Radiation detection method and scintillator device

Abstract

To highly accurately detect weak radiation, without increasing a facility cost.SOLUTION: A radiation detection method includes the steps of: immersing a thin film plastic scintillator attached with pure water in a first tank housing inspected liquid; pulling up the thin film plastic scintillator immersed in the first tank from the first tank, and removing at least a part of the inspected liquid attached to the thin film plastic scintillator; immersing the thin film plastic scintillator from which the inspected liquid has been removed in a second tank housing the inspected liquid; spirally winding the thin film plastic scintillator immersed in the second tank around a first shaft which is arranged on the second tank and is rotated by a motor; storing and sealing the thin film plastic scintillator spirally wound around the first shaft in a container permeating fluorescence; and multiplying the fluorescence emitted from the thin film plastic scintillator, and detecting concentration of a radioactive substance contained in the inspected liquid.SELECTED DRAWING: Figure 4A

Description

[Technical field]

[0001] The present disclosure relates to radiation detection methods and scintillator devices. [Background technology]

[0002] There has been growing interest in tritiated water contained in treated water from the Fukushima Daiichi Nuclear Power Plant, which suffered a meltdown due to the Great East Japan Earthquake. As a method for detecting the tritium concentration of tritiated water contained in treated water, various methods using plastic scintillators (hereinafter referred to as "Plasticin") have been proposed (see Patent Document 1, Patent Document 2, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 08-75863 [Patent Document 2] JP 2005-91334 A [Non-patent literature]

[0004] [Non-Patent Document 1] "Characteristics of "Ready Cap" solid scintillator for liquid scintillation counter measurements" RADIOISOTOPES, 39, 400-403 (1990) [Non-Patent Document 2] "Discrimination of C-14 and S-35 using plastic scintillators in liquid scintillation counters", Etsuko Furuta, Shigeaki Yokota, Hiroo Watanabe, Journal of the Japanese Society for Radiation Safety Management, Vol. 8, No. 1, 51-58 (2009) [Non-Patent Document 3] "Effect of atmospheric pressure plasma treatment on plastic scintillators for beta ray measurement" Etsuko Furuta, Ryuichiro Oyama, Shigeaki Yokota, Toshiya Nakajo, Yuka Yamada, Hiroo Watanabe Received: 1 July 2013 / Published online: 21 September 2013 Akademiai Kiado, Budapest, Hungary 2013 Summary of the Invention [Problem to be solved by the invention]

[0005] Plasin is a solid scintillator (hereinafter sometimes referred to as solid scintillator) made by dissolving phosphors in organic solvents such as styrene and polymerizing them. Plasin has the property of emitting fluorescence when exposed to radiation such as alpha rays, beta rays, or gamma rays. Plasin can perform optimal radiation measurements according to the type of radiation to be detected by adjusting the thickness according to the type of radiation.

[0006] Among beta rays, tritium (hydrogen tritium) and carbon-14, which have weak radiation energy, are called soft beta rays. In particular, tritium has an extremely low average radiation energy of 5.7 KeV, so the range of the beta rays it emits in water is about 5 μm. Water molecules in which at least one of the two hydrogen atoms in a water molecule has been replaced with a tritium atom are called tritiated water. When measuring the radiation concentration of a test liquid containing tritiated water using solid plasticine, the plasticine must be in close contact with the test liquid, and if the test liquid is not in close contact with the plasticine, high-precision radiation measurements cannot be performed.

[0007] Various radiation detection methods using solid plastic have been proposed. For example, Patent Document 1 proposes a method of flowing the test liquid into the gaps of a cylindrical or polygonal tubular plastic, a method of filling a container with many plastic spheres and flowing the test liquid into the gaps between them, and a method of filling a container with plastic fibers and flowing the test liquid into the gaps between them, with the aim of increasing the contact area between the test liquid containing tritium water and the plastic.

[0008] However, the radiation detection method of Patent Document 1 has the problem that the contact area of ​​the test liquid that comes into contact with the plasticine is small because the plasticine is water-repellent, and the tiny air bubbles generated by the water-repellent nature of the plasticine repel the test liquid, making the contact area even smaller.

[0009] For example, in the case of a method in which a large number of plastic spheres are packed into a container and the test liquid containing tritium water is poured into the gaps between them, the contact area can be increased by making the plastic spheres smaller. However, this means that the tiny air bubbles are more likely to repel the test liquid, so in reality, making the plastic spheres smaller does not increase the detection sensitivity.

[0010] Furthermore, when the number of micro air bubbles increases, the weak fluorescence generated by the plascin in the tritiated water is scattered by the micro air bubbles, and the number of times the light is refracted increases dramatically. This causes the test liquid containing tritiated water to become cloudy, reducing the amount of light that reaches the photomultiplier tube (hereinafter sometimes referred to as the photomultiplier), and lowering the detection sensitivity.

[0011] Furthermore, Patent Document 2 proposes a radiation detection method in which collected tritium is used as a carrier gas, and the carrier gas is made to emit light in a film-like scintillator disposed on the outer peripheral surface of an acrylic plate.

[0012] However, in the radiation detection method of Patent Document 2, for example, it is necessary to attach a film scintillator to the outer periphery of an acrylic plate, and even if the diameter of the outer periphery of the acrylic plate is increased to increase the area, the contact area cannot be increased with just one film scintillator. Also, a process of gasifying the test liquid containing tritiated water is required, which complicates the process.

[0013] Beckman sells the "Ready Cap" (product name) which uses a solid cinch (see Non-Patent Document 1). The "Ready Cap" has a solid cinch attached to a plastic disk with a diameter of 14 mm, and can hold 20 milliliters (cm 3 ) is inserted into the bottom of a vial to detect tritium water radiation.

[0014] However, the amount of the test liquid containing tritium water that is dropped onto a solid scintimeter with a diameter of 14 mm in the method of Non-Patent Document 1 is only 50 microliters (mm 3 The conventional measurement method is to add 5 to 10 milliliters (cm 3 ), the amount of water to be measured is less than 1 / 100, and the fluorescence is weaker and the photomultiplier measurement count is lower. This makes it unsuitable for measuring radiation in test liquids containing low-concentration tritium water, for example, at the Japanese regulatory value of 60,000 becquerels (Bq) / liter, or the operational target of 1,500 becquerels (Bq) / liter at the Fukushima Daiichi Nuclear Power Plant.

[0015] In Non-Patent Document 2, 20 microliters (mm 3 ) of tritiated water is sandwiched between two pieces of test liquid containing tritiated water, and the radiation of the tritiated water is measured. However, even with the radiation detection method in Non-Patent Document 2, the amount of test liquid containing tritiated water to be measured is 20 microliters (mm 3 ), and it is difficult to increase the amount of water beyond that. As in Non-Patent Document 1, Plasin is water repellent, so the contact area between Plasin and the test liquid cannot be increased, and the fluorescence measurement count is low, making it unsuitable for radiation measurement of test liquids containing low-concentration tritium water, for example, the Japanese regulatory value of 60,000 becquerels (Bq) / liter, or the operational target of 1,500 becquerels (Bq) / liter at the Fukushima Daiichi Nuclear Power Plant.

[0016] In addition, Non-Patent Document 3 proposes a technology to improve detection sensitivity by hydrophilizing the surface of Plasin through plasma treatment. Non-Patent Document 3 discloses that, in order to prevent hydrophilic degradation that occurs over time after the surface of Plasin is plasma-treated using argon gas, Plasin can be frozen and stored, allowing it to be reused for about a week. However, with the method of Non-Patent Document 3, it is difficult to suppress the hydrophilic degradation over a long period of time, such as several months or more. In particular, it is difficult to suppress the hydrophilic degradation when exposed to air at room temperature. Non-Patent Document 3 also mentions the use of other gases such as He, N2, O2, air, or a mixture of these gases, but the problem of long-term suppression of the hydrophilic degradation phenomenon has not been solved even when the type of gas is changed in various ways. In addition, the detection limit of Non-Patent Document 3 is 0.31 becquerels (Bq) / 20 microliters (mm 3 ), i.e. 15,500 becquerels / liter, and is not suitable for test liquids containing low-concentration tritium water of around 1,500 becquerels / liter.

