Radiation detection device

Abstract

To provide an inexpensive radiation detection device capable of detecting an incident direction of radiation such as neutrons.SOLUTION: In a radiation detection device 1, a detection chamber 10 is divided into multiple (four) regions circumferentially around its center, and an emission intensity (emitted light quantity) of each region is recognized, which allows an incident direction of neutrons in two dimensions within a plane of paper to be calculated. For this reason, in Fig.1, the circular detection chamber 10 is divided into four equally spaced regions R1 to R4 circumferentially. A boundary of each region is divided by a boundary layer 11 that reflects light (visible light, ultraviolet light, etc.). Photodetectors D1 to D4 that detect the emission intensity of each region are installed on an outer periphery of the circular detection chamber 10, and the incident direction is determined by a magnitude relation of the emitted light quantity of each region (or the total emitted light quantity of the combined regions).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a radiation detection device that detects the incident direction of radiation. [Background technology]

[0002] For visible light, which can easily be realized as an imaging optical system using lenses and reflecting mirrors, the intensity distribution of the light can be easily obtained as a two-dimensional image by using an imaging optical system and a two-dimensional image sensor, and when the visible light is spot-shaped, the direction of incidence can be easily recognized. In contrast, since it is generally difficult to realize an imaging optical system for radiation, it is not easy to recognize the direction of incidence in this way.

[0003] In particular, such imaging optics has not been realized at all for neutrons or gamma rays, so it is required to recognize the incident direction of radiation using a different principle without using lenses or reflecting mirrors.

[0004] For gamma rays, a Compton camera is known that can estimate the direction of incidence of gamma rays before scattering by utilizing the relationship between the energy loss during Compton scattering and the absolute value of the scattering angle in gamma rays in a material (see, for example, Patent Document 1). In a Compton camera, as shown in FIG. 12(a), a first scattering layer 110 and a second absorbing layer 120 are provided, and a gamma ray 200 is configured so that a portion of its energy is absorbed by the scattering layer 110 and the remaining energy is absorbed by the absorbing layer 120. By absorbing the energy of the gamma ray in this way, the scattering layer 110 and the absorbing layer 120 detect its incidence and its position of incidence along the vertical direction in the figure. In this case, the energy lost by scattering of the incident gamma ray in the scattering layer 110 can be calculated, and there is a one-to-one relationship between this lost energy and the absolute value of the scattering angle φ. Therefore, the absolute value φ of this scattering angle can be calculated, and if gamma rays are incident multiple times from the same radiation source, a cone with φ as the cone angle can be created for each incident, and the direction of incidence of the gamma rays can be calculated as the intersection point.

[0005] Since the principles for detecting neutrons and gamma rays are generally different, it is difficult to use this Compton camera directly for neutrons. However, for example, Non-Patent Document 1 describes a technology that measures the absolute value of the scattering angle of neutrons by measuring the energy of the recoil protons due to elastic scattering of neutrons and the neutrons after scattering, and then detects the incident direction of the neutrons using the same principle.

[0006] 12(b) describes a technique for calculating the incident direction of radiation 210 from the pattern of the detection distribution of radiation 210 (measurement results of multiple detection units 130) when a shielding body 140 is present. Here, the material that substantially constitutes the detection unit 130 can also be used as the shielding body 140, and in this case, the material used is lead or the like when the radiation 210 is gamma rays, or polyethylene, Li or the like when the radiation 210 is neutron rays. Non-Patent Document 2 particularly describes the use of Li crystals, which have a large absorption cross section, as such a material. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-48699 [Non-patent literature]

[0008] [Non-Patent Document 1] "Advances in Imaging Fission Neutrons with a Neuteon Scatter Camera", PA Marleau, J. Brennan, K. Krenz, J. Lund, N. Mascarenhas, and S. Mrowka, 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference, N10-2 (2007) [Non-patent document 2] "A Portable Fast-Neutron Imager with 6Li-Containing Scintillators", T.Matsumura and T.Shinkawa, 2016 IEEE Nuclear Science Symposium and Medical Imaging Conference, N33-2 (2016) Summary of the Invention [Problem to be solved by the invention]

[0009] Because the scattering cross section of neutrons is small, increasing the size of the device is necessary to improve the detection efficiency using the method described in Non-Patent Document 1, and the energy of neutrons that can be detected is limited to, for example, 2 MeV or more (fast neutrons). Also, a common problem when detecting gamma rays is that a Compton camera requires a detection device that can detect the incident position over a large area, which is very expensive.

[0010] Furthermore, in the technology described in Non-Patent Document 2, in order to detect fast neutrons, a moderator is required to slow them down, which increases the size of the device. Furthermore, when the crystal of Li or the like that constitutes the detection unit that also serves as a neutron shield is enlarged, the sensitivity to gamma rays, which becomes noise during neutron detection, increases, making it difficult to improve the neutron detection efficiency.

[0011] For this reason, there has been a demand for an inexpensive radiation detection device that can detect the incident direction of radiation such as neutrons.

