal addition method. Note that the scintillator-immobilized silicic acid particles 16 can be made of scintillator-silica powder. The process for preparing the paper sheet is not limited to the wet papermaking method, and other methods such as a coating method may also be used. The coating method is a method in which a coating liquid is applied to a papermaking sheet, and is called an external addition method.

Next, this paper sheet 10 is placed on top of the film substrate 8 as shown in FIG. 2A and subjected to heat and pressure processing to transfer the scintillator components to the film substrate 8. In the heat and pressure processing, for example as shown in FIG. 2B, the laminate of the paper sheet 10 and the film substrate 8 is heated while being pressed from both sides with a pair of press plates PR. The heating temperature is 80° C. or higher, for example, 80° C. to 200° C., preferably 120° C. to 160° C. The pressure is preferably 1 MPa or higher, more preferably 10 MPa or higher.

After leaving it in the heated and pressed state for about 2 minutes, the pressed state is released and the paper sheet 10 is removed as shown in FIG. 2C to obtain the radiation detection film. This manufacturing method makes it possible to eliminate the need to use binders for adhesion as in the conventional method of applying a scintillator layer to a substrate. This makes it easy to make the radiation detection film thinner and more flexible.

In addition, multiple radiation detection films onto which the scintillator components have been transferred may be stacked. This results in a radiation detection film with translucency, and stacking multiple sheets of this film makes it possible to increase the luminescence intensity.

The radiation detection film obtained in this manner is transparent and thin, and SEM photographs have confirmed that the scintillator-silica powder is adhered almost uniformly. In addition, compared to existing radiation detection sheets, the scintillator is not contained inside the sheet, but is adhered exposed to the surface of the film substrate 8, and therefore has excellent reactivity.
[Embodiment 2]

In the method of FIG. 2A, an example of thermal transfer using a paper sheet formed into a predetermined size by cutting or the like has been described. However, the present invention is not limited to this method, and a paper sheet wound into a roll may also be used. Such an example will be described based on FIG. 3 as a method for producing a radiation detection film according to embodiment 2. In the method for producing a radiation detection film shown in this figure, a paper sheet 10 wound into a roll in advance is prepared. Then, the paper is fed from the roll, and is overlapped with a film substrate 8 similarly fed from the roll, and heat-pressure processing is performed. For example, a pair of heating and pressurizing rolls 18 can be used for the heat-pressure processing. When the heating and pressurizing rolls 18 are used, the temperature is set to a high temperature (e.g., 160° C.) and the pressure is set to a high pressure (e.g., 100 kgf/cm or more in terms of linear pressure) so that thermal transfer can be performed in a short time (e.g., less than 1 second). In addition, both of the pair of heating and pressurizing rolls 18 may be metallic heating rolls, or one of them may be an elastic body such as a heat-resistant resin. Furthermore, multiple pairs of heating and pressurizing rolls may be provided so that thermal transfer can proceed sufficiently. This method allows continuous processing, so that the takt time can be shortened and the production efficiency can be significantly improved.
[Embodiment 3]

In the above method, a method has been described in which a film substrate is placed on one side of a paper sheet and a scintillator is thermally transferred onto the film substrate. However, the present invention is not limited to this configuration, and a film substrate may be placed on both sides of a paper sheet, and the scintillator may be thermally transferred onto the two film substrates at the same time. This method is shown in FIG. 4. Here, two film substrates 8 are prepared and placed on both sides of a paper sheet 10, and then subjected to heat and pressure processing. This makes it possible to form a transfer surface on each of the two film substrates 8A and 8B, and has the advantage of being able to produce two radiation detection films from one paper sheet, improving production efficiency.
[Embodiment 4]

Furthermore, in the above method, the method of thermally transferring the scintillator via a paper sheet has been described, but the present invention is not limited to this method for producing a radiation detection film, and the scintillator-immobilized silicic acid particles may be directly applied to the film substrate. For example, in the method for producing a radiation detection film according to embodiment 4 shown in FIG. 5, the scintillator-immobilized silicic acid particles 16 are filled into the recesses engraved on the gravure roll GR in the manner of gravure printing, and the scintillator-immobilized silicic acid particles 16 are attached to the film substrate 8 after the excess is scraped off with a doctor blade DB. This method has the advantage of eliminating the need to prepare a paper sheet once, eliminating the need to dispose of the paper sheet after thermal transfer, and suppressing the generation of waste.
[Example 1]

Next, a radiation detection film was produced using the method of embodiment 1 described above, and the obtained radiation detection film was subjected to XRD, surface fluorescence, SEM/elemental analysis, and radiation detection characteristics.

Here, scintillation paper (silica powder 2.6 μm) made using the method for producing scintillator silica powder described below was used as the paper sheet, with film substrates (PET resin sheets) placed on both sides and then sandwiched between cushion paper (linter pulp filter paper) on the outside, followed by heating and pressurization at approximately 100°C and 10 MPa. The following experiments were carried out on the obtained radiation detection film and the paper sheet after thermal transfer.

Figure 23 shows photographs of the surfaces of the radiation detection film and the film substrate that has not been thermally transferred, observed with an optical microscope (Carton Optical Co., Ltd.). Figures 23A and B are optical microscope photographs of the radiation detection film, and Figures 23C and D are optical microscope photographs of the film substrate that has not been thermally transferred. Figures 23A and C were photographed by irradiating the film from above with ultraviolet LED light of wavelengths 365 to 375 nm, while Figures 23B and D were photographed by irradiating the film with a visible light lamp attached to the microscope. As Figure 23A shows light emission, it was confirmed that the radiation detection film emits light when exposed to ultraviolet light. This suggests that the silica powder from the paper sheet has been transferred to the film substrate. The pattern in Figure 23B is due to the mold of the filter paper (linter pulp) that was placed between the film substrate and the press as a cushion being left on the backside, and the transfer surface is smooth.

Figure 6 shows the XRD patterns resulting from X-ray crystal diffraction measurements of the radiation detection film, the film substrate before thermal transfer, and the silica powder. In this figure, the radiation detection film is shown in blue, the film substrate in black, and the silica powder in green. As shown in this figure, with only the film substrate, a sharp peak was observed at 2θ = 26.02°. With the silica powder, the maximum sharp peak was observed at 2θ = 26.56°. On the other hand, with the radiation detection film, the peak was almost the same as with the film substrate, but it was shifted to the lower angle side at 2θ = 26.18°.

Next, X-ray crystal diffraction measurements were performed on the radiation detection film and the paper sheet after thermal transfer. The results are shown in the graph of Figure 7. In this figure, the scintillation paper is shown in black, the paper sheet after thermal transfer is shown in red, and the silica powder is shown in green. As shown in this figure, when comparing the radiation detection film with the paper sheet after thermal transfer, the peak near 2θ = 26° has disappeared. From the above, it was confirmed that the silica powder that was present on the surface of the scintillation paper has been transferred to the surface of the scintillation film.
(Surface fluorescence spectrum of radiation detection film)

Furthermore, the surface fluorescence was measured when the radiation detection film was excited at 280 nm using a Quantaurus Tau manufactured by Hamamatsu Photonics K.K. The results are shown in the graph of Figure 8. Here, a surface fluorescence spectrum similar to that of scintillation paper was obtained, with a peak at approximately 430 nm.
(Results of SEM observation and elemental analysis)

Next, SEM images and elemental analysis were performed on the paper sheet after thermal transfer. The results are shown in Figures 9A to 9H. In these figures, Figure 9A shows a low-magnification SEM photograph of the paper sheet, Figure 9B shows a high-magnification SEM photograph, Figure 9C shows an even higher-magnification SEM photograph, Figure 9D shows the qualitative spectrum in the green frame in Figure 9C, Figure 9E shows the qualitative spectrum in the blue frame, Figure 9F shows the qualitative spectrum in the red frame, Figure 9G shows the qualitative spectrum in the purple frame, and Figure 9H shows the elemental analysis results of Figures 9D to 9G. In the low-magnification SEM photograph of Figure 9A, white and black contrast areas were confirmed. In addition, in the high-magnification SEM photograph of Figure 9B, black amorphous objects, granular objects, and fibrous objects were confirmed. Furthermore, in Figure 9H, a substance that appears to be scintillator silica silica powder was seen, and in 001 (Figure 9D) and 004 (Figure 9G), 32.18% and 14.41% Si were seen. On the other hand, 003 (Figure 9F), which is thought to be a paper material, also contained 28.42% Si. 002 (Figure 9E) contained 93.99% C, suggesting the possibility that it is a polymer used as a binder.