[0017] In addition to solid plasticine, a method of detecting radiation from low-concentration tritium water using an emulsified scintillator liquid is also known. In this type of radiation detection method, a sample containing a mixture of tritium water and emulsified scintillator liquid in a vial is measured using a liquid scintillator device (hereinafter referred to as liquid scintillator device). In this measurement method, the amount of water to be measured is 5 to 10 milliliters (cm 3 ), and the detection efficiency is about 30%. It is known that the detection sensitivity (measured water volume x detection efficiency) is about 100 times higher than that of conventional methods using solid plastics.

[0018] However, since the emulsified scintillator liquid is an organic solvent, when it is mixed with the liquid to be tested, it becomes "organic waste liquid containing radioactive materials." The organic waste liquid must be incinerated at high temperatures in an incineration facility capable of managing radioactive materials, or it must be stored in a special container and then handed over to the Radioisotope Association for disposal, which requires costs for equipment and management. In addition, samples that have been used for measurement once cannot be recycled, so they must be discarded, and unused emulsified scintillator liquid is required for the next sample measurement. This means that the cost of emulsified scintillator liquid is incurred every time a measurement is made.

[0019] In radiation detection methods using solid plascin, the disposal of measurement samples can be done more easily than with emulsion scintillator liquid. In addition, the solid plascin used for radiation detection can be reused, so it is less expensive than emulsion scintillator liquid. However, as mentioned above, radiation detection methods for low-concentration tritium water using solid plascin have an issue with detection sensitivity.

[0020] To detect the radiation of tritiated water, the fluorescence emitted by the plasin due to the beta rays emitted from tritium is measured at 10 6 A radiation measuring device is required that is equipped with an ultra-high sensitivity photomultiplier that multiplies the fluorescence to about the same level as the photomultiplier effect, and a coincidence counting circuit that can count the number of fluorescent lights by canceling out circuit noise, and that satisfies conditions such as a constant temperature and complete light blocking. In order to measure low-concentration tritium water with this type of radiation measuring device, a liquid synchrotron device or a device with performance equivalent to a liquid synchrotron device is essential, and it is very costly to assemble the radiation measuring equipment.

[0021] Therefore, the present disclosure provides a radiation detection method and a scintillator device that can detect weak radiation with high accuracy without incurring equipment costs. [Means for solving the problem]

[0022] In order to solve the above problems, according to the present disclosure, a method for measuring a temperature of a thin film plastic scintillator having pure water attached thereto is provided, comprising the steps of: immersing a thin film plastic scintillator having pure water attached thereto in a first tank containing a test liquid; a step of removing the thin film plastic scintillator immersed in the first tank from the first tank and removing at least a portion of the test liquid adhering to the thin film plastic scintillator; immersing the thin film plastic scintillator from which the test liquid has been removed in a second tank containing the test liquid; a step of spirally winding the thin film plastic scintillator immersed in the second tank around a first shaft disposed on the second tank and rotated by a motor; a step of enclosing the thin film plastic scintillator wound in a spiral shape around the first axis in a container that is transparent to fluorescence and sealing the same; and detecting a concentration of a radioactive substance contained in the test liquid by amplifying the fluorescence emitted from the thin film plastic scintillator. A method for detecting radiation is provided.

[0023] By attaching one end of the thin film plastic scintillator to the first shaft and rotating the first shaft using the motor, the other end of the thin film plastic scintillator may be immersed in the first tank and then pulled out of the first tank, and after at least a portion of the test liquid has been removed from the thin film plastic scintillator, it may be immersed in the second tank and then wound around the first shaft.

[0024] The first tank and the second tank are arranged along a moving direction of the thin film plastic scintillator, The thin-film plastic scintillator may be hung across a second axis positioned between the first tank and the second tank at a position higher than the liquid levels in the first tank and the second tank, thereby removing pure water adhering to the thin-film plastic scintillator and removing at least a portion of the test liquid.

[0025] The method further includes a step of modifying the two main surfaces of the thin film plastic scintillator to which the test liquid is attached by a plasma treatment, After the two main surfaces have been modified by the plasma treatment, the thin-film plastic scintillator may be immersed in the first tank.

[0026] The method further includes a step of forming an acrylic acid graft polymer on the two main surfaces after modifying the two main surfaces by the plasma treatment, After the step of forming the acrylic acid grafted polymer, the thin film plastic scintillator may be immersed in the first bath.

[0027] removing the thin-film plastic scintillator from the container after detecting the concentration of the radioactive material, and immersing the thin-film plastic scintillator in the first tank containing pure water; a step of removing the thin film plastic scintillator immersed in the first tank from the first tank and removing the test liquid adhering to the thin film plastic scintillator together with at least a portion of the pure water; immersing the thin film plastic scintillator from which the test liquid has been removed in a second tank containing pure water; a step of spirally winding the thin film plastic scintillator immersed in the second tank around the first shaft by the motor; The method may further include a step of housing and sealing the thin film plastic scintillator spirally wound around the first axis in the container.

[0028] The thin film plastic scintillator may have a thickness of 50 μm or less.

[0029] The thin film plastic scintillator may have a longitudinal dimension of 2 m or more.

[0030] According to the present disclosure, a thin film plastic scintillator is wound in two or more layers in a spiral shape around an axis; a specular reflector disposed on one end side in a short direction of the thin-film plastic scintillator wound in two or more layers; a diffuse reflection plate disposed on the other end side of the thin film plastic scintillator wound in two or more layers in the short direction; the thin-film plastic scintillator, the specular reflector, and a container for housing the specular reflector; A graft polymer is disposed on two main surfaces of the thin film plastic scintillator, the graft polymer increasing the contact area between the thin film plastic scintillator and the test liquid, Two adjacent layers in the radial direction of the thin film plastic scintillator are disposed in close contact with each other with a test liquid layer of 10 μm or less therebetween. A scintillator device is provided. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 illustrates a scintillator device according to an embodiment of the present disclosure. [Diagram 2] FIG. 1 is a diagram illustrating a structure of a measurement sample according to an embodiment of the present disclosure. [Diagram 3] FIG. 1 is a cross-sectional view illustrating a scintillator device according to a comparative example. [Figure 4A] FIG. 2 is a top view of a plastic wrapper according to an embodiment of the present disclosure. [Figure 4B] FIG. 2 is a side view of a plastic winding machine according to an embodiment of the present disclosure. [Figure 4C] FIG. 2 is a front view of a plastic winding machine according to an embodiment of the present disclosure. [Diagram 5] FIG. [Figure 6A] FIG. 2 illustrates a first example of a plasma treatment process according to an embodiment of the present disclosure. [Figure 6B] FIG. 4 illustrates a second example of a plasma treatment process according to an embodiment of the present disclosure. [Figure 7A] FIG. 2 is a diagram showing a contact state between a thin film plastic and a test liquid before plasma irradiation. [Figure 7B] FIG. 13 is a schematic diagram showing a contact state between a thin film plastic and a test liquid after plasma irradiation. [Figure 8A] FIG. 2 shows the structural formula of vinyltoluene. [Figure 8B] FIG. 1 shows the structural formula of polyvinyl toluene. [Figure 8C]FIG. 1 is a diagram showing the structural formula of an acrylic acid graft polymer. [Figure 9A] FIG. 2 shows polymer chains produced by a first example of a plasma treatment process. [Figure 9B] FIG. 13 shows polymer chains produced by a second example of a plasma treatment process. [Figure 10A] FIG. 13 is a diagram showing the spreading of water droplets before plasma treatment. [Figure 10B] FIG. 13 is a diagram showing the spreading of water droplets after plasma treatment. [Figure 11] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Hereinafter, an embodiment of a radiation detection method and a scintillator device will be described with reference to the drawings. The following description will focus on the main components of the radiation detection method and the scintillator device, but the radiation detection method and the scintillator device may include components and functions that are not shown or described. The following description does not exclude components and functions that are not shown or described.

