Charged particle measuring device and method for controlling the charged particle measuring device

Abstract

To provide a charged particle measuring technique that can grasp the type of deterioration or the degree of deterioration of a gas detector and maintain constant measurement accuracy over a long period.SOLUTION: A charged particle measuring device 1 comprises: a plurality of gas detectors 33 that are filled with gas for detecting passage of charged particles μ; a locus calculation unit 16 that calculates the locus of the charged particles μ based on detection signals output from the plurality of gas detectors 33 and parameters associated with the gas detectors 33; a measuring unit 17 that measures an object 2 being a measuring object based on the locus of the charged particles μ; a signal strength acquisition unit 18 that acquires the signal strengths of the detection signals; an operating state monitoring unit 22 that evaluates the operating states of the gas detectors 33 based on the signal strengths corresponding to the gas detectors 33; and a parameter update unit 23 that, when the operating states of the gas detectors 33 change, updates the parameters associated with the gas detectors 33.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present invention relate to charged particle measurement techniques. [Background technology]

[0002] A known technique for imaging the inside of a measurement target is a radiography technique that uses charged particles such as muons. Charged particles, unlike light, X-rays, and electromagnetic waves, scatter as they pass through materials. Therefore, a feature of this technique is that it is possible to estimate the density or average atomic number of a material from the direction in which the electrons fly and the degree of scattering.

[0003] One type of charged particle is called a cosmic ray muon, which is generated by cosmic rays coming from outside the atmosphere. This cosmic ray muon has very high energy and high penetrating power. Therefore, it is used for imaging large structures such as volcanoes and pyramids. When performing such imaging, it is important to obtain the trajectory of the charged particle with high accuracy. As a conventional technique, there is a device using a plastic scintillator or a fiber scintillator. There is also a device using a drift tube detector as a gas detector.

[0004] For example, an inspection method has been proposed in which multiple drift tube detectors are arranged above and below an object to calculate the trajectories of charged particles above and below the object, and information about the inside of the object is obtained from these trajectories, while a gamma ray signal is obtained to detect radioactive materials. A measurement method for efficiently operating such an inspection method has also been proposed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5479904 [Patent Document 2] Patent No. 6342399 Summary of the Invention [Problem to be solved by the invention]

[0006] By using a drift tube detector, it is possible to measure an object using cosmic ray muons, but in order to perform the measurement with high accuracy, it is important to maintain a constant performance. However, since the drift tube detector is characterized by being filled with gas, its performance may change due to changes in the composition or pressure of the gas. In addition, the shape or position of the drift tube detector may change due to measurements with a heavy object placed on it or changes in temperature. Due to these factors, the performance may differ for each measurement. In particular, since changes in the composition of the gas or deviations in the position of the drift tube detector are minute changes, it is difficult to directly inspect them, and it is difficult to inspect and correct them in real time.

[0007] An embodiment of the present invention has been made in consideration of the above circumstances, and aims to provide a charged particle measurement technology that can grasp the type or degree of deterioration of a gas detector and maintain a constant measurement accuracy over a long period of time. [Means for solving the problem]

[0008] A charged particle measuring device according to an embodiment of the present invention includes a plurality of gas detectors filled with a gas for detecting the passage of a charged particle, a trajectory calculation unit that calculates a trajectory of the charged particle based on detection signals output from the plurality of gas detectors and parameters associated with each of the gas detectors, a measurement unit that measures an object to be measured based on the trajectory of the charged particle, a signal intensity acquisition unit that acquires a signal intensity of the detection signal, an operation status monitoring unit that evaluates an operation status of each of the gas detectors based on the signal intensity corresponding to each of the gas detectors, and a monitoring unit that monitors when the operation status of the gas detector changes. Is and a parameter update unit that updates the parameters associated with the gas detector when the parameter update unit detects a problem. Effect of the Invention

[0009] According to an embodiment of the present invention, a charged particle measurement technique is provided that is capable of grasping the type or degree of deterioration of a gas detector and maintaining a constant measurement accuracy over a long period of time. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a muon tomography apparatus according to a first embodiment. [Diagram 2] FIG. 1 is a block diagram showing a muon tomography apparatus according to a first embodiment. [Diagram 3] FIG. 2 is a block diagram showing a main control unit according to the first embodiment. [Figure 4] An explanatory diagram showing the scattering angles of muons. [Diagram 5] FIG. 2 is a perspective view showing an example of the arrangement of a drift tube detector. [Figure 6] FIG. 2 is a cross-sectional view showing a drift tube detector cut in half. [Figure 7] FIG. 2 is a cross-sectional view showing the entire drift tube detector in the longitudinal direction. [Figure 8] 13 is a graph showing an example of a time difference distribution. [Figure 9] 4 is a flowchart showing a control process of the muon tomography apparatus. [Figure 10] 13 is a flowchart showing an operation check process. [Figure 11] 1 is a flowchart showing a method of operating the muon tomography apparatus. [Figure 12] FIG. 13 is a diagram showing a muon tomography apparatus according to a second embodiment. [Figure 13] FIG. 11 is a block diagram showing a main control unit according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (First embodiment) Hereinafter, embodiments of a charged particle measuring device and a control method thereof will be described in detail with reference to the drawings. First, a first embodiment will be described with reference to FIGS.

[0012] Reference numeral 1 in FIG. 1 denotes a muon tomography device as a charged particle measuring device. This muon tomography device 1 is a non-destructive inspection system that inspects an object to be measured without destroying it. An example of the object to be measured is a vehicle 2 such as a truck transporting a container. For example, the muon tomography device is used to inspect whether or not a predetermined object 3 is present in the vehicle 2. The object may be a container transported by airplane or ship, luggage that can be carried by human power, or the like.

[0013] This muon tomography device 1 performs inspection (imaging) of a vehicle 2 by muon tomography (muon inspection) using muons μ as charged particles. For example, confirmation is made as to whether the items contained in the cargo being transported are consistent with the contents described in the application specification, or whether or not illegal substances are present. In particular, inspections are performed with the aim of detecting nuclear materials such as uranium concealed in the cargo. Since many inspections are performed consecutively, the inspections are performed without opening the inside of the transported cargo.

[0014] It is sufficient that the muon tomography device 1 can at least identify the type of material. The type of material includes the elements of the material, the composition of the material, the ratio of each element contained in the material, the density of the material, the amount of the material, etc. The type of material can be identified by utilizing the characteristic that the scattering angle of the muon μ differs for each material.

[0015] Muons used in muon tomography exist mainly as cosmic rays. Muons are a type of secondary cosmic ray that is produced when primary cosmic rays that enter the Earth from space react with the Earth's atmosphere. Muons have a positive or negative charge and a high energy of 3 to 4 GeV on average, so they have a much higher penetrating power than radiation such as X-rays.

[0016] Muons μ can also be artificially generated using an accelerator. In this embodiment, a form in which muons μ from cosmic rays are used is illustrated as an example, but artificially generated muons μ may also be used.

[0017] In this embodiment, the muon tomography device 1 is illustrated as an example of the charged particle measuring device, but other configurations are also possible. For example, this embodiment may be applied to a device that performs measurement using charged particles such as electrons.

