Radiation measuring apparatus and method

Abstract

To increase a surface area of a scintillator member (aggregate) for radiation measurement, and reduce influence of self absorption in a liquid sample.SOLUTION: An aggregate 22 is stored in a container 16. The aggregate 22 is made of a plurality of scintillator elements. Each scintillator element has a linear or belt-like slender form or has flexibility. The aggregate 22 itself has deformability. A complicated fine gap net 23 is generated in the aggregate 22 and the gap net 23 is filled with a liquid sample. The liquid sample is water that contains tritium.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to radiation measuring devices and methods, and more particularly to radiation measuring using scintillators. [Background technology]

[0002] Two methods for measuring the concentration (radioactivity) of radioactive isotopes in a liquid sample are the first method, which uses a liquid scintillator, and the second method, which uses a plastic scintillator. While the first method allows for highly sensitive measurements, the disposal of the waste liquid generated after measurement becomes a problem. Furthermore, the first method makes it difficult to continuously measure large quantities of liquid samples.

[0003] The second method does not generate waste liquid and allows for the continuous measurement of large quantities of liquid samples. However, with the second method, particularly the conventionally proposed second method, high-sensitivity measurement is difficult. For example, when measuring the radioactivity of tritium contained in a liquid sample, if a fairly small detection limit of 1500 Bq / L is required, it is difficult to meet this requirement using conventionally proposed plastic scintillators. The energy of the beta rays emitted from tritium is very low, and in water, the range of these beta rays is less than 10 μm (about 5-6 μm). Most of the beta rays emitted from tritium are absorbed by the liquid sample itself before they reach the surface of the plastic scintillator. This phenomenon is called self-absorption. When detecting radiation (alpha rays, beta rays) emitted from radioactive isotopes other than tritium, it is also required to lower the detection limit.

[0004] Patent Document 1 discloses a radiation measurement method using multiple scintillator plates placed inside a vial. Patent Document 2 discloses a radiation measurement method using multiple scintillator pellets placed inside a vial. Patent Document 3 discloses a radiation measurement method using multiple scintillator plates placed inside a flow cell. In the technologies disclosed in Patent Documents 1 to 3, each scintillator element (scintillator plate or scintillator pellet) has a certain thickness. Each scintillator element is not flexible or deformable. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-91159 [Patent Document 2] Japanese Patent Publication No. 2016-24133 [Patent Document 3] Japanese Patent Application Publication No. 63-32390 [Overview of the project] [Problems that the invention aims to solve]

[0006] The object of this disclosure is to increase the surface area of ​​a scintillator member for radiation measurement. Alternatively, the object of this disclosure is to reduce the effect of self-absorption in a liquid sample. Alternatively, the object of this disclosure is to realize a scintillator member that naturally spreads within a container and creates a fine, complex network of gaps. [Means for solving the problem]

[0007] The radiation measuring device according to this disclosure includes a container in which a liquid sample is placed, an assembly consisting of a plurality of scintillator elements disposed inside the container, and a detection unit for detecting light generated when radiation from the liquid sample reaches the assembly, wherein each of the scintillator elements has an elongated shape and is flexible. In the aforementioned assembly, the plurality of scintillator elements are intertwined, and the assembly as a whole is deformable, thereby the assembly has an external shape that conforms to the shape of the inner surface of the container.The gap network formed inside the aggregate is filled with the liquid sample The gap network is formed inside each scintillator element and diffuses the light that escapes to the outside. which is characterized in that.

[0008] The radiation measurement method according to the present disclosure includes a step of arranging an aggregate composed of a plurality of scintillator elements in a container and injecting a liquid sample containing tritium into the container, and a step of detecting light generated when beta rays from the tritium reach the aggregate. Each of the scintillator elements has an elongated shape and flexibility, In the aforementioned assembly, the plurality of scintillator elements are intertwined, and the assembly as a whole is deformable, thereby the assembly has an external shape that conforms to the shape of the inner surface of the container, the gap network formed inside the aggregate is filled with the liquid sample The gap network is formed inside each scintillator element and diffuses the light that escapes to the outside. which is characterized in that.