[0033] (Embodiments of the present disclosure) Fig. 1 is a diagram showing a scintillator device 1 according to an embodiment of the present disclosure. A measurement sample 1b in Fig. 1 includes a container 1a, a measurement sample 1b, and light reflectors 3a and 3b. The scintillator device 1 is used to measure the concentration of a radioactive substance contained in a test liquid. The test liquid in this embodiment is a mixture of pure water and low-concentration tritium water, and in this specification, the test liquid may be simply referred to as "water".

[0034] The container 1a is, for example, a vial for existing liquid scintillation measurement. The container 1a contains a measurement sample 1b and light reflectors 3a and 3b. The container 1a can transmit the fluorescence generated by the measurement sample 1b.

[0035] The measurement sample 1b is constructed by winding two or more layers of thin film plastic 2 in a spiral shape around an axis. When the scintillator device 1 is shipped, pure water is attached to the thin film plastic 2, and when the test liquid is measured, the test liquid is attached to the thin film plastic 2. After radiation measurement, the thin film plastic 2 is washed with pure water and the pure water is attached to it. This allows the scintillator device 1 to be used for multiple radiation measurements. Note that the state in which pure water is attached to the thin film plastic 2 at the time of shipment and after washing is sometimes referred to as the BG (Background) state in this specification.

[0036] The thin film plastic 2 in the BG state is prevented from drying by being immersed in pure water. If the thin film plastic 2 were rolled up and stored in the container 1a without being immersed in pure water, there would be a risk of the layers of the thin film plastic 2 (hereinafter referred to as plastic layers) adjacent in the radial direction sticking to each other. In this embodiment, as described above, the thin film plastic 2 is spirally wound around an axis with pure water adhering to the front and back sides and stored in the container 1a, so there is no risk of the plastic layers sticking to each other and hydrophilicity can be maintained for a long period of time. Maintenance of hydrophilicity will be described in detail later.

[0037] The light reflectors 3a and 3b are disposed at the upper and lower ends of the measurement sample 1b. One of the light reflectors 3a and 3b (e.g., the one with the lid of the container 1a) is a specular reflector (e.g., a silver reflector) that specularly reflects the fluorescence generated in the thin film plasticine 2, and the other is a diffuse reflector that scatters the fluorescence. In the following, an example will be described in which the light reflector 3a is a specularly reflecting silver reflector and the light reflector 3b is a diffuse reflector.

[0038] The fluorescence that strikes the light reflector 3a is reflected by the light reflector 3a and travels downward to the measurement sample 1b. The fluorescence that strikes the light reflector 3b is scattered and passes through the side of the container 1a, making it easier to be incident on a photomultiplier (not shown in FIG. 1). In this way, by specularly reflecting the fluorescence with the light reflector 3a, the proportion of fluorescence that is not incident on the photomultiplier and remains inside the container 1a and is quenched can be reduced. Also, by scattering the fluorescence with the light reflector 3b, the fluorescence can be efficiently guided in the direction of the photomultiplier.

[0039] In this specification, an example will be described in which the concentration of tritiated water contained in a test liquid is measured using the scintillator device 1. As described above, tritiated water (HTO) is a molecule in which one or both of the two hydrogens (H) in a water molecule (H2O) are replaced with a tritium atom (T). With the scintillator device 1, the tritium concentration of the test liquid can be measured by fluorescence emitted when beta rays emitted by tritium atoms in tritiated water contained in the measurement sample 1b hit the thin film plasticine 2.

[0040] In order to measure tritium concentration, it is important to increase the contact area between the thin film plasticine 2 in the container 1a and the test liquid, which contains tritiated water. In order to increase the contact area within the constraints of the dimensions of the container 1a, it is desirable to reduce the thickness of both the thin film plasticine 2 and the test liquid so that a thin film plasticine 2 with as large an area as possible can be accommodated in the container 1a with a limited diameter. The larger the area of ​​the thin film plasticine 2, the greater the amount of fluorescent light can be, and the greater the detection sensitivity of beta rays can be.

[0041] Tritium is a beta ray with an extremely low average energy of 5.7 KeV. Because of this, it is blocked by the water and does not propagate through the water, and often does not reach the solid membrane Plasin 2.

[0042] FIG. 2 is a cross-sectional view showing a schematic structure of the measurement sample 1b according to the embodiment of the present disclosure. The vertical direction of FIG. 2 indicates the radial direction of the measurement sample 1b (thin film plasticine 2). The measurement sample 1b has a plurality of plasticine layers of the thin film plasticine 2 having a thickness of, for example, 20 μm in the radial direction. Two radially adjacent plasticine layers of the thin film plasticine 2 are arranged in close contact with each other, sandwiching a layer of the test liquid 20. The layer thickness of the test liquid 20 containing tritiated water is set to 10 μm or less, more preferably about 5 μm, in accordance with the underwater range of beta rays emitted from the tritium atoms 31. Most of the beta rays emitted from the tritium atoms 31 contained in the layer of the test liquid 20 having a thickness of about 5 μm can reach the plasticine layer without being lost inside the test liquid 20.

[0043] 3 is a cross-sectional view that shows a schematic diagram of a scintillator device 100 according to a comparative example. The scintillator device 100 according to the comparative example has a layer of test liquid 20 containing tritiated water, about 1 mm thick, that is attached to the surface of a thin film plastic 2.

[0044] In the test liquid 20 in Fig. 3, beta rays emitted from tritium atoms 31 contained in the test liquid 20 within a distance of 5 µm from the thin film plasticine 2 penetrate the thin film plasticine 2, as in Fig. 2. Therefore, the thin film plasticine 2 in one comparative example can detect tritium in the test liquid 20 within a distance of 5 µm from the thin film plasticine 2, in the test liquid 20 having a thickness of 1 mm, as in Fig. 2.

[0045] On the other hand, beta rays emitted from tritium atoms 31 in the test liquid 20 that are more than 5 μm away from the thin film Plasin 2 are blocked by water, which is the solvent of the test liquid 20, and do not reach the thin film Plasin 2. For this reason, the thin film Plasin 2 cannot detect tritium located more than 5 μm away.

[0046] The contact area with the test liquid is 100cm 2 If the test liquid 20 containing tritium water is applied to the thin film plastic 2 with a thickness of 1 mm, the total volume of the test liquid 20 is 10 milliliters (cm 3) of which the water is 5 μm thick, 0.05 ml (cm 3 ) contributes to the emission of light in the thin film plasticine 2, while the remaining 9.95 ml (cm 3 ) does not contribute to the emission of light. The concentration of tritiated water contained in the test liquid 20 does not depend on the thickness of the layer of the test liquid 20, but as shown in FIG. 2, beta rays emitted from tritium atoms of tritiated water contained in a thin layer of the test liquid 20 tend to penetrate into either of the two plasticine layers arranged above and below. On the other hand, when the layer of the test liquid 20 is thick as in one comparative example, the beta rays emitted from the tritium atoms of the tritiated water contained in the test liquid 20 tend to disappear inside the test liquid 20, and the rate at which the beta rays reach either of the two plasticine layers sandwiching the layer of the test liquid 20 becomes lower than when the layer is 5 μm thick, and the detection efficiency of tritium cannot be improved. In addition, the thicker the layer of the test liquid 20, the shorter the total length of the thin film plasticine 2 that can be wound in a spiral shape around the axis and stored in the container 1a becomes. In other words, the thicker the layer of the test liquid 20, the smaller the area of ​​the thin film plasticine 2 that comes into contact with the test liquid 20, and the amount of fluorescent light decreases, resulting in a decrease in the detection sensitivity of radiation.