[0018] The muon tomography apparatus 1 of this embodiment includes a first muon trajectory detector 6, a second muon trajectory detector 7, and an analysis computer 8.

[0019] The first muon trajectory detector 6 and the second muon trajectory detector 7 are provided in positions facing each other across the vehicle 2. For example, they are provided in positions facing each other across the vehicle 2 in the vertical direction. This pair of muon trajectory detectors 6, 7 are devices that detect muons μ, which are cosmic rays that exist in nature.

[0020] Each of the muon trajectory detectors 6, 7 is housed in a predetermined housing (frame) 4. The first muon trajectory detector 6 on the upper side is supported by a support 5. The second muon trajectory detector 7 on the lower side is buried underground. The vehicle 2 is placed on a predetermined pedestal 9.

[0021] Next, the system configuration of the muon tomography apparatus 1 will be described with reference to the block diagrams shown in FIGS.

[0022] As shown in FIG. 2, the muon trajectory detectors 6 and 7 are connected to an analysis computer 8 and controlled by this analysis computer 8 .

[0023] The analysis computer 8 includes an input unit 10, an output unit 11, a communication unit 12, a storage unit 13, and a main control unit 14. The analysis computer 8 is configured as a computer having hardware resources such as a CPU, a ROM, a RAM, and a HDD, and in which information processing by software is realized using the hardware resources as the CPU executes various programs. Furthermore, the control method of the muon tomography apparatus 1 of this embodiment is realized by having the computer execute various programs.

[0024] Each component of the analysis computer 8 does not necessarily have to be provided in one computer. For example, one analysis computer 8 may be realized using a plurality of computers connected to each other via a network. For example, a computer for controlling the muon trajectory detectors 6 and 7 and a computer for inspecting the muon trajectory detectors 6 and 7 may each be provided separately.

[0025] Predetermined information is input to the input unit 10 in response to operations by a user who uses the analysis computer 8. The input unit 10 includes input devices such as a mouse and a keyboard. That is, the predetermined information is input to the input unit 10 in response to operations of these input devices.

[0026] The output unit 11 outputs predetermined information. The analysis computer 8 includes a device for displaying images, such as a display that outputs the analysis results. In other words, the output unit 11 controls the images displayed on the display. The display may be separate from the computer body, or may be integrated with the computer body.

[0027] The analysis computer 8 may control images displayed on a display of another computer connected via a network. In this case, the output unit 11 of the other computer may control the output of the analysis results of this embodiment.

[0028] In this embodiment, a display is exemplified as a device that displays an image, but other modes may be used. For example, information may be displayed using a head-mounted display or a projector. Furthermore, a printer that prints information on a paper medium may be used instead of a display. In other words, the objects controlled by the output unit 11 may include a head-mounted display, a projector, or a printer.

[0029] The communication unit 12 communicates with other computers via a communication line such as the Internet. In this embodiment, the analysis computer 8 and the other computers are connected to each other via the Internet, but other configurations are also possible. For example, they may be connected to each other via a LAN (Local Area Network), a WAN (Wide Area Network), or a mobile communication network.

[0030] The storage unit 13 stores various information required when performing a muon inspection. For example, the storage unit 13 includes a database that accumulates statistical values ​​of scattering angles of muon scattering and materials corresponding to each statistical value. This database is a collection of information stored in a memory, a HDD, or the cloud and organized so that it can be searched or stored. The storage unit 13 also stores various information required for controlling the muon tomography device 1. The storage unit 13 includes a data recording unit 15.

[0031] 3, the main control unit 14 comprehensively controls the muon tomography apparatus 1. The main control unit 14 includes a trajectory calculation unit 16, a measurement unit 17, a signal intensity acquisition unit 18, a shape comparison unit 19, a muon signal extraction unit 20, a passing position identification unit 21, an operation state monitoring unit 22, a parameter update unit 23, and a performance prediction unit 24. The signal intensity acquisition unit 18 includes an operation voltage characteristic acquisition unit 25 and a time difference distribution acquisition unit 26. These are realized by the CPU executing programs stored in the memory or HDD.

[0032] Here, with reference to Fig. 4, a detailed description will be given of the measurement of the scattering angle θ using the first muon trajectory detector 6 and the second muon trajectory detector 7. The first muon trajectory detector 6 and the second muon trajectory detector 7 are units of the same configuration. The first muon trajectory detector 6 will be described as the entrance side of muons μ, and the second muon trajectory detector 7 as the exit side of muons μ. Note that the second muon trajectory detector 7 may be the entrance side of muons μ, and the first muon trajectory detector 6 may be the exit side of muons μ.

[0033] The trajectory calculation unit 16 (FIG. 3) analyzes an incident vector 28 indicating the passing coordinates and passing angle of the muon μ at the time of incidence in the first muon trajectory detector 6. It also analyzes an exit vector 29 indicating the passing coordinates and passing angle of the muon μ at the time of extraction in the second muon trajectory detector 7. Furthermore, it extracts the trajectory of the muon μ based on the analyzed passing coordinates and passing angle of the muon μ.

[0034] Here, the trajectory calculation unit 16 considers the trajectories of muons μ detected by each muon trajectory detector 6, 7 within a certain time (for example, within a range of 1 microsecond or less) to be those of the same muon μ, and treats the trajectory of the muon μ at the time of incidence (incidence vector 28) and the trajectory at the time of extraction (exit vector 29) as one data set.

[0035] Furthermore, the trajectory calculation unit 16 generates, as a trajectory, imaginary straight lines 30, 31 extending from the muon trajectory detectors 6, 7 through which the muon μ has passed, based on the passing coordinates and the passing angle of the muon μ.

[0036] For example, the position where a virtual line 30 extending the direction of the incident vector 28 intersects with a virtual line 31 extending the direction of the outgoing vector 29 is specified. This position indicates the coordinate 32 where muon scattering occurs. The angle (difference in trajectories) between the virtual lines 30 and 31 is the angle when the traveling direction of the muon μ changes, and is the scattering angle θ of the muon μ. The scattering angle θ is the so-called magnitude of scattering of the muon μ.

[0037] The measurement unit 17 (FIG. 3) analyzes the scattering angle θ of the muon scattering based on the trajectory of the muon μ. Here, the measurement unit 17 sets the intersection point of virtual straight lines 30 and 31 as the coordinate 32 where muon scattering occurs, and analyzes the scattering angle θ of the muon μ.

[0038] Furthermore, the measurement unit 17 accumulates and stores the results of the scattering angle θ of the multiple muons μ for each coordinate position. A statistical value of the accumulated results is analyzed as the scattering angle θ at the coordinate 32 where the scattering of the muon μ occurred. For example, the measurement unit 17 analyzes the statistical value of the scattering angle θ of the muon scattering that occurred in the object 3 inside the vehicle 2 as the target, based on the trajectory of the muon μ.

[0039] When the trajectory calculation unit 16 extracts the trajectories of multiple muons μ that have passed through the object 3, the measurement unit 17 calculates at least one statistical value of the average value, median value, variance, or arbitrary value of the scattering angle θ when analyzing the scattering angle θ of each muon μ from the trajectories of the multiple muons μ. Note that the arbitrary value is a value that the user can set arbitrarily. For example, a value of 60% of the scattering angle θ or a value of 80% of the scattering angle θ may be used as the statistical value. Note that data indicating the statistical values ​​of the scattering angle θ and the type of material corresponding to each statistical value is stored in advance in the database of the storage unit 13.