Advantages of the Invention

[0009] According to the present disclosure, the surface area of the aggregate (scintillator member) for radiation measurement can be increased. Alternatively, according to the present disclosure, the influence of self-absorption in the liquid sample can be reduced. Alternatively, according to the present disclosure, an aggregate that forms a naturally spreading and fine and complex gap network in the container can be provided.

Brief Description of the Drawings

[0010] [Figure 1] It is a diagram showing the configuration of a radiation measurement device according to an embodiment. [Figure 2] It is a cross-sectional view showing an aggregate according to the first embodiment. [Figure 3] It is a cross-sectional view showing a first example of an isolation structure. [Figure 4] It is a block diagram showing a configuration example of a signal processing circuit. [Figure 5] It is a diagram showing an example of a measurement operation. [Figure 6] It is a cross-sectional view showing a second example of an isolation structure. [Figure 7] It is a cross-sectional view showing a third example of an isolation structure. [Figure 8] It is a diagram showing a plurality of compartments. [Figure 9] It is a diagram showing a modified example of a measurement unit. [Figure 10] It is a diagram showing an aggregate according to the second embodiment. [Figure 11] It is a diagram showing a manufacturing example of a scintillator element according to the second embodiment.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described based on the drawings.

[0012] (1) Outline of the Embodiment The radiation measurement device according to the embodiment has a container, an aggregate, and a detection unit. A liquid sample is placed in the container. The aggregate is disposed in the container and consists of a plurality of scintillator elements each having an elongated form and flexibility. The detection unit detects light generated when radiation from the liquid sample reaches the aggregate. A gap network formed inside the aggregate is filled with the liquid sample.

[0013] According to the above configuration, the surface area of the aggregate (substantive part excluding the gap network) can be increased, and a fine and complex gap network is formed inside the aggregate. Therefore, the radiation detection sensitivity can be enhanced. The above configuration functions effectively when detecting α-rays or β-rays, particularly when detecting low-energy β-rays. In the embodiment, the liquid sample is water containing tritium. The detected radiation is β-rays emitted from tritium.

[0014] In the embodiment, the aggregate as a whole has deformability. The aggregate has an outer shape conforming to the shape of the inner surface of the container. More specifically, when a plurality of scintillator elements are placed in the container, an aggregate that spreads throughout the internal space of the container (specifically, the accommodation space for accommodating the aggregate) naturally forms. In the embodiment, the aggregate has elasticity. The aggregate may be disposed in a compressed state in the container. All or part of the inner surface of the container contacts the aggregate, thereby determining the outer shape of the aggregate. That is, all or part of the inner surface exhibits a shaping effect.

[0015] In this embodiment, multiple scintillator elements are entangled within the aggregate. Light generated inside the aggregate is diffused by the gap network. The entanglement of multiple scintillators complicates the gap network formed inside the aggregate. Scattering the light generated inside the aggregate increases the amount of light reaching the detection unit. A fine gap network reduces the effect of self-absorption. In this embodiment, the container is transparent, and each scintillator element is also transparent.

[0016] In this embodiment, the container has a containment space for accommodating the aggregate. The volume ratio of the aggregate (the physical portion excluding the gap mesh) to the containment space is in the range of 5 to 80%. This volume ratio may also be in the range of 10 to 70% or 20 to 60%.

[0017] In the embodiment, each scintillator element has a linear shape. The diameter of each scintillator element is in the range of 3 μm to 80 μm. The linear shape can also be described as a thread-like or string-like shape. Alternatively, each scintillator element has a strip-like shape. The thickness of each scintillator element is in the range of 3 μm to 80 μm. The strip-like shape can also be described as a ribbon-like shape. The length of each scintillator element can be arbitrarily determined. It is possible to form an aggregate with a single scintillator element, but in practice, an aggregate is formed with multiple scintillator elements. The thickness of each scintillator element may be changed depending on the radiation to be detected. By reducing the diameter or thickness of each scintillator element and increasing the number of scintillator elements that make up the aggregate, the density of the gap network can be increased and the surface area of ​​the aggregate can be increased.