Similarly, SEM images and elemental analysis were performed on the radiation detection film and the film substrate. The results are shown in Figures 10A to 10H. In these figures, Figure 10A shows an SEM photograph of the radiation detection film, Figure 10B shows an SEM photograph of the film substrate, Figure 10C shows an enlarged SEM photograph of Figure 10A, Figure 10D shows the qualitative spectrum in the green frame in Figure 10C, Figure 10E shows the qualitative spectrum in the blue frame, Figure 10F shows the qualitative spectrum in the red frame, Figure 10G shows the qualitative spectrum in the purple frame, and Figure 10H shows the elemental analysis results of Figures 10D to 10G. In the SEM photograph of the radiation detection film in Figure 10A, the surface is uneven, and adhesion of Si fine particles and a sheet-like material containing Si was confirmed. Furthermore, in the SEM photograph of the film substrate in Figure 10B, adhesion of Si fine particles was confirmed. Furthermore, from Fig. 10H, 19.26% and 13.23% Si were observed in 001 (Fig. 10D) and 002 (Fig. 10E), where solid matter was observed, respectively, but almost no solid matter was observed in 003 (Fig. 10F) and 004 (Fig. 10G), where the Si percentages were 2.79% and 0%. Even with only the film substrate, 001, where solid matter was observed on the surface, contained 19.11% Si, but 002, where no solid matter was observed, contained a low percentage of Si at 1.61%, suggesting that the film substrate does not originally contain Si.
(Radiation detection)

Next, radiation was actually detected using the radiation detection film. First, the detection characteristics of radon gas in the air by the radiation detection film were examined. Here, a balloon was inflated and charged with static electricity using a handkerchief, and then it was left in a corner of a closed room for two hours to adsorb dust containing radon gas in the air. The balloon was then deflated, wrapped in radiation detection film, and placed in a glass vial. This state is shown in the photograph of Figure 11. In this figure, (a) shows a glass vial with a radiation detection film wrapped around it, and (b) shows a glass vial with a balloon that electrostatically adsorbs radon gas in the air and is wrapped in scintillation paper and placed inside it. Radiation was measured for these for 60 seconds using a Triaslar detector in ³² P mode. The results are shown in Figures 12A to 12D. In these figures, Fig. 12A shows an SEM photograph of the radiation detection film, Fig. 12B shows the qualitative spectrum within the green frame in Fig. 12A, Fig. 12C shows the qualitative spectrum within the blue frame, and Fig. 12D shows the elemental analysis results of Fig. 12B to Fig. 12C. Here, the background was 1569 cpm, the dust-adsorbed balloon containing radon gas was 7202 cpm, and the net count rate was 5633 cpm (7202 cpm - 1569 cpm). As described above, the radiation detection film was able to easily detect α rays from radon gas indoors.

Next, the alpha rays of a commercially available mantle impregnated with thorium-232 were measured. Here, the mantle was placed in a glass vial as shown in the photograph in Figure 13, and then the radiation detection film was set inside the glass vial, aligned cylindrically up to the top, and the count rate was obtained by measuring for 300 seconds in tritium mode using a HIDEX Triaslar detector. The results were: mantle + glass vial: 1476 cpm, mantle + radiation detection film + glass vial: 7912 cpm, net count rate: 7912 - 1476 = 6436 cpm.

Furthermore, the mantle was covered with radiation detection film, and the scintillation light was measured with a CCD camera. Here, a PerkinElmer LAS4000mini was used as the measuring device, and Figures 14A and 14B were obtained after a three-minute measurement in Precision mode, High. In these figures, Figure 14A shows a photograph of the mantle covered with radiation detection film, and Figure 14B shows an image in which a CCD image of the scintillation light is superimposed.

Next, 5 ml of an aqueous solution of tritium ( ^3H ) with a radioactivity concentration of 37 kBq/ml was added to the glass vial, and a radiation detection film (12.5 cm x 12.5 cm) was cut into five pieces as shown in Figure 15A. Each piece was immersed in the tritium aqueous solution in the glass vial as shown in Figure 15B, and the count rate was measured in the tritium mode of the Triaslar detector. Note that the portion of the cut film immersed in the tritium aqueous solution was about half. The results are shown in Figure 16. From these results, it was found that the net count rate measured by cutting the radiation detection film into five equal pieces and adding them cylindrically to 5 ml of an aqueous solution of tritium with a radioactivity concentration of 37 kBq/ml increased with the number of films.
(Tritium detection efficiency)

Next, the detection efficiency of tritium using the radiation detection film of Example 1 was confirmed. First, the maximum range of tritium ( ^3H ) β rays (18.6 keV) in water is 0.56 μm on average and 6 μm at maximum, so here we consider a volume of 0.0015625 ^cm3 up to 1 μm from the surface of a 15.625 ^cm2 sheet of radiation detection film. As mentioned above, the tritium aqueous solution is 37 kBq/ ^cm3 , so 0.0015625 x 37000 = 58 Bq of tritium is present in that volume. Since the radiation detection film was about half immersed, the amount is 58/2 = 29 Bq.

Furthermore, with five pieces of radiation detection film, there will be 29 x 5 = 145 Bq. Therefore, when converted to a net counting rate, it becomes 145 x 60 = 8700 dpm.

In this way, the net count rate using five sheets of radiation detection film was 839 cpm, and the counting efficiency was 839/8700×100=9.6%. The counting efficiency of the liquid scintillator is 60-70%.
(Laminate)

Next, it was confirmed whether it was possible to detect high-energy β-rays from Strontium-90/Yttrium-90 ( ⁹⁰ Sr: 0.546 MeV, ⁹⁰ Y: 2.274 MeV) using a laminate of radiation detection films. As a result, no light was emitted when the number of layers of the radiation detection film was 1 to 10, but when the number of layers was 32 to 64, scintillation light was confirmed with a CCD camera. From this, it was confirmed that the radiation detection film of the present invention can measure and detect radiation energy separately by adjusting the number of layers.
(Radiation detection powder)

Next, a radiation detection powder that can be used as a scintillator carried by a radiation detection film will be described as embodiment 5. The radiation detection powder contains a scintillator that emits light when excited by radiation, and the scintillator is a complex of organic scintillator molecules and silica nanoparticles. In this complex, the organic scintillator molecules are encapsulated in a clathrate compound, or the organic scintillator molecules and aromatic rings formed by a coupling agent are fixed to the inside or surface of the silica nanoparticles by a sol-gel method.

This radiation detection powder is manufactured by a first mixing step in which the organic scintillator molecules and the inclusion compound are added to an organic solvent and heated to dissolve the organic scintillator molecules or the organic scintillator molecules enclosed by the inclusion compound in the organic solvent; a second mixing step in which a silicic acid source and a coupling agent are added to the first mixed liquid obtained in the first mixing step and heated and stirred to form silica nanoparticles in which the organic scintillator molecules are fixed to the interior or surface by a sol-gel method and aromatic rings are fixed to the interior or surface by the coupling agent, thereby forming a composite of the organic scintillator molecules and the silica nanoparticles; and a heating and drying step in which the second mixed liquid obtained in the second mixing step is heated and dried to obtain the radiation detection powder.