[0047] Therefore, in the scintillator device 1 of this embodiment, as shown in Figure 2, a structure is adopted in which the layer of the test liquid 20 containing tritium water is set to a thickness of approximately 5 μm, and thin film plastic 2 is spirally wound around an axis, thereby sandwiching the layer of the test liquid 20 between two plastic layers.

[0048] The thickness of the thin film plastic 2 is set to at least 50 μm or less due to the constraint of placing the measurement sample 1b in the container 1a, and is preferably about 20 μm.

[0049] Generally, commercially available plasticine has a thickness of about 100 μm. When applying heat and pressure to thin a 100 μm-thick plasticine, problems such as cracking during processing, performance degradation due to heating, and clouding may occur. For this reason, when manufacturing the thin-film plasticine 2 of the present disclosure, it is preferable to process the plasticine raw material, which is a mixture of liquid and powdered materials, directly to a thickness of 20 to 50 μm.

[0050] In measuring the concentration of tritium water contained in the test liquid 20, other than the thickness of the thin film plasticine 2 and the thickness of the test liquid 20, there is an issue of minute air bubbles adhering to the thin film plasticine 2. When minute air bubbles adhere to the surface of the thin film plasticine 2, the contact area between the thin film plasticine 2 and the test liquid 20 decreases, decreasing the measurement efficiency. In addition, the minute air bubbles scatter the fluorescence, decreasing the amount of fluorescent light incident on the photomultiplier, which will be described later, and leading to a decrease in the radiation detection sensitivity.

[0051] In the radiation detection method according to the embodiment of the present disclosure, the adhesion of micro air bubbles is prevented by the following two methods (hereinafter, the first method and the second method). In the first method, as described below, the torque of the motor is adjusted to wind the thin film plastic 2 to which the test liquid is attached in a spiral shape around the shaft, thereby making the layer of the test liquid 20 adhere closely to the two plastic layers of the thin film plastic 2 while expelling the micro air bubbles.

[0052] The second technique involves modifying the front and back surfaces of the thin-film plasticine 2. Since plasticine is inherently water-repellent, the test liquid 20 containing tritium water is repelled by the plasticine, which may result in micro air bubbles being mixed into the layer of the test liquid 20. Therefore, in the second technique, the front and back surfaces of the thin-film plasticine 2 are modified from water-repellent to hydrophilic. In this specification, the front and back surfaces of the thin-film plasticine 2 may each be referred to as the main surface.

[0053] First, the above-mentioned first method will be specifically described. Fig. 4A to Fig. 4C are diagrams showing the main parts of a radiation detection device according to an embodiment of the present disclosure. Fig. 4A to Fig. 4C show the configuration of an apparatus 4 for producing a scintillator device 1 used in the radiation detection device. Hereinafter, the apparatus 4 may be referred to as a plastic winding machine 4.

[0054] The plastic film winding machine 4 is a device that winds the thin film plastic film 2 having the test liquid 20 attached thereto around a receiving shaft 8a. Fig. 4A is a top view of the plastic film winding machine 4. Fig. 4B is a side view of the plastic film winding machine 4. Fig. 4C is a front view of the plastic film winding machine 4.

[0055] The plastic sheet winding machine 4 is equipped with a motor 5, plastic sheet attachment / detachment devices 6a, 6b, a plastic sheet feed section 7, a plastic sheet receiving section 8, a receiving shaft (first shaft) 8a, a feed shaft 9, tank A (first tank) 10, tank B (second tank) 11, and a tank switching water squeezing shaft (second shaft) 12.

[0056] A test liquid 20 containing tritium water is placed in the A tank 10 and the B tank 11. The A tank 10 and the B tank 11 are arranged in this order along the moving direction of the thin film plastic 2.

[0057] The measurement specimen 1b, to which the pure water stored in the container 1a is attached, is removed from the container 1a. When the operator pulls the plastic attacher 6a, the distance between the two plastic feeders 7 arranged on both sides of the short side of the A tank 10 increases. In this state, the operator rotatably attaches both ends of the shaft of the measurement specimen 1b to the two plastic feeders 7, returns the plastic attacher 6a to its original position, and fixes the measurement specimen 1b so that it can rotate freely. Next, when the operator pulls one end of the thin film plastic 2 wound around the shaft of the measurement specimen 1b, the shaft of the measurement specimen 1b rotates, and the thin film plastic 2 is pulled out and immersed in the A tank 10.

[0058] In tank A 10 and tank B 11, multiple feed shafts 9 are arranged along the movement direction of the thin film plastic 2. In the example of Fig. 4A, two feed shafts 9 are arranged in each of tank A 10 and tank B 11. In addition, a tank switching water throttle shaft 12 is arranged between tank A 10 and tank B 11. Tank switching water throttle shaft 12 is arranged at a position higher than the liquid levels of the test liquids contained in tank A 10 and tank B 11.

[0059] As shown in FIG. 4B, the thin film plasticine 2 is pulled out by an operator from the measurement sample 1b attached to the plasticine feeder 7 and immersed in the A tank 10, and is guided by two feed shafts 9 provided in the A tank 10. When one end of the thin film plasticine 2 reaches the end of the A tank 10 on the B tank 11 side, the operator pulls up one end of the thin film plasticine 2, places it over the tank switching water squeeze shaft 12, and then immerses it in the B tank 11. The tank switching water squeeze shaft 12 is disposed above a threshold plate 13 disposed between the A tank 10 and the B tank 11. The tank switching water squeeze shaft 12 removes the test liquid and pure water attached to the front and back surfaces of the thin film plasticine 2 pulled out from the A tank 10. Before being immersed in the A tank 10, the thin film plasticine 2 is immersed in pure water inside the container 1a. When the thin film plasticine 2 is removed from the container 1a and immersed in the A tank 10, a mixture of pure water and the liquid to be inspected adheres to the thin film plasticine 2, and the proportion of tritium water is smaller than if only the liquid to be inspected adheres to the thin film plasticine 2. Therefore, by hanging the thin film plasticine 2 pulled out of the A tank 10 over the tank switching water throttle shaft 12, the pure water attached to the thin film plasticine 2 is removed together with the liquid to be inspected. In other words, by hanging the thin film plasticine 2 over the tank switching water throttle shaft 12, the pure water attached to the thin film plasticine 2 can be completely removed.

[0060] The operator pulls one end of the thin film plasticine 2 immersed in the B tank 11. As a result, the thin film plasticine 2 is guided by two feed shafts 9 provided in the B tank 11. The operator fixes one end of the thin film plasticine 2 to the receiving shaft 8a that is attached in advance to the plasticine receiving part 8 in the short direction of the B tank 11. The fixing can be performed with adhesive tape or the like. The receiving shaft 8a is made rotatable together with the rotating shaft of the motor 5. When the operator operates the motor 5, the receiving shaft 8a rotates with a predetermined torque, and the thin film plasticine 2 is wound in a spiral shape around the receiving shaft 8a. Since a predetermined torque is applied to the thin film plasticine 2 while the thin film plasticine 2 is wound around the receiving shaft 8a, the thin film plasticine 2 is wound in a spiral shape while expelling micro air bubbles contained in the test liquid 20 attached to the thin film plasticine 2, and a measurement sample 1b is produced in which a layer of the test liquid 20 of about 5 μm is arranged between two radially adjacent plasticine layers. When the operator pulls the plastic inserter 6b, the distance between the two plastic receiving sections 8 arranged on both sides of the short side of the B tank 11 increases, allowing the measurement sample 1b to be removed.