[0018] The radiation measuring device according to this embodiment includes an injection tube for injecting a liquid sample into a container and an outlet tube for discharging the liquid sample from the container. Radiation may be measured while the liquid sample is flowing, or radiation may be measured intermittently while the liquid sample is flowing intermittently.

[0019] The radiation measuring device according to this embodiment includes an isolation structure that separates the scintillator assembly from the inlet opening of the discharge pipe while allowing the liquid sample to reach the inlet opening of the discharge pipe. This configuration prevents the inlet opening from being blocked by one or more scintillator elements.

[0020] The radiation measurement method according to this embodiment comprises a preparation step and a detection step. In the preparation step, an assembly consisting of multiple scintillator elements is placed in a container, and a liquid sample containing tritium is injected into the container. In the detection step, light generated when beta rays from tritium reach the assembly is detected. Each scintillator element has an elongated shape and is flexible. Multiple scintillator elements are intertwined with each other in the assembly. The gap network formed inside the assembly is filled with the liquid sample.

[0021] According to the above configuration, during the process of introducing multiple scintillator elements into the container, the aggregate naturally deforms according to the shape of the container's inner surface. Simultaneously, a complex and fine network of gaps naturally forms inside the aggregate, and this network of gaps is filled with the liquid sample. Therefore, the probability that radiation emitted from the liquid sample reaches the surface of the aggregate without being absorbed by the liquid sample itself is increased. In addition, since the light generated inside the aggregate is diffused by the network of gaps, the amount of light reaching the detector can be increased. If the aggregate is arranged in a compressed state, the detection efficiency can be increased.

[0022] (2) Details of the embodiment Figure 1 shows a radiation measuring device according to an embodiment. In this radiation measuring device, the liquid sample is water containing tritium, and the detected radiation is low-energy beta rays emitted from tritium. Other radioisotopes or other radiation may be used as the target of measurement. In the embodiment, the liquid sample is measured continuously.

[0023] In Figure 1, the radiation measuring device consists of a measuring unit 10 and a signal processing unit 12. The measuring unit 10 has a measuring chamber 14 located inside a shielding container 45. The measuring chamber 14 has a well-like and cylindrical shape. A container 16 that functions as a flow cell is placed inside the measuring chamber 14. In the configuration example shown in Figure 1, the container 16 has a cylindrical shape. The container 16 is made of a transparent material. Examples of such materials include glass and resin.

[0024] The container 16 has a storage space 17 as an internal space. The storage space 17 is a space defined by the inner surface (bottom, sides, and top) of the container 16 and has a cylindrical shape. A portion of the internal space of the container 16 may be the storage space 17.

[0025] The housing space 17 is specifically a space for housing the assembly 22. The assembly 22 is a scintillator member composed of multiple scintillator elements. Each scintillator element has an elongated shape and is flexible (bendable, deformable). The assembly 22 is an assembly according to the first embodiment, and each scintillator element constituting the assembly 22 has a thin wire-like shape. The number of scintillator elements constituting the assembly 22 is in the range of several to several thousand, or in the range of tens to several hundred. However, all numerical values ​​given in this specification are examples only.

[0026] In the assembly 22, multiple scintillator elements are irregularly intertwined. Each scintillator element is made of a transparent plastic scintillator. That is, each scintillator element exhibits the function of converting radiation into light.

