WO2023031265A1

WO2023031265A1 - Magnetic field structure imaging using muons

Info

Publication number: WO2023031265A1
Application number: PCT/EP2022/074189
Authority: WO
Inventors: Tadahiro Kin; Eduardo CORTINA GIL; Andrea GIAMMANCO
Original assignee: National University Corporation Kyushu University; Université Catholique de Louvain
Priority date: 2021-08-31
Filing date: 2022-08-31
Publication date: 2023-03-09
Also published as: JP2023034808A

Abstract

Providing a magnetic field structure imaging apparatus capable of easily obtaining a magnetic field structure image of a target region. A magnetic field structure imaging apparatus comprising: a first detection unit that detects a passing position of a muon having passed through a target region; a second detection unit that detects a passing position of the muon having passed through the target region and the first detection unit; an analysis unit that calculates a magnetic field structure image of the target region on the basis of an arrival trajectory of the muon detected by the first detection unit and the second detection unit; and a display unit that displays at least one of the magnetic field structure image and magnitude and/or direction of two-dimensional magnetic flux density calculated from the magnetic field structure image, wherein a cosmic ray muon is used as the muon; and magnetic field structure imaging method.

Description

DESCRIPTION

Title of Invention: MAGNETIC FIELD STRUCTURE IMAGING USING MUONS

Technical Field

[0001]

The present invention relates to a magnetic field structure imaging apparatus using muons and a magnetic field structure imaging method using muons.

Background Art

[0002]

A method using muons is known as a non-destructive inspection method for inspecting or detecting a state of a target region containing a solid sample inside a molten iron furnace, a composite concrete structure, a volcano, or the like without giving physical or chemical adverse effects, (see, for example, PTLs 1 to 3).

[0003]

PTL 1 describes a pSR imaging apparatus including a unit for applying a magnetic field, a unit for providing a sample in the magnetic field, a unit for irradiating the sample with muons, a unit for detecting a change in direction of spin of the muons irradiated to the sample, and a unit for imaging and displaying a structure in the sample on the basis of the change in the direction of the spin. Note that pSR imaging refers to a method for measuring a magnetic field in a substance by using magnetic moment possessed by the muons as a microscopic magnetic needle (see [0030] of PTL 2 described below).

[0004]

PTL 2 discloses a non-destructive inspection apparatus which inspects an inside of a surface layer of a composite structure by using cosmic ray muons spin-polarized by a predetermined amount in a traveling direction and traveling in a substantially horizontal direction, including a positron/electron amount detection unit that detects an amount of positrons/electrons reflected and emitted with a characteristic time constant in a direction opposite to an irradiation direction of the cosmic ray muons due to decay of the cosmic ray muons stopping inside the composite structure, and a radiography data processing unit that processes and outputs as radiography a state of a second substance different from a first substance on the surface layer existing inside the surface layer of the composite structure from the amount of positrons/electrons detected by the positron/electron amount detection unit.

[0005]

PTL 3 discloses a method for estimating conditions inside a blast furnace, the method including, on the basis of data accumulated by actual measurement, in which a measuring apparatus for measuring the cosmic ray muons accumulates for a certain period of time intensity of the cosmic ray muon transmitted and arriving through the blast furnace, information on determining a direction of coming direction of the cosmic ray muon transmitted through the blast furnace, and intensity of the cosmic ray muon not transmitted through the blast furnace, expressing a state of the blast furnace as a density by an intensity ratio of the intensity of the cosmic ray muons transmitted through a bottom of the furnace to the intensity of the cosmic ray muons not transmitted therethrough, and estimating filling by obtaining a density of the filling in the furnace from an intensity ratio estimated to be refractory of the blast furnace and an intensity ratio of the filling in the furnace that forms a boundary with the refractory.

Citation List

Patent Literature

[0006]

PTL 1 : JP-A-H03-025359

PTL 2: W02009/107575

PTL 3: JP-A-2008-145141

Summary of Invention

Technical Problem

[0007]

However, the method described in PTL 1 can, according to the upper right column on page 8, identify a location of dislocations, defects, segregated heavy ions, or the like generated near a surface of a Si substrate, and non-destructively images a minute region. Therefore, in PTL 1, the cosmic ray muon is not used, and it is not considered to detect an arrival trajectory of the muon by using a plurality of detectors.

PTLs 2 and 3 describe the inspection method and the imaging method using the cosmic ray muons, but they are merely methods for estimating a density structure image of the target region or the type and thickness of the solid sample from the density structure image, and it was not intended to image the magnetic field structure of the target region. [0008]

An object to be solved by the present invention is to provide a magnetic field structure imaging apparatus capable of easily obtaining a magnetic field structure image of a target region.

Solution to Problem

[0009]

As a result of diligent studies, the present inventors have found that the magnetic field structure image of the target region can be easily obtained by calculating the magnetic field structure image of the target region on the basis of the arrival trajectory of the cosmic ray muon, and solved the above problems.

A configuration of the present invention, which is a specific means for solving the above problems, and a preferred configuration of the present invention will be described below.

[0010]

[1] A magnetic field structure imaging apparatus comprising: a first detection unit that detects a passing position of a muon having passed through a target region; a second detection unit that detects a passing position of the muon having passed through the target region and the first detection unit; an analysis unit that calculates a magnetic field structure image of the target region on the basis of an arrival trajectory of the muon detected by the first detection unit and the second detection unit; and a display unit that displays at least one of the magnetic field structure image and magnitude and/or direction of two-dimensional magnetic flux density calculated from the magnetic field structure image, wherein a cosmic ray muon is used as the muon.

[2] The magnetic field structure imaging apparatus according to [1], which does not have a probe to be directly inserted into the target region.

[3] The magnetic field structure imaging apparatus according to [1] or [2], further comprising: a third detection unit that detects a passing position of the muon having passed through the first detection unit and the second detection unit; a magnetic field applying unit that applies a magnetic field between the second detection unit and the third detection unit; and a discrimination unit that discriminates between positive and negative of muons having passed through the target region, wherein the display unit creates and displays the magnetic field structure image of the target region using at least one of a positive muon and a negative muon.

[4] The magnetic field structure imaging apparatus according to [3], wherein the display unit displays at least one of the magnetic field structure image by the positive muon created by using the positive muon, the magnetic field structure image by the negative muon created by using the negative muon, and a positive and negative composite magnetic field structure image obtained by mirror-transforming one of the magnetic field structure image by the positive muon and the magnetic field structure image by the negative muon and synthesizing it with the other.

[5] The magnetic field structure imaging apparatus according to [3] or [4], wherein the magnetic field applying unit is a permanent magnet, or an electromagnet having a constant magnetic flux density.

[6] The magnetic field structure imaging apparatus according to any one of [3] to [5], further comprising a moving unit of the third detection unit, wherein the moving unit can move the third detection unit so that the muon having passed through the first detection unit and the second detection unit passes through the third detection unit.

[7] The magnetic field structure imaging apparatus according to any one of [3] to [6], further comprising a deflection analysis unit that analyzes the degree of deflection of the muon having passed through the known magnetic field applied between the second detection unit and the third detection unit, wherein the deflection analysis unit analyzes momentum of the muon on the basis of the degree of deflection of the muon.

[8] The magnetic field structure imaging apparatus according to any one of [1] to [7], wherein the target region contains a solid sample, and the magnetic field structure imaging apparatus creates the magnetic field structure image of an inside of the solid sample. [9] The magnetic field structure imaging apparatus according to claim 8, wherein the solid sample is a fusion reactor, a plasma generator, a nuclear reactor, a superconducting coil, an accelerator, a medical device having a strong magnetic field, a packaged strong magnetic field material, or a concrete structure.

[10] The magnetic field structure imaging apparatus according to any one of [1] to [9], wherein the analysis unit further creates a density structure image of the target region, and calculates the magnitude of the magnetic flux density of the target region on the basis of a difference between the magnetic field structure image and the density structure image.

[11] The magnetic field structure imaging apparatus according to [10], which calculates and displays the magnitude and the direction of the two-dimensional magnetic flux density of the target region.

[12] The magnetic field structure imaging apparatus according to any one of [1] to [11], comprising: a fourth detection unit and a fifth detection unit that detect passing positions of the muon, on a side opposite to the first detection unit side of the target region; and a flight time measuring unit that measures a flight time of a predetermined section of the muon having passed through the fifth detection unit, the fourth detection unit, the target region, the first detection unit, and the second detection unit in this order.

[13] A magnetic field structure imaging method comprising: a first detection step of detecting a passing position of a muon having passed through a target region; a second detection step of detecting a passing position of the muon having passed through the target region and the first detection unit; an analysis step of calculating a magnetic field structure image of the target region on the basis of an arrival trajectory of the muon detected in the first detection step and the second detection step; and a display step of displaying at least one of the magnetic field structure image and magnitude and/or direction of two-dimensional magnetic flux density calculated from the magnetic field structure image, wherein a cosmic ray muon is used as the muon.