[0012] The present invention has been made in view of the above problems, and an object of the present invention is to provide an invention that solves the above problems. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention has the following configurations. The present invention is a radiation detection device that calculates the direction of incidence of radiation, such as neutrons or gamma rays, within space, and is characterized by comprising: a detection tank divided into a plurality of regions, each of which is filled with a substance that emits light when the radiation is incident thereon, so that the luminescence amount, which is the intensity of the luminescence within a certain period of time within each region, can be recognized; a photodetector provided in each of the regions to detect the luminescence amount for each of the regions; and an analysis unit that calculates the direction of incidence based on the luminescence amount for each of the regions. The present invention is characterized in that in the detection chamber, the regions are separated by a boundary layer that reflects the emitted light. In the present invention, the analysis unit determines a main region, which is the region with the largest amount of light emission, and calculates the incident direction using the amount of light emission in the main region and the amount of light emission in multiple sub-regions, which are the regions surrounding the main region. In the present invention, the analysis unit sets two ranges that are symmetrical to the main region, and calculates the incident direction using the sum of the light emission amounts of the multiple sub-regions within one of the ranges and the sum of the light emission amounts of the multiple sub-regions within the other range. In the present invention, the analysis unit sets a plurality of combinations of a plurality of adjacent regions, and calculates the incident direction using the sum of the light emission amounts of the plurality of regions in each combination. In the present invention, the analysis unit calculates the energy of the radiation from the ratio of the amount of light emitted in the region on the front side to the amount of light emitted in the region on the back side when viewed from the calculated incident direction. The present invention is characterized in that the detection tank is divided along the circumferential direction from the center of the detection tank to form multiple regions, and the analysis unit calculates the incident direction in accordance with the angle around the center. The present invention is characterized in that a plurality of the regions are formed in the detection reservoir along each of a plurality of intersecting directions. The present invention is characterized in that the luminescent substance in the detection reservoir is water. In the present invention, the radiation is neutrons. In the present invention, the analysis unit is characterized in that it calculates the position of the radiation source that emitted the radiation from the incident direction obtained for each location using a combination of the detection tank and the photodetector installed in different locations. In the present invention, the analysis unit calculates the intensity of the radiation source from at least one of the calculated position and the count rate in the detection tank obtained for each location. [Effects of the Invention]

[0014] Since the present invention is configured as described above, it is possible to obtain an inexpensive radiation detection device that can detect the incident direction of radiation such as neutrons. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing a configuration of a radiation detection apparatus according to an embodiment of the present invention; [Figure 2] This figure shows the process of light emission in water due to the incidence of neutrons (a), the distribution of light emission intensity (b), and the recognition of light emission intensity for each region (c). [Figure 3] The distribution of neutron emission intensity in the detection chamber was calculated for four different incident angles. [Figure 4] 5 is a diagram showing the definition of the amount of luminescence used in the matrix method in the radiation detection device according to the embodiment of the present invention; FIG. [Figure 5] FIG. 3 is a diagram showing the configuration of a first modified example of a detection tank in a radiation detection apparatus according to an embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing the configuration of a second modified example of the detection tank in the radiation detection device according to the embodiment of the present invention. [Figure 7] The figure shows the results of calculating the ratio of the amount of light emitted in the area in front of the incident direction to the amount of light emitted in the area behind it for each neutron energy when a detection chamber divided into four parts is used. [Figure 8]The results show the incidence angle dependence of the ratio of the two light emissions calculated for each neutron energy using the matrix method. [Figure 9] This shows the result of measuring the incidence angle dependency of the ratio of two light emission amounts in the matrix method for each combination of ratios. [Figure 10] 10A and 10B are diagrams showing configurations of third and fourth modified examples of the detection tank in the radiation detection device according to the embodiment of the present invention. [Figure 11] 4 is a flowchart illustrating an operation of the radiation detection apparatus according to the embodiment. [Figure 12] 1A and 1B are diagrams showing an example of the configuration of a conventional detection device that calculates the incident direction of gamma rays (a) and radiation (b). DETAILED DESCRIPTION OF THE INVENTION

[0016] A radiation detection device according to an embodiment of the present invention can detect the direction of incidence of incident radiation (neutrons or gamma rays) and can also calculate the energy. FIG. 1 is a block diagram showing a simplified configuration of this radiation detection device 1. Here, the object to be detected is assumed to be neutrons, and a detection tank 10 made of a material that emits light when neutrons are incident on it is used. The main body of the detection tank 10 is, for example, water, which is sealed in a container.

[0017] When neutrons are incident on water, 2.223 MeV gamma rays are emitted by the neutron capture reaction of hydrogen. High-energy electrons are generated by Compton scattering of these gamma rays, which then emit Cherenkov light (visible light, ultraviolet light, etc.). Furthermore, when Gd is added to water, a total of approximately 8 MeV gamma rays are emitted by the neutron capture reaction of Gd. These gamma rays also form high-energy electrons, which then emit Cherenkov light. Therefore, light is emitted through various processes in response to the incident neutrons. As will be described later, this process is complex, and even if neutrons are incident from a common direction and position, there is considerable variation in the position and direction of the light emission. Therefore, in this case, a large spatial spread occurs in the light emission within a certain period of time. Furthermore, the light emission intensity (number of photons) in this case is low compared to, for example, scintillators used to detect neutrons.