[0027] The aggregate 22 as a whole is deformable. When the aggregate 22 is placed inside the container 16, the aggregate 22 naturally deforms according to the shape of the inner surface of the container 16. In other words, the aggregate 22 naturally expands to fill the entire containment space inside the container 16. The degree of compression or the ratio of gaps in the aggregate 22 can be adjusted by adjusting the number of scintillator elements that make up the aggregate 22. A complex and fine network of gaps naturally forms inside the aggregate 22.

[0028] Inside the container 16, when beta rays emitted from tritium in the liquid sample reach the surface of the assembly 22, light is generated. This light is diffused by the gap mesh. The diffused light 28 is detected by multiple photomultiplier tubes (PMTs) 24, 26, and a detection pulse is output from each PMT 24, 26. The PMTs 24, 26 constitute a detection unit. The detection unit may be composed of three or more PMTs. The light-receiving surfaces of each PMT 24, 26 are facing each other in close proximity to the side surface of the container 16.

[0029] The injection pipe 18 and the discharge pipe 20 penetrate the lid (ceiling wall) of the container 16. The injection pipe 18 is for injecting the liquid sample into the container 16, and the discharge pipe 20 is for discharging the liquid sample from the container 16 to the outside. Pump P1 indicates the injection pump, and pump P2 indicates the discharge pump. Only one of pumps P1 or P2 may be installed.

[0030] A filter F is provided in the middle of the injection tube 18. The filter F removes foreign matter from the liquid sample to prevent clogging in the assembly 22. A tank for storing the liquid sample is provided upstream of the pump P1.

[0031] A guard detection unit is provided around the measurement chamber 14. The guard detection unit is for excluding noise caused by the detection of high-energy radiation such as cosmic rays. Specifically, the guard detection unit consists of a scintillator 32 and multiple PMTs 34 and 36. When high-energy radiation enters the scintillator 32, it generates light 38, which is detected by the multiple PMTs 34 and 36. In this case, a detection pulse is output from each PMT 34 and 36.

[0032] The scintillator 32 has a cylindrical shape, with a well-shaped recess formed in a part of it. This recess is the measurement chamber 14. A light-reflecting layer 42 is formed on the surface of the scintillator 32. The light-receiving ends of each PMT 24, 26 penetrate through openings formed in the light-reflecting layer 42. A light guide or mirror is provided on the inner surface of the measurement chamber 14. The light-receiving ends of the PMT 34, 36 enter the interior of the scintillator 32. The scintillator 32 is made of plastic scintillator. If the above noise is not a problem, the guard detection unit may be removed.

[0033] The shielding container 45 is made of lead of a certain thickness. A lid 44 for opening and closing the measuring chamber 14 is provided on the upper side of the measuring chamber 14. The lid 44 is part of the shielding container 45 and is also made of lead.

[0034] Next, the signal processing unit 12 will be described. In the illustrated configuration example, the signal processing unit 12 includes a signal processing circuit 46, a multi-channel analyzer (MCA) 50, an arithmetic control unit 54, a display unit 56, an input unit 58, etc. The signal processing circuit 46 allows only detection pulses caused by light generated in the assembly 22 to pass through, and blocks detection pulses corresponding to noise. A specific configuration example of the signal processing circuit 46 will be explained later with reference to Figure 4.

[0035] The MCA50 counts detection pulses for each radiation energy (β-ray energy), thereby generating an energy spectrum. The arithmetic control unit 54 calculates the concentration (radioactivity) of tritium based on the energy spectrum. The arithmetic control unit 54 also has a flow rate control function, a graph generation function, an abnormality determination function, etc.

[0036] The radioactivity of tritium, which is the measurement result, is displayed on the display unit 56. Operating conditions and the like are set by the user using the input unit 58. The display unit 56 and the input unit 58 are constituted by, for example, a touch screen panel.

[0037] Plastic scintillators are generally manufactured by adding a solute to a solvent. Representative solvents include PVT_(C9H 10 ) n H2, PS_(C8H8) n H2, PMMA_(C5H8O2) n H2, etc. Representative solutes include PPO (or DPO)_C 15 H 11 NO, PBD_C 20 H 14 N2O, butyl-PBD_C 24 H 22 N2O, pTP_C 18 H 14 , POPOP_C 24 H 16 N2O2, BDB_C 32 H 30 , etc.