[14] The magnetic field structure imaging method according to [13], comprising: recording time variation of the magnetic field structure image; and monitoring the degree of deterioration of the magnetic field structure of the target region. [15] A magnetic field structure imaging method comprising: a first detection step of detecting a passing position of a muon having passed through a target region; a second detection step of detecting a passing position of the muon having passed through the target region and the first detection unit; and a display step of displaying a magnetic field imaging obtained by analyzing a muographic image of the muon detected in the first detection step and the second detection step, wherein the magnetic field structure imaging method records time variation of the magnetic field imaging and monitors variation of the magnetic field imaging of the target region, and uses a cosmic ray muon as the muon.

[16] The magnetic field structure imaging method according to any one of [13] to [15], which creates and displays the magnetic field structure image or the magnetic field imaging, using muons detected between one week and three months.

[17] The magnetic field structure imaging method according to any one of [13] to [16], comprising: a step of measuring the target region from optical axes that differ by 90° and obtaining magnetic field structure images that differ by 90° of the target region; and a step of reconstructing a three-dimensional magnetic field structure image from the magnetic field structure images that differ by 90° of the target region.

Advantageous Effects of Invention

[0011]

According to the present invention, it is possible to provide the magnetic field structure imaging apparatus capable of easily obtaining the magnetic field structure image of the target region.

Brief Description of Drawings

[0012]

[Fig. 1] Fig. 1 is a schematic diagram of an example of the magnetic field structure imaging apparatus of the present invention.

[Fig. 2] Fig. 2 is a schematic diagram of another example of the magnetic field structure imaging apparatus of the present invention. [Fig. 3] Fig. 3 is a schematic diagram of another example of the magnetic field structure imaging apparatus of the present invention.

[Fig. 4] Fig. 4 is an example of a hardware configuration diagram of the magnetic field structure imaging apparatus of the present invention.

[Fig. 5] Fig. 5(A) is an image of the arrival trajectories of the muons in an xy plane of the target region obtained in Example 1. Fig. 5(B) is an image of the arrival trajectories of the muons in the xz plane of the simulation space including the target region obtained in Example 1.

[Fig. 6] Fig. 6 is an image of the arrival trajectory of the negative muons in the xy plane of the target region created by using only the negative muons obtained in Example 11.

[Fig. 7] Fig. 7(A) is an image of the arrival trajectory of the positive muons in the xy plane of the target region created by using only the positive muons obtained in the Example 12. Fig. 7(B) is an image of the arrival trajectory of the positive muons in the xz plane of the simulation space including the target region obtained in Example 12.

[Fig. 8] Fig. 8(A) is a schematic diagram illustrating the evaluation region for measuring the magnitude of the magnetic flux in Fig. 7(A). Fig. 8(B) is a graph illustrating the number of counts of the cosmic ray muons in the evaluation region in Fig. 8(A) as the proj ection on the x-axis. Fig. 8(C) is a schematic diagram of an example of the magnetic flux density of the target region calculated from Fig. 8(B).

[Fig. 9] Fig. 9(A) is an image of the arrival trajectories of the muons in the xy plane at a position -400 cm of the z-axis created by using the positive muons and the negative muons obtained in Reference Example 21. Fig. 9(B) is an image of the arrival trajectories of the muons in the xz plane of the simulation space including the target region obtained in Reference Example 21.

[Fig. 10] Fig. 10(A) is an image of the arrival trajectories of the muons of the target region obtained in Example 31. Fig. 10(B) is an image of the arrival trajectories of the muons of the target region obtained in Example 32. Fig. 10(C) is an image of the arrival trajectories of the muons of the target region obtained in Example 33.

[Fig. 11] Fig. 11 is a flowchart illustrating an example of the first aspect of the magnetic field structure imaging method of the present invention.

[Fig. 12] Fig. 12 is a flowchart illustrating another example of the first aspect of the magnetic field structure imaging method of the present invention.

[Fig. 13] Fig. 13 is a flowchart illustrating another example of the magnetic field structure imaging method of the present invention. [Fig. 14] Fig. 14 is a flowchart illustrating another example of the first aspect of the magnetic field structure imaging method of the present invention.

Description of Embodiment

[0013]

Hereinafter, the present invention will be described. Hereinafter, there are cases in which constituent requirements will be described on the basis of typical embodiments or specific examples of the present invention, but the present invention is not limited to the embodiments or the specific examples. Meanwhile, in the present description, numerical ranges expressed using “to” include numerical values before and after “to” as the lower limit value and the upper limit value.

[0014]

[Magnetic field structure imaging apparatus]

A magnetic field structure imaging apparatus of the present invention includes: a first detection unit that detects a passing position (transmitted position) of a muon having passed through a target region; a second detection unit that detects a passing position of the muon having passed through the target region and the first detection unit; an analysis unit that calculates a magnetic field structure image of the target region on the basis of an arrival trajectory of the muon detected by the first detection unit and the second detection unit; and a display unit that displays at least one of the magnetic field structure image and magnitude and/or direction of two-dimensional magnetic flux density calculated from the magnetic field structure image, and a cosmic ray muon is used as the muon.

With this configuration, it is possible to provide the magnetic field structure imaging apparatus capable of easily obtaining the magnetic field structure image of the target region.

Note that in the present description, when a transmission method and a deflection method for detecting deflection in a magnetic field (a system sandwiched between detectors) are not distinguished, “transmission of the muon” is synonymous with “passing of the muon”.

Hereinafter, preferred aspects of the present invention will be described. [0015]

A preferred aspect of the magnetic field structure imaging apparatus of the present invention will be described with reference to the drawings together with a magnetic field structure imaging method of the present invention. However, the present invention is not limited to the drawings, and for example, a plurality of units described in each figure may exist, or an integrated circuit (IC) in which the units are integrated may be used.

[0016]

Fig. 1 is a schematic diagram of an example of the magnetic field structure imaging apparatus of the present invention.

A magnetic field structure imaging apparatus 100 illustrated in Fig. 1 includes: a first detection unit 21 that detects a passing position of a muon (a positive muon 11 or a negative muon 12) having passed through a target region 1; a second detection unit 22 that detects a passing position of the muon having passed through the target region 1 and the first detection unit 21; an analysis unit 31 that calculates a magnetic field structure image of the target region on the basis of the arrival trajectory of the muon detected by the first detection unit 21 and the second detection unit 22; and a display unit 32 that displays at least one of the magnetic field structure image and magnitude and/or direction of two-dimensional magnetic flux density calculated from the magnetic field structure image.

The magnetic field structure imaging apparatus 100 illustrated in Fig. 1 further includes a control unit 33. The control unit 33 controls information detected by the first detection unit 21 and the second detection unit 22, the analysis unit 31, and the display unit 32. The control unit 33 includes a CPU and the like, and can execute various controls by an application (an app; or a program) executing a predetermined function.

Note that the units constituting the magnetic field structure imaging apparatus 100 may be electrically connected to each other, or may be connected to each other via a network as a client-server system or a cloud system.

[0017]

A magnetic field (B) of the target region is unknown, and is imaged as the magnetic field structure image of the target region by the magnetic field structure imaging apparatus illustrated in Fig. 1.

The magnetic field structure imaging apparatus illustrated in Fig. 1 does not have a probe that is directly inserted into the target region. By not inserting the probe directly into the target region, the magnetic field structure of the target region can be imaged without adversely affecting the magnetic field (B) of the target region physically or chemically.

[0018]

Note that the magnetic field structure imaging apparatus illustrated in Fig. 1 is described as a transmission type magnetic field structure imaging apparatus that measures the muon that transmits or passes through the target region. However, the magnetic field structure imaging apparatus of the present invention may be a reflection type magnetic field structure imaging apparatus that measures the muon reflected in the target region. [0019]

Fig. 2 is a schematic diagram of another example of the magnetic field structure imaging apparatus of the present invention.

The magnetic field structure imaging apparatus illustrated in Fig. 2 further includes, in addition to a configuration of the magnetic field structure imaging apparatus illustrated in Fig. 1, a third detection unit 23 that detects a passing position of the muon having passed through the first detection unit 21 and the second detection unit 22, a magnetic field applying unit 41 that applies the magnetic field between the second detection unit 22 and the third detection unit 23, and a discrimination unit 34 that discriminates between positive and negative of muons having passed through the target region 1.

The magnetic field structure imaging apparatus illustrated in Fig. 2 further includes a moving unit 51 of the third detection unit 23.

The magnetic field applying unit 41 can apply a known magnetic field Bm. [0020]

Fig. 3 is a schematic diagram of another example of the magnetic field structure imaging apparatus of the present invention.