[0040] Then, the measurement unit 17 identifies the type of material present in the object 3 based on the scattering angle θ. For example, the measurement unit 17 identifies the type of material present in the object 3. Or, the measurement unit 17 generates information indicating the identification result of the material type. This result may be shown in text or in a predetermined graph. Furthermore, a predetermined warning may be output. For example, if the type of material is a nuclear material such as uranium or a hazardous material such as an explosive, a predetermined warning may be output.

[0041] Furthermore, the measurement unit 17 refers to the database in the storage unit 13, identifies a substance that is preset in correspondence with the statistical value, and identifies the type of substance present in the object 3. In this way, the accuracy of automatically identifying the type of substance is improved.

[0042] Conventionally, as a fluoroscopy technique that utilizes the penetrating power of charged particles, there is a method called the transmission method, which evaluates the density of a material by its transmittance in the material. There is also a method called the scattering method, which evaluates the degree of scattering in the material. Either method can obtain information about the inside of a very large structure by utilizing the high penetrating power of the cosmic ray muon μ. In order to obtain this information about the inside with high accuracy, it is important to measure the trajectory of the muon μ with high accuracy. However, due to the characteristics of muon μ, the measurement target becomes large, and there is a limit to the number of muons that reach the earth's surface, so detectors that are large (several meters or more) are often used.

[0043] In this case, a large number of detectors are required, but by arranging multiple detectors, it is possible to calculate the trajectory from the position information of each detector that detects the passage of the muon μ. When identifying these passage positions and obtaining the position information of the detectors, it is necessary to achieve both a large measurement area and the acquisition of highly accurate position information, which makes the scale of the device very large.

[0044] In contrast to this, there is a type of gas detector called the drift tube detector 33 (Fig. 5). This determines the passage position of an electron from the travel time of the electron inside the drift tube detector 33, called the drift time. When the drift tube detector 33 is used, it is possible to obtain a resolution of 1 mm or less, which is much smaller than the size of the drift tube detector itself. For example, when a cylindrical drift tube detector 33 with a diameter of 50 mm is used, the passage position of a muon μ can be determined with an accuracy of less than 0.5 mm.

[0045] 5, each of the muon trajectory detectors 6, 7 is composed of multiple cylindrical drift tube detectors 33 extending in the axial direction. The drift tube detectors 33 are gas detectors filled with gas for detecting the passage of charged particles. The drift tube detectors 33 are arranged in a plane (X direction or Y direction), and these drift tube detectors 33 arranged in a plane are further stacked in the vertical direction (Z direction) to form one module.

[0046] In this embodiment, a drift tube multi-wire type gas detector is exemplified, but the gas detector may be of another type as long as it can measure charged particles on a particle-by-particle basis. The gas detector is not particularly limited in detection type and outer shape. A type that can specify an X position and a Y position with one gas detector can also be applied, but a structure of four or more layers is desirable in order to calculate the trajectory of muon μ.

[0047] For example, a plurality of drift tube detectors 33 arranged in a plane are alternately stacked in two layers, so that 12 layers of drift tube detectors 33 are formed. In the example of FIG. 5, six layers of drift tube detectors 33 arranged in the X direction and six layers of drift tube detectors 33 arranged in the Y direction are stacked in the Z direction. Then, by arranging the vehicle 2 to be measured in the Z direction, data on muons μ entering from the Z direction can be acquired. In this way, by stacking the drift tube detectors 33 while orthogonally arranging them, the trajectories of muons μ passing through each of the muon trajectory detectors 6, 7 can be detected three-dimensionally.

[0048] 6 to 7, drift tube detector 33 includes a cylindrical tube 34 and a core wire 35. For example, core wire 35 made of an anode wire or the like is stretched along the central axis of cylindrical tube 34 made of aluminum. A high voltage is applied to each drift tube detector 33.

[0049] An ionization gas mainly composed of a rare gas is sealed inside each drift tube detector 33. When a muon μ as a charged particle passes through the drift tube detector 33, the gas is ionized at the passage position 36 (FIG. 6) and separated into ions and electrons.

[0050] Here, the separated electrons move toward the core wire 35 due to the voltage applied to the drift tube detector 33, and an event called an electron avalanche occurs near the core wire 35. Then, a minute charge of several pC to several hundred pC is generated. At this time, a detection signal is output from the drift tube detector 33, and the passage of the muon μ is detected. For example, when an ion moves toward the core wire 35, a pulse-like current flows, and this current is amplified to a measurable level, and the time when the detection signal is generated is measured.

[0051] By utilizing the property that a current flows in the shortest distance, it is possible to detect at which passing position 38 (FIG. 7) in the axial direction of the drift tube detector 33 ionization has occurred.

[0052] In addition, the travel time of the electrons to the core wire 35 is determined based on the time when electrons are generated by ionization of the gas and the time when these electrons reach the core wire 35. By calculating the travel distance of the electrons to the core wire 35 from this travel time, the passage position 36 of the muon μ inside the drift tube detector 33 can be measured.

[0053] The time taken from the time when the muon μ passes to the generation of a detection signal is called drift time, and is a value that correlates with the distance (radial distance) from the passage position 36 to the core wire 35. In other words, it is a value that correlates with the passage position 36 of the muon μ in the radial direction of the drift tube detector 33. The drift time is the time it takes for an electron to move from the passage position 36 of the muon μ to the core wire 35 (see arrow 37 in FIG. 6). This drift time is determined by the type, shape, and operating voltage of the gas in the drift tube detector 33. Therefore, for example, if the composition of the gas inside the drift tube detector 33 changes or the shape of the drift tube detector 33 changes (bends or distorts), the measurement performance changes.

[0054] If the measurement performance changes, the accuracy of calculating the final muon μ trajectory also changes. Therefore, in order to measure with a certain measurement performance, it is necessary to ensure that the performance has not changed, and if it has changed, it is necessary to make corrections or replace the device.

[0055] Therefore, the analytical computer 8 of this embodiment monitors the operating state of the drift tube detector 33 from data related to the detection signal output from the drift tube detector 33.

[0056] Next, the control process executed by the analytical computer 8 will be described with reference to the flowchart of Fig. 9. The above-mentioned drawings will be referred to as appropriate.

[0057] First, in step S1, the drift tube detector 33 (FIGS. 6 and 7) serving as a gas detector detects the passage of a muon μ. Here, a detection signal is output from the drift tube detector 33.

[0058] In the next step S2, the main control unit 14 (FIG. 3) executes a trajectory calculation process. In this trajectory calculation process, the trajectory calculation unit 16 (FIG. 3) calculates the trajectory of the muon μ based on the detection signals output from the respective drift tube detectors 33 and the parameters associated with the respective drift tube detectors 33.

[0059] In the next step S3, the main control unit 14 executes a measurement process. In this measurement process, the measurement unit 17 (FIG. 3) measures the internal state of the vehicle 2 (FIG. 1) that is the measurement target based on the trajectory of the muon μ. For example, the type of a predetermined object 3 inside the vehicle 2 is identified.