[0038] In FIG. 2, the container 16 is shown. The container 16 is made of a transparent material as already described, and it consists of a main body 16A and a lid 16B. The container 16 has a cylindrical form, but the form may be a disc shape, a prismatic shape, etc. The inside of the container 16 is the accommodation space 17. In the illustrated configuration example, the accommodation space 17 is a space defined by the inner surface (bottom surface, side surface, and ceiling surface) of the container 16. The assembly 22 according to the first embodiment extends over the entire accommodation space 17.

[0039] As already explained, the aggregate 22 is composed of multiple scintillator elements 22a. Each scintillator element 22a has an elongated shape, specifically a thread-like shape. Each scintillator element 22a is flexible and easily deformed by external force. This deformation is either elastic or plastic. The aggregate 22 is cotton-like or fibrous.

[0040] In the assembly 22 according to the first embodiment, the diameter of each scintillator element 22a is set to, for example, within the range of 3 to 80 μm. The length of each scintillator element 22a can be arbitrarily determined. For example, its length can be set to within the range of 5 mm to 10 m, or within the range of 1 cm to 1 m. By making the length somewhat larger, outflow of scintillator elements and localized concentration of many scintillator elements can be avoided. A complex and fine gap network 23 is formed inside the assembly 22. The gap network 23 is filled with the liquid sample. For example, the volume ratio of the assembly (substantial part excluding the gap network 23) to the containment space is set to, for example, within the range of 5 to 80%, or within the range of 10 to 70%.

[0041] In this embodiment, the aggregate 22 is arranged in a compressed state within the container 16. This increases the surface area of ​​the aggregate 22 and also increases the density of the gap network 23. In other words, the probability of beta rays emitted from tritium reaching the surface of the aggregate 22 is increased. As will be described later, each scintillator element may be in the shape of a strip. Alternatively, each scintillator element may be in other elongated shapes (for example, shapes with varying thickness or width).

[0042] The end of the injection pipe 18, specifically its outlet opening 18A, is located near the bottom of the container 16. On the other hand, the end of the discharge pipe 20, specifically its inlet opening, is located near the ceiling of the container 16. Since the outlet opening 18A and the inlet opening are separated from each other vertically and horizontally, the replacement of the liquid sample within the container 16 can be promoted. In other words, the occurrence of partial stagnation can be avoided. A filter 60 is provided so as to surround the end of the discharge pipe 20. This filter 60 is the first example of an isolation structure.

[0043] Figure 3 shows a cross-section of the filter 60. The filter 60 has a cylindrical shape and non-contactively encloses the inlet opening 20A of the discharge pipe 20. The filter 60 allows the liquid sample to pass through while restricting the passage of the scintillator element 22a. The filter 60 prevents the inlet opening 20A from becoming blocked. The filter 60 is composed of, for example, a mesh-like transparent material.

[0044] Figure 4 shows an example of the configuration of the signal processing circuit 46. The coincidence counting circuit 62 receives detection pulses 24A and 26A output from two PMTs that detect light generated inside the container. The coincidence counting circuit 62 outputs a pass pulse G when detection pulses 24A and 26A are input simultaneously. The pulse summing circuit 64 adds the detection pulses 24A and 26A and outputs a detection pulse train 70. The coincidence counting circuit 66 receives detection pulses 34A and 36A output from two PMTs that detect high-energy radiation. The coincidence counting circuit 66 outputs a rejection pulse R when detection pulses 34A and 36A are input simultaneously.

[0045] The gate circuit 68 allows the input detection pulse to pass when a pass pulse G is obtained within the detection pulse train. However, it prohibits the input detection pulse from passing when a reject pulse R is obtained. This prevents false counting caused by the detection of high-energy radiation.

