Density estimating device, density estimating method, density estimating system, and program

Abstract

The present invention is capable of accurately estimating the density of an object by measuring cosmic rays that are transmitted through the object. A spectrum acquiring unit acquires a first energy spectrum of first cosmic rays that arrive at a predetermined zenith angle without being transmitted through an object, and acquires a second energy spectrum on the basis of a measurement result of second cosmic rays that arrive at the predetermined zenith angle after being transmitted through the object. A spectrum comparison unit compares the first and second energy spectra to analyze the energy loss of the second cosmic rays due to the transmission through the object. An estimating unit calculates, on the basis of the energy loss analysis result, the amount of matter on a path through the object along which the second cosmic rays were transmitted, and calculates an estimated value of the density of the object by dividing the amount of matter by the length of the path.

Description

Density estimation device, density estimation method, density estimation system and program

[0001] The present disclosure relates to a density estimation device, a density estimation method, a density estimation system, and a program.

[0002] A method of observing cosmic ray muons is known as a method for investigating the interior of large structures, mountain bodies, etc. For example, Patent Document 1 proposes a method of obtaining information about the internal structure of a structure by observing muons that arrive from a horizontal direction and pass through the structure, thereby identifying the path that the muons took.

[0003] Cosmic ray muons can also be used to estimate the density of an object. In general density estimation using cosmic ray muons, the number of muons that pass through the object is counted and compared with an existing theoretical model of the cosmic ray muon energy spectrum. Because muons lose energy when passing through an object, there is a lower limit to the energy of muons that can pass through an object. Therefore, it can be expected that the number of muons that pass through an object will be equal to the value obtained by integrating the existing theoretical model of the cosmic ray muon energy spectrum over the range from the lower limit energy value to infinity. Using this, the lower limit energy value can be calculated from the number of muons counted that have passed through the object. Because the calculated lower limit energy value of muons is a function of the density of the object through which they pass, the density of the object can be estimated using this.

[0004] Japanese Patent Application Laid-Open No. 2006-284329

[0005] DONALD E. GROOM, et al., “MUON STOPPING POWER AND RANGE TABLES 10 MeV-100 TeV”, Atomic Data and Nuclear Data Tables, Vol. 76, No. 2, July 2001, pp.1-37Tatsuhiko Sato, “Analytical Model for Estimating Terrestrial Cosmic Ray Fluxes Nearly Anytime and Anywhere in the World: Extension of PARMA / EXPACS”, PLOS ONE, DOI:10.1371 / journal.pone.0144679, December 16, 2015Tatsuhiko Sato, “Analytical Model for Estimating the Zenith Angle Dependence of Terrestrial Cosmic Ray Fluxes”, PLOS ONE DOI:10.1371 / journal.pone.0160390, August 4, 2016

[0006] In the above-mentioned method, the muon energy spectrum is integrated in a relatively high energy range, so the calculation of the lower energy limit depends heavily on the variation in the muon counts in the high-energy region. Meanwhile, the higher the energy of muons, the lower the arrival frequency, resulting in a large statistical error in short-term measurements. Therefore, in the high-energy region, the muon measurement results may deviate from the theoretical model of the cosmic-ray muon energy spectrum. In other words, the above-mentioned method, due to the difficulty of measuring high-energy muons, makes it fundamentally difficult to accurately estimate the density of an object. In particular, if the measurement time is insufficient, the deviation between the muon measurement results and the theoretical model of the cosmic-ray muon energy spectrum becomes large, resulting in a decrease in accuracy.

[0007] A density estimation device according to one aspect of the present disclosure includes a spectrum acquisition unit that acquires a first energy spectrum based on measurement results of a first cosmic ray that arrives at a predetermined zenith angle without passing through an object, and acquires a second energy spectrum based on measurement results of a second cosmic ray that arrives after passing through the object at the predetermined zenith angle; a spectrum comparison unit that compares the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object; and an estimation unit that calculates the amount of substance along a path that the second cosmic ray passed through the object based on the analysis results of the energy loss, and calculates an estimate of the density of the object by dividing the amount of substance by the length of the path.