[0060] In the next step S4, the main control unit 14 executes an operation check process. In this operation check process, the signal intensity acquisition unit 18 (FIG. 3) acquires the signal intensity of the detection signal. Furthermore, the operation state monitoring unit 22 (FIG. 3) evaluates the operation state of each drift tube detector 33 based on the signal intensity corresponding to each drift tube detector 33. Furthermore, the parameter update unit 23 (FIG. 3) updates the parameters associated with the drift tube detector 33 when the operation state of the drift tube detector 33 has changed. The parameter update unit 23 records individual parameters required for calculating the trajectory of the muon μ in a predetermined recording area of ​​the memory unit 13. Also, it calculates values ​​to be updated, updates values ​​in the recording area, and so on.

[0061] Then, the control process is terminated. This control process is repeated at regular time intervals. By repeating this process, the control method for the charged particle measuring device of this embodiment is executed. This process may be executed by interrupting the analytical computer 8 while it is executing another main process.

[0062] Next, the operation check process will be described with reference to the flowchart in Fig. 10. Note that the above-mentioned drawings will be referred to as appropriate.

[0063] First, in step S11, the muon signal extraction unit 20 (FIG. 3) extracts detection signals for operation confirmation. For example, among various types of detection signals output from the drift tube detector 33, only detection signals caused by the passage of muons μ are extracted. The operation state monitoring unit 22 evaluates the operation state of the drift tube detector 33 based on the signal intensity of the detection signal output due to the passage of muons μ. In this way, it is possible to exclude detection signals caused by the passage of gamma rays and the like other than muons μ and eliminate their influence, thereby improving the evaluation accuracy of the operation state of the drift tube detector 33.

[0064] For example, the drift tube detector 33 is also affected by gamma rays in the environment. Therefore, the detection signals output from the drift tube detector 33 are a mixture of signals caused by muons μ and gamma rays. In the case of gamma rays, electrons generated by the interaction between the gamma rays and a substance ionize the gas. However, gamma rays have different energy compared to muons μ. For example, the amount of energy transferred per unit length (dE / dx) is different. In addition, the angular distribution of the direction of arrival is different. Therefore, by excluding the detection signals caused by gamma rays and using the signal of muons μ, which is the actual measurement target, a more reliable performance evaluation is possible.

[0065] The muon signal extraction unit 20 extracts detection signals by utilizing the fact that muons μ are high-energy charged particles. For example, muons μ have high penetrating power and continuously give energy when passing through a material, so that detection signals are generated almost simultaneously in multiple drift tube detectors 33. On the other hand, electrons caused by gamma rays do not give energy to all of the materials they pass through, but rather cause a probabilistic reaction. Therefore, in the case of gamma rays, it is rare for detection signals to be generated almost simultaneously in multiple drift tube detectors 33. Therefore, the muon signal extraction unit 20 extracts detection signals by assuming that events that occur almost simultaneously in multiple drift tube detectors 33 are caused by muons μ.

[0066] Incidentally, the generated event (passage of a muon μ) is a set of data obtained by multiple drift tube detectors 33. For example, the time when the event occurred is used as a reference (event ID), and various information is recorded, such as the time when the detection signal was output, identification information (detector ID) that can identify each drift tube detector 33, and the operating voltage. This information is stored in the memory unit 13 (FIG. 2).

[0067] Furthermore, the passing position identification unit 21 (Fig. 3) identifies the passing position 38 (Fig. 7) of the muon μ in the axial direction of the drift tube detector 33. The operation state monitoring unit 22 evaluates the operation state of the drift tube detector 33 based on the signal intensity of the detection signal output when the muon μ passes through a preset setting range 41 (Fig. 7) out of the entire axial range 40 of the drift tube detector 33. In this way, the setting range 41 effective for evaluation of the drift tube detector 33 can be set in advance and the evaluation can be performed, thereby improving the evaluation accuracy.

[0068] For example, as shown in FIG. 7, of the entire range 40 in the axial direction (longitudinal direction) of the drift tube detector 33, predetermined ranges at both ends are set as set ranges 41. This setting can be arbitrarily performed in advance by the user. The set ranges 41 at both ends of the drift tube detector 33 are parts that are firmly supported by the housing 4 (FIG. 1) and the like, so there is little bending or distortion, and the drift tube detector 33 has a normal shape. In contrast, the non-set range 42 at the center of the drift tube detector 33 often has bending or distortion, and the shape of the drift tube detector 33 may change. Therefore, in this embodiment, both ends of the drift tube detector 33 are set as set ranges 41, and the operating state of the drift tube detector 33 is evaluated based on the muons μ that have passed through these set ranges 41.

[0069] In this embodiment, both ends of drift tube detector 33 are set as set range 41, but other configurations are also possible. For example, if the center of drift tube detector 33 is firmly supported by housing 4 and both ends are free ends, the center of drift tube detector 33 may be set as the set range and both ends as non-set ranges.

[0070] Furthermore, in this embodiment, the passing position 38 (FIG. 7) of the muon μ is identified by the passing position identification unit 21, but the configuration of the passing position identification unit 21 may be omitted. For example, the entire axial range 40 of the drift tube detector 33 may be set as the set range, and the operating state may be evaluated regardless of the position at which the muon μ is detected.

[0071] Returning to FIG. 10, in the next step S12, the signal intensity acquisition unit 18 (FIG. 3) acquires the signal intensity of the detection signal output from the drift tube detector 33.

[0072] In the next step S13, the operating voltage characteristics acquisition unit 25 (FIG. 3) acquires the operating voltage characteristics of the detection signals output from each drift tube detector 33. Note that, for these operating voltage characteristics, a reference value is set in advance when the drift tube detector 33 is designed.

[0073] For example, the operating voltage characteristics acquisition unit 25 acquires the event rate of the detection signal for each operating voltage of the drift tube detector 33. As the operating voltage of the drift tube detector 33 increases, its own gain increases, and when the gain reaches a certain level or more, the sensitivity to the pulse signal to be measured becomes constant. This region is called the plateau region. By operating the drift tube detector 33 in this plateau region, a constant sensitivity can be obtained even if the operating voltage changes slightly.

[0074] It is known that the sensitivity drops significantly at operating voltages before reaching the plateau region. The change point at which the sensitivity change occurs depends on the change in the gas composition or the change in the shape of the drift tube detector 33. Therefore, the drift tube detector 33 is operated at several points, including the normal operating voltage and the voltage at which the sensitivity change occurs, and the sensitivity is evaluated to confirm whether the standard value is satisfied or whether the voltage at which the sensitivity changes is equivalent to that of past measurements.

[0075] If the voltage at which the sensitivity changes falls within the reference value, the operating voltage characteristics are judged to be correct, and if it deviates from the reference value, it is considered that some abnormality has occurred. In this embodiment, it is referred to as the "change point at which the sensitivity change occurs," but other aspects are also acceptable. For example, the evaluation point may be any voltage, such as the voltage at which the sensitivity change begins or the voltage at which the sensitivity becomes constant. In addition, the operating voltage acquired by the operating voltage characteristics acquisition unit 25 is not particularly limited as long as it is within the range in which the above-mentioned matters can be understood.