[0061] As described above, by hanging the thin film plasticine 2 on the tank switching water restricting shaft 12, the pure water that was attached to the thin film plasticine 2 while it was stored in the container 1a is completely removed, so that the test liquid 20 that is attached to the thin film plasticine 2 wrapped around the receiving shaft 8a contains tritium water of the same concentration as the original test liquid.

[0062] As a comparative example, when preparing a measurement sample by stacking multiple thin film plastics 2 to which a test liquid containing tritium water is attached, it is not easy to expel the micro air bubbles contained in the layer of the test liquid between two adjacent thin film plastics 2 in the layer direction, and the fluorescence emitted by the thin film plastics 2 is scattered by the micro air bubbles, which may reduce the amount of fluorescent light incident on the photomultiplier. Also, in the comparative example, multiple thin film plastics must be prepared and stacked in the layer direction while aligning them, which requires a lot of effort to prepare the measurement sample compared to the method of wrapping a single thin film plastic around the receiving shaft 8a as in this embodiment, and additional material costs are required for preparing multiple thin film plastics.

[0063] In this embodiment, the length of the thin film plastic 2 is, for example, 4 cm wide by 200 cm (2 m) long, and the thickness is 50 μm or less, as in FIG. 2, and more desirably 20 μm. The shaft (receiving shaft 8a) around which the thin film plastic 2 is wound can be, for example, an acrylic rod with a diameter of about 6 mm. When the thin film plastic 2 is spirally wound around the receiving shaft 8a by the plastic winding machine 4 with the test liquid 20 containing tritium water with a thickness of 5 μm adhered thereto, a measurement sample 1b with a diameter of about 15 mm is produced. This measurement sample 1b is a 20 milliliter (cm) container with a typical aperture of 16 mm and a height of 5 cm. 3 ) vial. Therefore, in this embodiment, a vial for liquid scintillation measurement can be used as the container 1a for storing the measurement sample 1b. 3 The length of the thin film plastic 2 may be 2 m or more as long as it can be stored in a vial for use in a liquid storage device.

[0064] The area of ​​the thin film plastic 2 is 4cm wide x 200cm long = 800cm 2 In addition, the plastic winding machine 4 can apply the test liquid 20 containing tritium water to both the front and back surfaces of the thin film plastic 2. Therefore, the contact area of ​​the thin film plastic 2 with the test liquid 20 is a maximum of 800 cm. 2 ×2=1,600cm 2The amount of the test liquid 20 to be measured can be increased to 800 cm 2 × 5μm = 4 milliliters (cm 3 As described above, in the plastic winding machine 4, the contact area of ​​the test liquid 20 and the amount of water to be measured can be significantly improved as compared with the conventional radiation detection method using a solid plastic, and the radiation detection sensitivity can be improved.

[0065] When a vial for liquid scintillation measurement is used as the container 1a, vials of various sizes can be used. For example, the above-mentioned 20 milliliter (cm 3 ) with a diameter larger than 100 milliliters (cm 3 ) or 160 milliliters (cm 3 ) the measurement sample 1b can be stored in a vial with an aperture of 1 mm, allowing the use of a thin film plasticine 2 with a larger surface area. As described above, the larger the surface area of ​​the thin film plasticine 2, the larger the contact area with the test liquid 20 can be, and the greater the amount of fluorescent light can be, leading to a further improvement in the detection sensitivity of radiation.

[0066] The thickness of the test liquid 20 adhering to the thin film plasticine 2 can be adjusted by the torque of the motor 5 when winding the thin film plasticine 2 around the receiving shaft 8a. The larger the torque of the motor 5, the thinner the layer of the test liquid 20 between two radially adjacent plasticine layers can be. The torque of the motor 5 is adjusted so that the layer of the test liquid 20 is 10 μm or less, preferably about 5 μm, which is the range of tritium in water.

[0067] By measuring the weight of the measurement sample 1b after the thin film plasticine 2 is wrapped around the receiving shaft 8a, the weight of the test liquid 20 containing tritium water attached to the thin film plasticine 2 can be grasped. For example, when the area of ​​the thin film plasticine 2 is 800 cm 2 If the weight of the measurement sample 1b after wrapping increases by 4 g, the amount of tritiated water contained in the measurement sample 1b is 4 milliliters (cm 3 ), which shows that the thickness of the tritium water was adjusted to 5 μm.

[0068] Next, a method for modifying the front and back surfaces of the thin film plastic 2 from water repellency to hydrophilicity will be described. The radiation detection method according to an embodiment of the present disclosure includes a step of modifying the thin film plastic 2 by plasma treatment (hereinafter, plasma treatment step).

[0069] FIG. 5 is a diagram explaining plasma. As shown in FIG. 5, plasma refers to a gas in which electrons and ions move freely when energy is applied to the gas. When oxygen is made into plasma, it changes into active oxygen species including oxygen radicals (superoxide and hydroxyl radicals). In the plasma treatment process, the thin film plasticine 2 is irradiated with these superoxide and hydroxyl radicals to make the thin film plasticine 2 hydrophilic.

[0070] When the plasma treatment process is performed, some of the polymer bonds on the front and back surfaces of the thin film PLASIN 2 are cut and bonded with the generated oxygen radicals (superoxide and hydroxyl radicals), introducing polar functional groups such as hydroxyl groups or carbonyl groups. In this way, the plasma treatment process can perform surface modification that changes the material properties of only the front and back surfaces of the thin film PLASIN 2 while maintaining the physical properties of the thin film PLASIN 2 as a whole.

[0071] 2, in the scintillator device 1 according to this embodiment, it is necessary to attach the test liquid 20 to the front and back surfaces of the thin film plastic 2. For this reason, in the plasma treatment step, a surface modification treatment is performed on both the front and back surfaces of the thin film plastic 2. Hereinafter, the front and back surfaces of the thin film plastic 2 may be collectively referred to as the surface of the thin film plastic 2.

[0072] 6A is a diagram showing a first example of a plasma treatment process according to an embodiment of the present disclosure. In the first example of the plasma treatment process, plasma irradiation is performed in, for example, a CH4 gas + H2O gas environment. As a result, as shown in FIG. 6A, fine crater-like holes are formed on the surface of the thin film plastic 2.

[0073] FIG. 7A is a diagram showing a contact state between the thin film plasticine 2a and the test liquid 20 before plasma irradiation. As described above, the thin film plasticine 2a itself has water repellency. As shown in FIG. 7A, when a drop of the test liquid 20 is dropped onto the water repellent thin film plasticine 2a, the thin film plasticine 2a rises up in a round shape due to surface tension, and the contact area with the thin film plasticine 2a becomes small. Therefore, the thin film plasticine 2a cannot sufficiently contact the test liquid 20, and the test liquid 20 is likely to contain micro air bubbles. In addition, as the test liquid 20 rises up, the thickness of the test liquid 20 exceeds 5 μm, and some of the tritium cannot be detected as in FIG. 3.

[0074] FIG. 7B is a diagram showing a contact state between the thin film plasticine 2b and the test liquid 20 after plasma irradiation. The surface of the thin film plasticine 2b is modified to be hydrophilic by plasma irradiation. When a drop of the test liquid 20 is dropped on the hydrophilic thin film plasticine 2b, it does not rise up but becomes wet. As a result, the thin film plasticine 2b can eliminate micro air bubbles more effectively than the thin film plasticine 2a, and the thickness of the test liquid 20 can be reduced, so that the thin film plasticine 2 can be tightly wound around the receiving shaft 8a, and the area of ​​the thin film plasticine 2 that comes into contact with the test liquid 20 can be increased, thereby improving the detection sensitivity of tritium.