[0008] A density estimation method according to one aspect of the present disclosure includes acquiring a first energy spectrum of a first cosmic ray that arrives at a predetermined zenith angle without passing through an object, acquiring a second energy spectrum based on measurement results of a second cosmic ray that arrives after passing through the object at the predetermined zenith angle, comparing the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object, calculating the amount of matter along a path that the second cosmic ray passed through in the object based on the analysis results of the energy loss, and calculating an estimated value of the density of the object by dividing the amount of matter by the length of the path.

[0009] A density estimation system according to one aspect of the present disclosure includes a detector that measures second cosmic rays that have passed through an object at a predetermined zenith angle and then arrived therefrom, and a density estimation device that estimates the density of the object based on the detection results of the detector. The density estimation device includes a spectrum acquisition unit that acquires a first energy spectrum of a first cosmic ray that has passed through the object at the predetermined zenith angle without passing through it, and acquires a second energy spectrum based on the measurement results of the second cosmic ray; a spectrum comparison unit that compares the first and second energy spectra to analyze the energy loss of the second cosmic ray due to its passage through the object; and an estimation unit that calculates the amount of substance along a path that the second cosmic ray has passed through the object based on the analysis results of the energy loss, and calculates an estimate of the density of the object by dividing the amount of substance by the length of the path.

[0010] A program according to one aspect of the present disclosure causes a computer to execute the following steps: acquiring a first energy spectrum of a first cosmic ray that has traveled without passing through an object at a predetermined zenith angle; acquiring a second energy spectrum based on measurement results of a second cosmic ray that has traveled after passing through the object at the predetermined zenith angle; comparing the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object; calculating the amount of substance along a path that the second cosmic ray has traveled through the object based on the analysis results of the energy loss; and calculating an estimated value of the density of the object by dividing the amount of substance by the length of the path.

[0011] According to the present disclosure, the density of an object can be estimated with high accuracy by measuring cosmic rays that pass through the object.

[0012] 1 is a diagram schematically showing the configuration of a density estimation system according to an embodiment; FIG. 2 is a diagram showing the direction of arrival of muon flux used in density estimation; FIG. 3 is a block diagram schematically showing the configuration of a density estimation device; FIG. 4 is a diagram showing an example of a hardware configuration for realizing a density estimation device; FIG. 5 is a diagram showing an example of the energy spectrum when cosmic ray muons arriving from a certain zenith angle are directly incident on a detector; FIG. 6 is a diagram comparing a reference energy spectrum and an estimation target energy spectrum; FIG. 7 is a graph showing the stopping power for muons that have passed through a material; FIG. 8 is a diagram showing an overview of calculation of the amount of substance by integration; FIG. 9 is a flowchart of the operation for estimating the density of an object in a density estimation system according to an embodiment; FIG. 10 is a diagram showing an example of the reference energy spectrum and the measurement target energy spectrum of cosmic ray muons arriving at a certain zenith angle in an example;

[0013] First Embodiment A density estimation system according to this embodiment estimates the density of an object by observing cosmic ray muons passing through the object.

[0014] To observe cosmic ray muons, a detector is used to measure the number of muons that pass through an object. The path of a muon incident on a detector can be expressed using the zenith angle θ, where the zenith direction of the detector is the reference axis, and the azimuth angle φ at the ground plane. The amount of energy lost by muons that pass through an object varies depending on the density of the material present in their flight path. If the energy loss is large, the flight path will change significantly due to scattering by the atomic nuclei of the object being observed, and the muon will follow a path that deviates from the detector. This is observed as a decrease in the number of muons.

[0015] In addition, since the energy of cosmic ray muons reaching the detector varies, it is also possible to obtain the energy spectrum of the muons that reach the detector. Various common methods can be used to obtain the energy spectrum of cosmic ray muons.

[0016] In the density estimation system according to the present embodiment, the density of an object is estimated based on the energy loss between the energy spectrum of cosmic ray muons that pass through the object and enter a detector at a certain zenith angle and the energy spectrum of cosmic ray muons that enter the detector directly at the same zenith angle. Note that, hereinafter, the cosmic ray muons to be measured will also be simply referred to as muons.

[0017] A density estimation system according to the present embodiment will be described below. Fig. 1 is a diagram schematically illustrating a configuration of a density estimation system according to one embodiment. The density estimation system 100 shown in Fig. 1 includes a density estimation device 10 and a detector 20.