[0018] In this radiation detection device 1, the detection chamber 10 is divided into multiple (four) regions in the circumferential direction around its center, and the emission intensity (amount of light emitted) of each region is recognized, thereby calculating the incident direction of neutrons in two dimensions within the plane of the paper. For this reason, in Figure 1, the circular detection chamber 10 is divided into four regions R1 to R4 at equal intervals in the circumferential direction. The boundaries of each region are defined by boundary layers 11 that reflect light (visible light, ultraviolet light, etc.).

[0019] Here, photodetectors D1 to D4 are installed around the circumference of the circular detection chamber 10 to detect the luminescence intensity of each region. Each photodetector can be, for example, a photomultiplier tube or a silicon photomultiplier (SiPM), and it is preferable to use detectors with common specifications. Since a boundary layer 11 is provided at the boundary between each region, each photodetector can detect almost all photons generated only within the corresponding region, and recognize the amount of luminescence within a certain period of time. The definition of the amount of luminescence will be described later.

[0020] In this case, the boundary layer 11 is required to reflect visible light, ultraviolet light, etc., as well as to transmit neutrons, gamma rays generated by neutrons, and high-energy electrons with a sufficiently high transmittance, and for example, a thin layer of fluororesin or metal material can be used for the boundary layer 11. This makes it possible to reduce the effect of the presence of the boundary layer 11 on the distribution of luminescence generated by neutrons inside the detection chamber 10.

[0021] The outputs of the photodetectors D1 to D4 are input to a computer 30, and an analysis unit 31 in the computer 30 calculates the incident direction of the neutrons from the amount of light emitted in each region recognized from the results. The computer 30 is also provided with a memory unit 32 that stores data during this analysis, and a display unit 33 that displays the results.

[0022] The calculation results for the occurrence of a certain spread of light emission when neutrons are incident on the detection tank 10 are explained below. Figure 2(a) is a schematic diagram showing the process contributing to the light emission when neutrons are incident on the water in the detection tank 10 from below. Here, the neutrons are repeatedly scattered in various directions as they are decelerated in the water. During this process, the Gd nuclei that capture the neutrons emit gamma rays, but the direction and number of these gamma rays emitted vary. In addition, the traveling direction of the high-energy electrons generated by Compton scattering of these gamma rays also varies. Therefore, the position of the light emission and the direction from which the light is emitted when a single neutron is incident are not constant. In addition, multiple light emissions may occur due to the incidence of a single neutron.

[0023] For this reason, as shown in Figure 2(b), when neutrons are repeatedly irradiated from the center of the bottom of a rectangular body of water with sides of 20 cm as shown, the emission intensity in the water over a certain period of time will have a spread as shown in Figure 2(b). Here, the area surrounded by the solid line is an area of ​​high emission intensity, and the areas surrounded by the dashed line and dotted line are areas of decreasing emission intensity. As shown here, for example, if the size of the detection tank 10 is about 20 cm as mentioned above, this spread is relatively large, and it is generally not easy to accurately calculate the direction of incidence from the results of Figure 2(b) alone.

[0024] Here, if the results of Figure 2(b) are divided into nine regions (3 vertical x 3 horizontal) as shown in Figure 2(c), and the emission intensity for each region is calculated as shown in Figure 2(b), and the emission amount is classified as "L (large)," "M (medium)," and "S (small)," the emission intensity distribution for each region can be recognized as shown in Figure 2(c). Here, the emission is not only observed in the region where the neutron actually entered, but also throughout the entire region within the detection chamber 10, and the intensity distribution is biased toward the neutron entrance side. The analysis unit 31 detects the incident direction of the neutron based on the relationship between the emission amount for each region. When each region is divided using the thin boundary layer 11 as described above, the emission for each region is not affected by the presence of the boundary layer 11, and the emission intensity for each region can be properly recognized.

[0025] The following is a specific explanation based on the simulation results of the method for calculating the incident direction performed by the analysis unit 31. Here, the amount of light emitted in each region when a small neutron source is moved around the detection tank 10 in FIG.

[0026] Here, the light emission amount is an evaluation quantity of the intensity of light emission caused by multiple incidences of neutrons over a certain period of time (measurement time), and is obtained from the output of each photodetector as a measurement quantity that can be used in the following analysis. As mentioned above, what is directly detected by a photodetector is not neutrons, but light (visible light, ultraviolet light, etc.) generated by the incidence of neutrons. As is well known, in the output (output voltage) of a photodetector (photomultiplier tube, etc.), an output corresponding to one light emission is recognized as a pulse. Therefore, in the simplest case, the number of these pulses (count number) within the measurement time can be used as the light emission amount.

[0027] Furthermore, the pulse height of the pulse is generally not uniform, and varies depending on, for example, the energy of the gamma ray that caused the light emission, even if the measurement conditions of the photomultiplier tube are the same. Taking this into consideration, when the pulse height is not constant in this way, a histogram (frequency distribution) of the pulse height (or pulse area, which will be described later) within the measurement time may be created, and this area may be defined as the light emission amount.

[0028] During these measurements, it is preferable to remove (not count) pulses that become noise components (not caused by neutrons). To achieve this, in either case, it is preferable to set a threshold value for the pulse height of the pulses to be counted and count only pulses whose pulse height exceeds this threshold. For example, if a uniform threshold value is set for each region, the difference in the amount of light emitted in each region can be measured as the difference in the number of counts in each region. Furthermore, as mentioned above, the total energy of gamma rays caused by neutrons is approximately 8 MeV, and the pulse height of the detection pulse for the light emitted by these gamma rays corresponds to this energy. If the energy of background gamma rays (noise components) is smaller than this, such noise components can be removed by setting the threshold value for the pulse height higher than the pulse height of such noise components but lower than the pulse height corresponding to 8 MeV.