[0075] As described above, the thin film plasticine 2 can be made hydrophilic by the method of Fig. 6A. However, the hydrophilicity of the thin film plasticine 2 deteriorates over time when exposed to air at room temperature, and there is a risk that it will return to its original water repellency.

[0076] It is known that the deterioration of hydrophilicity of thin film Plasin 2 can be suppressed for about one week by storing it frozen. However, from the viewpoint of ease of use of thin film Plasin 2, it is desirable that the hydrophilicity can be maintained stably for a long period of time at room temperature.

[0077] Therefore, in this embodiment, a plasma-initiated graft polymerization method is adopted as a second example of the plasma treatment process. Specifically, the thin film plasticine 2 is brought into contact with low-temperature glow discharge generated under reduced pressure for a certain period of time. More precisely, the thin film plasticine 2 is brought into contact with plasma gas generated by the low-temperature glow discharge. As a result, radical sites having reactive activity are formed on the surface of the thin film plasticine 2.

[0078] In order not to deactivate the radicals formed on the surface of the thin film plasticine 2, various monomer vapors having polar groups are rapidly introduced into the reaction vessel under reduced pressure. This allows graft polymers to be synthesized on the surface of the thin film plasticine 2 in post-polymerization.

[0079] A graft polymer is a so-called graft, which is a polymer chain bonded to another polymer chain. In the graft polymer method, active sites are formed on the polymer chain by plasma irradiation, and the polymerization of another monomer is initiated from these active sites to synthesize the graft polymer. There are also other methods for forming active sites on the polymer chain, such as using a catalyst.

[0080] 6B is a diagram showing a second example of the plasma treatment process according to an embodiment of the present disclosure. In the second example of the plasma treatment process, first, plasma irradiation similar to that in FIG. 6A is performed, and then nano-level acrylic acid particles are added to the thin film plastic 2. As a result, acrylic acid graft polymer 32 is grafted onto the surface of the thin film plastic 2.

[0081] The graft polymer method according to the embodiment of the present disclosure will be described below from a chemical aspect. The thin film plastic 2 according to the embodiment of the present disclosure uses polyvinyltoluene 33, which is obtained by polymerizing vinyltoluene, as a base material. FIG. 8A shows the structural formula of vinyltoluene. FIG. 8B shows the structural formula of polyvinyltoluene 33. Polyvinyltoluene 33 is a C9H 10 It has a structure in which n units (monomers) are linked together in a chain (also called the main chain).

[0082] In the graft polymer method, an acrylic acid graft polymer 32 is synthesized on polyvinyl toluene 33. FIG.

[0083] Fig. 9A is a schematic diagram showing polymer chains generated by a first example of the plasma treatment process. As shown in Fig. 9A, by plasma irradiation, oxygen-containing polar groups 34 such as carbonyl groups are newly introduced into the main chain of polyvinyl toluene 33 on the surface of the thin film plasticine 2. Since these oxygen-containing polar groups 34 are hydrophilic, the surface of the thin film plasticine 2 is made hydrophilic.

[0084] When a new polar group is introduced into the main chain, new repulsion occurs between the main chains of adjacent polyvinyltoluene 33. The main chain of polyvinyltoluene 33 twists and rotates to minimize the repulsive energy, wrapping the oxygen-containing polar group 34 from the surface of polyvinyltoluene 33 to the inside, and achieving a new thermodynamic balance. As the oxygen-containing polar group 34 is wrapped inside polyvinyltoluene 33, hydrophilicity is lost from the surface of polyvinyltoluene 33, which is the base material of the thin film plastic 2.

[0085] Fig. 9B is a diagram showing polymer chains produced by a second example of the plasma treatment process. In Fig. 9B, an acrylic acid graft polymer 32 is introduced into the main chain of polyvinyl toluene 33 on the surface of the thin film plastic 2. The acrylic acid graft polymer 32 (hereinafter also referred to as a segment) has hydrophilicity, similar to the oxygen-containing polar group 34 in Fig. 9A.

[0086] The acrylic acid graft polymer 32 shown in FIG. 9B is larger in size than the oxygen-containing polar group 34 in FIG. 9A. The introduction of the acrylic acid graft polymer 32 disrupts the thermodynamic balance of the main chain of the polyvinyltoluene 33. This causes the main chain of the polyvinyltoluene 33 to twist and rotate, attempting to roll the segments into the interior of the polyvinyltoluene 33. However, the size of the segments is large enough that they cannot be physically rolled into the interior of the polyvinyltoluene 33. Therefore, the segments remain on the surface of the polyvinyltoluene 33. This makes it possible to prevent the hydrophilicity of the surface of the thin film plastic 2 from being lost over a long period of time.

[0087] As described above, in the second example of the plasma treatment process, it is possible to impart hydrophilicity to the surface of the thin film plastic 2 that is stable for a long period of time at room temperature, and it is also possible to impart semi-permanent hydrophilicity.

[0088] There are various conditions for the plasma irradiation method, and the degree of hydrophilicity of the thin film plasticine 2 changes depending on the conditions. For this reason, the inventor conducted experiments with multiple plasma irradiation methods. In the experiments on the plasma irradiation method conducted by the inventor, the thin film plasticine 2 was placed in a vacuum container, and various injected gases, including CH4, air, oxygen, water vapor, and a mixture of these gases, were used, and the output was changed to 30 W, 60 W, and 90 W, and the plasma irradiation time was changed to 1 minute, 2 minutes, 3 minutes, and 5 minutes.

[0089] In the inventor's experiments, an example of the plasma irradiation conditions that gave the best results is as follows.

[0090] Gas flowing into the vacuum chamber: CH4:H2O gas = 1:1 mixed gas, Mixed gas flow rate: 50 SCCM (Standard Cubic Centi-Meter), Pressure: 67Pa, Power: 60W, Processing time: 1 min.

[0091] The hydrophilicity of the thin film plasticine 2 is such that the thin film plasticine 2 is 25 μl (mm3 10A is a diagram showing the spread of a water droplet 20a before plasma treatment. In the thin-film plastic 2 before plasma treatment, the size of the water droplet 20a is 4.5 mm long × 4.5 mm wide ≈ 20 cm. 2 It became.

[0092] FIG. 10B is a diagram showing the spread of the water droplets 20a after the plasma treatment. In the thin film plastic 2 immediately after the plasma treatment, the size of the water droplets 20a is 12×12 mm≈140 cm 2 In addition, water droplets 20a were dropped on the first day, one week, two weeks, four weeks, and ten weeks after the plasma treatment, and the size of the water droplets was measured to confirm whether hydrophilicity was maintained. As a result, the same results as those in FIG. 10B were obtained even after ten weeks, and it was confirmed that hydrophilicity was maintained.

[0093] One of the factors that reduces the transparency of thin film plasticin 2 is the clouding of thin film plasticin 2 that occurs during manufacturing. Thin film plasticin 2 becomes cloudy due to subtle changes in conditions such as temperature control during the process of gradually changing from a monomer to a polymer over a period of several days. Also, in the manufacturing method of plasticin that thins the film to 20 μm, the scintillation liquid injected into the glass hardens, and the thin film plasticin 2 that has adhered to the glass is prone to becoming cloudy when removed. Therefore, the inventors have improved the factors that reduce transparency and are now able to manufacture a highly transparent film that is not cloudy. However, slight clouding can still occur, so it has been decided to select and use a highly transparent film.

[0094] The inventor took measures such as controlling the temperature during the manufacturing process of the thin film plastic 2 to prevent it from becoming cloudy and preventing dust from adhering to it. By improving the transparency of the thin film plastic 2, it becomes easier for fluorescence to pass through the thin film plastic 2.