The organic scintillator molecules that make up the radiation detection powder are scintillator particles that have the fluorescent properties of emitting light when excited by radiation, and examples of these include the following:

Benzoxazole derivatives: 1,1'-biphenyl, 4-yl-6-phenyl-benzoxazole TLA, 2-phenylbenzoxazole, 2-(4'-methylphenyl)-benzoxazole, 2-(4'-methylphenyl)-5-methylbenzoxazole, 2-(4'-methylphenyl)-5-t-butylbenzoxazole, 2-(4'-t-butylphenyl)-benzoxazole, 2-phenyl-5-t-butyl-benzoxazole, 2-(4'-t-butylphenyl)-5-t-butylbenzoxazole, 2-(4'-biphenylyl)-benzoxazole, 2-(4'-biphenylyl)-5-t-butylbenzoxazole, 2-(4'-biphenylyl)-6-phenyl-benzoxazole (PBBO), etc.

Oxazole derivatives: 2-p-biphenylyl-5-phenyloxazole (BPO), 2,2'-p-phenylenebis(5-phenyloxazole) (POPOB), 2,5-diphenyloxazole (DPO), 1,4-bis[2-(5-phenyloxazolyl)]benzene (POPOP), 1,4-bis-2-(4-methyl-5-phenyloxazolyl)benzene (DMPOPOP), etc.

Oxadiazole derivatives: 2,5-diphenyloxadiazole (PPD), 2,5-diphenyl-1,3,4-oxadiazole, 2-(4'-t-butylphenyl)-5-phenyl-1,3,4-oxadiazole, 2,5-di-(4'-t-butylphenyl)-1,3,4-oxadiazole, 2-phenyl-5-(4''-biphenylyl)-1,3,4-oxadiazole (PBD), 2-(4'-t-butylphenyl)-5-(4''-biphenylyl)-1,3,4-oxadiazole (butyl-PBD), etc.

Terphenyl derivatives: 4,4''-di-tert-amyl-p-terphenyl (DAT), etc.

Polynuclear aromatic compounds: 4,4'-bis(2,5-dimethylstyryl)diphenyl (BDB), p-terphenyl scintillator, etc.

Pyrazoline derivatives: 1-phenyl-3-mesityl-2-pyrazoline (PMP), 1,5-diphenyl-3-(4-phenyl-1,3-butadienyl)-2-pyrazoline (DBP), 1,5-diphenyl-β-styrylpyrazoline (DSP), etc.

Phosphoramide derivatives: Anilinobis(1-aziridinyl)phosphine oxide (PDP), etc.

Thiophene derivatives: 2,5-bis-benzoxazolyl (2')-thiophene, 2,5-bis-[5'-methylbenzoxazolyl (2')]-thiophene, 2,5-bis-[4',5'-dimethylbenzoxazolyl (2')]-thiophene, 2,5-bis-[4',5'-dimethylbenzoxazolyl (2')]-3,4-dimethylthiophene, 2,5-bis-[5'-isopropylbenzoxazolyl (2')]-3,4-dimethylthiophene, 2-benzoxazolyl (2')-5-[7'-sec-butyl-benzoxazolyl (2')]-thiophene, 2-benzoxazolyl (2')-5-[5'-t-butyl-benzoxazolyl (2')]-thiophene, 2,5-bis-[5'-t-butylbenzoxazolyl (2')]-thiophene (BBOT), etc.

The organic scintillator molecules used in the radiation detection powder may be one type alone, but preferably two or more types are used in combination. The organic scintillator molecules can be used in appropriate combinations as long as they can detect radiation. For example, a combination of a first solute and a second solute used in a liquid scintillator can be used. Examples of the first solute include p-terphenyl, 2,5-diphenyloxazole (DPO), 2-(4'-t-butylphenyl)-5-(4''-biphenylyl)-1,3,4-oxadiazole (butyl-PBD), etc. Examples of the second solute include 1,4-bis[2-(5-phenyloxazolyl)]benzene (POPOP), 1,4-bis-2-(4-methyl-5-phenyloxazolyl)benzene (DMPOPOP), etc. A preferred combination is a combination of DPO and POPOP.

The organic scintillator molecule complex is not particularly limited as long as it is a complex of organic scintillator molecules and silica nanoparticles, and is preferably a complex of multiple types of organic scintillator molecules and silica nanoparticles. The silica nanoparticles are bonded with the organic scintillator molecules attached to the particle surface or with the organic scintillator molecules contained within the particles to form a complex. It is preferable that the organic scintillator molecules are contained within the silica nanoparticles.

The silica nanoparticles can have a particle size that can be obtained by a conventional method for producing silica nanoparticles. The average particle size of the silica nanoparticles can be, for example, about 10 to 500 nm, preferably 30 to 400 nm, more preferably 70 to 300 nm, and even more preferably about 100 to 200 nm.

A composite of organic scintillator molecules and silica nanoparticles can be obtained according to a known method. For example, silica nanoparticles containing organic scintillator molecules can be obtained by forming silica nanoparticles in the presence of organic scintillator molecules. For example, silica nanoparticles containing organic scintillator molecules can be obtained by dissolving the organic scintillator molecules in an organic solvent (lower alcohol), adding water, a silicic acid source, and a catalyst to the organic scintillator molecules, and then using the sol-gel method.

Examples of organic solvents that dissolve the organic scintillator molecules include ethanol. The blending ratio of the organic scintillator molecules to the organic solvent (organic scintillator molecule weight:organic solvent weight) is not particularly limited as long as the organic scintillator molecules can be dissolved in the organic solvent. The blending ratio can be, for example, about 1:10 to 90, and preferably about 1:30 to 70. The organic scintillator molecules can be easily dissolved in ethanol by being enclosed in cyclodextrin.

Other organic solvents that can be used are not particularly limited as long as they are lower alcohols that can be used to form silica nanoparticles. Examples of lower alcohols include methanol, ethanol, n-propanol, and 2-propanol, and ethanol is preferred. In this embodiment, ethanol is used as the organic solvent that dissolves the organic scintillator molecules.

In this embodiment, in the first mixing step in which the organic scintillator molecules are dissolved in the organic solvent, an inclusion compound is added to the organic solvent (lower alcohol). For the inclusion compound, for example, cyclodextrin, which is a type of cyclic oligosaccharide, specifically β-cyclodextrin sulfated sodium salt (β-cyclodextrine, sulfated, sodium salt) can be used. The inner pores of β-cyclodextrin sulfated sodium salt have a pore size of 0.6 to 0.8 nm, and the inside of the pores is prone to include hydrophobic molecules, so that it has the characteristic of being prone to include water-insoluble molecules inside. In this way, by including the organic scintillator molecules in the inclusion compound, the organic scintillator molecules can be quickly dissolved in the organic solvent. In addition, since sulfated β-cyclodextrin has the same structure as Si(O-) ₄ of TEOS, which is a silicic acid source described later, such as -SO ₃ O-, it is easily fixed to the inside or surface of silica nanoparticles during silica formation. In the first mixing step, the clathrate is added in a weight ratio of 1 wt % or more, preferably 1.6 wt % or more.

Furthermore, in order to form silica nanoparticles with organic scintillator molecules fixed on the surface or inside, in the second mixing step, a coupling agent is added to the first mixed liquid obtained in the first mixing step in addition to the silicic acid source, which is the silica source. That is, in the second mixing step, water, a silicic acid source, a coupling agent, and a catalyst are added to the first mixed liquid, which is heated and stirred, forming silica nanoparticles with organic scintillator molecules fixed on the interior or surface by the sol-gel method and aromatic rings fixed on the interior or surface by the coupling agent, thereby forming a composite of the organic scintillator molecules and the silica nanoparticles.

The silicic acid source is not particularly limited as long as it is a silicic acid source that can be used to form silica nanoparticles. Examples of silicic acid sources include tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetrapropyl orthosilicate (TPOS), etc., and preferably tetraethyl orthosilicate is used. The amount of the silicic acid source to be blended can be, for example, about 1/500 to 1/5 of the amount of the lower alcohol.

For example, a silane coupling agent can be used as the coupling agent, specifically p-styryltrimethoxysilane. The silane coupling agent p-styryltrimethoxysilane has functional groups in its molecule that bond with both organic and inorganic materials, and has the property of bonding organic and inorganic materials. However, any coupling agent can be used as long as it has an aromatic ring, such as a benzene ring structure such as a styryl group or a phenyl group. In the second mixing step, the coupling agent is added in a molar ratio of 0.2 or more, preferably 2 or more, relative to the organic scintillator molecules.