[0029] Furthermore, a single pulse can be recognized as an output over a short period of time in which the output voltage, when plotted on the horizontal axis with time elapsed and the output voltage (absolute value) on the vertical axis, increases from the point at which the output voltage is zero, reaches a maximum wave height (the pulse wave height described above), and then decreases again to zero. However, the same result can be obtained by using the integral value of the output voltage at this time (pulse area) instead of the pulse wave height described above and setting a threshold value for this in the same way as above.

[0030] Furthermore, when the simple count number is used as the amount of light emission as described above, a threshold value may also be set for this count number, and only when the count number exceeds this threshold value may the amount of light emission be defined, or a certain level may be assumed in advance as noise, and the amount of light emission may be determined by subtracting this level from the count number. However, even when various threshold values ​​are used as described above and noise removal is not sufficient, the amount of light emission for each region is compared in the analysis described below, and in particular only the magnitude relationship or ratio is used, making it possible to calculate the direction of incidence with the resolution described below.

[0031] Therefore, what is required for the luminescence amount is that the magnitude relationship between the regions can be meaningfully recognized. As long as this magnitude relationship can be recognized using the luminescence intensity distribution shown in Figure 2(b), other definitions of luminescence amount can be used. Furthermore, the measurement time required to obtain such luminescence amount is determined so as to obtain a number of events (number of detected pulses) that allows the magnitude relationship between the luminescence amounts between regions based on the luminescence intensity distribution shown in Figure 2(b) to be recognized with a sufficiently small statistical error. Therefore, the length of the required measurement time is appropriately set depending on the intensity of the radiation source, etc. For example, the number of events can be increased by enlarging the detection chamber 10, thereby shortening the measurement time.

[0032] Figure 3 shows a schematic diagram of neutrons entering the detection tank 10, and Figures 3(a) to (d) show the cases where the radiation source 300 is positioned around the center of the detection tank 10 and the incident direction θ relative to the vertical direction is 0°, 22.5°, 45°, and 67.5°, respectively.

[0033] Here, the amount of light emitted in each region is designated as M1 to M4 corresponding to regions R1 to R4, and values ​​calculated by simulation for 2.0 MeV neutrons are shown as numerical values ​​in the figure. Also, in Figure 3, the shape of the light emission distribution corresponding to Figure 2 is shown schematically by a dotted line.

[0034] In this case, the procedure for calculating the incident direction θ will be specifically described. There are several methods for this procedure, but first, a method for calculating θ from the light emission amount for each region (M1 to M4) (hereinafter referred to as the region method) will be described.

[0035] In the case of Figure 3(a) (θ=0°), the light emission situation is symmetric on both sides (left and right) with respect to the incident direction, so M1 = M4 > M2 = M3. In the case of Figure 3(c) (θ=45°), M1 is the largest, and similarly due to symmetry with respect to the incident direction, M2 = M4. In the case of Figure 3(b) (θ=22.5°), M1 is the largest, and because the incident direction is lower than in Figure 3(c), M4 > M2. In the case of Figure 3(d) (θ=67.5°), M1 is the largest, and in this case, conversely, M2 > M4.

[0036] Therefore, when θ is calculated in units of 22.5°, if M1 is the largest among M1 to M4, the analyzer 31 can determine θ=0° when M1=M4, θ=45° when M2=M4, θ=22.5° when M4>M2, and θ=67.5° when M2>M4. Using similar criteria, for example, when M2 is the largest, the analyzer 31 can determine θ=90°, 112.5°, 135°, or 157.5° based on the relationship between M2, M1, and M3. Similarly, when M3 is the largest, the analyzer 31 can determine θ=180°, 202.5°, 225°, or 247.5° based on the relationship between M3, M2, and M4. When M4 is the largest, the analyzer 31 can determine θ=270°, 292.5°, 315°, or 337.5° based on the relationship between M4, M1, and M3. That is, using the above method, θ can be calculated in units of 22.5° (or ±11.25°). Here, the angular range corresponding to θ occupied by each region in Figure 1 is 90°, but this resolution is 1 / 4 of that.

[0037] That is, in the area method, first, the area with the largest light emission amount (main area) is recognized. Then, the incident angle is determined based on the magnitude relationship between the light emission amount of this area and the light emission amounts of a plurality of areas (sub-areas) around this area. The sub-areas selected at this time are the area adjacent to the main area and two areas in a symmetrical positional relationship with respect to the main area.

