Scintillator unit and radiation source detection module

Abstract

To detect a radiation source such as tritium in water with very high accuracy.SOLUTION: A scintillator unit 8 of a radiation source detection device that detects radiation sources in water includes: a scintillator lamination part 13 in which a plurality of scintillator plates 14 having light transmissivity are laminated at predetermined intervals from each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a scintillator unit and a radiation source detection module for detecting a radiation source such as tritium contained in water. [Background technology]

[0002] Currently, there is a demand for technology that can accurately detect radioactive sources such as tritium contained in water. Patent Document 1 is an example of technology in this regard. Patent Document 1 addresses the issue of providing a water monitor that can accurately detect the tritium concentration in wastewater. As a solution to this issue, it discloses a configuration in which "tritiated water, the sample to be measured, is introduced into a thin, hollow sampling container 3 that has a wide sensitive area on the detection surface, and two detection systems, a first detection unit 1a and a second detection unit 1b, are arranged closely facing each other on both sides (detection surfaces) of the sampling container 3." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-178336 Summary of the Invention [Problem to be solved by the invention]

[0004] The maximum range of beta rays from radioactive sources contained in water is very short. In particular, while the maximum range of tritium is said to be 0.006 mm, in most cases it is very short, at around 0.001 mm. Therefore, it is necessary to bring the water containing the detection target into contact with the detection surface of the detector almost entirely, and to make the most of the detector's detection capability. However, with the configuration described in Patent Document 1, the tritiated water comes into contact with only one side of the solid scintillator, and it is difficult to say that the efficiency is sufficiently high. The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a scintillator unit that can accurately detect a radioactive source such as tritium contained in water. [Means for solving the problem]

[0005] The scintillator unit according to the present invention is a scintillator unit for a radiation source detection device that detects a radiation source in water, and has a scintillator stack in which a plurality of light-transmitting scintillator plates are stacked at predetermined intervals. The scintillator plate has grooves on both surfaces thereof to increase the surface area, and the grooves on one surface of the scintillator plate and the grooves on the other surface of the scintillator plate do not face each other. .

[0006] Furthermore, a radiation source detection module according to the present invention includes a housing having a flow path through which water containing a radiation source flows, a pair of photomultiplier tubes arranged opposite each other within the housing with the flow path sandwiched therebetween, and a scintillator unit arranged between the pair of photomultiplier tubes within the flow path and emitting scintillation light in response to radiation emitted from the radiation source, the scintillator unit having a scintillator stack portion in which a plurality of optically transparent scintillator plates are stacked at predetermined intervals, and a holding frame that holds the scintillator stack portion within the flow path. The scintillator plate has grooves on both surfaces thereof to increase the surface area, and the grooves on one surface of the scintillator plate and the grooves on the other surface of the scintillator plate do not face each other. . [Effects of the Invention]

[0007] The scintillator unit according to the present invention makes it possible to detect radioactive sources such as tritium contained in water with high accuracy. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an overview of a radiation source detection module according to an embodiment of the present invention. [Figure 2] Fig. 2(a) is a perspective view showing the configuration of a scintillator unit according to one embodiment of the present invention, Fig. 2(b) is a cross-sectional view illustrating a scintillator laminate portion, taken along the line AA in Fig. 2(a). [Figure 3] Figure 3(a) is a top view of the radiation source detection module, and Figure 3(b) is a top view of the scintillator unit. [Figure 4] FIG. 10 is a diagram for explaining the relationship between the number of scintillators and the detection efficiency of tritium. [Figure 5] 3A and 3B are diagrams for explaining the shape of a scintillator plate according to an embodiment of the present invention. [Figure 6] FIG. 2 is a diagram showing an example of beta ray spectrum measurement using a liquid tritium source in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking tritium as an example of a radiation source to be detected. 1 is a diagram showing the configuration of a radiation source detection module 1 according to an embodiment of the present invention. The radiation source detection module 1 according to the embodiment of the present invention includes a housing 2, a pair of photomultiplier tubes (PMTs) 3, and a scintillator unit 8.

[0010] 2, the scintillator unit 8 in this embodiment has a configuration in which multiple light-transmitting scintillator plates (fluorescent plates) are stacked at predetermined intervals. A scintillator is a substance that has the property of emitting light (fluorescence) when excited by radiation, and there are various types of scintillators, such as organic crystals, organic liquids, plastics, inorganic crystals, and gases. The term "light-transmitting" as used herein refers to a level of light transmittance such that, for example, when multiple identical scintillator plates are stacked and placed opposite the light-receiving surface of a detector, light emitted from the scintillator plate farther from the light-receiving surface can pass through other scintillator plates between them and be detected by the light-receiving surface.