The catalyst is not particularly limited as long as it is a catalyst that can be used to form silica nanoparticles. Examples of the catalyst include base catalysts and acid catalysts, and preferably base catalysts. Examples of base catalysts include ammonia, and examples of acid catalysts include hydrochloric acid, sulfuric acid, nitric acid, and acetic acid.

The proportion of the organic scintillator molecules in the total weight of the complex of the organic scintillator molecules can be, for example, 5 to 80% by weight, preferably 15 to 70% by weight, more preferably 25 to 60% by weight, and further preferably 30 to 55% by weight.
[Example 2]

The radiation detecting powder having the above structure is manufactured by the following steps.
(1) First mixing step

To 40 mL of ethanol, about 4.6 g of DPO (2,5 diphenyloxazole) and about 0.53 g of POPOP (1,4-bis(5-phenyl-2-oxazolyl)benzene) were added as organic scintillator molecules, and then about 0.4 g of β-cyclodextrin sulfate Na salt was added as an inclusion compound. The mixture was heated on a hot stirrer at about 80° C. for 30 minutes to dissolve the organic scintillator molecules in ethanol (first mixed solution).
(2) Second mixing step

9 mL of TEOS (Tetraethylorthosilicate) as a silicic acid source, 10 mL of p-styryltrimethoxysilane as a first coupling agent, 100 mL of distilled water, and 10 mL of concentrated aqueous ammonia as a catalyst are added to the ethanol solution in which the organic scintillator molecules have been dissolved. At this time, the molar ratio of p-styryltrimethoxysilane to DPO is adjusted to be approximately twice that of DPO, and the weight ratio of β-cyclodextrin sodium sulfate is adjusted to be approximately 1.6 wt%. In addition, the amount of water added in the second mixing step is adjusted to be 100 mL for every 400 mL of ethanol in the first mixing step, i.e., the volume ratio of ethanol:water is adjusted to be 4:1.

The mixed liquid prepared as described above is heated and stirred on a hot stirrer at approximately 80°C for 2 hours to form silica nanoparticles containing the organic scintillator molecules, thereby forming a composite of the organic scintillator molecules and the silica nanoparticles (second mixed liquid).
(3) Heating and drying process

The second mixture, in which a complex of organic scintillator molecules and silica nanoparticles was formed in the solution, was heated to dryness on a hot stirrer to obtain approximately 14.5 g of a white powder (radiation detection powder).

The radiation detection powder produced in the above manner had a ratio of organic scintillator molecules of approximately 35 wt% relative to the total radiation detection powder. The radiation detection powder was not dispersible in ethanol at room temperature, but was uniformly dispersed when heated to approximately 80°C, but was not uniformly dispersed in water. This radiation detection powder also exhibited the physical property of swelling when it absorbed ethanol and solidifying at low temperatures (refrigerator). In particular, in the above production method, the use of cyclodextrin in the first mixing step made it easier to disperse silica nanoparticles in ethanol.

As described above, the radiation detection powder according to an embodiment of the present invention has a ratio of organic scintillator molecules to the entire radiation detection powder of approximately 35 wt%, which is significantly higher than conventional methods. This makes it possible to realize the feature of simplifying radiation detection while increasing the detection sensitivity of radiation per unit amount. Furthermore, in the second mixing step, the time required to form a complex of the organic scintillator molecules and silica nanoparticles was reduced to several hours, which is significantly shorter than the conventional manufacturing method. This shortens the time required to manufacture the radiation detection powder, making it possible to mass-produce it at low cost.

The radiation detecting powder produced in the above manner can be used for various purposes as a powder for detecting radiation that emits light when excited by radiation. Furthermore, in the present invention, as one example of the use of the radiation detecting powder, the radiation detecting powder can be contained in a paper sheet and used as a paper sheet. The paper sheet containing the radiation detecting powder and the method for producing the same will be described in detail below.
[Embodiment 6]

A paper sheet according to one embodiment of the present invention is shown in the schematic cross-sectional view of Figure 17. The paper sheet 10 shown in Figure 17 includes a paper sheet-like substrate 1 made into a sheet, and a coating layer 2 containing a radiation detection powder applied to the surface of the sheet-like substrate 1. The paper sheet 10 is manufactured by a preparation step of preparing a paper sheet-like substrate 1 made into a sheet, a coating step of applying a dispersion liquid in which a radiation detection powder is dispersed in a solvent as a coating liquid to the surface of the sheet-like substrate 1, and a drying step of removing all or part of the solvent from the coating liquid applied to the sheet-like substrate 1 to form the coating layer 2. In this way, a paper sheet containing a radiation detection powder such as scintillator-immobilized silicic acid particles is manufactured by a coating method.
(Sheet-like substrate 1)

The sheet-like substrate 1 is made of paper, and is manufactured by wet-sheeting natural or synthetic fibers. As natural fibers, cellulose-based fibers, such as wood fibers, seed hair fibers, bast fibers, and leaf vein fibers, can be used. On the other hand, as synthetic fibers, for example, polyamide-based, polyolefin-based, polyester-based, polyacrylonitrile-based, and polyvinyl alcohol-based synthetic fibers can be suitably used. The fiber diameter of the fibers constituting the paper sheet-like substrate 1 is, for example, 0.05 μm to 100 μm, preferably 0.1 μm to 80 μm, taking into consideration the average diameter of the radiation detecting powder contained therein. In particular, it is preferable that the fiber diameter is 1 μm to 60 μm. This allows the radiation detecting powder to be held effectively.

In the example of Fig. 17, for the purpose of explanation, a two-layered paper sheet in which the coating layer 2 is applied to one surface of the sheet-like substrate 1 is shown, but the sheet-like substrate 1 and the coating layer 2 do not necessarily need to be clearly separated into layers, and it is sufficient that the coating layer 2 is formed on the surface of the sheet-like substrate 1. That is, as described below, when the coating layer 2 is formed by applying a coating liquid to the paper fibers constituting the sheet-like substrate 1, as shown in the enlarged cross-sectional view of the main part of Fig. 18, the coating layer 2 is formed on the surface of the fibers 6 of the sheet-like substrate 1. Such an embodiment in which the coating layer 2 is formed on the surface of the fibers 6 constituting the sheet-like substrate 1 microscopically is also included in the coating layer 2 formed on the surface of the sheet-like substrate 1 in the present invention.
(Coating Layer 2)

The coating layer 2 is formed by a coating liquid applied to the surface of the sheet-like substrate 1. The coating liquid is a dispersion liquid in which a radiation detection powder is dispersed in a solvent. In the paper sheet according to this embodiment, the radiation detection powder is a complex of the organic scintillator molecules and silica nanoparticles described above, in which the organic scintillator molecules or the organic scintillator molecules enclosed in an inclusion compound are fixed to the inside or surface of the silica nanoparticles by a sol-gel method, and aromatic rings are fixed to the inside or surface of the silica nanoparticles by a coupling agent. This radiation detection powder does not disperse in water but disperses in organic solvents, so the coating liquid uses the radiation detection powder dispersed in an organic solvent. As the organic solvent, a solvent such as ethanol can be used as a liquid that easily disperses the radiation detection powder. As described above, this radiation detection powder disperses uniformly in ethanol heated to about 80°C. Therefore, this radiation detection powder is used as the coating liquid in a state where it is dispersed in heated ethanol. However, a polar solvent such as methanol can be used as the organic solvent instead of ethanol.

The coating liquid, in which the radiation detecting powder is dispersed while being heated to a high temperature, is applied to the sheet-like substrate 1, and then cooled to promote solidification. At the same time, all or part of the solvent is evaporated and removed, so that the solute radiation detecting powder is solidified and fixed to the fibers of the sheet-like substrate 1.

For example, a bar coater 9 can be used to apply the coating liquid, as shown in Figure 20. The bar coater 9 has a wire wound around the surface of a rod-shaped body, and the coating liquid is held between the wires, making it possible to control the amount of coating. Other coating methods include a roll coater, gravure coater, knife coater, blade coater, rod coater, air doctor coater, curtain coater, fountain coater, kiss coater, screen coater, and extrusion coater. Furthermore, the coating liquid can also be applied by spray or brush.