[0076] In the next step S14, the operating state monitoring unit 22 determines whether or not the operating voltage of the detection signal acquired by the operating voltage characteristics acquiring unit 25 satisfies a reference value.

[0077] Here, if the operating voltage meets the reference value (YES in step S14), the process proceeds to step S15. On the other hand, if the operating voltage does not meet the reference value (NO in step S14), the process proceeds to step S26. That is, the operating state monitoring unit 22 evaluates the operating state of the drift tube detector 33 based on the operating voltage characteristics corresponding to the drift tube detector 33. In this way, it is possible to determine whether or not the drift tube detector 33 has failed. For example, if the operating voltage does not meet the reference value, it can be considered that the core wire 35 is broken or that gas is leaking.

[0078] In step S26, which is reached if the answer is NO in step S14, the main control unit 14 issues a notification that the drift tube detector 33 has failed. For example, the output unit 11 (FIG. 2) is used to display identification information (detector ID) that identifies the failed drift tube detector 33 and a notification of the failure. Alternatively, a data exclusion process is set so that data from the failed drift tube detector 33 is not used in subsequent measurements. Then, the operation check process ends.

[0079] In step S15, which is reached if the answer is YES in step S14, the time difference distribution acquisition unit 26 (FIG. 3) acquires a time difference distribution of the detection signals output from each drift tube detector 33.

[0080] In the next step S16, the shape comparison unit 19 (FIG. 3) generates a histogram corresponding to each drift tube detector 33. In this way, it is possible to obtain information regarding update of parameters of the drift tube detector 33. Note that the time difference distribution acquisition unit 26 may generate the histogram.

[0081] For example, as shown in Fig. 8, when the frequency of passage of muons μ detected by the drift tube detector 33 is accumulated over a predetermined period, a histogram of the time difference distribution is obtained. Note that a histogram is generated for each drift tube detector 33. For example, when there are 20,000 drift tube detectors 33, 20,000 histograms are generated.

[0082] The time difference distribution acquisition unit 26 acquires a distribution of the times at which detection signals are output (time difference distribution) using the occurrence time of an event as a reference (event ID). For example, in the case of drift tube detectors 33 operating normally, the time difference distribution is the distribution of the difference ΔT (ΔT=DTn-DT0) between the drift time DT0 of the drift tube detector 33 that first detected a detection signal in each event and the drift time DTn (n=1 or more) of each drift tube detector 33.

[0083] Since each drift time DT is distributed from 0 seconds to the maximum drift time TMAX, the difference between the two, ΔT, is also distributed from 0 seconds to the maximum drift time TMAX. The correct drift time distribution can be calculated experimentally and analytically, so if the distribution of the positions through which muons μ pass can be specified, the ideal ΔT distribution (reference shape) can be determined. On the other hand, the difference between the ideal ΔT distribution and the measured ΔT distribution depends on the time resolution of the muon tomography device 1 and the performance change of the drift tube detector 33.

[0084] Specifically, in the drift tube detector 33 (FIG. 7), the core wire 35 may bend or the shape of the cylindrical tube 34 may be distorted, causing a deviation in the relative positional relationship between the core wire 35 and the inner diameter of the cylindrical tube 34. In this case, not only does the electric field become distorted, but the distance that the electrons drift (see arrow 37 in FIG. 6) also changes. This causes the maximum drift time TMAX to vary. Furthermore, if the gas composition changes, the drift time characteristics change, and the value of TMAX, that is, the distribution of ΔT, changes. By obtaining this information, it is possible to evaluate whether the core wire 35 is bent, the shape of the cylindrical tube 34 is distorted, or the gas composition is changing.

[0085] The degree of bending or distortion in the core wire 35 or the cylindrical tube 34 often varies depending on the axial position of the drift tube detector 33. Therefore, by limiting the set range 41 (FIG. 7) in advance in the passing position identification unit 21 and performing the evaluation, it is possible to perform the evaluation more accurately.

[0086] Returning to Fig. 10, in the next step S17, the operation state monitoring unit 22 evaluates the operation state of the drift tube detector 33 based on the time difference distribution corresponding to the drift tube detector 33. For example, the operation state monitoring unit 22 judges whether or not the maximum value of the time difference distribution (Fig. 8) satisfies a reference value. For example, a maximum drift time TMAX serving as a reference value is set for each drift tube detector 33. It is judged whether or not the maximum value of the time difference distribution is greater than this maximum drift time TMAX, or whether or not the excess amount exceeds a predetermined range 43 (Fig. 8).

[0087] If the maximum value of the time difference distribution satisfies the reference value (YES in step S17), the process proceeds to step S20. On the other hand, if the maximum value of the time difference distribution does not satisfy the reference value (NO in step S17), the process proceeds to step S18.

[0088] For example, if the maximum value of the time difference distribution does not satisfy the reference value, it can be assumed that the gas sealed in the drift tube detector 33 has deteriorated or is leaking. Therefore, the parameters of the drift tube detector 33 are updated.

[0089] In step S18, the parameter update unit 23 (FIG. 3) calculates an update RT curve.

[0090] In the next step S19, the parameter update unit 23 updates the parameters of the drift tube detector 33. Here, the parameter update unit 23 updates the correlation function (RT curve) between the passage position 36 (FIG. 6) of the muon μ and the drift time.

[0091] Let us assume that there is a drift tube detector 33 that is leaking gas but is outputting a detection signal with the correct signal strength. In this case, it is considered that the composition of the gas has changed slightly, and the correct passage position 36 can be calculated by updating the RT curve, which indicates the correlation function between the passage position 36 of the muon μ and the drift time. On the other hand, if distortion or the like has occurred in the drift tube detector 33, the position of the core wire 35 and the amount of distortion are corrected.

[0092] If the operating voltage characteristics described above have changed, the amount of gas leakage is large and the gas composition ratio is often unclear, making it impossible to estimate a correct RT curve. Therefore, this cannot be dealt with by correcting the RT curve, and is treated as a failure of the drift tube detector 33. The RT curve is also an example of a parameter, and other parameters may be updated.

[0093] In the next step S20, the shape comparison unit 19 (FIG. 3) compares the shape of the histogram (FIG. 8) of the time difference distribution with a reference shape that serves as a reference. In this way, it is possible to grasp minute changes in the performance of the drift tube detector 33. Then, the operation status monitoring unit 22 evaluates the operation status of the drift tube detector 33 based on the result of the histogram comparison. For example, the operation status monitoring unit 22 determines whether the falling edge shape of the time difference distribution is within a reference range.

[0094] If the falling shape of the time difference distribution is within the reference range (YES in step S20), the process proceeds to step S23. On the other hand, if the falling shape of the time difference distribution is not within the reference range (NO in step S20), the process proceeds to step S21.

[0095] For example, if the falling edge shape of the time difference distribution is not within a reference range, it can be considered that the shape of the core wire 35 or the cylindrical tube 34 has changed, for example, has been distorted. Therefore, the parameters of the drift tube detector 33 are updated.

[0096] In step S21, the parameter update unit 23 (FIG. 3) calculates update parameters. The update parameters are used to update parameters used in the trajectory calculation process, for example.