[0011] The housing 2 is made of a metal such as stainless steel, and is preferably provided with a shield made of lead to prevent the penetration of external radiation (γ rays). From the viewpoint of reducing costs, it is preferable to use iron or lead for the shield, but tungsten may be used instead of iron or lead.

[0012] The housing 2 also has a main body 7. As will be described in detail later, the main body 7 is provided with a water inlet 4, a drain outlet 5, and an air vent 6, and a scintillator unit 8 is disposed within the main body 7. The main body 7 also functions as a water flow path during measurement.

[0013] A pair of photomultiplier tubes 3 are arranged inside the housing 2, facing each other across the main body 7 (water flow path). The photomultiplier tube 3 has a structure in which a photocathode, several secondary electron multiplying electrodes called dynodes, an anode, and other electrodes are sealed in a high-vacuum glass (or metal) container. When scintillation light from the scintillator strikes the photocathode, the generated photoelectrons are accelerated and strike the secondary electron emitting surface, generating a multiplied secondary electron stream. This process is repeated, resulting in a multiplication factor of several million. By detecting these amplified photoelectrons with a detection circuit, even extremely weak light can be detected with high accuracy. While this embodiment uses two photomultiplier tubes 3 as a pair to achieve high-accuracy measurements, a single photomultiplier tube 3 may be used if cost considerations mean a slight loss of accuracy is acceptable. Furthermore, by selecting a potassium-free photomultiplier tube, the glass container of the photomultiplier tube 3 does not contain potassium, noise due to K-40 can be reduced, resulting in more accurate radiation detection.

[0014] As described above, the main body 7 is provided with the water inlet 4 and the drain outlet 5. When measuring a radiation source, water is poured into the main body 7 from the water inlet 4 and passed through. In other words, the main body 7 serves as a flow path for water containing the radiation source. By disposing the scintillator unit 8 on this flow path, tritium contained in the water reacts with the scintillator, causing the scintillator to emit scintillation light.

[0015] In this embodiment, as shown in Fig. 1, the scintillator unit 8 is arranged so that the scintillator plates of the scintillator unit 8 are approximately parallel to the light-receiving surfaces of the photomultiplier tubes 3. With this configuration, the scintillation light emitted from the surfaces of the scintillator plates is incident perpendicularly, improving detection efficiency. Furthermore, the water flowing from the water inlet 4 toward the drain outlet 5 flows along the surfaces of each scintillator plate of the scintillator unit 8, maximizing the contact area (reaction area) between the water and the scintillator plates. The scintillation light thus emitted is amplified by the photomultiplier tubes 3 described above and detected by the detection circuit.

[0016] The detection circuit includes charge amplifiers 110a and 110b (charge AMPs) and single-channel analyzers 111a and 111b (SCAs) corresponding to the two photomultiplier tubes 3, a coincidence circuit 112, a multi-channel analyzer 11 (MCA), and a PC 12 for controlling the detection circuit and processing detected data. Photoelectrons emitted from the two photomultiplier tubes 3 are amplified by the charge amplifiers 110a and 110b and converted into digital information by the single-channel analyzers 111a and 111b. Of the signals from the two photomultiplier tubes 3, only those counted within a certain period of time are extracted by the coincidence circuit 112. The multi-channel analyzer 11 receives these pulse signals and accumulates the frequency of pulse signals of the same magnitude as a histogram, based on which the value of the radiation source is calculated.

[0017] The main body 7 is also provided with an air vent 6. The air vent 6 opens, for example, on the top surface of the housing 2. The air vent 6 has an openable and closable structure, such as a lid. At the start of measurement, the main body 7 needs to be filled with water to maximize the contact area between the water and the scintillator unit 8. The air vent 6 functions to release the pressure inside the main body 7 to the outside while water is poured into the main body 7 with the drain outlet 5 closed until the main body 7 is filled with water.

[0018] Therefore, when starting measurement, first close drain outlet 5, open vent 6, and pour water through water inlet 4. Then, once main body 7 is filled with water, close vent 6 and open drain outlet 5. Thereafter, pour water while adjusting the amount of water discharged using a pump connected to drain outlet 5, and then perform measurement.