[0046] Figure 5 shows an example of operation. This example illustrates the operation when a liquid sample is continuously flowed and beta rays emitted from tritium in the liquid sample are continuously detected. The horizontal axis t is the time axis. (A) and (B) show the liquid sample injection and liquid sample discharge that start at the beginning of the measurement. The timing of the liquid sample discharge may be delayed. As shown in (C), the counting results are accumulated for each measurement period, and the radioactivity is calculated based on the accumulated value. In practice, as shown in (D), the average value is calculated for each display period, for example, from k radioactivity values. The display period is k times the measurement period.

[0047] As indicated by symbol 82, the average value is displayed, and an abnormal or normal result is determined based on this average value. The average value is updated for each measurement period. Also, as indicated by symbol 80, it is determined for each measurement period whether there has been a sharp increase in tritium concentration. If the tritium concentration rises sharply, an abnormality is determined.

[0048] The liquid sample in the container is replaced very slowly. Of course, the flow rate of the liquid sample may be adjusted depending on the purpose and conditions of the measurement. The set of steps consisting of liquid sample injection, liquid sample measurement, liquid sample injection, and cleaning of the container may be repeated.

[0049] The detection limit for the aggregate according to the first embodiment shown in Figures 1 and 2 is calculated as follows. The target detection limit is, for example, 1500 Bq / L.

[0050] Assume the volume of the container filled with scintillator water is 20 ml and the background count rate is 15 cpm. Assume the diameter of each individual scintillator element is 7 μm and the volume ratio of the aggregate (substance portion excluding the gap network) within the container is 30%. For the sake of simplification of the calculation, assume that the aggregate is composed of a single scintillator element. From these parameters, the length of the scintillator element is determined to be 15,590,688 cm, and based on this, the surface area of ​​the aggregate is 34,286 cm². 2 This is how it is determined. Although the detailed calculation formula is omitted, under the above assumptions, if we assume a measurement time of 1 minute, the detection limit for the first embodiment is 246.9 Bq / L for a measurement time of 1 minute. This is a considerably smaller value than the target detection limit of 1500 Bq / L. According to the embodiment, a satisfactory detection limit can be achieved even with a short measurement time.

[0051] Incidentally, reducing the volume percentage of the aggregate within the container naturally increases the detection limit. When the volume percentage is reduced to 5%, the detection limit for the first embodiment is 1481 Bq / L with a measurement time of 1 minute. Even when the volume percentage is reduced to 5%, a detection limit lower than the target detection limit of 1500 Bq / L can be achieved. For example, if the volume percentage is increased to 50% or 60%, it is possible to achieve a very low detection limit. According to the embodiment, any detection limit can be achieved by manipulating the volume percentage.

[0052] For reference, let's estimate the detection limits for Comparative Example 1 and Comparative Example 2. For Comparative Example 1, we assume that tritium-containing water is measured using 10 scintillator plates placed in a vial. The background count rate is assumed to be 15 cpm, and the amount of tritium-containing water is assumed to be 20 ml. We assume that the size of each scintillator plate is 1.5 × 4.5 × 0.05 cm. In that case, the total surface area of ​​the 10 scintillator plates is 141 cm². 2 Therefore, if we assume a measurement time of 720 minutes (12 hours), the detection limit would be 1725 Bq / L, which falls short of the target detection limit of 1500 Bq / L. In fact, a measurement time of 720 minutes is not realistic.

[0053] As a comparative example 2, we consider measuring tritium-containing water using a large number of scintillator pellets placed in a vial. The background count rate is assumed to be 15 cpm, and the amount of tritium-containing water in the container is 8 ml. The container is filled with 556 scintillator pellets, and each scintillator pellet is assumed to be a 3 x 3 x 3 mm cube. In this case, the total surface area of ​​the scintillator pellet assembly is 300 cm². 2 This is the result. If the measurement time were set to 240 minutes (4 hours), the target detection limit of 1500 Bq / L would be achieved, but a measurement time of 240 minutes is not realistic.