The magnetic field structure imaging apparatus illustrated in Fig. 3 includes, in addition to the configuration of the magnetic field structure imaging apparatus illustrated in Fig. 2, a fourth detection unit 24 and a fifth detection unit 25 that detect passing positions of the muon, on a side opposite to the first detection unit 21 side of the target region 1. Further, the magnetic field structure imaging apparatus illustrated in Fig. 3 includes a flight time measuring unit 61 that measures a flight time of a predetermined section of the muon having passed through the fifth detection unit 25, the fourth detection unit 24, the target region 1, the first detection unit 21, and the second detection unit 22 in this order.

[0021] Fig. 4 is an example of a hardware configuration diagram of the magnetic field structure imaging apparatus of the present invention. The magnetic field structure imaging apparatus of the present invention can include, for example, a personal computer (PC), the display unit 32 which is a display, an input unit 37 which is a keyboard or the like, an output unit 38 which is a printer or the like, the first detection unit 21, the second detection unit 22, and the third detection unit 23 for detecting the passing positions of the muon, and the magnetic field applying unit 41 such as a permanent magnet or an electromagnet. The personal computer (PC) can include the analysis unit 31 , the control unit 33 including the CPU, the discrimination unit 34 that is a program or an application (App), a deflection analysis unit 36 such as a template matching method or a deconvolution method, a second discrimination unit 39, an automatic alert unit 40, and a storage unit 35 such as a memory or a local disk.

Hereinafter, a preferred aspect will be described for each component constituting the magnetic field structure imaging apparatus of the present invention.

[0022]

The target region is not particularly limited. The target region may be in a vacuum state or simply a space filled with gas only. The target region may include a liquid sample or a solid sample.

In the target region, a magnet or the like may be disposed inside or outside the target region to form an artificial magnetic field, or a naturally generated magnetic field may be formed.

Size of the target region is not particularly limited. As density structure imaging described in W02009/107575, the target region may be a space including a volcano or a large outdoor type industrial device such as a melting furnace, a space including an indoor type device such as a medical device or a nuclear magnetic resonance device, or a space including a precision equipment having a long axis of 1 m or less or 1 cm or less, such as a magnetic field created by an inductor (a coil) on a substrate. [0023] (Solid sample)

In the present invention, it is particularly preferable to include the solid sample in the target region. The present invention is preferably applied when the solid sample forms a complex and has a target interior (target object) and an outer shell portion covering the target interior. In the present invention, it is more preferred that the target region includes the solid sample and the magnetic field structure image inside the solid sample is created. In particular, according to the present invention, since the probe is not inserted directly into the target region, it does not adversely affect the magnetic field structure of the target region physically or chemically, and the magnetic field structure of the target region including the solid sample or the like for which it is difficult to measure the magnetic field can be imaged from the outside of the target region, and the magnitude and/or the direction of the magnetic flux density can be determined.

Note that a conventional magnetic field exploring device that directly inserts the probe into the target region has a problem that it is not possible to measure the magnetic field of, for example, a nuclear fusion reactor and a plasma generator that are physically or chemically adversely affected by the inserted probe disturbing the internal magnetic field, and an (particle) accelerator in operation that cannot be approached a position where the probe can be inserted directly due to high radioactivity.

More specifically, in the present invention, the solid sample is preferably the nuclear fusion reactor, the plasma generator, a nuclear reactor, a superconducting coil, an accelerator, a medical device having a strong magnetic field, a packaged strong magnetic field material, or a concrete structure.

The magnetic field structure imaging apparatus of the present invention can be used for inspecting and diagnosing deterioration of the magnetic field inside the nuclear fusion reactor, the plasma generator, the nuclear reactor, the superconducting coil, and the accelerator. They are difficult to obtain information on a state of the interior covered with metal, and although shape change of the state of the interior can be observed by the conventional density structure imaging (muography or tomography), the deterioration of the magnetic field (without shape change) could not be detected.

Examples of the medical device having a strong magnetic field include an MRI (a magnetic resonance imaging) diagnostic apparatus.

Examples of the concrete structure include concrete structures containing metal in the interior, such as bridges, piers, tunnels, dams, and harbor facilities. That is, the magnetic field structure imaging apparatus of the present invention can be used for nondestructive inspection and diagnosis for the concrete structures.

Examples of the packaged strong magnetic field material include a strong magnetic field material hidden in cargo or luggage to be loaded on an aircraft. That is, the magnetic field structure imaging apparatus of the present invention can be used for inspecting contents without opening the package at a security checkpoint or the like of an airfield or an airport.

[0024]

Further, grasping the magnetic field structure image of the target region is important in that information that cannot be obtained only by grasping the density structure image of the target region can be obtained. By grasping the magnetic field structure image of the target region, even when size and density of the solid sample contained in the target region do not change, but the magnetic field is abnormal or deteriorated, internal information on abnormality or deterioration of the magnetic field can be obtained. In particular, in the nuclear fusion reactors (research facilities and commercial reactors) and the like, there is a demand to obtain the internal information on such an abnormality and deterioration of the magnetic field. When applied to the solid sample having a strong magnetic field such as a nuclear fusion reactor, the magnetic field is too strong to use the template matching method, and a completely disturbed magnetic field structure image and the arrival trajectory (magnetic field imaging) of the muon can be obtained, but when the magnetic field weakens due to deterioration of the coil of the nuclear fusion reactor or the like, disturbance of the magnetic field structure image or the like is eliminated so that the image gradually comes into focus, and thus the deterioration can be determined. However, the magnetic field structure image of the target region may be used for the purpose of grasping as a substitute for the density structure image of the target region.

In the magnetic field structure imaging method of the present invention, it is preferable to record time variation of the magnetic field structure image and monitor the magnetic field structure of the target region, and it is more preferable to monitor the degree of deterioration of the magnetic field structure of the target region.

[0025]

The first detection unit detects a passing position of the muon having passed through the target region.

The second detection unit detects the passing position of the muon having passed through the target region and the first detection unit.

The first detection unit and the second detection unit are not particularly limited, and a known detection unit (a muon position sensitive detector (mu-PSD)) can be used. Examples thereof include a detection unit configured such that first detectors for horizontal direction detection extending in a vertical direction are arranged in m rows in the horizontal direction, second detectors for vertical direction detection extending in a horizontal direction are arranged in n columns in the vertical direction, and the first detectors in the m rows and the second detectors in the n columns are arranged in a frontrear direction. Examples of the first detector and the second detector include a detector configured such that a plastic scintillator that emits light due to, for example, incidence of the muon is disposed, for example, in an aluminum case along a length direction thereof, and a plurality of photomultiplier tubes are arranged at equal pitches along the length direction of the aluminum case, behind the plastic scintillator.

Therefore, when the plastic scintillator emits light, a pulse signal is output from the photomultiplier tube at a position behind a point emitting the light. In this case, pulse signals are respectively output from the first detector and the second detector.

Further, positional relationships between the first detectors and between the second detectors in the first detection unit and the second detection unit are set in advance, and for each row of the first detector arranged in the horizontal direction, for example, a distance in a radial direction from a center point of the target region is known in advance, and for each column of the second detector arranged in the vertical direction, a distance in the vertical direction with respect to a predetermined point in the target region is known in advance.

Here, it is assumed that a muon p having passed through the target region has been detected at a certain moment. The muon p is transmitted through the first detector and the second detector of the first detection unit, and the transmitted muon p is transmitted through the second detection unit. Focusing on the first detectors arranged in m rows in the horizontal direction, if it is assumed that in the first detection unit through which the muon p has been transmitted, the first detector is, for example, the sixth from the left end, and in the second detection unit, the first detector is the seventh from the left end, an incident angle of the muon p in the horizontal direction can be obtained, and the arrival trajectory of the muon p in the horizontal direction with respect to a measurement region can be obtained. The arrival trajectory of the muon p in the vertical direction is also obtained. The direction in which the detectors are arranged is not limited to the horizontal direction and the vertical direction, and the detectors may have another configuration capable of obtaining an arrival trajectory.

It is preferred, among muon position sensitive detectors, that the first detection unit and the second detection unit are each a set of two resistive plate chambers (RPCs). [0026] (Muon)

In the present invention, cosmic ray muons are used as muons. The cosmic ray muons refer to muons obtained from cosmic rays which are environmental radiation.

Overview of the muon (hereinafter, appropriately referred to as “p”) used in the present invention will be described.

The muon is an elementary particle having a mass of about 1/9 times the mass of a proton and about 207 times the mass of an electron, and there are two types of p⁺ and p" respectively having a positive and a negative charge. Although p+ and p- in vacuum die with a lifetime of 2.2 ps, they generate a positron e+, an electron e-, and a neutrino, which have energy of 50 mega electron volt (MeV), when they die. The cosmic ray muons arrive at a surface of the earth as the cosmic rays. 60% of the cosmic ray muons are positive muons, and are spin-polarized by about 30% in a traveling direction.