[0019] Although this embodiment shows a configuration in which the water inlet 4 is provided on the top surface of the housing 2 and the drain outlet 5 is provided on the bottom surface of the housing 2, the reverse configuration can also be adopted. The former configuration (the configuration in this embodiment) allows for easy drainage from the main body 7 at the end of measurement, which is advantageous in terms of replacement and maintenance. The latter configuration (a configuration in which water is poured from the bottom) is advantageous in that it can prevent bubbles from forming on the water surface, which is a concern when pouring water from the top surface at the start of measurement. Furthermore, a water pouring member, which is a pipe extending vertically within the main body 7, may be disposed within the main body 7, and the water pouring member may have multiple water pouring holes spaced apart from each other. A swirling flow can be generated within the main body 7 by adjusting the direction of the water pouring holes so that water poured from the water pouring member's water pouring holes flows along a wall surface other than the wall surface on which the water inlet 4 and drain outlet 5 of the main body 7 are provided. There is a concern that continuous water injection through the water injection hole will cause radioactive materials and the like to accumulate inside the main body 7, but by generating a swirling flow inside the main body 7, it is possible to measure radiation while eliminating the accumulation of radioactive materials and the like on wall surfaces other than those on which the water injection hole and drain outlet 5 are located inside the main body.

[0020] The radiation source detection module 1 also includes a cooler 9. The cooler 9 is disposed opposite at least a portion of the pair of photomultiplier tubes 3 via the housing 2. In this embodiment, an electronic cooler including a Peltier element can be used as the cooler 9. By using this cooler 9 to cool the photomultiplier tubes 3, it is possible to reduce thermal noise caused by thermoelectrons emitted from the photocathode of the photomultiplier tubes 3, and to suppress a decrease in detection accuracy. In FIG. 1, two coolers 9 are provided for each photomultiplier tube 3, but the number and size of the coolers 9 are not limited to those in this embodiment.

[0021] Next, a scintillator unit 8 according to one embodiment of the present invention will be described with reference to Fig. 2. Fig. 2(a) is a perspective view showing the configuration of the scintillator unit 8, and Fig. 2(b) is a cross-sectional view for explaining the scintillator stack 13, showing the cross section AA of Fig. 2(a).

[0022] 2(a) and 2(b), the scintillator unit 8 has a scintillator stack 13 in which a plurality of light-transmitting sheet-like scintillators (scintillator plates) 14 (seven in this embodiment) are stacked at predetermined intervals. Note that the predetermined interval, i.e., the distance between the scintillator plates 14, needs to be such that when the scintillator unit 8 is placed in the main body 7 and water is passed through the main body 7, a sufficient amount of water passes between the opposing scintillator plates 14. For example, if the capacity of the main body 7 is 200 cc and the number of stacked scintillator plates 14 is seven as in this embodiment, the distance between the scintillator plates 14 is approximately 2 mm.

[0023] In this embodiment, multiple scintillator plates 14 are stacked, and therefore it is preferable that the scintillator plates 14 are thin so that the number of stacked plates can be adjusted appropriately depending on the size of the space inside the main body 7 and the object to be detected. From this perspective, in this embodiment, a plastic scintillator is used as the scintillator plate 14. A plastic scintillator is a light-transmitting material, for example, made by mixing a fluorescent material into a transparent plastic, and is configured so that several percent of the energy of excited molecules is emitted as light.

[0024] When a plastic scintillator is used as the scintillator plate 14, deformation due to the pressure of flowing water and strength problems at the joint between the scintillator plate 14 and the frame 15 arise. Therefore, in this embodiment, reinforcing members 17 are used to reinforce the scintillator plate 14 by dividing it into multiple regions. The reinforcing members 17 are made of, for example, an aluminum alloy and have a rectangular outer frame whose size corresponds to the size of the frame 15 and an inner frame that defines multiple rectangular openings arranged in a grid pattern inside the outer frame. For example, the scintillator plate 14 can be reinforced by sandwiching the scintillator plate 14 between a pair of reinforcing members 17 and bonding them together, and the scintillator plate 14 comes into contact with water through the rectangular openings in the inner frame. Note that the size and arrangement of these openings are not limited to this embodiment. Alternatively, the reinforcing members 17 may be arranged on only one side of the scintillator plate 14.

[0025] Furthermore, in this embodiment, a configuration is shown in which one scintillator plate 14 is sandwiched between a pair of reinforcing members 17, but this is not limited to this, and for example, a scintillator plate 14 of a size corresponding to the opening defined by the inner frame of the reinforcing member 17 may be fixed and used for each opening.