[0054] According to Comparative Examples 1 and 2, it is difficult to lower the detection limit, or a very long measurement time is required to obtain a satisfactory detection limit. In contrast, according to the configuration of the embodiment, a considerably low detection limit can be easily achieved even with short measurement times.

[0055] Figure 6 shows a filter unit 84, which is a first modified example of the isolation structure. The filter unit 84 is detachably attached to the end of the discharge pipe 20. The filter unit 84 has a cylindrical body 86. The end of the discharge pipe 20 is inserted into an opening formed in the upper part of the body 86. The end and the body 86 are screwed together. A filter 88 is sandwiched between the end of the discharge pipe 20 and the internal step of the body 86. Specifically, the filter 88 is provided so as to cover the inlet opening 20A. The filter 88 allows the liquid sample to pass through but prevents the passage of foreign matter. The body 86 blocks the aggregate and prevents the aggregate from blocking the inlet opening 20A. Even if a scintillator element or a fragment thereof enters the filter unit 84, it will not enter the inlet opening 20A.

[0056] Figure 7 shows a second modified example of the partition structure. The internal space of the container 16 is divided into two subspaces 92 and 94 by a mesh partition wall 90. Subspace 92 is a containment space that houses the aggregate 22. The end of the injection tube 18 is provided at the bottom of subspace 92. The partition wall 90 allows the liquid sample to pass through while restricting the movement of the aggregate.

[0057] The partial space 94 is the upper space that does not include the assembly 22, and the end of the discharge pipe 20 is located inside it. The partition wall 90 separates the inlet opening of the discharge pipe 20 from the assembly 22, thus preventing the inlet opening from being blocked by the assembly 22. When this configuration is adopted, the two PMTs are positioned so that the centers of the light-receiving surfaces of each PMT are aligned at the middle height of the partial space 92, which is the housing space.

[0058] Figure 8 shows two mesh members 96 and 98 arranged inside the container 16. The two mesh members 96 and 98 divide the containment space inside the container 16 into three compartments 100A, 100B, and 100C. The three parts 22A, 22B, and 22C that constitute the assembly 22 are contained within the three compartments 100A, 100B, and 100C. Each mesh member 96 and 98 allows the permeation of the liquid sample but restricts the permeation of the scintillator element. The configuration shown in Figure 8 prevents the assembly 22 from shifting or collapsing inside the container 16.

[0059] Figure 9 shows a modified version of the measurement unit. The container 102 has a cubic shape, and an assembly 104 consisting of multiple scintillator elements is arranged inside it. An injection pipe is provided that penetrates the top plate of the container 102, and a discharge pipe is provided that penetrates the bottom plate of the container 102. The light-receiving surface of the first PMT 106 faces the first side surface of the container 102. The light-receiving surface of the second PMT 108 faces the second side surface of the container 102.

[0060] Figure 10 shows an assembly 116 according to the second embodiment. The assembly 116 extends throughout the interior of the container 114 and is composed of a plurality of scintillator elements 116a. Each scintillator element 116a has an elongated, strip-like shape. Its length can be arbitrarily determined. The thickness of each scintillator element is set, for example, within the range of 3 to 80 μm. Its width is set, for example, within the range of 3 mm to 2 cm. As a result of the entanglement of the plurality of scintillator elements 116a, a complex network of fine gaps 117 is formed inside the assembly 116. The network of gaps 117 is filled with the liquid sample.

[0061] Figure 11 shows a method for manufacturing a scintillator element according to a second embodiment. An ingot 120 is held by a lathe 118. The ingot 120 is made of plastic scintillator. The tip of a cutting tool is applied to the ingot 120 while it is rotating. This produces a thin, skin-like or ribbon-like scintillator element with a certain thickness.