As a method for obtaining high-intensity muons, a method for generating 7t⁺ and 7i' is known in which high-energy protons and electrons are obtained using an elementary particle accelerator, 71 mesons (Yukawa mesons, 7t⁺ and 7i ) are generated by reaction with atomic nuclei, and a large amount of 7t⁺ and 7i' are generated by their decay.

On the other hand, in the present invention, the cosmic ray muons are used instead of the muons artificially generated by such an elementary particle accelerator. In a substance, the muon mainly interacts with a force from an electric field, but the present inventors have found that interaction of the muon with a force from a “magnetic field” is so great to the extent that it has been previously unknown and can be detected at a level that can be applied to imaging.

The cosmic ray muon has an almost constant energy spectrum at any place and at any time when a zenith angle is determined. The zenith angle is not particularly limited, and can be 0° to 90°, preferably 10° to 80°, and more preferably 20° to 70° from the viewpoint of good transparency of the cosmic ray muon that is close to horizontal.

An energy range to be detected is not particularly limited, but can be, for example, 1 MeV to 100 GeV, and preferably 10 MeV to 10 GeV.

[0027]

The third detection unit detects a passing position of the muon having passed through the first detection unit and the second detection unit. The third detection unit preferably detects the passing position of the muon having passed through the target region, the first detection unit, and the second detection unit. [0028]

(Moving unit)

It is preferred that the magnetic field structure imaging apparatus of the present invention further includes the moving unit of the third detection unit. It is preferred that the moving unit can move the third detection unit so that the muon having passed through the first detection unit and the second detection unit passes through the third detection unit.

The moving unit is not particularly limited, and a known unit can be used. The moving unit may autonomously move or may be moved by being operated from the outside by radio or the like so that the muon having passed through the first detection unit and the second detection unit passes through the third detection unit.

Other preferred aspects of the third detection unit are the same as the preferred aspects of the first detection unit.

[0029]

The magnetic field structure imaging apparatus of the present invention preferably has the magnetic field applying unit that applies the magnetic field between the second detection unit and the third detection unit from the viewpoint of enabling discrimination between the positive muon and the negative muon.

The magnetic field applying unit is not particularly limited, and a known unit such as the permanent magnet and the electromagnet can be used. The electromagnet may have a constant or variable magnetic flux density. In the present invention, the magnetic field applying unit is preferably the permanent magnet, or the electromagnet having a constant magnetic flux density, from the viewpoint of making it easy to apply a known magnetic field between the second detection unit and the third detection unit over a long period of time and making it easy to discriminate between positive and negative of the muons having passed the target region.

It is preferable to adjust the magnetic flux density of the permanent magnet or the electromagnet so that the muon having passed through the first detection unit and the second detection unit passes through the third detection unit. However, when the third detection unit includes the moving unit, instead of adjusting the magnetic flux density of the permanent magnet or the electromagnet, the third detection unit may be moved to be adjusted so that the muon having passed through the first detection unit and the second detection unit passes through the third detection unit. Alternatively, adjustment of the magnetic flux density of the permanent magnet or the electromagnet and movement of the third detection unit may be used in combination.

[0030] discrimination unit>

The magnetic field structure imaging apparatus of the present invention preferably has the discrimination unit for discriminating between positive and negative of the muons having passed through the target region, from the viewpoint of making it easy to obtain the magnetic field structure image of the target region and of obtaining the magnitude and/or the direction of the two-dimensional magnetic flux density calculated from the magnetic field structure image.

Examples of a method for discriminating between positive and negative of the muons include a method for analyzing the degree of deflection of the muon having passed through a known magnetic field applied between the second detection unit and the third detection unit.

[0031]

< Analysis unit>

The analysis unit calculates the magnetic field structure image of the target region on the basis of the arrival trajectory of the muon detected by the first detection unit and the second detection unit.

Here, in the conventional density structure imaging or the like, thickness has been obtained by measuring intensity attenuation when the cosmic ray muon passes through an object having an unknown thickness (density*length). By using two or more position-sensitive detectors (positron/electron charge detectors) to measure the intensity attenuation one after another for a path of the muon passing through a structure to be inspected, a mapping of spatial distribution of the thickness inside the object has been obtained. At this time, the mass of muon is 200 times heavier than that of the electron, only the interaction by the electric field works, and the energy is high, and thus for example, the muon passes up to several kilometers for rocks and up to 100 meters for iron, so that it has been conventionally a target of radiography (muography).

On the other hand, in the present invention, the magnetic field structure image of the target region is calculated on the basis of the arrival traj ectory of the muon. There is no particular limitation on the method for calculating the magnetic field structure image of the target region on the basis of the arrival trajectory of the detected muon. For example, PHITS-based Analytical Radiation Model in the Atmosphere (PARMA), which is an analysis model developed by the Japan Atomic Energy Agency and used for calculating a cosmic ray spectrum in the atmosphere, can be used.

[0032]

In the present invention, it is preferred that the analysis unit further creates the density structure image of the target region and calculates the magnitude of the magnetic flux density of the target region on the basis of a difference between the magnetic field structure image and the density structure image.

Specifically, the magnitude of the magnetic flux (the magnetic flux density) of the target region can be calculated on the basis of a difference between a graph illustrating the number of counts of the cosmic ray muons in an evaluation region of the magnetic field structure image of the target region as a projection in a certain direction (for example, x-axis) and the density structure image of the target region created separately.

Here, a method for creating the density structure image of the target region is not particularly limited, and a known method can be used. For example, reflective radiography and/or transmission radiography described in [0005] to [0062] of W02009/107575 can be used, and the contents of which are incorporated herein by reference.

[0033]

The direction of the two-dimensional magnetic flux (or magnetic flux density) calculated from the magnetic field structure image is preferably calculated by the analysis unit with reference to data of the discrimination unit.

Specifically, the direction of the two-dimensional magnetic flux (or magnetic flux density) can be calculated from a relationship between a position where concentration of the positive muon is high in the magnetic field structure image by the positive muon and a position where concentration of the negative muon is high in the magnetic field structure image by the negative muon.

[0034]

The magnetic field structure imaging apparatus of the present invention preferably include the fourth detection unit and the fifth detection unit that detect the muon having passed through the target region, the first detection unit, and the second detection unit, on the side opposite to the first detection unit side of the target region. Since the degree of deflection of how much the muon has been deflected in the magnetic field region can be known, all transmission components of the muon can be used.

Further, the magnetic field structure imaging apparatus of the present invention preferably includes a muon energy measuring unit that measures a velocity of muons such as the Cherenkov detector or the flight time measuring unit that measures the flight time of the predetermined section of the muon having passed through the fifth detection unit, the fourth detection unit, the target region, the first detection unit, and the second detection unit in this order. By a preferred aspect including these configurations, the flight time (Time of Flight; ToF) of the predetermined section of the muon can be obtained. Specifically, the flight time can be calculated using an absolute time for a specific muon to pass through each detection unit or a relative time for the specific muon to pass through each detection unit after synchronizing each detection unit.

Preferred aspects of the fourth detection unit and the fifth detection unit are the same as the preferred aspects of the first detection unit and the second detection unit.

It is preferred that the magnetic field structure imaging apparatus of the present invention further includes the deflection analysis unit that analyzes the degree of deflection of the muon having passed through the magnetic field applied between the second detection unit and the third detection unit, and the deflection analysis unit analyzes momentum of the muon on the basis of the degree of deflection of the muon. The deflection analysis unit can preferably perform analysis by the template matching method, the deconvolution method, or the like.

[0035]

The display unit displays at least one of the magnetic field structure image and the magnitude and/or the direction of the two-dimensional magnetic flux density calculated from the magnetic field structure image. That is, the present invention also includes an aspect in which only the magnitude and/or the direction of the two- dimensional magnetic flux density calculated from the magnetic field structure image is displayed without displaying the magnetic field structure image.

The display unit preferably displays at least the magnetic field structure image, and preferably displays both the magnetic field structure image and the magnitude and/or the direction of the two-dimensional magnetic flux density calculated from the magnetic field structure image.

The magnetic field structure image displayed in the present invention is not particularly limited. Examples of the magnetic field structure image include an aspect in which a magnitude of a two-dimensional muon flux (Flux; unit is l/cm²/source) or the magnitude of the magnetic flux on a certain plane on the target region is visualized by color or concentration, and mapped together with a scale thereof. The examples include another aspect in which positions of an N pole and an S pole in the certain plane of the target region are mapped.

In the magnetic field structure imaging apparatus of the present invention, it is more preferred that the two-dimensional magnetic flux density and direction of the target region are calculated (by the analysis unit) and displayed (by the display unit).