[0026] In this way, in this embodiment, the scintillator plate 14 is reinforced with the reinforcing member 17 made of aluminum alloy, so that sufficient strength can be ensured, which is advantageous in terms of maintenance and cost.

[0027] The scintillator unit 8 also has a frame portion 15 that holds the scintillator stack portion 13. The frame portion 15 is a rectangular frame made of a metal such as stainless steel, and has an upper frame 15a, a pair of opposing side frames 15b, and a lower frame 15c that are joined together with rivets or the like.

[0028] Openings 16 are provided in a pair of opposing side frames 15b of frame section 15. Openings 16 communicate with the space between the opposing scintillator plates 14 of scintillator stack section 13. Therefore, when scintillator unit 8 is placed in main body section 7 and measurement is started, water poured from water pouring port 4 passes through scintillator unit 8 through openings 16. Then, beta rays emitted from tritium contained in the water cause a fluorescent reaction on scintillator plate 14, and scintillation light is emitted from scintillator plate 14.

[0029] 2(a), a lid 18 equipped with a handle 19 is attached to the upper frame 15a of the frame 15. This lid 18 covers an opening that communicates with the inside of the main body 7 when the scintillator unit 8 is inserted and fixed in the main body 7 of the radiation source detection module 1. Furthermore, as will be described in detail later, a seal 22 made of, for example, rubber is provided on the back surface of the lid 18 so as to fit along the outer periphery of the frame 15. Therefore, when the scintillator unit 8 is inserted into the main body 7, the lid 18 and the housing 2 form a watertight seal.

[0030] 2(b), each scintillator plate 14 is fixed by being inserted into a slit portion 20 provided in the upper frame 15a and the lower frame 15c. In this case as well, by using the reinforcing member 17 as in this embodiment, it is possible to ensure sufficient strength of the scintillator plate 14 at the slit portion 20.

[0031] As described above, the scintillator unit 8 according to this embodiment has a configuration in which multiple scintillator plates 14 are stacked at predetermined intervals, and when this is placed inside the main body 7 and water is passed through it, the water spreads evenly throughout the spaces between the scintillator plates 14. In particular, since both sides of each scintillator plate 14 come into contact with water, it is possible to greatly increase the overall contact area (reaction area) between the water and the scintillator plates 14, and a significant improvement in detection efficiency can be expected.

[0032] Furthermore, since the scintillator plate 14 in this embodiment is reinforced with a reinforcing member such as aluminum, it is possible to solve the strength problem that is a concern when a plastic scintillator is used.

[0033] Next, the relationship between the scintillator unit 8 and the main body 7 of the radiation source detection module 1 in this embodiment will be described with reference to Fig. 3. Fig. 3(a) is a top view of the radiation source detection module 1, and Fig. 3(b) is a top view of the scintillator unit 8. Note that Fig. 3 does not show components that are not necessary for the description, such as the cooler 9 and the handle 19.

[0034] 3(a), the radiation source detection module 1 is provided with an opening for placing the scintillator unit 8 inside the main body 7. A frame corresponding to the lid 18 of the scintillator unit 8 is provided so as to surround the opening, and screw holes 21a are provided on both ends.

[0035] On the other hand, as shown in Figure 3(b), the lid portion 18 of the scintillator unit 8 also has a through hole 21b at a position corresponding to the screw hole 21a provided in the radiation source detection module 1, and after inserting the scintillator unit 8 into the main body portion 7, the scintillator unit 8 is fixed by passing a screw from the through hole 21b into the screw hole 21a.

[0036] In addition, a seal portion 22 made of, for example, rubber is provided on the underside of the lid portion 18 so as to fit along the outer periphery of the frame portion 15 of the scintillator unit 8, and this seal portion 22 forms a watertight seal between the main body portion 7 and the scintillator unit 8.

[0037] As described above, in this embodiment, the scintillator unit 8 is inserted through an opening communicating with the main body 7 and fixed with screws. In other words, the frame 15 of the scintillator unit 8 is configured as a cartridge that is detachable from the housing 2. Therefore, the scintillator unit 8 can be easily replaced, and for example, when the expiration date of the scintillator unit 8 has passed, only the scintillator unit 8 needs to be replaced, which is advantageous in terms of cost and effort. Furthermore, although the detection target in this embodiment has been described as tritium in water, it is possible to detect other radiation sources by changing the type of scintillator.