[0062] Let's calculate the detection limit for the aggregate according to the second embodiment. Assume the container capacity is 20 ml, the background count rate is 15 cpm, the amount of tritiated water in the container is 8 ml, and 44,444 scintillator elements are provided in the container. Assume that the size of each scintillator is 1.5 mm in width, 4.5 mm in length, and 50 μm in thickness. In that case, the surface area of ​​the aggregate in the container is 6,267 cm². 2 Assuming a measurement time of 1 minute, the detection limit is calculated to be 1351 Bq / L. This is below the target detection limit. Thus, even when using a strip-shaped scintillator element instead of a linear scintillator element, highly sensitive measurement of beta rays from tritium is possible.

[0063] The above-mentioned assembly may be placed in a vial instead of a flow cell. If the assembly deteriorates, it may be replaced. For example, the degree of deterioration of the assembly may be evaluated from measurement results when the assembly is irradiated with radiation from an external source. [Explanation of symbols]

[0064] 10 Measurement unit, 12 Signal processing unit, 16 Container, 17 Containment space, 18 Injection tube, 20 Discharge tube, 22 Assembly, 22a Scintillator element, 23 Gap mesh.

Claims

1. A container in which a liquid sample can be placed, The container is arranged with an assembly consisting of multiple scintillator elements, A detection unit for detecting light generated when radiation from the liquid sample reaches the aggregate, Includes, Each of the aforementioned scintillator elements has an elongated shape and is flexible. In the aforementioned assembly, the plurality of scintillator elements are intertwined, The assembly as a whole is deformable, and as a result, the assembly has an external shape that conforms to the shape of the inner surface of the container. The gap network formed inside the aggregate is filled with the liquid sample. The aforementioned gap network is formed inside each of the scintillator elements and diffuses the light that escapes to the outside. A radiation measuring device characterized by the following features.

2. In the radiation measuring device according to claim 1, The container has a storage space that accommodates the assembly, The volume ratio of the assembly to the aforementioned containment space is within the range of 5 to 80%. A radiation measuring device characterized by the following features.

3. In the radiation measuring device according to claim 1, Each of the aforementioned scintillator elements has a linear shape. A radiation measuring device characterized by the following features.

4. In the radiation measuring device according to claim 3, The diameter of each of the aforementioned scintillator elements is in the range of 3 μm to 80 μm. A radiation measuring device characterized by the following features.

5. In the radiation measuring device according to claim 1, Each of the aforementioned scintillator elements has a band-like shape. A radiation measuring device characterized by the following features.

6. In the radiation measuring device according to claim 5, The thickness of each scintillator element is in the range of 3 μm to 80 μm. A radiation measuring device characterized by the following features.

7. In the radiation measuring device according to claim 1, An injection tube for injecting the liquid sample into the container, A discharge pipe for discharging the liquid sample from the container, A radiation measuring device characterized by including [a certain component].

8. In the radiation measuring device according to claim 7, The structure includes an isolation structure that separates the assembly from the inlet opening of the discharge pipe while allowing the liquid sample to reach the inlet opening of the discharge pipe, A radiation measuring device characterized by the following features.

9. In the radiation measuring device according to claim 1, The aforementioned liquid sample contains tritium, The aforementioned radiation is beta radiation emitted from the tritium. A radiation measuring device characterized by the following features.

10. The process involves placing an assembly consisting of multiple scintillator elements inside a container and injecting a liquid sample containing tritium into the container. A step of detecting light generated when beta rays from the tritium reach the aggregate, Includes, Each of the aforementioned scintillator elements has an elongated shape and is flexible. In the aforementioned assembly, the plurality of scintillator elements are intertwined, The assembly as a whole is deformable, and as a result, the assembly has an external shape that conforms to the shape of the inner surface of the container. The gap network formed inside the aggregate is filled with the liquid sample. The aforementioned gap network is formed inside each of the scintillator elements and diffuses the light that escapes to the outside. A radiation measurement method characterized by the following features.

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