[0036]

In the present invention, the display unit preferably creates and displays the magnetic field structure image of the target region using at least one of the positive muon and the negative muon.

The display unit more preferably displays at least one of the magnetic field structure image by the positive muon created by using the positive muon, the magnetic field structure image by the negative muon created by using the negative muon, a magnetic field structure image using both positive and negative muons created by using the positive muon and the negative muon, and a positive and negative composite magnetic field structure image obtained by mirror-transforming one of the magnetic field structure image by the positive muon and the magnetic field structure image by the negative muon and synthesizing it with the other. The display unit particularly preferably displays at least one of the magnetic field structure image by the positive muon created by using the positive muon, the magnetic field structure image by the negative muon created by using the negative muon, and the positive and negative composite magnetic field structure image obtained by mirror-transforming one of the magnetic field structure image by the positive muon and the magnetic field structure image by the negative muon and synthesizing it with the other.

The magnetic field structure imaging apparatus of the present invention may include an image conversion unit (or program) for comparing the magnetic field structure image using both positive and negative muons created by using the positive muon and the negative muon with the magnetic field structure image by the positive muon or the magnetic field structure image by the negative muon to improve accuracy, or for reconstructing the magnetic field structure images to improve accuracy.

There is no particular limitation on a method for obtaining the positive and negative composite magnetic field structure image obtained by mirror-transforming one of the magnetic field structure image by the positive muon and the magnetic field structure image by the negative muon and synthesizing it with the other, and it can be performed by the image conversion unit (or program) for performing mirror transformation and image synthesis by a known method. Performing a step of extracting only a magnetic field component and then a step of performing the mirror transformation is to extract the magnetic field component from a distorted muography image, so that the mirror transformation and the image synthesis can be performed.

[0037]

The magnetic field structure imaging apparatus of the present invention may include other units. It is preferable to have, for example, the control unit illustrated in Fig. 1, and the input unit, the output unit, the storage unit, the second discrimination unit, the automatic alert unit, and the like illustrated in Fig. 4.

[0038]

The storage unit preferably records, for example, a direction in which the muon has arrived and a time (time stamp) in which the muon has arrived. By recording the time stamp, for example, it is possible to compare it with a figure for the past one month, and to compare it with a result of two-week measurement one year ago. Further, the storage unit preferably records the time variation of the magnetic field structure image. It is more preferable to record the time variation of the magnetic field structure image and monitor the degree of deterioration of the magnetic field structure of the target region.

Further, the magnetic field structure imaging apparatus preferably includes the second discrimination unit for determining that the degree of deterioration of the magnetic field structure of the target region has increased as a result of monitoring the magnetic field structure of the target region. The second discrimination unit is not particularly limited, and may be one in which a predetermined threshold value is set, or one may use a trained model in which Al is trained on the degree of deterioration of the magnetic field structure.

The magnetic field structure imaging apparatus preferably includes an automatic alert unit that automatically notifies the outside of a determination that the degree of deterioration of the magnetic field structure of the target region has increased. In the nuclear fusion reactor and the like, since human judgment as to whether the degree of deterioration of the magnetic field structure has increased may be delayed for various reasons, it is preferable to include such an automatic alert unit from the viewpoint of suppressing human intervention in the judgment. For example, in the nuclear fusion reactor, it is known that the superconducting coil that creates the magnetic field deteriorates, and a method for determining the deterioration by monitoring current flowing through the superconducting coil is known. However, with this method, it is not known where in the superconducting coil the deterioration has occurred. In contrast, the magnetic field structure imaging apparatus of the present invention is preferable from the viewpoint of knowing the position where the deterioration of the coil has occurred because strength of the magnetic field can be grasped from a broad perspective.

[0039]

[Magnetic field structure imaging method]

A first aspect of the magnetic field structure imaging method of the present invention includes: a first detection step of detecting the muon having passed through the target region; a second detection step of detecting the muon having passed through the target region and the first detection unit; an analysis step of calculating the magnetic field structure image of the target region on the basis of the arrival trajectory of the muon detected in the first detection step and the second detection step; and a display step of displaying at least one of the magnetic field structure image and the magnitude and/or the direction of the two-dimensional magnetic flux density calculated from the magnetic field structure image, and the cosmic ray muon is used as the muon. Fig. 11 is a flowchart illustrating an example of the first aspect of the magnetic field structure imaging method of the present invention.

SI: START;

S2: MEASURE POSITION WHERE MUON PASSES THROUGH FIRST DETECTION UNIT;

S3: MEASURE POSITION WHERE MUON PASSES THROUGH SECOND DETECTION UNIT;

S4: DETECT ARRIVAL TRAJECTORY OF MUON (MAGNETIC FIELD IMAGING); S5: CALCULATE MAGNETIC FIELD STRUCTURE IMAGE OF TARGET REGION; S6: CALCULATE MAGNITUDE OF MAGNETIC FLUX DENSITY FROM MAGNETIC FIELD STRUCTURE IMAGE;

S7: ANALYSIS END? IF YES, TO S8; IF NO, TO S2;

S8: DISPLAY DESIRED DATA;

S9: END.

It is preferred that the first aspect of the magnetic field structure imaging method further includes: a third detection step of detecting the passing position of the muon having passed through the first detection unit and the second detection unit; a magnetic field applying step of applying the known magnetic field between the second detection unit and the third detection unit; and a discrimination step of discriminating between positive and negative of the muons having passed through the target region, and the display unit creates and displays the magnetic field structure image of the target region using at least one of the positive muon and the negative muon. Fig. 12 illustrates this preferred aspect. Fig. 12 is a flowchart illustrating another example of the first aspect of the magnetic field structure imaging method of the present invention.

S10: START;

Sil: MEASURE POSITION WHERE MUON PASSES THROUGH FIRST DETECTION UNIT;

S12: MEASURE POSITION WHERE MUON PASSES THROUGH SECOND DETECTION UNIT;

S13: MEASURE POSITION WHERE MUON PASSES THROUGH THIRD DETECTION UNIT;

S14: DISCRIMINATE BETWEEN POSITIVE AND NEGATIVE OF MUON;

SI 5: DETECT ARRIVAL TRAJECTORY OF EACH OF POSITIVE AND NEGATIVE MUONS (MAGNETIC FIELD IMAGING);

SI 6: CALCULATE MAGNETIC FIELD STRUCTURE IMAGE OF TARGET REGION;

SI 7: CALCULATE MAGNITUDE AND DIRECTION OF MAGNETIC FLUX DENSITY FROM MAGNETIC FIELD STRUCTURE IMAGE;

S18: ANALYSIS END? IF YES, TO S19; IF NO, TO SI 1 ;

SI 9: DISPLAY DESIRED DATA;

S20: END.

A second aspect of the magnetic field structure imaging method of the present invention includes: a first detection step of detecting the muon having passed through the target region; a second detection step of detecting the muon having passed through the target region and the first detection unit; and a display step of displaying a magnetic field imaging obtained by analyzing (by the MLEM method or the like reconstruction methods) a muographic image of the muon detected in the first detection step and the second detection step, and the magnetic field structure imaging method records the time variation of the magnetic field imaging, monitors variation of the magnetic field imaging of the target region, and uses the cosmic ray muon as the muon. Fig. 13 is a flowchart illustrating another example of the magnetic field structure imaging method of the present invention.

S21 : START;

S22: MEASURE POSITION WHERE MUON PASSES THROUGH FIRST DETECTION UNIT;

S23: MEASURE POSITION WHERE MUON PASSES THROUGH SECOND DETECTION UNIT;

S24: DETECT ARRIVAL TRAJECTORY OF MUON (MAGNETIC FIELD IMAGING);

S25: RECORD TIME VARIATION OF MAGNETIC FIELD IMAGING;

S26: MONITOR VARIATION OF MAGNETIC FIELD IMAGING;

S27: ABNORMAL? IF YES, TO S28; IF NO, TO S22;

S28: DISPLAY DESIRED DATA, AUTOMATIC ALERT, THRESHOLD COMPARISON;

S29: CONTINUE OPERATION? IF YES, TO S22; IF NO, TO S30;

S30: END.

Specifically, it is preferable to make a direct comparison with before applying the magnetic field to the target region (do not close to the magnetic field imaging before applying the magnetic field). Further, it is preferable to record the variations in a one month moving average, a three month moving average, a six month moving average, and the like, and use them for monitoring the variations by a comparative method.

A preferred aspect of the magnetic field structure imaging method of the present invention is the same as the preferred aspect of the magnetic field structure imaging of the present invention.

[0040]

In the magnetic field structure imaging method, a detection period is not particularly limited, but is preferably longer from the viewpoint that the number of events of the muon to be detected is increased and imaging accuracy is improved. The detection period is preferably shorter from the viewpoint that the industrial applicability is increased by reducing an actual measurement period and reducing measurement cost.