[0038] Furthermore, the scintillator unit 8 has a frame 15 and a lid 18 made of highly rigid stainless steel or the like, and a handle 19 attached to the lid 18. This improves the convenience of transporting and managing the scintillator unit 8. In other words, the scintillator unit 8 can be easily carried using the handle 19, and can be easily inserted into and removed from the main body 7. Furthermore, because the frame 15 and the lid 18 are highly rigid, there is no problem with storing multiple scintillator units 8 stacked together, for example.

[0039] Figure 4 includes a graph illustrating the relationship between the number of stacked scintillator plates and the detection accuracy of tritium. The more scintillator plates are stacked, the greater the overall contact area (reaction area) between the water and the scintillator, and therefore the detectability of the scintillator unit. However, increasing the number of scintillator plates also increases the probability that the scintillation light emitted from one scintillator plate will be blocked by a scintillator plate closer to the photomultiplier tube 3. Therefore, there is a trade-off between the improvement in tritium detection efficiency due to the increase in the number of scintillator plates and the loss of detection opportunities due to the blocking of scintillation light, and a balance must be considered.

[0040] The inventors then conducted extensive experiments and found that there is a relationship between the number of scintillator plates and tritium detection efficiency, as shown in Figure 4. The greater the number of scintillator plates, the greater the detectability of the detector as a whole. On the other hand, they found that there is a relationship with self-shielding by stacked scintillator plates, as shown in the graph in the upper right of Figure 4. In other words, the more other scintillator plates there are between the photomultiplier tube and the scintillation light emitted from that scintillator, the fewer photons detected by the photomultiplier tube.

[0041] Therefore, the detection efficiency of the entire detector changes as shown in the graph at the bottom right of Figure 4. The graph shows that the detection efficiency improves as the number of scintillator plates increases, but the trend toward improvement in detection efficiency rapidly slows when the number of scintillator plates exceeds three. Because one photomultiplier tube 3 is disposed on each side of the main body 7, it is most preferable to have two to four scintillator plates per photomultiplier tube 3 in terms of size and cost reduction. From the perspective of ensuring acceptable detection efficiency, it is desirable to limit the number of scintillators per photomultiplier tube 3 to nine. Therefore, it is preferable that the total number of scintillators be four to 18, and it has been found that the number of scintillators can be adjusted within this range in consideration of the relationship between detection accuracy, cost, etc. In other words, in the context of this embodiment, the scintillator stack 13 of the scintillator unit 8 is preferably configured with four to 18 scintillator plates 14 stacked together.

[0042] The shape of the scintillator plate is not particularly limited, but from the viewpoint of improving the tritium detection efficiency, it may be shaped to increase the contact area between water and the scintillator plate. Fig. 5 shows scintillator plate 14a that has been processed to increase the surface area by providing grooves 14a1 and 14a2 on the surface of scintillator plate 14 to increase the contact area.

[0043] Although there are no particular limitations on the number or depth of grooves 14a1, 14a2 provided in scintillator plate 14a, the scintillator plate will be subjected to water pressure, and so these must be set in consideration of the strength of scintillator plate 14a. For example, to give a specific example of groove depth d, it is preferable to set it to less than 1 / 3 of the thickness t of scintillator plate 14a from the perspective of ensuring strength.

[0044] In this embodiment, grooves 14a1 and 14a2 are provided on both sides of scintillator plate 14a, respectively, and their arrangement has also been devised. The lower diagram of FIG. 5 is an enlarged view of part B shown in FIG. 5. In this embodiment, groove 14a1 provided on one side of scintillator plate 14a and groove 14a2 provided on the other side of scintillator plate 14a are offset so that they do not overlap and face each other. This is because if groove 14a1 and groove 14a2 were arranged so that they overlap and face each other, extremely thin portions of scintillator plate 14a would be created, which could cause scintillator plate 14a to break when water pressure is applied.

[0045] Therefore, in order to avoid providing an extremely thin portion in scintillator plate 14a, it is preferable that width w1 between grooves 14a1 provided on one surface be wider than width w2 of groove 14a1 in the X direction, and groove 14a2 be provided on the other surface so as to face that portion (portion where groove 14a1 is not provided). In other words, determining the groove width determines the maximum number of grooves to be provided on one surface of scintillator plate 14a.

[0046] In this example, the groove width and number were adjusted to prepare a scintillator plate 14a with a surface area that was approximately 2.5 times larger, and tritium detection was performed.The background was approximately 1 / 20, and the lower detection limit after 3,600 seconds of detection was approximately 1 / 10, demonstrating how important it is to ensure a sufficient contact area between water and the scintillator plate when detecting tritium.