[0097] The update parameter may be an update RT curve. If an update RT curve has already been calculated in step S19, a difference from the update RT curve may be calculated to obtain a new update RT curve.

[0098] In the next step S22, the parameter update unit 23 updates the parameters of the drift tube detector 33.

[0099] For example, as shown in Fig. 8, the falling shape of the time difference distribution refers to the shape of the part of the histogram where the graph falls in range 43 closest to the maximum drift time TMAX (see the solid line graph in Fig. 8). Ideally, this falling shape falls sharply at the maximum drift time TMAX. However, when the drift tube detector 33 deteriorates, this falling shape becomes more gradual (see the dotted line graph in Fig. 8). In this embodiment, a reference shape of the histogram is set, and the deterioration of the drift tube detector 33 is evaluated by comparing this reference shape with the shape of an actually measured histogram.

[0100] When all drift tube detectors 33 are manufactured in a factory, their parameters (RT curves) are the same. However, when used for a long period of time, the parameters are updated and become different. Note that the update parameters in this embodiment may indicate the difference from the parameters set immediately before the update.

[0101] It should be noted that information obtained from either the operating voltage characteristics acquisition unit 25 or the time lag distribution acquisition unit 26 alone cannot identify that an abnormality has occurred, either a change in the gas or a change in the shape of the drift tube detector 33. Therefore, in this embodiment, an evaluation is performed using information obtained from both the operating voltage characteristics acquisition unit 25 and the time lag distribution acquisition unit 26, thereby making it possible to grasp the operating state of the drift tube detector 33 and determine countermeasures. This allows the drift tube detector 33 for which countermeasures have been taken to continue to be used. Furthermore, data from a broken drift tube detector 33 is not used in subsequent measurements.

[0102] 10, in the next step S23, the main control unit 14 records the evaluation results evaluated by the operation status monitoring unit 22 in the data recording unit 15 (FIG. 2) of the memory unit 13. In this way, it is possible to predict the time when the drift tube detector 33 will malfunction in the future based on data indicating the evaluation results accumulated in the past.

[0103] In the next step S24, the performance prediction unit 24 (FIG. 3) predicts, based on past evaluation results, when the performance of the drift tube detector 33 will no longer satisfy the reference performance standard. For example, it predicts whether the drift tube detector 33 will malfunction in several months or years. The performance prediction unit 24 can also perform a comparative evaluation of past data and current data.

[0104] In the next step S25, the main control unit 14 uses the output unit 11 (FIG. 2) to display identification information (detector ID) for identifying the drift tube detector 33 and information showing the corresponding prediction result, and then ends the operation checking process.

[0105] When evaluating the operating state of the drift tube detector 33, each piece of data may be used to classify or determine the state by machine learning. For example, the histogram of the time difference distribution may be determined by machine learning.

[0106] For example, the muon tomography apparatus 1 of the present embodiment may include a computer equipped with artificial intelligence (AI) that performs machine learning. For example, the analysis computer 8 may include a deep learning unit that extracts a specific pattern from multiple patterns based on deep learning.

[0107] The analysis using the computer of this embodiment can use an analysis technique based on learning of artificial intelligence. For example, a learning model generated by machine learning using a neural network, a learning model generated by other machine learning, a deep learning algorithm, a mathematical algorithm such as regression analysis, etc. In addition, the form of machine learning includes forms such as clustering and deep learning.

[0108] The system of the present embodiment includes a computer equipped with artificial intelligence that performs machine learning. For example, the system may be configured with one computer equipped with a neural network, or may be configured with multiple computers equipped with neural networks.

[0109] Here, a neural network is a mathematical model that represents the characteristics of brain functions through computer simulation. For example, this model shows that artificial neurons (nodes) that form a network through synaptic connections change the strength of synaptic connections through learning, and acquire problem-solving abilities. Furthermore, neural networks acquire problem-solving abilities through deep learning.

[0110] For example, a neural network is provided with an intermediate layer having six layers. Each intermediate layer is composed of 300 units. In addition, by having the multi-layered neural network learn in advance using learning data, it is possible to automatically extract features in the pattern of changes in the state of a circuit or system. In addition, the multi-layered neural network can be configured on the user interface with any number of intermediate layers, any number of units, any learning rate, any number of learning times, and any activation function.

[0111] In addition, deep reinforcement learning may be used in the neural network, in which a reward function is set for each information item to be learned, and the information item with the highest value is extracted based on the reward function.

[0112] For example, we use a Convolution Neural Network (CNN), which has a proven track record in image recognition. In this CNN, the intermediate layer is composed of a convolution layer and a pooling layer. The convolution layer obtains a feature map by applying filtering to nearby nodes in the previous layer. The pooling layer further reduces the feature map output from the convolution layer to create a new feature map. At this time, by obtaining the maximum value of the pixels contained in the region of interest in the feature map, it is possible to absorb slight deviations in the position of the feature amount.

[0113] The convolution layer extracts local features of an image, and the pooling layer performs processing to consolidate local features. These processes reduce the size of the image while maintaining the features of the input image. In other words, CNN can significantly compress (abstract) the amount of information contained in an image. Then, the input image can be recognized and classified using the abstracted image stored in the neural network.

[0114] Note that there are various methods for deep learning, such as autoencoder, recurrent neural network (RNN), long short-term memory (LSTM), generative adversarial network (GAN), etc. These methods may be applied to the deep learning of the present embodiment.

[0115] Next, a method of operating the muon tomography apparatus 1 will be described with reference to the flowchart of Fig. 11. The above-mentioned drawings will be referred to as appropriate.

[0116] In this embodiment, after the muon tomography device 1 is started, the operation of the drift tube detector 33 is checked using data acquired during at least two periods, that is, a period in which the target object is present and a period in which the target object is not present.

[0117] For example, assume that one muon tomography device 1 is used to measure multiple vehicles 2 in sequence (FIG. 1). Here, when using muons μ of cosmic rays, the number of muons μ is limited only to the components that rain down from space, and the measurement time is determined by the number of these muons μ. Therefore, if the measurement time is used only to check the operation of the drift tube detector 33, there is a risk that the measurement time of the original vehicle 2 will be reduced, and the number of vehicles 2 that can be measured in a day will also be reduced. Therefore, muon μ is continuously detected between the intervals between the sequential installation of multiple vehicles 2 and the measurements. The operation of the drift tube detector 33 is checked using data accumulated multiple times during this interval. This makes it possible to periodically monitor the operation status of the drift tube detector 33 and always keep it in the best condition without reducing the measurement time of the original vehicle 2.

[0118] First, in step S31, the user starts up the muon tomography apparatus 1.

[0119] In the next step S32, the operation check is performed at the start-up of the muon tomography apparatus 1. Here, the above-mentioned operation check process (FIGS. 9 and 10) is executed, the operating state of the drift tube detector 33 is monitored, and the parameters are updated.

[0120] In the next step S33, the vehicle 2 is carried into the muon tomography apparatus 1.

[0121] In the next step S34, a muon inspection of the vehicle 2 is performed using the muon tomography device 1.

[0122] In the next step S35, the operation during measurement of the muon tomography device 1 is checked. Here, the above-mentioned operation checking process (FIGS. 9 and 10) is executed, the operating state of the drift tube detector 33 is monitored, and the parameters are updated.