[0038] Next, a method (hereinafter referred to as the matrix method) for calculating θ from the sum of combinations of the light emission amounts (M1 to M4) for each area will be described. Here, as shown in FIG. 4, considering the sum of the light emission amounts of two adjacent areas, let M3 + M4 = MA, M4 + M1 = MB, M1 + M2 = MC, and M2 + M3 = MD in FIG. 3. Also in this case, first, the largest among MA to MD is obtained. When MB becomes the largest, when θ is considered in units of 22.5° as described above, the possible values of θ are any of θ = 315°, 337.5°, 0°, 22.5°, 45°. In this case, if MA = MB, then θ = 315°; if MA > MC, then θ = 337.5°; if MA = MC, then θ = 0°; if MA < MC, then θ = 22.5°; if MB = MC, then θ = 45°. Similar to the case of the area method, after recognizing the largest among MA to MD, by the same procedure, cases of θ = 67.5°, 90°, 112.5°, 135°, 157.5, 180°, 202.5°, 225°, 247.5°, 270°, 292.5° can be determined. Also, for example, if MA / MC > 1, it can be estimated that θ is between 180° and 360°, and if MD / MB, it can be estimated that θ is between 90° and 270°.

[0039] There are statistical errors in M1 to M4 measured in the above cases, and this statistical error becomes particularly large when the count number is small. In the matrix method, since the total count number of a plurality (two in the above example) of areas is used, this statistical error can be made smaller compared to the area method. Also, in both the above area method and matrix method, the incident direction is determined based on the magnitude relationship of the light emission amount for each area (or the total light emission amount of a combination of areas). Therefore, this calculation is extremely easy and has high robustness.

[0040] Conventional technologies (such as those described in Non-Patent Documents 1 and 2) use multiple detection units, but each detection unit functions as a single detection element, that is, as a single pixel in a two-dimensional or three-dimensional radiation image. Therefore, conventional technologies do not focus on the light emission distribution within each detection unit (pixel), and do not utilize such information in calculating the incident direction. In contrast, the present invention utilizes the distribution of light emission within a single detection unit.

[0041] Furthermore, in the above configuration, the regions in the detection unit (detection tank) do not function as pixels, and as mentioned above, the resolution of the incident angle (corresponding to a pixel) is smaller than the angle range corresponding to this region. In other words, by the above analysis, the incident angle can be calculated with a resolution smaller than the size of each region.

[0042] In the above example, the detection reservoir 10 is divided into four sections as shown in Figures 2 and 3, and in this case, θ is recognized in increments of 22.5°. However, in the detection reservoir 20 (first modified example) shown in Figure 5, the detection reservoir 20 is divided into eight sections, R11 to R18. In this case, the same method is possible even when the amount of luminescence in each section is M11 to M18. In this case, for example, in the above-mentioned region method, when M11 (main region) is largest, θ is set to 0° if M11 = M18. However, while other values ​​of θ were estimated based on the magnitude relationship between M2 and M4 in the case of Figure 3, here, instead of M2 and M4 as in the above case, a similar estimation can be made using M14 + M13 + M12, which is the integrated luminescence intensity of three regions R14-R12 (sub-regions) positioned symmetrically with respect to R11, and M16 + M17 + M18, which is the integrated luminescence intensity of three regions R16-R18 (sub-regions). In this case, instead of the integrals of the three regions, the integrals M13 + M12 and M17 + M18 of two symmetrical regions that become the sub-regions may be used instead. Alternatively, a single region (e.g., M12 and M18, M13 and M17, or M14 and M16) may be used as the sub-region. That is, among the sub-regions selected as described above, the two regions that are symmetrically positioned relative to the main region can be a combination of multiple regions or a single region, and the combination can be set appropriately. The analysis unit 31 can set this combination appropriately.

[0043] Furthermore, when using the matrix method, in the case of four divisions (Figure 4), two combinations of each of the four luminescence intensities (MA to MD) were used in the analysis, whereas in the case of eight divisions (Figure 5), a similar analysis can be performed using many more combinations, such as the combinations M11+M12+M13+M14 and M15+M16+M17+M18, and the combinations M12+M13+M14+M15 and M16+M17+M18+M11. In this way, the area method and matrix method can be applied in the same way even in the case of eight divisions.

[0044] In the case of eight divisions, θ can be calculated with higher accuracy in units of 11.25° using the same method as above. In this way, if the number of divisions is n, θ can be calculated using the same method with an angular resolution of 360 / n / 4 (°). Furthermore, when the number of divisions is increased, the amount of light detected by each photodetector decreases. Therefore, when the amount of light emitted from a single region is used, the statistical error increases compared to the case of four divisions as described above. However, for example, if M11+M12, M12+M13, M13+M14, M14+M15, M15+M16, M16+M17, M17+M18, and M18+M11 are defined as matrices in FIG. 5, θ can be calculated with the same statistical error as M1, M2, M3, and M4, respectively. In this way, when the number of divisions is large, the angular resolution can be increased and the calculation can be handled in the same way as when the number of divisions is small. The number of divisions is set appropriately depending on the required characteristics and performance (measurement time, angular resolution, etc.) and the situation (expected detection intensity, calculation processing speed, etc.).

[0045] In the above example, the incident direction in a two-dimensional plane (paper surface) was estimated using regions obtained by equally dividing a circle in the circumferential direction. Similarly, the incident direction in three-dimensional space can be estimated using regions obtained by equally dividing a sphere in three-dimensional space. Figure 6 shows the configuration of detection reservoir 25, a second modified example, in which the sphere is divided into eight regions, 2 (length) × 2 (width) × 2 (height). In this case, regions R21U–R24U and regions R21D–R24D, corresponding to regions R1–R4 in detection reservoir 10, are provided on the lower side, thereby dividing the sphere into eight equal parts. In this case, with the x, y, and z axes taken as illustrated with the center of the sphere as the origin, A and B represent regions in the xy plane on the positive and negative sides of z, respectively, and C and D represent regions in the yz plane on the positive and negative sides of x, respectively. Similarly, E and F are defined as regions in the xz plane on the positive and negative sides of y, respectively.