In the magnetic field structure imaging method, it is preferable to further perform the fourth detection step and the fifth detection step of detecting the passing positions of the muon on the side opposite to the first detection unit side of the target region from the viewpoint that the analysis can be performed without waiting for the muography image to be visible. That is, the target region is preferably sandwiched between the detection units (between a set of the first detection unit and the second detection unit and a set of the fourth detection unit and the fifth detection unit). When the target region is sandwiched between the detection units, both the incident angle of the muon and an angle of the muon after having passed through the magnetic field of the target region are known, so that all the transmitted muons can be used, and the magnetic field structure image can be created and displayed for about 10 minutes (almost all of the cosmic ray muons with a frequency of penetrating a palm one per second can be used) using the same concept as a muography scattering method. Fig. 14 is a flowchart illustrating another example of the first aspect of the magnetic field structure imaging method of the present invention. S31 : START;

S32: MEASURE POSITION WHERE MUON PASSES THROUGH FIRST DETECTION UNIT;

S33: MEASURE POSITION WHERE MUON PASSES THROUGH SECOND DETECTION UNIT;

S34: MEASURE POSITION WHERE MUON PASSES THROUGH THIRD DETECTION UNIT;

S35: DETECT ARRIVAL TRAJECTORY OF MUON (MAGNETIC FIELD IMAGING);

S36: ANALYZE DEGREE OF DEFLECTION OF MUON HAVING PASSED THROUGH KNOWN MAGNETIC FIELD BETWEEN SECOND AND THIRD DETECTION UNITS;

S37: DISCRIMINATE BETWEEN POSITIVE AND NEGATIVE OF MUON;

S38: CALCULATE MAGNETIC FIELD STRUCTURE IMAGE OF TARGET REGION;

S39: CALCULATE MAGNITUDE AND DIRECTION OF MAGNETIC FLUX DENSITY FROM MAGNETIC FIELD STRUCTURE IMAGE;

S40: ANALYSIS END? IF YES, TO S41; IF NO, TO S32;

S41 : DISPLAY DESIRED DATA;

S42: END;

S43: MEASURE POSITION WHERE MUON PASSES THROUGH FIFTH AND FOURTH DETECTION UNITS;

S44: ANALYZE INCIDENT ANGLE OF MUON ON MEASUREMENT REGION AND FLIGHT TIME OF PREDETERMINED SECTION;

S45: ANALYZE MOMENTUM OF MUON;

S46: CREATE DENSITY STRUCTURE IMAGE;

S47: COMPARE AND ANALYZE DENSITY STRUCTURE IMAGE UNDER CONDITIONS WITHOUT MAGNETIC FIELD.

From the viewpoint of shortening a measurement time, instead of or in addition to obtaining the incident angle of the muon on the target region, the flight time of the predetermined section may be obtained and the momentum of the muon may be calculated, to be used in the analysis step.

When the target region is not sandwiched between the detection units, since an image with poor contrast in which highly penetrating muons are slightly absorbed is obtained, it is preferable to wait for the muography image to be visible. In this case, in the present invention, it is preferable to create and display the magnetic field structure image using the muons detected between one week and three months, and it is more preferable to create and display the magnetic field structure image using the muons detected between two weeks and two months.

[0041]

The magnetic field structure imaging method preferably includes: a step of measuring the target region from optical axes that differ by 90° and obtaining magnetic field structure images that differ by 90° of the target region; and a step of reconstructing a three-dimensional magnetic field structure image from the magnetic field structure images that differ by 90° of the target region.

If it can be measured once from a vertically lower side, this condition can be satisfied no matter where on a ground surface it is measured. When performing monitoring, as a set of magnetic field structure imaging apparatuses in which at least two magnetic field structure imaging apparatuses of the present invention are used in combination, it is preferable to install one of the magnetic field structure imaging apparatuses of the present invention underground.

The following method can be mentioned as a method for reconstructing the three-dimensional magnetic field structure image.

Obtain two-dimensional xy plane information of the target region measured and analyzed from a certain one axis direction and two-dimensional yz plane information of the target region measured and analyzed from the other axis direction different by 90° from the one axis. Since these pieces of two-dimensional information have the same information in the Y-axis direction, the three-dimensional magnetic field structure image can be easily obtained.

[0042]

The following methods can be mentioned as a method for analyzing the magnitude and/or the direction of the two-dimensional magnetic flux density calculated from the two-dimensional magnetic field structure image and the magnetic field structure image.

Obtain the muography image under conditions without the magnetic field by simulation or actual measurement. Divide it and use it as a template. The muography image distorted by the magnetic field is analyzed by the template matching method, and how much each template has moved from an original position is calculated. The larger an amount of this movement amount, the stronger the magnetic field.

In addition, it is also possible to directly estimate two-dimensional magnetic flux density distribution with high accuracy without deriving the above-mentioned movement amount by using a Maximum-Likelihood Expectation-Maximization (MLEM) method or the like. This method includes a process of applying an estimated magnetic field to calculate distortion of the muography image due to the magnetic field, and a process of comparing the distorted muography image with the muography image obtained by actual measurement to adjust the estimated magnetic field so that the muography image closer to the actual measurement can be obtained. By repeating this a sufficient number of times, the magnetic field distribution required to obtain the muographic image obtained by the actual measurement can be obtained (Shepp and Vardi, 1982).

[Examples]

[0043]

Hereinafter, the present invention will be more specifically described using examples and comparative examples. Materials, amounts used, ratios, processing contents, processing orders, and the like described in the following examples can be appropriately modified within the scope of the gist of the present invention. Therefore, the scope of the present invention is not limited to specific examples described below. [0044] [Example 1]

Using the magnetic field structure imaging apparatus having a configuration illustrated in Fig. 1, a simulation was performed to obtain the magnetic field structure image of the target region. Nothing was placed in the target region, and the magnetic field was applied in a range of 300 cm in length (y-axis direction), 200 cm in width (x-axis direction), and 100 cm in height (z-axis direction). A rectangular (rectangular parallelepiped) portion drawn on a right side of the paper in Figs. 1 and 5(B) is a portion to which the magnetic field is applied.

Analysis unit, energy spectrum: PHITS-based Analytical Radiation Model in the Atmosphere (PARMA), which is the analysis model developed by the Japan Atomic Energy Agency and used for calculating the cosmic ray spectrum in the atmosphere, was used. The zenith angle was 70°.

Measured energy range: 10 MeV to 10 GeV.

Measured elementary particles: Positive cosmic ray muon (p⁺) and negative cosmic ray muon (p‘).

Simulation space was filled with vacuum.

A set of two muon position sensitive detectors (herein Resistive Plate Chambers (RPCs)) was placed as the first detection unit at a position 400 cm away in the z-axis direction from a center in the z-axis direction of the target region. Further, a set of two muon position sensitive detectors (herein RPCs) was placed as the second detection unit at a position 25 cm away in the z-axis direction from that position. A distance between the first detection unit and the second detection unit can be set to a position away by 15 to 34 cm in the z-axis direction.

The first detection unit detected the passing position of the muon having passed through the target region. In addition, the second detection unit detected the passing position of the muon having passed through the target region and the first detection unit.

By predicting the arrival trajectory of the muon by the analysis unit and determining the magnetic flux density of the target region from a displacement amount of the arrival trajectory of the muon, the magnetic field structure image of the target region was calculated on the basis of the arrival trajectory of the muon detected by the first detection unit and the second detection unit.

Note that when the cosmic ray muon is incident parallel to the first detection unit, since a position where the cosmic ray muon passes through the first detection unit and a position where the cosmic ray muon passes through the second detection unit are almost the same, the arrival trajectory of the muon may be determined using only the position where the muon having passed through the first detection unit as a representative.

As the control unit and the display unit, a general -purpose PC including the CPU, and an attached monitor were used to display the arrival trajectory of the muon and the magnetic field structure image of the target region on the monitor.

[0045]

Obtained results are illustrated in Figs. 5(A) and 5(B). Fig. 5(A) is an image of the arrival trajectories of the muons in an xy plane of the target region obtained in Example 1. Fig. 5(B) is an image of the arrival trajectories of the muons in the xz plane of the simulation space including the target region obtained in Example 1. Note that in each figure, the two-dimensional muon flux (Flux) (unit is /cm²/source) is illustrated by concentration, and concentration scale of the muon flux is illustrated at a right end of the paper in each figure.

From Figs. 5(A) and 5(B), there is a high-concentration portion in the range of - 100 cm to 100 cm in the x-axis direction and -150 cm to 150 cm in the y-axis direction, and it was found that the magnetic field structure image of the target region can be accurately obtained. Note that in the magnetic field structure imaging apparatus having the configuration illustrated in Fig. 1, the direction of the magnetic flux of the target region could not be obtained.