[0095] In the embodiment of the present disclosure, a measurement sample 1b is prepared by attaching the test liquid 20 shown in Figures 4A to 4C to the thin film plasticine 2 whose surface has been modified by the first example of the plasma treatment process or the second example of the plasma treatment process, and wrapping the test liquid 20 around a receiving shaft 8a, and the measurement sample 1b is stored in a container 1a and sealed. Thereafter, the container 1a is attached to a liquid-sink device 40, and the concentration of tritium water contained in the test liquid 20 is measured.

[0096] 11 is a diagram showing a liquid synthesizer 40. The liquid synthesizer 40 in FIG.

[0097] The two photomultipliers 41 are arranged on either side of the container 1a of the scintillator device 1 in Fig. 1. These photomultipliers 41 amplify the fluorescence emitted from the thin film plastic 2 in the measurement sample 1b stored in the container 1a, and generate an electric pulse signal according to the amount of the amplified fluorescence. The electric pulse signal has an amplitude according to the amount of fluorescence, a pulse width according to the emission time of the fluorescence, and a pulse number according to the number of fluorescence.

[0098] The coincidence circuit 42 extracts an electric pulse signal commonly detected by the two photomultipliers 41. By providing the coincidence circuit 42, the noises of the two photomultipliers 41 can be cancelled out, making it possible to detect the true amount of fluorescence.

[0099] The liquid sink device 40 detects the concentration of radioactive materials (for example, tritium) in the test liquid 20 attached to the thin film plastic 2 based on the amount of fluorescence detected by the coincidence circuit 42.

[0100] As shown in FIG. 11, the scintillator device 1 according to this embodiment is capable of measuring radioactive substances using a conventional liquid scintillator device or the like.

[0101] After the measurement is completed by the liquid scintillator 40, the test liquid containing tritiated water in the scintillator device 1 is discarded as waste liquid. That is, the test liquid in the container 1a shown in FIG. 1 and the test liquid in the A tank 10 and the B tank 11 shown in FIG. 4A are discarded as waste liquid. The scintillator device 1 does not contain any organic solvent, but is merely water containing tritium. For this reason, it is possible to discard the waste liquid by storing it in a waste liquid tank and diluting it to a concentration that complies with the drainage standard. As described above, the radiation detection method according to the embodiment of the present disclosure makes it easy to discard the waste liquid.

[0102] Furthermore, the thin film plastic 2 of the scintillator device 1 can be reused by cleaning. The thin film plastic 2 can be cleaned using the plastic winding machine 4 shown in FIG. 4A etc. During cleaning, pure water is poured into tank A 10 and tank B 11. Furthermore, after the concentration of the radioactive material has been detected, the measurement sample 1b is removed from the container 1a and attached to the plastic feeder 7.

[0103] Thereafter, similar to the step of attaching the test liquid, the operator pulls out one end of the thin film plasticine 2 constituting the measurement sample 1b attached to the plasticine feeder 7 and immerses it in the pure water of the A tank 10. Then, the operator pulls up one end of the thin film plasticine 2 from the A tank 10 and hangs it over the tank switching water restricting shaft 12 to remove the test liquid and pure water attached to the thin film plasticine 2. This allows the test liquid attached to the thin film plasticine 2 to be completely removed. Then, the operator immerses one end of the thin film plasticine 2 in the B tank 11 and then fixes one end of the thin film plasticine 2 to the receiving shaft 8a. Then, by rotating the motor 5, the other end side of the thin film plasticine 2 is immersed in the A tank 10, and the test liquid is completely removed by the tank switching water restricting shaft 12, and then it is immersed in the B tank 11 and wound around the receiving shaft 8a. The thin film plasticine 2 (measurement sample 1b) spirally wound around the receiving shaft 8a is stored in the container 1a and sealed.

[0104] By the above operation, the test liquid 20 attached to the thin film plastic 2 in the scintillator device 1 can be decontaminated with pure water, and the measurement sample 1b can be brought into a BG state. As a result, in the radiation detection method according to the embodiment of the present disclosure, the scintillator device 1 can be used for repeated measurements. Note that the thin film plastic 2 may be cleaned by equipment and methods other than the plastic winding machine 4.

[0105] In the above-described embodiment, an example of detecting the concentration of tritium contained in the test liquid has been described, but the scintillator device 1 and radiation detection method according to the present disclosure are also applicable to the detection of various types of radiation, such as beta rays emitted from radioactive substances other than tritium, and alpha rays or gamma rays other than beta rays.

[0106] In this manner, in the scintillator device 1 and radiation detection method according to an embodiment of the present disclosure, the front and back surfaces are modified to be hydrophilic by plasma treatment, and graft polymers are synthesized on the front and back surfaces. This allows the hydrophilicity of the front and back surfaces of the thin-film plasticine 2 to be maintained for a long period of time. In the present scintillator device 1, the thin-film plasticine 2 is wound spirally around an axis with a test liquid containing tritium water attached to the front and back surfaces of a thin-film plasticine 50 μm or less that has been made hydrophilic, and the test liquid having a thickness of about 5 μm is placed between two radially adjacent plasticine layers. When winding the thin-film plasticine 2 around the axis, the torque of the motor 5 is appropriately adjusted to expel micro air bubbles from the test liquid, and the interval between the two plasticine layers can be set to about 5 μm. This allows the preparation of a measurement sample 1b in which the thin-film plasticine 2 has a sufficiently long longitudinal length while having a diameter size that can be stored in a container 1a such as a vial for liquid scintillation measurement of an existing size. The A tank 10 and the B tank 11 used for preparing the measurement sample 1b do not contain any organic solvent other than the test liquid 20, and therefore waste liquid can be easily disposed of.

[0107] After the radiation measurement of the measurement sample 1b in the liquid washing device 40 is completed, the measurement sample 1b is removed from the container 1a, and the same process as that of attaching the test liquid 20 to the thin film plastic 2 is repeated with pure water placed in the A tank 10 and the B tank 11 shown in FIG. 4A, whereby the test liquid can be completely removed from the thin film plastic 2, and the measurement sample 1b with the pure water attached thereto can be stored in the container 1a. This measurement sample 1b can be repeatedly reused for the radiation measurement of the next test liquid. Since the A tank 10 and the B tank 11 do not contain organic solvents during cleaning, waste liquid can be easily disposed of.

[0108] Thus, according to the scintillator device 1 and radiation detection device of the present embodiment, the test liquid can be attached to the front and back surfaces of the large-area thin-film plastic 2 with a thickness of about 5 μm without generating micro air bubbles, and can be stored in an existing vial for liquid scintillation measurement, so that highly accurate radiation measurement can be performed using an existing liquid scintillation device 40. Furthermore, the thin-film plastic used for radiation measurement can be washed and reused, and waste liquid during measurement and washing can be easily disposed of, so radiation measurement can be performed at low cost. The radiation detection method according to the embodiment of the present disclosure is particularly suitable for detecting low-concentration tritium water, etc.

[0109] The aspects of the present disclosure are not limited to the above-mentioned individual embodiments, but include various modifications that may be conceived by a person skilled in the art, and the effects of the present disclosure are not limited to the above-mentioned contents. In other words, the present disclosure allows various additions, modifications, and partial deletions within the scope of the conceptual idea and intent of the present disclosure derived from the contents defined in the claims and their equivalents.