[0046] In this case, too, the horizontal and vertical components of the incident angle can be estimated by calculating the area with the greatest amount of light emission in the area method and applying the same method to each of the horizontal and vertical directions. Also, in the matrix method, for example, the horizontal component of the incident angle can be estimated by using the integral value of the amount of light emission in each of the areas C, D, E, and F instead of the above-mentioned MA to MD, and the vertical component of the incident angle can be estimated by using the integral value of the amount of light emission in each of the areas A, B, C, and D instead of the above-mentioned MA to MD.

[0047] The procedure for estimating the incident direction of neutrons has been described above. After the incident direction has been estimated, the analysis unit 31 can estimate the energy of the incident neutrons as shown below. To estimate the incident direction, as described above, the light emission amounts of two regions (including cases where each region is further divided into smaller regions) that are basically symmetrical in a direction perpendicular to the incident direction are obtained. In contrast, the light emission distribution caused by neutron incidence in the detection tank 10 depends on the energy of the neutrons, so the energy of the neutrons can be obtained from the light emission amounts of two or more regions along the incident direction.

[0048] Basically, when neutrons of the same energy are repeatedly incident from the same direction, resulting in an emission intensity distribution like that shown in Figure 2(b) (corresponding to the case where the neutron source is located at a single point in space), the ratio of the emission intensity on the near side of the incident direction to the emission intensity on the far side (incident direction emission intensity ratio) becomes larger when the neutron energy is small. Therefore, the neutron energy can be calculated from this ratio.

[0049] In the case of Figure 3(b) (θ=22.5°), the results of simulations where M1 (corresponding to the front side) and M2 (corresponding to the back side) are set to neutron energies of 0.1 MeV, 0.5 MeV, 2.0 MeV, and 5.0 MeV are shown in Figure 7. From these results, it is clear that M1 / M2 is dependent on the neutron energy.

[0050] The region for calculating the energy can be set in the same manner as in the matrix method. Fig. 8 shows the results of simulating the MA / MC value by changing the neutron incident angle θ in the configuration of Fig. 4. MA / MC corresponds to the above-mentioned incident direction light intensity ratio when θ = 270°, but it is clear that MA / MC depends on the neutron energy near θ = 270°. Therefore, if the neutron energy dependence of the incident direction light intensity ratio is calculated in advance and stored in the memory unit 32, it is possible to determine the region corresponding to the MA and MC in accordance with the estimated incident direction, calculate the incident direction light intensity ratio, and estimate the energy of the incident neutrons from this value.

[0051] Figure 9 shows the results of actually measuring MA to MD in the matrix method when the configuration in Figure 4 is a 20 cm square rectangle and θ is changed by changing the position of the radiation source 300, and calculating the ratio between them. From this result, for example, at θ = 270°, MA / MC > 1 and MB / MD = 1, which coincides with the relationship of the light emission amount when θ = 270°, where MA is the largest in the matrix method when divided into four as described above. Similarly, at θ = 315°, MA / MC = MB / MD > MC / MD, which coincides with the relationship of the light emission amount when θ = 315°, where MA is the largest in the matrix method when divided into four as described above.

[0052] In other words, it was confirmed that the neutron incident direction can be estimated as described above by dividing a two-dimensional plane into four parts and using the matrix method. In this case, for example, the maximum values ​​of MA / MC and MB / MD in Figure 9 are approximately 2.0. This value corresponds to the case where the neutron energy in Figure 8 is 2.0 MeV. In other words, the neutron energy in the measurement in Figure 9 can be estimated to be approximately 2.0 MeV.

[0053] In the above example, the neutron energy was calculated from the ratio of the light emission in two regions along the incident direction. However, if the neutron energy dependence of the relationship between the light emission in three or more regions along the incident direction (distribution of light emission) is known in advance, the neutron energy can be determined from this relationship in a similar way. In this case, the energy can be determined more accurately.

[0054] In the above explanation, when the region is divided into four in this way, θ is calculated in 22.5° increments, for example, depending on the magnitude relationship between MB and MD (whether MB / MD > 1, MB = MD, or MB / MD < 1). However, for example, in Figure 9, MB / MD is θ = 247.5°, 258.75°, 270°, 281.25°, and 292.5°, which are 0.75, 0.85, 1.0, 1.2, and 1.3, respectively. Therefore, when MA is at its largest, θ can be calculated with a resolution smaller than 22.5° depending on the value of the MB / MD ratio, rather than simply the magnitude relationship between MB and MD.

[0055] Furthermore, when there is a single radiation source, if two combinations of the above-described detection tank and photodetector are installed at different locations and the analysis unit 31 calculates the direction of incidence of neutrons on each detection tank, the position of the radiation source in space can be recognized, and the distance from each detection tank to the radiation source can be calculated.