Furthermore, the amount of coating liquid applied is 10 g or more, preferably 100 g to 400 g, per ^m2 of the sheet-like substrate 1. The coating layer 2 can be provided over the entire surface of the sheet-like substrate 1 as shown in Fig. 17, or can be provided partially in a specific region of the sheet-like substrate 1 as shown in Fig. 20.

The paper sheet 10 shown in Figure 17 can be used for radiation detection testing with the surface on which the coating layer 2 is formed (the upper surface in the figure) as the inspection surface 5. As shown in the figure, the structure in which the coating layer 2 containing radiation detection powder is provided on the surface of the sheet-like substrate 1 allows the radiation detection powder to be concentrated on one side of the sheet-like substrate 1, so that radiation can be effectively detected by using this surface as the inspection surface 5.

Furthermore, the paper sheet 10 can also have a surface layer 3 on the surface of the coating layer 2, as shown by the dashed line in Figure 17. This surface layer 3 can be, for example, a thin film made of paper. This paper sheet 10 has the advantage of being able to effectively prevent the radiation detecting powder adhered to the coating layer 2 from falling off from the surface of the coating layer 2.

Furthermore, the paper sheet may have a release sheet 4 laminated on the surface of the coating layer 2 as shown in Fig. 19. By covering the surface of the coating layer 2 with the release sheet 4, the paper sheet 30 can protect the coating layer 2 when not in use, and can be used by peeling off the release sheet 4 to expose the inspection surface 5 when the paper sheet 30 is used. As such a release sheet 4, for example, a sheet made of a hydrophobic material, for example, a resin such as PET, PP, PE, PMP, PTFE, or PVDF, or a sheet of paper or film coated with silicone or fluorine can be suitably used. However, the radiation detecting powder may be in a state where the coating layer is exposed without necessarily providing a surface layer or release sheet on the surface of the coating layer.
[Example 3]

The paper sheet having the above structure is manufactured by the following process.
(1) Preparation process

A paper sheet-like substrate 1 made of paper that has been made into a sheet is prepared. For example, a paper sheet made by wet-processing cellulose fibers can be used as the paper sheet-like substrate 1. The sheet-like substrate 1 can have a thickness of 50 μm and a basis weight of 30 g/ ^m2 .
(2) Coating process

The radiation detection powder is dispersed in a solvent to prepare a coating liquid. Here, the radiation detection powder used is the radiation detection powder manufactured in Example 2, which is composed of a complex of organic scintillator molecules and silica nanoparticles. Ethanol is used as the organic solvent in which this radiation detection powder is dispersed. 50 g of ethanol is prepared and stirred at 200 rpm while being heated to 75°C. 0.5 g of radiation detection powder is added to the heated ethanol, and the mixture is further stirred at 200 rpm for 60 minutes while being maintained at 75°C. This results in a coating liquid in which the radiation detection powder is uniformly dispersed in the ethanol.

The above coating liquid is applied to the surface of the sheet-like substrate 1. A predetermined amount of the coating liquid is applied to the surface of the sheet-like substrate 1, for example, by using a bar coater 9 shown in Fig. 20. The amount of the coating liquid applied is, for example, 100 g/ ^m2 .
(3) Drying process

The coating liquid applied to the sheet-like substrate 1 is dried at 100° C. for 30 minutes to vaporize and remove all or a part of the solvent in the coating liquid, and the radiation detecting powder, which is the solute in the coating liquid, is solidified and fixed to the fibers of the sheet-like substrate 1. As a result, a coating layer 2 is formed on the surface of the sheet-like substrate 1.
[Embodiment 7]

Furthermore, a paper sheet according to another embodiment of the present invention will be described in detail. In this paper sheet, the radiation detection powder is a complex of the aforementioned organic scintillator molecules and silica nanoparticles, and this radiation detection powder and cellulose nanofiber aggregates are assembled and made into a sheet. In this way, a paper sheet containing a radiation detection powder such as scintillator-immobilized silicic acid particles is produced by a wet papermaking method in which silicic acid particles are aggregated on the surface of the fibers and then made into a sheet. This paper sheet is manufactured by the following steps: a preparation step of preparing a radiation detection powder, which is a composite of organic scintillator molecules and silica nanoparticles, in which organic scintillator molecules enclosed in an inclusion compound or organic scintillator molecules are fixed to the inside or surface of silica nanoparticles by a sol-gel method, and aromatic rings are fixed to the inside or surface of the silica nanoparticles by a coupling agent; a first dispersion step of dispersing the radiation detection powder in an organic solvent to obtain a first dispersion; a second dispersion step of dispersing cellulose nanofibers in water to obtain a second dispersion; an aggregation step of mixing the first dispersion and the second dispersion to aggregate the radiation detection powder and the cellulose nanofibers; and a papermaking step of filtering the mixture containing the aggregates of the radiation detection powder and the cellulose nanofibers and making the mixture into a sheet.

This paper sheet is manufactured by a papermaking method using the radiation detection powder shown in the above-mentioned embodiment 5. As described above, the radiation detection powder used here is a composite of organic scintillator molecules and silica nanoparticles with an average particle size of nano-size, so that the composite passes through a mesh and cannot be made into paper by a normal papermaking method. In addition, this radiation detection powder does not disperse in water, which also makes it difficult to make paper by a normal method.

To solve this problem, in the paper sheet manufacturing method according to this embodiment, as shown in FIG. 21 , the radiation detecting powder is dispersed in an organic solvent to form a first dispersion liquid 11, and the cellulose nanofibers are dispersed in water to form a second dispersion liquid 12. By mixing these dispersion liquids, the radiation detecting powder and the cellulose nanofibers are aggregated to form an aggregate 15, and this aggregate 15 is filtered to produce a sheet.
[Example 4]

The paper sheet having the above structure is manufactured by the following process.
(1) Preparation process

As the radiation detecting powder, the radiation detecting powder composed of the composite of the organic scintillator molecules and the silica nanoparticles manufactured in the above-mentioned Example 2 is prepared.
(2) First dispersion step

In this step, the radiation detection powder is dispersed in an organic solvent to prepare a first dispersion liquid 11. Ethanol is used as the organic solvent in which the radiation detection powder is dispersed. 100 g of ethanol is prepared and stirred at 200 rpm while being heated to 75° C. 0.50 g (50 parts by weight) of the radiation detection powder is added to the heated ethanol, and the mixture is further stirred at 200 rpm for 60 minutes while being kept at 75° C. This prepares a first dispersion liquid 11 in which the radiation detection powder is uniformly dispersed in the ethanol.
(3) Second Dispersion Step

In this step, cellulose nanofibers are dispersed in water to form a second dispersion liquid 12. The cellulose nanofibers used preferably have a fiber diameter of 3 nm to 200 nm, and more preferably have a fiber diameter of 50 nm to 100 nm. Here, fine fibrous cellulose (manufactured by Daicel Corporation) is used as the cellulose nanofibers. A predetermined amount of fine fibrous cellulose is suspended and dispersed in water, which is the dispersion liquid, to prepare 50 parts by weight of a 0.5 wt % aqueous solution of the fine fibrous cellulose.
(4) Flocculation step

The first dispersion 11 and the second dispersion 12 are mixed to aggregate the radiation detection powder and the cellulose nanofibers (fine fibrous cellulose) (for 2 minutes). In this way, by dispersing the respective good solvents (radiation detection powder: ethanol, cellulose nanofibers: water) and then mixing the respective poor solvents (radiation detection powder: water, cellulose nanofibers: ethanol), an aggregate 15 of the radiation detection powder and the cellulose nanofibers can be obtained. Since the radiation detection powder dispersed in the organic solvent and the cellulose nanofibers dispersed in water are both nano-sized, there is no yield as is, but by agglomerating and filtering them, it becomes possible to make paper.
(5) Papermaking process

The mixture 13 in which the radiation detection powder and cellulose nanofibers are aggregated is filtered and made into a sheet. In this process, the mixture containing the radiation detection powder and cellulose nanofiber aggregates 15 is filtered using qualitative filter paper No. 1 (manufactured by Advantec Toyo Co., Ltd.). However, the mixture 13 can also be filtered by suction using a Nutsche filter. The filtered aggregates 15 are peeled off from the filter paper and dried at 100°C for 10 minutes to form a paper sheet. The obtained paper sheet had a thickness of 0.23 mm and a basis weight of 106 g/ ^m2 .