[0123] In the next step S36, the vehicle 2 is carried out from the muon tomography apparatus 1.

[0124] In the next step S37, a check is performed on the operation during non-measurement when the vehicle 2 is not installed in the muon tomography device 1. Here, the above-mentioned operation check process (FIGS. 9 and 10) is executed, and the operating state of the drift tube detector 33 is monitored and the parameters are updated.

[0125] In the next step S38, the user determines whether or not there are any unmeasured vehicles 2 remaining. If there are any unmeasured vehicles 2 remaining (YES in step S38), the process returns to the above-mentioned step S33. On the other hand, if there are no unmeasured vehicles 2 remaining (NO in step S38), the process proceeds to step S39.

[0126] In step S39, the user stops the muon tomography apparatus 1. Then, the operation method is terminated.

[0127] In this way, the operation state monitoring unit 22 evaluates the operation state of the drift tube detector 33 based on the signal strength acquired during both the period when the vehicle 2 is being measured (measurement time) and the period when the vehicle 2 is not being measured (non-measurement time). In this way, the operation state of the drift tube detector 33 can be continuously grasped. Also, the muon tomography device 1 can be always maintained in the best condition. Furthermore, it can be operated while successively checking for the occurrence of an abnormality.

[0128] Generally, in an environment where sufficient muons μ can be measured, the measurement time by the muon tomography device 1 is about several minutes to several tens of minutes, and a certain amount of information can be obtained. In contrast, the replacement of the target object takes several minutes in the case of a large vehicle 2 such as a truck. Therefore, in this embodiment, it is possible to monitor the operating state of the drift tube detector 33 and update the parameters about once for every 10 measurements.

[0129] Note that, with only information obtained from one drift tube detector 33, it is only possible to know the passage position 36 (FIG. 6) of the muon μ, but it is not possible to specify its trajectory. However, by processing the passage position 36 and distance information obtained from multiple drift tube detectors 33 for the passage of the same muon μ in the trajectory calculation unit 16, it is possible to calculate the trajectory. In addition, in this embodiment, it is possible to calculate the trajectory even if the time at which the muon μ passed cannot be clearly identified. It is also possible to measure the passage time of the muon μ with another drift tube detector 33 and use that information for evaluation.

[0130] According to the first embodiment, it is possible to detect performance changes in the drift tube detector 33 and to exclude data on defective drift tube detectors 33 that cannot be used for evaluation, based on data that can be acquired from the drift tube detector 33. This makes it unnecessary to disassemble and inspect the muon tomography device 1, and allows the muon tomography device 1 to be capable of monitoring and diagnosing the drift tube detector 33.

[0131] Second embodiment Next, a second embodiment will be described with reference to Figures 12 and 13. Note that the same components as those shown in the above-described embodiment are denoted by the same reference numerals and duplicated description will be omitted.

[0132] 12, in the muon tomography device 1 of the second embodiment, there are other objects, such as the housing 4 and the support pillars 5, whose positional relationships are fixed in advance, in addition to the object. In checking the operation of the drift tube detector 33 (FIG. 5), imaging of these objects is performed to check that they are operating correctly.

[0133] Among the muon tomography techniques, when using a scattering method that performs imaging based on the degree of scattering in the target, the variation in the scattering angle θ of muons μ that pass through the target is utilized. Here, if the detection performance of muons μ changes, the scattering angle θ may vary, and the measurement results may change. Therefore, the muons μ are used to measure a housing 4 (frame), a support 5, or a specified test piece (not shown) whose structure is known and exists outside the area where the target is installed.

[0134] For example, the area that can be measured by the drift tube detector 33 is divided into a measurement target area 44 where the vehicle 2 (target object) is placed, and a non-measurement target area 45 where the vehicle 2 is not placed. The measurement target area 44 and the non-measurement target area 45 can be arbitrarily set in advance by the user in consideration of the size of the vehicle 2. In the second embodiment, the areas in front of and behind the vehicle 2 are the non-measurement target areas 45. When the measurement target area 44 is imaged, an image of the vehicle 2 is included in addition to the housing 4 and the support pillar 5, but when the non-measurement target area 45 is imaged, an image of the housing 4 and the support pillar 5 is included, but an image of the vehicle 2 is not included.

[0135] 13, the main control unit 14A of the second embodiment includes a non-measurement area data acquisition unit 46 instead of the passing position identification unit 21 (FIG. 3) described above. This non-measurement area data acquisition unit 46 acquires detection signals corresponding to the non-measurement area 45. Then, the operation state monitoring unit 22 evaluates the operation state of the drift tube detector 33 based on the signal strength of the detection signals acquired corresponding to the non-measurement area 45. This operation state also includes information such as the positional deviation of the drift tube detector 33.

[0136] For example, the non-measurement area data acquisition unit 46 extracts data on muons μ that have passed through the non-measurement area 45 during an operation check. The operation status monitoring unit 22 then monitors the scattering angle distribution and transmittance distribution of the non-measurement area 45 and compares them with reference values. If the reference values ​​are met, it is determined that the drift tube detector 33 is in good condition. If the reference values ​​are not met, it is determined that an abnormality has occurred.

[0137] If there is an abnormality, it is possible that the relative positions of the upper and lower muon trajectory detectors 6, 7 have shifted due to distortion of the housing 4 or vibrations due to an earthquake, etc. In that case, the coordinate system of the entire structure of the muon tomography device 1 is updated to deal with the problem.

[0138] In addition, by recording the temporal variation of the evaluation results, it is possible to obtain the aging of the muon tomography device 1. Except for damage to the device that occurs instantaneously due to an earthquake or the like, many things such as gas leaks and distortions of the drift tube detector 33 change slowly over time. Therefore, by measuring the aging, it is possible to predict the progress of deterioration. In particular, it is possible to calculate the time when the prediction exceeds the operating conditions of the drift tube detector 33 and becomes defective, and the time when the proportion of defective drift tube detectors 33 exceeds the allowable number, and the like, and to utilize this for long-term monitoring or maintenance. In addition, any method such as machine learning can be applied to the prediction, and it can be performed by taking into account not only simple aging but also the influence of seasonal fluctuations such as temperature changes.

[0139] According to the second embodiment, the drift tube detector 33 can be evaluated by the trajectory of muons μ that is not affected by the vehicle 2, and therefore the evaluation accuracy can be improved. For example, it becomes possible to monitor the distortion of the housing 4 that supports the drift tube detector 33, and to predict deterioration. This eliminates the need for detailed disassembly and inspection, and enables long-term monitoring.

[0140] Note that even if an object exists in the measurement target area 44, it can be used as a standard for evaluation if the structure of the base 9 or the like is known.

[0141] The charged particle measurement device and its control method have been described based on the first and second embodiments, but the configuration applied in any one of the embodiments may be applied to the other embodiment, or the configurations applied in each embodiment may be combined.