[0056] Furthermore, if information about the type of radiation source is known in advance, the strength of the radiation source (e.g., in Bq units) can be calculated from the counting rate (corresponding to the aforementioned number of counts per unit time) throughout the entire detection tank and this distance. For example, there are fewer types of neutron radiation sources than gamma-ray sources, and the average energy of the neutrons emitted varies depending on the radiation source (e.g., 2.3 MeV for a Cf radiation source and 4.4 MeV for an Am-Be radiation source). Therefore, the type of radiation source can be determined from the calculated energy. If the relationship between the counting rate in the detection tank and the dose rate in the detection tank (e.g., in μSv / h units) is stored in advance in the memory unit 32, the analysis unit 31 can calculate the strength of the radiation source (e.g., in Bq units) according to the type from the relationship between the distance from the detection tank to the radiation source and this dose rate.

[0057] In this case, it is not necessary to simultaneously install two combinations of detection tank and photodetector at different locations; it is sufficient to be able to determine the incident direction θ at multiple different locations. For example, if results (incident direction θ) using a single combination are obtained at different locations, they are the same even if these results are obtained at different times. Therefore, it is not necessary to use multiple detection tanks, etc., when calculating the intensity of the radiation source; a configuration using multiple detection tanks, etc., may be used to obtain measurement results at multiple locations.

[0058] 1, detection reservoir 10 is inexpensive because it is mainly made of water. Furthermore, the multiple regions inside it can be easily formed, for example, by forming boundary layer 11 inside a container and then filling it with water. This makes it easy to make detection reservoir 10 smaller or larger.

[0059] In addition to neutrons, gamma rays are also included as radiation for which the incident direction can be calculated using the above configuration. While FIG. 2(a) shows the case of incident neutrons, the location of Compton scattering and the direction of electron emission also vary when gamma rays are incident, so the emission distribution has a certain degree of spread, just like neutrons. Therefore, for example, if it is known in advance that there is no neutron source and only a gamma ray source, the incident direction of the gamma ray can be calculated using the same detection chamber. In this case, for example, the target to be detected can be limited by setting a threshold value for the pulse height in the photodetector as described above. For example, based on this setting alone, it is possible to select whether to preferentially detect neutrons only or to simultaneously detect neutrons and gamma rays.

[0060] The medium constituting the detection chamber can be appropriately selected depending on the type of radiation to be detected. For example, Li crystals, which have been used in conventional technology to measure neutrons, can be used. In this case, the angle of incidence can be calculated in a similar manner by dividing each region into appropriate sizes according to the spread of the emission distribution (for example, a few μm or less for Li crystals) and measuring the difference in the amount of emission in each region, or by diffusing Li or the like in the moderator to spread the emission distribution.

[0061] In the above example, each region is formed by dividing it into equal angles from the center of the detection tank. However, this setting can be adjusted as needed. For example, if the range in which the incident direction is to be determined is predetermined, the angle can be reduced to increase the number of divisions in this range, and the number of divisions can be reduced in other regions. When the sizes of the regions differ, a similar analysis can be performed using the detection efficiency or luminescence intensity corrected (normalized) according to the size. As described above, it is preferable to set each region in the detection tank so that the subregions required for analysis are obtained in a symmetrical positional relationship. However, in this case, a symmetrical positional relationship is not necessary, and a similar analysis can be performed after appropriate corrections are made.

[0062] Furthermore, although the detection reservoir in the above example was assumed to be circular or spherical, it can also be divided in the circumferential direction viewed from the central axis and analyzed in the same way for a square (rectangle), regular hexagon, or regular octagon (or any of these three-dimensional shapes).When dividing the detection reservoir in the horizontal and vertical directions as shown in Figure 6 to calculate the horizontal and vertical components of the incident angle, the number of divisions in the horizontal and vertical directions may be different.

[0063] As mentioned above, it is particularly preferable to use a material for the boundary layer 11 that has high reflectivity for visible light, ultraviolet light, etc., and high transmittance for neutrons, gamma rays, and high-energy electrons. However, even if these properties are poor, calculation of the incident direction is possible, although the accuracy of the calculation will be reduced. For example, if an acrylic plate with poor properties is used for the boundary layer 11 and each region is rectangular, the detection tank can be constructed by combining acrylic water tanks (corresponding to each region), which makes it particularly easy and inexpensive to obtain the detection tank.

[0064] An example of the configuration of a detection reservoir in such a case (third modified example) is shown schematically in FIG. 10. Here, the entire detection reservoir is rectangular, and each region corresponds to a structure obtained by dividing it into four parts. Detection reservoir 40 (first modified example) in FIG. 10(a) is configured by tightly combining water reservoirs 41-44 (corresponding to each region), separated by boundary layers 45 made of acrylic plates. In this case, a certain reflectivity for light can be obtained by coating the surface of boundary layer 45 with a thin layer of fluororesin or the like. However, since no light is emitted by the incident neutrons in boundary layer 45 in this case, boundary layer 45 becomes an insensitive region, which reduces detection sensitivity. However, even in this case, it is possible to calculate the incident direction of radiation by comparing the amount of light emitted in each region, as described above.

[0065] In the detection reservoir 50 (fourth modification) of FIG. 10(b), in which the water reservoirs 41-44 are not in close contact but are combined via a gap (air layer), the incident direction can be calculated in a similar manner, although the dead zone increases. That is, as long as a certain level of measurement accuracy can be obtained, various materials can be used for the boundary layer 11, and the configuration of the detection reservoir can be set accordingly. Furthermore, as long as the amount of luminescence in each zone divided by a certain standard can be properly evaluated, the boundary layer 11 is not necessary.