Furthermore, the present invention can use, as a radiation detection powder for use in paper sheets, a radiation detection powder in which silica nanoparticles containing organic scintillator molecules are fixed on the surface of particles or fibers, instead of a radiation detection powder composed of a complex in which the organic scintillator molecules or the organic scintillator molecules enclosed in the above-mentioned inclusion compound are fixed inside or on the surface of silica nanoparticles by a sol-gel method, and aromatic rings are fixed inside or on the surface of the silica nanoparticles by a coupling agent. In this radiation detection powder, inorganic particles such as silica particles can be used as the particles on which the silica nanoparticles containing organic scintillator molecules are fixed, and supporting fibers having a predetermined fiber diameter can be used as the fibers on which the silica nanoparticles containing organic scintillator molecules are fixed.

A radiation detection powder using silica particles as particles to fix silica nanoparticles (hereinafter also referred to as scintillator silica powder) comprises silica particles and a scintillator fixed on the surface of the silica particles, the scintillator being silica nanoparticles containing organic scintillator molecules. This radiation detection powder (scintillator silica powder) can have an average particle size of the silica particles of 0.5 to 50 μm, preferably 1 to 30 μm, and more preferably 1.5 to 20 μm, and an average particle size of the silica nanoparticles of 30 to 400 nm. In addition, this radiation detection powder can also fix the scintillator to the silica particles via an adhesive.

This radiation detecting powder (scintillator silica powder) is produced as follows.
(1) First mixing step

To 240 mL of dimethyl sulfoxide (DMSO) solution, which is an organic solvent, about 0.53 g of benzoic acid, about 4.6 g of DPO (2,5 diphenyloxazole), and about 5.1 g of POPOP (1,4-Bis(5-phenyl-2-oxazolyl)benzene) are added as organic scintillator molecules, and then 160 mL of ethanol is added. The mixture is heated to about 80°C on a hot stirrer and stirred until the organic scintillator molecules are dissolved and a transparent solution is obtained.
(2) Second mixing step

Next, to the mixture in which the organic scintillator molecules have been dissolved, add about 1.2 g of silica powder (6.78 μm) in 25 mL of 0.5 wt % water glass solution, which has been heated and stirred at about 80°C, 75 mL of distilled water, 10 mL of TEOS (Tetraethylorthosilicate) as a silicic acid source, and 10 mL of 28 wt % concentrated aqueous ammonia as a catalyst. At this time, the mixture is prepared so that 100 mL of water is added to 400 mL of ethanol solution containing DMSO, in other words, the ratio of the ethanol solution to the aqueous solution to be added is 4:1.

The mixed liquid prepared as described above was heated to about 80°C on a hot stirrer and stirred for about 2 days to form silica nanoparticles containing organic scintillator molecules, and the silica nanoparticles containing the organic scintillator molecules were bonded to the surface of the silica powder.
(3) Heating and drying process

The above mixture was heated on a hot stirrer to dryness, and a powder was obtained.
(4) Filtration and washing process

The powder obtained in the heating and drying process was washed and filtered using 400 to 600 mL of distilled water through a filter with a pore size of 0.1 μm, and the process was repeated to remove water-soluble sulfur compounds.

After drying in a desiccator, the mixture was heated and dried in a hot stirrer to obtain approximately 31.4 g of white powder (scintillator silica powder).

The radiation detection powder in which silica nanoparticles are fixed to fibers (hereinafter also referred to as scintillator silica fiber powder) comprises a carrier fiber having a predetermined fiber diameter and a scintillator fixed on the surface of the carrier fiber, and the scintillator is a silica nanoparticle containing organic scintillator molecules. This radiation detection powder (scintillator silica fiber powder) can use inorganic fibers such as glass fibers and carbon fibers, or organic fibers such as synthetic fibers and natural fibers as the carrier fiber. The fiber diameter of the carrier fiber can be 3 nm to 200 nm, preferably 3 nm to 40 nm. This radiation detection powder can also fix silica nanoparticles containing an organic scintillator on the surface of the fiber via binder fibers. For example, micro-order cellulose nanofibers can be used as such binder fibers. This radiation detection powder (scintillator silica fiber powder) is manufactured in the same manner as the manufacturing process described above, except that in the second mixing process described above, carrier fibers are added instead of silica powder.

Furthermore, it can be produced in the same manner as the above-mentioned production process using supporting fibers having a fiber diameter of 0.1 μm to 100 μm, preferably 10 μm to 50 μm.
[Embodiment 8]

A paper sheet manufactured using the radiation detection powder (scintillator silica powder) manufactured as described above will be described in detail below as another embodiment of the present invention. This paper sheet uses a coating method similar to the paper sheet of the above-mentioned embodiment 6, and includes a paper sheet-like substrate made into a sheet and a coating layer containing radiation detection powder applied to the surface of the sheet-like substrate. This paper sheet is manufactured by a preparation process of preparing a paper sheet-like substrate made into a sheet, a coating process of applying a dispersion of radiation detection powder (scintillator silica powder) dispersed in a solvent as a coating liquid to the surface of the sheet-like substrate, and a drying process of removing all or part of the solvent from the coating liquid applied to the sheet-like substrate to form a coating layer.

Furthermore, the paper sheet, in which the radiation detection powder is a scintillator silica powder in which silica nanoparticles containing organic scintillator molecules are fixed on the surface of silica particles, uses a coating liquid in which the radiation detection powder (scintillator silica powder) is dispersed in a dispersion liquid containing cellulose nanofibers. This coating liquid uses a predetermined amount of radiation detection powder (scintillator silica powder) dispersed in a dispersion liquid containing cellulose nanofibers at a predetermined concentration. The concentration of the dispersion liquid containing cellulose nanofibers can be 0.01 wt% to 5 wt%, and the mass ratio of the dispersion liquid containing cellulose nanofibers to the radiation detection powder (scintillator silica powder) can be 10:90 to 3:97. The cellulose nanofibers are physically opened in advance before being mixed with the radiation detection powder (scintillator silica powder). For example, wood pulp or the like can be mixed with a solvent such as water and pulverized with a grinder or the like.
[Example 5]

The paper sheet having the above structure is manufactured by the following process.
(1) Preparation process

A paper sheet-like substrate is prepared by papermaking into a sheet. For example, a paper sheet made by wet-processing polyester fibers can be used as the paper sheet-like substrate. The sheet-like substrate can have a thickness of 130 μm and a basis weight of 100 g/m ² .
(2) Coating process

The radiation detection powder is dispersed in a solvent to prepare a coating liquid. Here, a scintillator silica powder in which silica nanoparticles containing organic scintillator molecules are fixed on the surface of silica particles is used as the radiation detection powder. A 2 wt % aqueous solution of cellulose nanofibers is used as the dispersion liquid in which this radiation detection powder is dispersed. 95 parts by weight of the radiation detection powder (scintillator silica powder) is added to 5 parts by weight of this aqueous solution of cellulose nanofiber to prepare a coating liquid. This results in a coating liquid in which the radiation detection powder is uniformly dispersed on the cellulose nanofibers.