[0046]

[Examples 11 and 12]

Using the magnetic field structure imaging apparatus having a configuration illustrated in Fig. 2, a simulation was performed to obtain the magnetic field structure image of the target region.

Nothing was placed in the target region, and the magnetic field was applied in the range of 300 cm in length (y-axis direction), 200 cm in width (x-axis direction), and 20 cm in height (z-axis direction). The rectangular (rectangular parallelepiped) portion in Figs. 2 and 6 is the portion to which the magnetic field is applied.

Analysis unit, energy spectrum: PARMA was used as in Example 1. The zenith angle was 70°.

Measured energy range: 10 MeV to 10 GeV.

Measured elementary particles: In Example 11, only the negative cosmic ray muon (p-) was used. In Example 12, only the positive cosmic ray muon (p +) was used.

The simulation space was filled with vacuum.

A set of two muon position sensitive detectors (herein Resistive Plate Chambers (RPCs)) was placed as the first detection unit at the position 400 cm away in the z-axis direction from the center in the z-axis direction of the target region. Further, a set of two muon position sensitive detectors (herein RPCs) was placed as the second detection unit at the position 25 cm away in the z-axis direction from that position. Further, a set of two muon position sensitive detectors (herein RPCs) was placed as the third detection unit at a position away from that position by a predetermined distance in the z-axis direction. Note that by adjusting the moving unit attached to the third detection unit, the third detection unit was moved so that the muon having passed through the first detection unit and the second detection unit passes through the third detection unit.

The first detection unit detected the passing position of the muon having passed through the target region. In addition, the second detection unit detected the passing position of the muon having passed through the target region and the first detection unit. The third detection unit detected the passing position of the muon having passed through the first detection unit and the second detection unit.

The known magnetic field Bm was applied between the second detection unit and the third detection unit by the magnetic field applying unit.

The discrimination unit discriminated between positive and negative of the muons having passed through the target region on the basis of the arrival trajectory of each muon.

As the control unit and the display unit, the general-purpose PC including the CPU, and the attached monitor were used to display the arrival trajectory of the muon and the magnetic field structure image of the target region on the monitor.

[0047]

The results obtained in Example 11 are illustrated in Fig. 6, and the results obtained in Example 12 are illustrated in Figs. 7(A) and 7(B). Fig. 6 is the arrival trajectory of the negative muons in the xy plane of the target region created by using only the negative muons obtained in Example 11. Fig. 7(A) is an image of the arrival trajectory of the positive muons in the xy plane of the target region created by using only the positive muons obtained in the Example 12. Fig. 7(B) is an image of the arrival trajectory of the positive muons in the xz plane of the simulation space including the target region obtained in Example 12. Note that in each figure, the two-dimensional muon flux (unit is /cm²/source) is illustrated by concentration, and the concentration scale of the muon flux is illustrated at the right end of the paper in each figure. Note that Fig. 6 schematically illustrates that among the negative muons indicated by arrows, those having passed through the target region are deflected.

From Fig. 6, it is understood that there is a high concentration portion in the range of -200 cm to -150 cm in the x-axis direction and -150 cm to 150 cm in the y-axis direction, there is a portion in which the muon was not detected in the range of 120 cm to 140 cm in the x-axis direction and -150 cm to 150 cm in the y-axis direction, and the negative muons were deflected in a negative direction of the x-axis (direction of the arrow in Fig. 6).

On the other hand, from Fig. 7(A), it is understood that there is a high concentration portion in the range of 150 cm to 200 cm in the x-axis direction and -150 cm to 150 cm in the y-axis direction, there is a portion in which the muon was not detected in the range of -150 cm to -130 cm in the x-axis direction and -150 cm to 150 cm in the y-axis direction, and the positive muons were deflected in a positive direction of the x- axis (direction opposite to the direction of the arrow in Fig. 6) in Fig. 7(A). Further, from Fig. 7(B), it is understood that there is a high concentration portion in a triangular shape in the range of 150 cm to 200 cm in the x-axis direction and -500 cm to 300 cm in the z-axis direction, there is a portion in which the muon was not detected in the range of -150 cm to -130 cm in the x-axis direction and -500 cm to 300 cm in the z-axis direction, and the positive muons were deflected in the positive direction of the x-axis in Fig 7(B).

From the above, it is understood that the magnetic field structure imaging apparatus having the configuration illustrated in Fig. 2 can accurately obtain the magnetic field structure image of the target region, and can further determine the direction of the two-dimensional magnetic flux of the target region from the magnetic field structure image.

[0048]

In Example 12, the magnitude of the magnetic flux (magnetic flux density) of the target region was obtained from the magnetic field structure image. In the magnetic field structure image of the target region obtained in Example 12, the evaluation region for measuring the magnitude of the magnetic flux was set to -200 cm to 200 cm in the x- axis direction and 0 cm to 50 cm in the y-axis direction. Then, the number of counts of cosmic ray muons in the evaluation region was obtained as a projection on the x-axis. Fig. 8(A) is a schematic diagram illustrating the evaluation region for measuring the magnitude of the magnetic flux in Fig. 7(A). Fig. 8(B) is a graph illustrating the number of counts of the cosmic ray muons in the evaluation region in Fig. 8(A) as the projection on the x-axis.

On the other hand, using the same analysis unit, the density structure image of the target region was further created by the known method.

The magnitude of the magnetic flux (magnetic flux density) of the target region was calculated on the basis of the difference between the graph illustrating the number of counts of the cosmic ray muons in the evaluation region of the magnetic field structure image of the target region as the projection on the x-axis and the density structure image of the target region. In the case of this example, the magnetic flux density was predicted from the fact that an uncounted portion of the muon appears due to less high-energy muons with less displacement. In addition, a central portion was predicted that the magnetic field is uniform because an outside of the magnetic field and the muon flux are close to each other and an amount of change is small.

Note that if there is a component in the zenith angle direction, the above- mentioned template matching method and deconvolution method and the like can be used for analysis if a long-term measurement time is taken even in a vacuum (because it does not occur that the muons arrive only from the horizontal direction). An absorber can be installed to speed up the measurement time, and since there is some object behind the magnetic field of the target region (unless it is a desert or the like), it can be used as the absorber.

Fig. 8(C) is a schematic diagram of an example of the magnetic flux density of the target region calculated from Fig. 8(B).

From the above, it is understood that the magnitude and direction of the two- dimensional magnetic flux density of the target region can be calculated using the magnetic field structure imaging apparatus of the present invention.

[0049]

[Reference Example 21]

Using the magnetic field structure imaging apparatus having the configuration illustrated in Fig. 2, a simulation was performed to evaluate effects of the magnetic field of the cosmic ray muons.

Nothing was placed in the target region.

The analysis unit, the energy spectrum, the first to third detection units, the discrimination unit, the control unit, and the display unit were the same as those in Example 11.

Measured energy range: 316 MeV to 1 GeV.

The simulation space was filled with vacuum.

The known magnetic field Bm was applied between the second detection unit and the third detection unit, specifically, between -500 cm and -150 cm in the z-axis direction, by the magnetic field applying unit.

[0050]

The results obtained in Reference Example 21 are illustrated in Figs. 9(A) and 9(B). Fig. 9(A) is an image of the arrival trajectories of the muons in the xy plane at a position -400 cm of the z-axis created by using the positive muons and the negative muons obtained in Reference Example 21. Fig. 9(B) is an image of the arrival trajectories of the muons in the xz plane of the simulation space including the target region obtained in Reference Example 21. Note that in each figure, the magnitude of the two- dimensional muon flux (unit is /cm²/source) is illustrated by concentration, and the concentration scale of the muon flux is illustrated at the right end of the paper in each figure.

From Fig. 9(A), it is understood that there is a portion in which the concentration is low to some extent in the range of -200 cm to -100 cm and 100 cm to 200 cm in the x- axis direction, -150 cm to 150 cm in the y-axis direction, and there is a portion in which the muon was hardly detected in the range of -100 cm to 100 cm in the x-axis direction and -150 cm to 150 cm in the y-axis direction. The portion in which the muon was hardly detected is the region created because the muons with high energy that can go straight up to this point rarely exist in nature. Energy distribution can be predicted by the PARMA model, an average value is 2 GeV, and the intensity is reduced sharply in a region in which the energy is higher than that. Since the region in which the muons do not arrive corresponds to this portion in which the intensity is reduced sharply, from a figure obtained by the simulation and the PARMA model, it can be analyzed that the wider the portion in which the muon was not detected, the higher the magnetic flux density. Further, from Fig. 9(B), it is understood that the portion in which the concentration is low and the portion in which the muon was not detected coexist in the range of -100 cm to 100 cm in the x-axis direction and -500 cm to -150 cm in the z-axis direction. From the above, in the magnetic field structure imaging apparatus having the configuration illustrated in Fig. 2, it is understood that the cosmic ray muon was deflected by the magnetic field applied between the second detection unit and the third detection unit.