[0110] The present disclosure can be summarized as follows. [Item 1] A step of immersing the thin film plastic scintillator with the pure water attached thereto in a first tank containing a liquid to be inspected; a step of removing the thin film plastic scintillator immersed in the first tank from the first tank and removing at least a portion of the test liquid adhering to the thin film plastic scintillator; immersing the thin film plastic scintillator from which the test liquid has been removed in a second tank containing the test liquid; a step of spirally winding the thin film plastic scintillator immersed in the second tank around a first shaft disposed on the second tank and rotated by a motor; a step of enclosing the thin film plastic scintillator wound in a spiral shape around the first axis in a container that is transparent to fluorescence and sealing the same; and detecting a concentration of a radioactive substance contained in the test liquid by amplifying the fluorescence emitted from the thin film plastic scintillator. Radiation detection methods. [Item 2] One end of the thin film plastic scintillator is attached to the first shaft and the first shaft is rotated by the motor, so that the other end of the thin film plastic scintillator is immersed in the first tank and then pulled out of the first tank, and after at least a portion of the test liquid is removed from the thin film plastic scintillator, the other end of the thin film plastic scintillator is immersed in the second tank and then wound around the first shaft. 2. The radiation detection method according to item 1. [Item 3] The first tank and the second tank are arranged along a moving direction of the thin film plastic scintillator, The thin film plastic scintillator is hung on a second axis disposed between the first tank and the second tank at a position higher than the liquid levels of the first tank and the second tank, and the pure water adhering to the thin film plastic scintillator is removed, and at least a part of the test liquid is removed. 3. The radiation detection method according to item 1 or 2. [Item 4] The method further includes a step of modifying the two main surfaces of the thin film plastic scintillator to which the test liquid is attached by a plasma treatment, After the two main surfaces are modified by the plasma treatment, the thin film plastic scintillator is immersed in the first tank. 4. A radiation detection method according to any one of items 1 to 3. [Item 5] The method further includes a step of forming an acrylic acid graft polymer on the two main surfaces after modifying the two main surfaces by the plasma treatment, After the step of forming the acrylic acid grafted polymer, the thin film plastic scintillator is immersed in the first bath. 5. The radiation detection method according to item 4. [Item 6] removing the thin-film plastic scintillator from the container after detecting the concentration of the radioactive material, and immersing the thin-film plastic scintillator in the first tank containing pure water; a step of removing the thin film plastic scintillator immersed in the first tank from the first tank and removing the test liquid adhering to the thin film plastic scintillator together with at least a portion of the pure water; immersing the thin film plastic scintillator from which the test liquid has been removed in a second tank containing pure water; a step of spirally winding the thin film plastic scintillator immersed in the second tank around the first shaft by the motor; and housing and sealing the thin film plastic scintillator spirally wound around the first axis in the container. 6. A radiation detection method according to any one of items 1 to 5. [Item 7] The thin film plastic scintillator has a thickness of 50 μm or less. 7. A radiation detection method according to any one of items 1 to 6. [Item 8] The thin film plastic scintillator has a longitudinal length of 2 m or more. 8. A radiation detection method according to any one of items 1 to 7. [Item 9] A thin film plastic scintillator wound in two or more layers in a spiral shape around an axis; a specular reflector disposed on one end side in a short direction of the thin-film plastic scintillator wound in two or more layers; a diffuse reflection plate disposed on the other end side of the thin film plastic scintillator wound in two or more layers in the short direction; the thin-film plastic scintillator, the specular reflector, and a container for housing the specular reflector; A graft polymer is disposed on two main surfaces of the thin film plastic scintillator, the graft polymer increasing the contact area between the thin film plastic scintillator and the test liquid, Two adjacent layers in the radial direction of the thin film plastic scintillator are disposed in close contact with each other with a test liquid layer of 10 μm or less therebetween. Scintillator device. [Explanation of symbols]

[0111] 1, 100 scintillator device, 1a container, 1b measurement sample, 2, 2a, 2b thin film plastic, 3a, 3b light reflector, 4 plastic winding machine, 5 motor, 6a, 6b plastic attacher, 7 plastic feed section, 8 plastic receiver, 8a receiver shaft, 9 feed shaft, 10 A tank, 11 B tank, 12 tank switching water squeeze shaft, 13 threshold plate, 20 test liquid, 20a water droplet, 31 tritium atom, 32 acrylic acid graft polymer, 33 polyvinyl toluene, 34 oxygen-containing polar group, 40 liquid scintillator device, 41 photomultiplier, 42 coincidence circuit

Claims

1. A step of immersing the thin film plastic scintillator to which the pure water is attached in a first tank containing a liquid to be inspected; a step of removing the thin film plastic scintillator immersed in the first tank from the first tank and removing at least a portion of the test liquid adhering to the thin film plastic scintillator; immersing the thin film plastic scintillator from which the test liquid has been removed in a second tank containing the test liquid; a step of spirally winding the thin film plastic scintillator immersed in the second tank around a first shaft disposed on the second tank and rotated by a motor; a step of enclosing the thin film plastic scintillator spirally wound around the first axis in a fluorescent light-transmitting container and sealing it; and detecting a concentration of a radioactive substance contained in the test liquid by amplifying the fluorescence emitted from the thin film plastic scintillator. Radiation detection methods.

2. One end of the thin film plastic scintillator is attached to the first shaft and the first shaft is rotated by the motor, so that the other end of the thin film plastic scintillator is immersed in the first tank and then pulled out of the first tank, and after at least a portion of the test liquid is removed from the thin film plastic scintillator, the other end of the thin film plastic scintillator is immersed in the second tank and then wound around the first shaft. The radiation detection method according to claim 1 .

3. The first tank and the second tank are arranged along a moving direction of the thin film plastic scintillator, the thin film plastic scintillator is hung on a second axis disposed between the first tank and the second tank at a position higher than the liquid levels of the first tank and the second tank, and the pure water adhering to the thin film plastic scintillator is removed, and at least a part of the test liquid is removed. The radiation detection method according to claim 1 .

4. The method further includes a step of modifying the two main surfaces of the thin film plastic scintillator to which the test liquid is attached by a plasma treatment, After the two main surfaces are modified by the plasma treatment, the thin film plastic scintillator is immersed in the first tank. The radiation detection method according to claim 1 .

5. The method further includes a step of forming an acrylic acid graft polymer on the two main surfaces after modifying the two main surfaces by the plasma treatment, After the step of forming the acrylic acid grafted polymer, the thin film plastic scintillator is immersed in the first bath. The radiation detection method according to claim 4.

6. removing the thin-film plastic scintillator from the container after detecting the concentration of the radioactive material, and immersing the thin-film plastic scintillator in the first tank containing pure water; a step of removing the thin film plastic scintillator immersed in the first tank from the first tank and removing the test liquid adhering to the thin film plastic scintillator together with at least a portion of the pure water; immersing the thin film plastic scintillator from which the test liquid has been removed in a second tank containing pure water; a step of spirally winding the thin film plastic scintillator immersed in the second tank around the first shaft by the motor; and sealing the thin film plastic scintillator spirally wound around the first axis in the container. The radiation detection method according to claim 1 .

7. The thin film plastic scintillator has a thickness of 50 μm or less. The radiation detection method according to claim 1 .

8. The thin film plastic scintillator has a longitudinal length of 2 m or more. The radiation detection method according to claim 1 .

9. a thin film plastic scintillator wound in two or more layers in a spiral shape around an axis; a specular reflector disposed on one end side in a short side direction of the thin-film plastic scintillator wound in two or more layers; a diffuse reflection plate disposed on the other end side of the thin film plastic scintillator wound in two or more layers in the short direction; the thin-film plastic scintillator, the specular reflector, and a container for housing the specular reflector; a graft polymer is disposed on two main surfaces of the thin film plastic scintillator, the graft polymer increasing the contact area between the thin film plastic scintillator and the test liquid; Two layers adjacent to each other in the radial direction of the thin film plastic scintillator are disposed in close contact with each other with a test liquid layer of 10 μm or less therebetween. Scintillator device.

Images