The above coating liquid is applied to the surface of the sheet-like substrate. A predetermined amount of the coating liquid is applied to the surface of the sheet-like substrate 1, for example, by using a bar coater 9 shown in Fig. 20. The amount of the coating liquid applied is, for example, 309 g/ ^m2 .
(3) Drying process

The coating liquid applied to the sheet-like substrate is dried at 100° C. for 30 minutes to vaporize and remove all or part of the solvent in the coating liquid, and the radiation detection powder (scintillator silica powder), which is the solute in the coating liquid, is solidified and fixed to the fibers of the sheet-like substrate, thereby forming a coating layer on the surface of the sheet-like substrate.
[Embodiment 9]

Further, another embodiment of a paper sheet manufactured using a radiation detection powder (scintillator silica powder) is shown in Fig. 22. This paper sheet 40 is formed into a sheet by wet-processing the radiation detection powder and fibers containing binder fibers, using silica nanoparticles containing organic scintillator molecules as the radiation detection powder. This paper sheet is manufactured through a preparation step of preparing a radiation detection powder (scintillator silica powder 7) in which silica nanoparticles containing organic scintillator molecules are fixed on the surfaces of silica particles, and a papermaking step of suspending the radiation detection powder and fibers 6 containing binder fibers in a dispersion liquid to form a papermaking slurry, and wet-processing the papermaking slurry to form a paper sheet in the form of a sheet.
(Papermaking slurry)

The paper sheet is produced by wet-laid papermaking of a papermaking slurry prepared by suspending radiation detection powder (scintillator silica powder) and fibers containing binder fibers in a dispersion liquid. The dispersion liquid in which the radiation detection powder and fibers containing binder fibers are suspended can be, for example, water.

Natural cellulose fibers, polyolefin fibers, polyacrylonitrile fibers, and aramid fibers can be used as binder fibers to be mixed into the papermaking slurry. Pulp-like fibers are particularly suitable. In addition to these fibers, resin fibers such as PET can also be added to the binder fibers.

Furthermore, the papermaking slurry can also contain fibers other than the binder fibers. For example, the fibers contained in the papermaking slurry can be the same as those used in the papermaking of the sheet-like substrate described above, or natural fibers, recycled fibers, synthetic fibers, inorganic fibers, etc. can be used as appropriate.

Furthermore, a coagulant or flocculant can be added to the papermaking slurry as a fixing agent. Specifically, fixing agents such as aluminum sulfate, alum, polydiallyldimethylammonium, polyethyleneimine, cationic starch, colloidal silica, colloidal aluminum, bentonite, polyphenol, etc. can be used. Alternatively, starch, polyacrylamide, polyvinyl alcohol can be used as a dry strength agent, and polyethyleneimine, melamine formaldehyde, urea formaldehyde, polyamide epichlorohydrin, polyvinylamine, etc. can be used as a wet strength agent.
[Example 6]

The paper sheet having the above structure is manufactured by the following process.
(1) Preparation process

As the radiation detection powder, a scintillator silica powder is prepared in which silica nanoparticles containing organic scintillator molecules are fixed on the surface of silica particles.
(2) Papermaking process

The radiation detection powder (scintillator silica powder) and fibers containing binder fibers are suspended in a dispersion liquid to prepare a papermaking slurry. The papermaking slurry is prepared as follows:

10 parts by weight of polyolefin synthetic pulp (manufactured by Mitsui Chemicals) is added to 1 L of water and stirred 300 times. 20 parts by weight of microglass fiber (manufactured by H&V) and 70 parts by weight of paper sheet (scintillator silica powder) are further added and stirred 100 times to uniformly disperse the fiber and radiation detection powder.

The above slurry is diluted to 1.5 L and stirred at 300 rpm. 1% polyamide epichlorohydrin resin (Seiko PMC) is added as a binder fiber and stirred for 1 minute. 1% polyacrylamide resin (Arakawa Chemical Industries) is added as a binder fiber and stirred for 1 minute. 0.2% aluminum sulfate is added and stirred for 1 minute.

The papermaking slurry prepared as above is made into a sheet using a 250 mm square sheet machine.

The paper sheet was dried at 100° C. for 20 minutes to obtain a paper sheet, which had a thickness of 0.35 mm and a basis weight of 160.3 g/m ² .

The paper sheet of the present invention manufactured as described above is cut into a predetermined shape and used for radiation wipe testing, etc. For the paper sheet to be wiped, the surface of the portion to be tested is wiped with the test surface of the paper sheet, and the radiation count rate is measured by detecting the light emitted from the scintillator in the paper sheet with a scintillation counter. The paper sheet emits light when the scintillator contained in the radiation detection powder is excited by radiation. The scintillation counter amplifies the light emitted by the paper sheet set in the scintillation counter with a photomultiplier tube and converts it into a current value, and the radiation count rate is measured from the detected value.
[Additional Notes]

The radiation detection powder contains a scintillator that emits light when excited by radiation. The scintillator is a composite of organic scintillator molecules and silica nanoparticles. In this composite, the organic scintillator molecules are encapsulated in a clathrate compound, or the organic scintillator molecules and aromatic rings formed by a coupling agent are fixed inside or on the surface of the silica nanoparticles by the sol-gel method.

The radiation detection powder is a composite containing two or more types of organic scintillator molecules.

The radiation detection powder uses a cyclic oligosaccharide as the inclusion compound and a silane coupling agent as the coupling agent.

The method for producing radiation detection powder contains a scintillator that emits light when excited by radiation, and includes a first mixing step of adding organic scintillator molecules and an inclusion compound to an organic solvent and heating the organic scintillator molecules or the organic scintillator molecules enclosed by the inclusion compound in the organic solvent; a second mixing step of adding a silicic acid source and a coupling agent to the first mixed liquid obtained in the first mixing step and heating and stirring the mixture to form silica nanoparticles in which the organic scintillator molecules are fixed to the interior or surface by a sol-gel method and aromatic rings are fixed to the interior or surface by the coupling agent, thereby forming a composite of the organic scintillator molecules and the silica nanoparticles; and a heating and drying step of heating and drying the second mixed liquid obtained in the second mixing step to obtain the radiation detection powder.

The method for producing the radiation detection powder uses a cyclic oligosaccharide as the inclusion compound, a silane coupling agent as the coupling agent, and any one of tetraethyl orthosilicate, tetramethyl orthosilicate, and tetrapropyl orthosilicate as the silica source.

The paper sheet is a paper sheet equipped with radiation detection powder containing a scintillator that emits light when excited by radiation, and includes a paper sheet-like substrate that is made into a sheet, and a coating layer containing the radiation detection powder that is applied to the surface of the sheet-like substrate. The radiation detection powder is a composite of organic scintillator molecules and silica nanoparticles, in which scintillator molecules or organic scintillator molecules enclosed in an inclusion compound and aromatic rings formed by a coupling agent are fixed inside or on the surface of silica nanoparticles by a sol-gel method, or silica nanoparticles containing organic scintillator molecules are fixed on the surface of particles or fibers.

The paper sheet is provided with radiation detection powder containing a scintillator that emits light when excited by radiation. The radiation detection powder is a composite of organic scintillator molecules and silica nanoparticles, in which organic scintillator molecules enclosed in an inclusion compound or organic scintillator molecules and aromatic rings formed by a coupling agent are fixed inside or on the surface of silica nanoparticles by a sol-gel method. The radiation detection powder and cellulose nanofiber aggregates are assembled and papered into a sheet.

The paper sheet is provided with radiation detection powder containing a scintillator that emits light when excited by radiation. The radiation detection powder is made by fixing silica nanoparticles containing organic scintillator molecules onto the surface of particles or fibers, and the radiation detection powder and fibers containing binder fibers are wet-laid to form a sheet.

The method for manufacturing a paper sheet is a method for manufacturing a paper sheet equipped with a radiation detection powder containing a scintillator that emits light when excited by radiation, and includes a preparation step of preparing a paper sheet-like substrate that has been made into a sheet, a coating step of applying a coating liquid obtained by dispersing the radiation detection powder in a solvent to the surface of the sheet-like substrate, and a drying step of removing all or part of the solvent from the coating liquid applied to the sheet-like substrate to form a coating layer.

The method for manufacturing the paper sheet involves forming the radiation detection powder into a composite of organic scintillator molecules and silica nanoparticles, in which the organic scintillator molecules are enclosed in an inclusion compound, or the organic scintillator molecules and aromatic rings formed by a coupling agent are fixed inside or on the surface of the silica nanoparticles by a sol-gel method, and dispersing this radiation detection powder in an organic solvent to form a coating liquid.