[0066] Furthermore, the detection tanks of Figures 1, 5 (planar structure), and 6 (three-dimensional structure) can calculate the incident direction of neutrons in all directions in a two-dimensional plane or three-dimensional space, and then the neutron energy can be calculated as described above. However, if it is known in advance that the incident direction is within a certain range, the division of the areas in the detection tank can be appropriately set accordingly. In this case, it is possible to calculate only the incident direction, but not the energy. Furthermore, in the above example, the incident direction and energy were calculated from the common measurement results of the detectors, but the measurements for calculating the incident direction and the measurements for calculating the energy may be performed separately.

[0067] 11 is a flowchart showing the operation of the analysis unit 31 based on the above. First, the analysis unit 31 recognizes the amount of light emitted in all regions within a predetermined time (S1), and then, as described above, calculates the incident direction of neutrons from this result using the region method or matrix method (S2). However, the incident direction may also be calculated from similar results using a method other than this method.

[0068] Next, the analysis unit 31 calculates the amount of light emitted in the region in front of the detection tank and the region behind the detection tank in the direction of incidence based on the calculated incidence direction, and calculates the energy of the incident neutrons from the ratio of these amounts (S3). Note that this step is omitted if the detection tank is configured in such a way that the region in front and the region behind cannot be set. Alternatively, the orientation of the detection tank may be changed so that this calculation is possible.

[0069] Next, when two sets of detection tanks are used as described above (including when two sets of detection tanks are essentially used as described above), the position of the radiation source in space is calculated (S4) from the incident angle (S2) calculated for each, thereby making it possible to recognize the distance between each detection tank and the radiation source. Then, when the type of radiation source is known in advance as described above and the relationship between the counting rate in the entire detection tank and the dose rate in the detection tank is known, the analysis unit 31 can calculate the intensity of the radiation source (e.g., in Bq units) using, for example, the counting rate in the entire detection tank and this distance as described above (S5). This calculation may be based on the results of only one detection tank, or may be the average of the results of both detection tanks. Furthermore, two or more sets of detection tanks may be used.

[0070] The present invention has been described above based on an embodiment. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0071] 1. Radiation detection equipment 10, 20, 25, 40, 50 detection tank 11, 45 boundary layer 30 Computer 31 Analysis Department 32 Storage section 33 Display section 41~44 Aquarium 110 Scattering layer 120 Absorbing layer 130 Detection Unit 140 Shield 200 gamma rays 210 Radiation 300 source D1~D4 Photodetectors

Claims

1. A radiation detection device that calculates the incident direction in space of radiation that is a neutron or a gamma ray, a detection chamber divided into a plurality of regions each filled with a substance that emits light upon incidence of radiation, so that the intensity of the light emitted within each region within a certain period of time, i.e., the amount of light emitted, can be recognized; a photodetector provided for each of the regions to detect the amount of light emitted for each of the regions; A radiation detection device comprising: an analysis unit that calculates the incident direction based on the amount of light emitted for each of the regions.

2. 2. The radiation detection device according to claim 1, wherein the regions in the detection chamber are separated by boundary layers that reflect the emitted light.

3. 3. The radiation detection device according to claim 1, wherein the analysis unit determines a main region, which is the region with the largest amount of light emission, and calculates the incident direction using the amount of light emission in the main region and the amount of light emission in a plurality of sub-regions, which are the regions surrounding the main region.

4. 4. The radiation detection device according to claim 3, wherein the analysis unit sets two ranges that are symmetrical with respect to the main region, and calculates the incident direction using a sum of the light emission amounts of the sub-regions in one of the ranges and a sum of the light emission amounts of the sub-regions in the other range.

5. 3. The radiation detection device according to claim 1, wherein the analysis unit sets a plurality of combinations of a plurality of adjacent regions and calculates the incident direction using a sum of the light emission amounts of the plurality of regions in each combination.

6. 3. The radiation detector according to claim 1, wherein the analysis unit calculates the energy of the radiation from a ratio of the amount of light emitted in the region on the front side to the amount of light emitted in the region on the back side when viewed from the calculated incident direction.

7. the detection reservoir is divided into a plurality of regions along a circumferential direction as viewed from the center of the detection reservoir, 3. The radiation detection device according to claim 1, wherein the analysis unit calculates the incident direction in accordance with an angle around the center.

8. 3. The radiation detection device according to claim 1, wherein a plurality of the regions are formed in the detection tank along each of a plurality of intersecting directions.

9. 3. A radiation detection apparatus according to claim 1, wherein the luminescent substance in the detection tank is water.

10. 10. The radiation detection device according to claim 9, wherein the radiation is neutrons.

11. The radiation detection device according to claim 1 or 2, wherein the analysis unit calculates the position of the radiation source that emitted the radiation from the incident direction obtained for each location using a combination of the detection tank and the photodetector installed in different locations.

12. The radiation detection device according to claim 11, wherein the analysis unit calculates the intensity of the radiation source from at least one of the calculated position and the count rate in the detection tank obtained for each location.

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