[0047] In this embodiment, grooves are provided on both sides of scintillator plate 14 a, but from the perspective of ensuring strength, grooves may be provided on only one side of scintillator plate 14 a. Furthermore, the surface of the scintillator plate may be processed in any shape other than grooves as long as it ensures a contact area with water.

[0048] Furthermore, when using a scintillator plate 14a with grooves, it is advisable to make the grooves parallel to the direction of the flowing water. This configuration allows water to flow easily in the grooves and prevents buildup of debris, thereby ensuring the detection accuracy of the radiation source detection module.

[0049] Figure 6 shows an example of a beta-ray spectrum obtained in this example using an actual liquid tritium source. Compared with the beta-ray spectrum measured using pure water containing no tritium (BG: background), a significant increase in count rate can be seen in the 20 to 300 channel range.

[0050] Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to the above embodiments and various modifications are possible. For example, the above embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to embodiments including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment. It is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to delete part of the configuration of each embodiment, or to add or replace other configurations. [Explanation of symbols]

[0051] 1 radiation source detection module, 2 housing, 3 photomultiplier tube, 4 water inlet, 5 drain outlet, 6 ventilation port, 7 main body, 8 scintillator unit, 9 cooler, 10 time-to-pulse-height converter, 11 multi-channel analyzer, 12 PC, 13 scintillator stack, 14, 14a scintillator plate (sheet-shaped scintillator), 14a1, 14a2 groove, 15 frame, 16 opening, 17 reinforcing member, 18 lid, 19 handle, 20 slit, 21a screw hole, 21b through hole, 22 seal, 110 charge amplifier, 111 single-channel analyzer, 112 coincidence circuit

Claims

1. A scintillator unit of a radiation source detection module for detecting a radiation source in water, comprising: a scintillator stack portion in which a plurality of light-transmitting scintillator plates are stacked at predetermined intervals, Both surfaces of the scintillator plate are grooved to increase the surface area, A scintillator unit according to claim 1, wherein the grooves provided on one surface of said scintillator plate and the grooves provided on the other surface of said scintillator plate do not face each other.

2. 2. The scintillator unit according to claim 1, a holding frame for holding the scintillator stack, The scintillator unit is characterized in that the holding frame disposes the scintillator laminate in a flow path through which water containing the radiation source flows, the flow path being provided in a housing of the radiation source detection module.

3. 3. The scintillator unit according to claim 2, The scintillator unit is characterized in that the holding frame is detachably attached to a housing of the radiation source detection module.

4. 3. The scintillator unit according to claim 2, The scintillator unit according to claim 1, wherein the holding frame holds the scintillator stack so that the plurality of scintillator plates are parallel to light-receiving surfaces of photomultiplier tubes of the radiation source detection module in the flow path.

5. 5. The scintillator unit according to claim 1, A scintillator unit, wherein the scintillator stack has 4 to 18 scintillator plates.

6. 5. The scintillator unit according to claim 1, The scintillator unit is characterized in that the scintillator laminate portion has a reinforcing member that divides the scintillator plate into a plurality of regions and reinforces the scintillator plate.

7. 7. The scintillator unit according to claim 6, The scintillator unit is characterized in that the scintillator plate is a plastic scintillator.

8. A radiation source detection module for detecting a radiation source in water, comprising: a housing having a flow path through which water containing the radiation source flows; a pair of photomultiplier tubes disposed opposite each other with the flow channel interposed therebetween within the housing; a scintillator unit disposed in the flow path between the pair of photomultiplier tubes and configured to emit scintillation light in response to radiation emitted from the radiation source; Equipped with the scintillator unit includes a scintillator stack in which a plurality of light-transmitting scintillator plates are stacked at predetermined intervals, and a holding frame that holds the scintillator stack within the flow path; Both surfaces of the scintillator plate are grooved to increase the surface area, 10. A radiation source detection module, wherein the grooves provided on one surface of the scintillator plate and the grooves provided on the other surface of the scintillator plate do not face each other.

9. 9. The radiation source detection module of claim 8, The radiation source detection module, wherein the holding frame holds the scintillator stack so that the plurality of scintillator plates are parallel to the light receiving surfaces of the photomultiplier tubes in the flow path.

10. 9. The radiation source detection module of claim 8, The radiation source detection module is characterized in that the holding frame is detachably attached to the housing.

11. 9. The radiation source detection module of claim 8, a radiation source detection module comprising a cooler disposed opposite at least a portion of the pair of photomultiplier tubes with the housing interposed therebetween;

Images