The method for manufacturing the paper sheet involves forming a radiation detection powder in which silica nanoparticles containing organic scintillator molecules are fixed onto the surface of particles or fibers, and dispersing this radiation detection powder in a dispersion liquid containing cellulose nanofibers to form a coating liquid.

The method for manufacturing a paper sheet is a method for manufacturing a paper sheet provided with a radiation detection powder containing a scintillator that emits light when excited by radiation, and includes a preparation step of preparing a radiation detection powder that is a composite of organic scintillator molecules and silica nanoparticles, in which organic scintillator molecules enclosed in an inclusion compound or organic scintillator molecules and aromatic rings formed by a coupling agent are fixed inside or on the surface of silica nanoparticles by a sol-gel method; a first dispersion step of dispersing the radiation detection powder in an organic solvent to obtain a first dispersion; a second dispersion step of dispersing cellulose nanofibers in water to obtain a second dispersion; an aggregation step of mixing the first dispersion and the second dispersion to aggregate the radiation detection powder and the cellulose nanofibers; and a papermaking step of filtering the mixture containing the aggregates of the radiation detection powder and the cellulose nanofibers and forming the mixture into a sheet.

The method for manufacturing a paper sheet is a method for manufacturing a paper sheet provided with a radiation detection powder containing a scintillator that emits light when excited by radiation, and includes a preparation step of preparing a radiation detection powder in which silica nanoparticles containing organic scintillator molecules are fixed on the surface of particles or fibers, and a papermaking step of suspending the radiation detection powder and fibers containing binder fibers in a dispersion liquid to prepare a papermaking slurry, and wet-processing the papermaking slurry to produce a paper sheet in the form of a sheet.

The above-described radiation detection powder and its manufacturing method can increase the ratio of organic scintillator molecules to the entire radiation detection powder, thereby realizing the feature of increasing the radiation detection sensitivity per unit amount. In addition, the time required to form silica nanoparticles containing organic scintillator molecules can be significantly reduced, making it possible to mass-produce the powder at low cost.

Furthermore, the paper sheet and its manufacturing method described above have the advantage that by making the radiation detection material out of paper, it can be mass-produced at low cost while simplifying the testing process. Also, like liquid scintillators, it can eliminate the complicated issues associated with the treatment and storage of radioactive waste liquid, and has the excellent advantage of being able to measure water.

The radiation detection film and manufacturing method thereof, as well as the radiation detection film laminate of the present invention, can be used easily while increasing the radiation detection sensitivity, making them convenient for use at radiation inspection sites. For example, by stacking 32 to 64 sheets of radiation detection film, the scintillation light caused by beta rays of Sr-90/Y-90 can be detected by a CCD. Note that when the energy of beta rays is low, such as tritium, it can be detected with a single sheet of radiation detection film. When the energy of beta rays is high, they can be detected by stacking radiation detection films.

Reference Signs List 10, 20, 30, 40...Paper sheet 1...Sheet-like substrate 2...Coating layer 3...Surface layer 4...Release sheet 5...Inspection surface 6...Fiber 7...Scintillator silica powder 8, 8A, 8B...Film substrate 9...Bar coater 11...First dispersion 12...Second dispersion 13...Mixed liquid 15...Agglomerate 16...Scintillator-immobilized silicic acid particles 18...Heating and pressurizing roll PR...Press plate GR...Gravure roll DB...Doctor blade

Claims (12)

A method for producing a radiation detection film containing a scintillator that emits light when excited by radiation, comprising the steps of:
Providing a paper sheet containing scintillator-immobilized silicic acid particles;
a step of overlapping the paper sheet with a film substrate and heat-pressing the paper sheet to transfer the scintillator component to the film substrate;
A method for producing a radiation detection film comprising: A method for producing the radiation detection film according to claim 1, comprising the steps of:
The method for producing a radiation detection film, wherein the step of preparing the paper sheet is a step of forming a coating layer containing the scintillator-immobilized silicic acid particles on a sheet produced by a wet papermaking method in which silicic acid particles are agglomerated on the surfaces of fibers and then papermade, or a step of forming a sheet from a raw material containing fibers carrying the scintillator-immobilized silicic acid particles by a wet papermaking method. A method for producing the radiation detection film according to claim 1, comprising the steps of:
The method for producing a radiation detection film, wherein the step of preparing the paper sheet is a step of forming a coating layer containing the scintillator-immobilized silicic acid particles on a sheet prepared by a coating method in which a coating liquid is applied to a papermaking sheet, or a step of forming a sheet from a raw material containing fibers carrying the scintillator-immobilized silicic acid particles by a wet papermaking method. A method for producing the radiation detection film according to any one of claims 1 to 3, comprising the steps of:
a step of overlapping the paper sheet with the film substrate and heat-pressing the paper sheet to transfer the scintillator component to the film substrate,
The method for producing a radiation detection film includes the steps of preparing two sheets of the film substrate, placing the two sheets on either side of the paper sheet, and subjecting the two sheets to heat and pressure processing. A method for producing the radiation detection film according to any one of claims 1 to 4, comprising the steps of:
The method for producing a radiation detection film, wherein the film substrate has light-transmitting properties. A method for producing the radiation detection film according to any one of claims 1 to 5, comprising the steps of:
The method for producing a radiation detection film, wherein the film substrate is made of PET. The method for producing a radiation detection film according to any one of claims 1 to 6, further comprising a step of stacking a plurality of radiation detection films onto which the scintillator component has been transferred. A method for producing the radiation detection film according to any one of claims 1 to 7, comprising the steps of:
The process for producing a radiation detection film comprises the steps of overlapping the paper sheet with the film substrate, subjecting them to heat and pressure processing, and transferring the scintillator component to the film substrate, the steps being carried out at a temperature of 80° C. or higher. A method for producing the radiation detection film according to any one of claims 1 to 8, comprising the steps of:
a step of overlapping the paper sheet with the film substrate and heat-pressing the paper sheet to transfer the scintillator component to the film substrate,
A method for producing a radiation detection film, comprising the step of applying heat and pressure to a flat or roll-shaped film substrate to transfer a scintillator component to the film substrate. A method for producing the radiation detection film according to any one of claims 1 to 9, comprising the steps of:
the scintillator is a composite of organic scintillator molecules and silica nanoparticles,
The complex is a method for producing a radiation detection film in which the organic scintillator molecule is encapsulated in an inclusion compound, or the organic scintillator molecule and an aromatic ring formed by a coupling agent are fixed to the inside or surface of the silica nanoparticles by a sol-gel method. A method for producing the radiation detection film according to any one of claims 1 to 10, comprising the steps of:
The step of providing a paper sheet comprises:
a first mixing step of adding the organic scintillator molecules and an inclusion compound to an organic solvent and heating the organic solvent to dissolve the organic scintillator molecules or the organic scintillator molecules in the organic solvent;
a second mixing step of adding a silicic acid source and a coupling agent to the first mixed solution obtained in the first mixing step, heating and stirring the mixture, and forming silica nanoparticles having the organic scintillator molecules fixed to the interior or surface thereof and aromatic rings fixed to the interior or surface thereof by the coupling agent by a sol-gel method, thereby forming a composite of the organic scintillator molecules and the silica nanoparticles;
a heating and drying step of heating and drying the second mixture obtained in the second mixing step to obtain scintillator-immobilized silicic acid particles;
and forming a coating layer containing the scintillator-immobilized silicic acid particles on a sheet formed by a wet papermaking method, or forming a raw material containing fibers carrying the scintillator-immobilized silicic acid particles into a sheet by a wet papermaking method to obtain a paper sheet. A method for producing the radiation detection film according to any one of claims 1 to 9, comprising the steps of:
The scintillator-immobilized silicic acid particles are
The present invention relates to a method for producing a scintillator comprising the steps of:
The silica particles have an average particle size of 1.5 to 20 μm;
The method for producing a radiation detection film, wherein the scintillator is silica nanoparticles containing organic scintillator molecules, and the average particle size of the silica nanoparticles is 30 to 400 nm.

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