[0051]

[Examples 31 to 33]

Using the magnetic field structure imaging apparatus having the configuration illustrated in Fig. 2, a simulation was performed to obtain the magnetic field structure image of the target region.

A quadrupole magnet was placed in the target region. Specifically, an S pole of a first magnet was placed at a position of 0 cm in the x-axis direction and -150 cm in the y-axis direction, an S pole of a second magnet was placed at a position of 0 cm in the x-axis direction and 150 cm in the y-axis direction, an N pole of a third magnet was placed at a position of -150 cm in the x-axis direction and 0 cm in the y-axis direction, and an N pole of a fourth magnet was placed at position of 150 cm in the x-axis direction and 0 cm in the y-axis direction.

The analysis unit, the energy spectrum, the measured energy range, the first to third detection units, the discrimination unit, the control unit, and the display unit were the same as those in Example 11.

Measured elementary particles: In Example 31, the positive cosmic ray muon (p⁺) and the negative cosmic ray muon (p‘) were used. In Example 32, only the positive cosmic ray muon (p⁺) was used. In Example 33, only the negative cosmic ray muons (p‘) was used.

The simulation space was filled with vacuum.

The magnetic field structure image of the target region was calculated by the analysis unit on the basis of the arrival trajectories of the muons detected by the first detection unit and the second detection unit.

The general-purpose PC including the CPU, and the attached monitor were used as the control unit and the display unit, so that the magnetic field structure image of the target region was displayed on the monitor.

[0052]

The obtained results are illustrated in Figs. 10(A) to 10(C). Fig. 10(A) is an image of the arrival trajectories of the muons of the target region obtained in Example 31. Fig. 10(B) is an image of the arrival trajectories of the muons of the target region obtained in Example 32. Fig. 10(C) is an image of the arrival trajectories of the muons of the target region obtained in Example 33. Note that in each figure, the two-dimensional muon flux (unit is /cm²/source) is illustrated by concentration, and the concentration scale of the muon flux is illustrated at the right end of the paper in each figure.

Further, from Fig. 10(A), it is understood that the magnetic field structure image of the target region reflecting the magnetic field of the quadrupole magnet was accurately obtained.

From Fig. 10(B), it is understood that the positive muon was deflected in a direction in which the S pole of the quadrupole magnet was placed. On the other hand, from Fig. 10(C), it is understood that the negative muon was deflected in a direction in which the N pole of the quadrupole magnet was placed. Further, it is understood that when the positive and negative composite magnetic field structure image obtained by synthesizing Figs. 10(B) and 10(C) is obtained, it is in good agreement with Fig. 10(A).

Reference Signs List

[0053]

1 : target region, 11 : positive muon, 12: negative muon, 21 : first detection unit, 22: second detection unit, 23: third detection unit, 24: fourth detection unit, 25: fifth detection unit, 31 : analysis unit, 32: display unit, 33: control unit, 34: discrimination unit, 35: storage unit, 36: deflection analysis unit, 37: input unit, 38: output unit, 39: second discrimination unit, 40: automatic alert unit, 41 : magnetic field applying unit, 51 : moving unit, 61 : flight time measuring unit, 100: magnetic field structure imaging apparatus, Bm: known magnetic field, B: magnetic field of target region, PC: personal computer.

Claims

[Claim 1]

A magnetic field structure imaging apparatus comprising: a first detection unit that detects a passing position of a muon having passed through a target region; a second detection unit that detects a passing position of the muon having passed through the target region and the first detection unit; an analysis unit that calculates a magnetic field structure image of the target region on the basis of an arrival trajectory of the muon detected by the first detection unit and the second detection unit; and a display unit that displays at least one of the magnetic field structure image and magnitude and/or direction of two-dimensional magnetic flux density calculated from the magnetic field structure image, wherein a cosmic ray muon is used as the muon.

[Claim 2]

The magnetic field structure imaging apparatus according to claim 1, which does not have a probe to be directly inserted into the target region.

[Claim 3]

The magnetic field structure imaging apparatus according to claim 1 or 2, further comprising: a third detection unit that detects a passing position of the muon having passed through the first detection unit and the second detection unit; a magnetic field applying unit that applies a magnetic field between the second detection unit and the third detection unit; and a discrimination unit that discriminates between positive and negative of muons having passed through the target region, wherein the display unit creates and displays the magnetic field structure image of the target region using at least one of a positive muon and a negative muon.

[Claim 4]

The magnetic field structure imaging apparatus according to claim 3, wherein the display unit displays at least one of the magnetic field structure image by the positive muon created by using the positive muon, the magnetic field structure image by the negative muon created by using the negative muon, and a positive and negative composite magnetic field structure image obtained by mirror-transforming one of the magnetic field structure image by the positive muon and the magnetic field structure image by the negative muon and synthesizing it with the other.

[Claim 5]

The magnetic field structure imaging apparatus according to claim 3 or 4, wherein the magnetic field applying unit is a permanent magnet, or an electromagnet having a constant magnetic flux density.

[Claim 6]

The magnetic field structure imaging apparatus according to any one of claims 3 to 5, further comprising a moving unit of the third detection unit, wherein the moving unit can move the third detection unit so that the muon having passed through the first detection unit and the second detection unit passes through the third detection unit.

[Claim 7]

The magnetic field structure imaging apparatus according to any one of claims 3 to 6, further comprising a deflection analysis unit that analyzes the degree of deflection of the muon having passed through the known magnetic field applied between the second detection unit and the third detection unit, wherein the deflection analysis unit analyzes momentum of the muon on the basis of the degree of deflection of the muon.

[Claim 8]

The magnetic field structure imaging apparatus according to any one of claims 1 to 7, wherein the target region contains a solid sample, and the magnetic field structure imaging apparatus creates the magnetic field structure image of an inside of the solid sample.

[Claim 9]

The magnetic field structure imaging apparatus according to claim 8, wherein the solid sample is a fusion reactor, a plasma generator, a nuclear reactor, a superconducting coil, an accelerator, a medical device having a strong magnetic field, a packaged strong magnetic field material, or a concrete structure.

[Claim 10] The magnetic field structure imaging apparatus according to any one of claims 1 to 9, wherein the analysis unit further creates a density structure image of the target region, and calculates the magnitude of the magnetic flux density of the target region on the basis of a difference between the magnetic field structure image and the density structure image.

[Claim 11]

The magnetic field structure imaging apparatus according to claim 10, which calculates and displays the magnitude and the direction of the two-dimensional magnetic flux density of the target region.

[Claim 12]

The magnetic field structure imaging apparatus according to any one of claims 1 to 11, comprising: a fourth detection unit and a fifth detection unit that detect passing positions of the muon, on a side opposite to the first detection unit side of the target region; and a flight time measuring unit that measures a flight time of a predetermined section of the muon having passed through the fifth detection unit, the fourth detection unit, the target region, the first detection unit, and the second detection unit in this order.

[Claim 13]

A magnetic field structure imaging method comprising: a first detection step of detecting a passing position of a muon having passed through a target region; a second detection step of detecting a passing position of the muon having passed through the target region and the first detection unit; an analysis step of calculating a magnetic field structure image of the target region on the basis of an arrival trajectory of the muon detected in the first detection step and the second detection step; and a display step of displaying at least one of the magnetic field structure image and magnitude and/or direction of two-dimensional magnetic flux density calculated from the magnetic field structure image, wherein a cosmic ray muon is used as the muon.

[Claim 14]

The magnetic field structure imaging method according to claim 13, comprising: recording time variation of the magnetic field structure image; and monitoring the degree of deterioration of the magnetic field structure of the target region.

[Claim 15]

A magnetic field structure imaging method comprising: a first detection step of detecting a passing position of a muon having passed through a target region; a second detection step of detecting a passing position of the muon having passed through the target region and the first detection unit; and a display step of displaying a magnetic field imaging obtained by analyzing a muographic image of the muon detected in the first detection step and the second detection step, wherein the magnetic field structure imaging method records time variation of the magnetic field imaging and monitors variation of the magnetic field imaging of the target region, and uses a cosmic ray muon as the muon.

[Claim 16]

The magnetic field structure imaging method according to any one of claims 13 to 15, which creates and displays the magnetic field structure image or the magnetic field imaging, using muons detected between one week and three months.

[Claim 17]

The magnetic field structure imaging method according to any one of claims 13 to 16, comprising: a step of measuring the target region from optical axes that differ by 90° and obtaining magnetic field structure images that differ by 90° of the target region; and a step of reconstructing a three-dimensional magnetic field structure image from the magnetic field structure images that differ by 90° of the target region.