[0142] In the above-described embodiment, the judgment of an arbitrary value (voltage, maximum value of time difference distribution, falling shape of time difference distribution) using a reference value (reference shape, reference range) may be a judgment of "whether the arbitrary value is equal to or greater than the reference value" or a judgment of "whether the arbitrary value exceeds the reference value". Alternatively, it may be a judgment of "whether the arbitrary value is equal to or less than the reference value" or a judgment of "whether the arbitrary value is less than the reference value". In addition, the reference value may not be fixed but may be variable. Therefore, a value in a predetermined range may be used instead of the reference value to judge whether the arbitrary value falls within the predetermined range. In addition, an error occurring in the device may be analyzed in advance, and a predetermined range including the error range centered on the reference value may be used for the judgment.

[0143] In the flowcharts of the above-described embodiment, the steps are executed in series, but the order of the steps is not necessarily fixed, and some steps may be executed in reverse. Also, some steps may be executed in parallel with other steps.

[0144] The computer of the above embodiment includes a control device with a highly integrated processor such as a dedicated chip, a Field Programmable Gate Array (FPGA), a Graphics Processing Unit (GPU), or a Central Processing Unit (CPU), a storage device such as a Read Only Memory (ROM) or a Random Access Memory (RAM), an external storage device such as a Hard Disk Drive (HDD) or a Solid State Drive (SSD), a display device such as a display, an input device such as a mouse or a keyboard, and a communication interface. This computer can be realized with a hardware configuration using a normal computer.

[0145] The programs executed by the computers of the above-described embodiments are provided by being pre-installed in a ROM, etc. Alternatively, the programs may be provided by being stored in a non-transitory computer-readable storage medium such as a CD-ROM, CD-R, memory card, DVD, or flexible disk (FD) in the form of an installable or executable file.

[0146] The programs executed by this computer may be stored on a computer connected to a network such as the Internet and provided by downloading them via the network. This computer may also be configured by combining separate modules that independently perform the functions of the components and are interconnected via a network or dedicated lines.

[0147] In the above embodiment, the pair of muon trajectory detectors 6, 7 are provided at positions facing each other with the vehicle 2 sandwiched between them in the vertical direction, but other configurations are also possible. For example, the two pairs of muon trajectory detectors 6, 7 may be provided at positions facing each other with the vehicle 2 sandwiched between them in the vertical and horizontal directions, respectively. Also, the muon trajectory detectors do not need to be a pair, and an odd number of muon trajectory detectors may be provided. For example, three or more muon trajectory detectors may be provided.

[0148] According to at least one of the embodiments described above, by providing an operation status monitoring unit that evaluates the operation status of each gas detector based on the signal strength corresponding to each gas detector, it is possible to grasp the type or degree of deterioration of the gas detector and maintain a certain level of measurement accuracy over a long period of time.

[0149] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments or modifications thereof are within the scope of the invention and its equivalents as described in the claims, as well as within the scope and spirit of the invention. [Explanation of symbols]

[0150] 1...muon tomography device, 2...vehicle, 3...object, 4...casing, 5...pillar, 6...first muon trajectory detector, 7...second muon trajectory detector, 8...analysis computer, 9...base, 10...input section, 11...output section, 12...communication section, 13...storage section, 14(14A)...main control section, 15...data recording section, 16...trajectory calculation section, 17...measurement section, 18...signal intensity acquisition section, 19...shape comparison section, 20...muon signal extraction section, 21...passing position identification section, 22...operation status monitoring section, 23...parameter data update unit, 24...performance prediction unit, 25...operating voltage characteristic acquisition unit, 26...time difference distribution acquisition unit, 28...entrance vector, 29...exit vector, 30, 31...virtual line, 32...coordinates, 33...drift tube detector, 34...cylindrical tube, 35...core wire, 36...passing position, 37...arrow, 38...passing position, 40...entire range, 41...set range, 42...non-set range, 43...predetermined range, 44...measurement area, 45...non-measurement area, 46...non-measurement area data acquisition unit, θ...scattering angle, μ...muon.

Claims

1. a plurality of gas detectors filled with a gas for detecting the passage of a charged particle; a trajectory calculation unit that calculates trajectories of the charged particles based on detection signals output from the plurality of gas detectors and parameters associated with each of the gas detectors; a measurement unit that measures an object to be measured based on the trajectories of the charged particles; a signal strength acquisition unit for acquiring a signal strength of the detection signal; an operational status monitoring unit that evaluates an operational status of each of the gas detectors based on the signal strength corresponding to each of the gas detectors; a parameter update unit that updates the parameters associated with the gas detector when the operating state of the gas detector changes; Equipped with Charged particle measurement device.

2. the signal strength acquisition unit includes an operating voltage characteristics acquisition unit that acquires an operating voltage characteristic of the detection signal; the operation status monitoring unit evaluates the operation status of the gas detector based on the operating voltage characteristic corresponding to the gas detector. The charged particle measuring device according to claim 1 .

3. the signal strength acquisition unit includes a time difference distribution acquisition unit that acquires a time difference distribution of the detection signal, the operation state monitoring unit evaluates the operation state of the gas detector based on the time difference distribution corresponding to the gas detector.

3. The charged particle measuring device according to claim 1 or 2.

4. a shape comparison unit that generates a histogram of the time difference distribution and compares a shape of the histogram with a reference shape serving as a reference; the operation status monitoring unit evaluates the operation status of the gas detector based on a comparison result of the histograms. The charged particle measuring device according to claim 3 .

5. a non-measurement area data acquisition unit that acquires the detection signal corresponding to a non-measurement area where the target object is not placed, among areas that can be measured by the gas detector; the operation state monitoring unit evaluates the operation state of the gas detector based on the signal intensity of the detection signal acquired corresponding to the non-measurement target region. The charged particle measuring device according to claim 1 .

6. the charged particles include at least muons; a muon signal extraction unit that extracts only the detection signal resulting from the passage of the muon from the detection signals output from the gas detector, the operation state monitoring unit evaluates the operation state of the gas detector based on the signal intensity of the detection signal output due to the passage of the muon. The charged particle measuring device according to claim 1 .

7. a passage position identification unit for identifying a passage position of the charged particle in the gas detector, the operation state monitoring unit evaluates the operation state of the gas detector based on the signal intensity of the detection signal output when the charged particle passes through a preset range out of the entire range of the gas detector. The charged particle measuring device according to claim 1 .

8. a data recording unit for recording the evaluation results evaluated by the operation status monitoring unit; a performance prediction unit that predicts a time when the performance of the gas detector will no longer satisfy a reference performance standard based on the past evaluation results; Equipped with The charged particle measuring device according to claim 1 .

9. A plurality of the objects are sequentially measured, the operation state monitoring unit evaluates the operation state of the gas detector based on the signal strength acquired during both a period in which the object is being measured and a period in which the object is not being measured. The charged particle measuring device according to claim 1 .

10. detecting passage of the charged particles using a plurality of gas detectors filled with gas; a trajectory calculation unit calculating trajectories of the charged particles based on detection signals output from the plurality of gas detectors and parameters associated with each of the gas detectors; A measurement unit measures an object to be measured based on the trajectories of the charged particles; A signal strength acquisition unit acquires a signal strength of the detection signal; an operational status monitoring unit evaluating an operational status of each of the gas detectors based on the signal strength corresponding to each of the gas detectors; a parameter update unit updating the parameters associated with the gas detector when the operating state of the gas detector changes; Including, A method for controlling a charged particle measuring device.

Images