[0018] The density estimation device 10 and the detector 20 are communicatively connected by a wireless, wired, or a combination of wired and wireless communication means. In the example of Fig. 1, the density estimation device 10 and the detector 20 are communicatively connected by a cable 30.

[0019] For example, a nuclear emulsion plate, a scintillator, a gas-type detector, etc. can be used as the detector 20. However, these are merely examples, and any type of detector can be used as the detector 20 as long as it can measure the energy of the incoming muons and identify the direction of their arrival.

[0020] The density estimation device 10 acquires the energy spectrum of the muon flux that has passed through the object based on the detection signal DET from the detector 20 .

[0021] In this embodiment, the upward direction perpendicular to the horizontal plane at the position where detector 20 is installed is defined as the Z direction. The direction in which the orientation of detector 20 is projected onto the horizontal plane is defined as the Y direction, and the direction perpendicular to the Y direction is defined as the X direction. When indicating the direction of muons arriving toward detector 20, the angle of the muon's arrival direction from the Z direction is defined as the zenith angle θ, and the angle in the clockwise direction from the Y direction on the X-Y plane is defined as the azimuth angle φ.

[0022] 2 is a diagram showing the direction of arrival of muons used for density estimation. Muon flux F1 is the flux of muons that do not pass through the object OBJ but directly enter the detector 20, and is expressed by the zenith angle θ and the azimuth angle φ １ The muon flux F2 is the flux of muons that pass through the object OBJ and then enter the detector 20, and is defined by the zenith angle θ and the azimuth angle φ ２ Hereinafter, the muon flux F1 will also be referred to as the first cosmic ray, and the muon flux F2 will also be referred to as the second cosmic ray.

[0023] 3 is a block diagram schematically illustrating the configuration of a density estimation device according to one embodiment. The density estimation device 10 includes a spectrum acquisition unit 1, a spectrum comparison unit 2, and an estimation unit 3. The spectrum acquisition unit 1 acquires an energy spectrum of muons that have not passed through an object and an energy spectrum of muons that have passed through the object. The spectrum comparison unit 2 compares the two energy spectra acquired by the spectrum acquisition unit 1. The estimation unit 3 calculates an estimate of the density of the muons along the path that they have passed through the object, based on the comparison result of the two energy spectra made by the spectrum comparison unit 2.

[0024] FIG. 4 shows an example of the hardware configuration of a density estimation device 10. FIG. 4 is a diagram showing an example of the hardware configuration for realizing the density estimation device. The density estimation device 10 can be realized by a computer 1000, such as a dedicated computer or a personal computer (PC). However, the computer does not need to be physically single; multiple computers may be used when performing distributed processing. As shown in FIG. 4, the computer 1000 has a CPU (Central Processing Unit) 1001, a ROM (Read Only Memory) 1002, and a RAM (Random Access Memory) 1003, which are interconnected via a bus 1004. Note that although explanation of the OS software for operating the computer will be omitted, it is assumed that the computer that builds this network analysis system also has such software.

[0025] An input / output interface 1005 is also connected to the bus 1004. To the input / output interface 1005, for example, an input unit 1006 including a keyboard, mouse, sensor, etc., a display including a CRT, LCD, etc., an output unit 1007 including headphones, speakers, etc., a storage unit 1008 including a hard disk, etc., and a communication unit 1009 including a modem, terminal adapter, etc. are connected.

[0026] The CPU 1001 executes various processes in accordance with various programs stored in the ROM 1002 or various programs loaded from the storage unit 1008 to the RAM 1003. In this embodiment, for example, the processes of the various units of the density estimation device described below. A graphics processing unit (GPU) may be provided to execute various processes in accordance with various programs stored in the ROM 1002 or various programs loaded from the storage unit 1008 to the RAM 1003, similar to the CPU 1001. In this embodiment, for example, the processes of the various units of the network analysis system described below. The GPU is suitable for performing routine processing in parallel, and by applying it to neural network processing described below, it is possible to improve processing speed compared to the CPU 1001. The RAM 1003 also stores data necessary for the CPU 1001 and the GPU to execute various processes.

[0027] The communication unit 1009 performs communication processing via the Internet (not shown), for example, transmits data provided by the CPU 1001, and outputs data received from a communication partner to the CPU 1001, RAM 1003, and storage unit 1008. The storage unit 1008 exchanges data with the CPU 1001 and stores and erases information. The communication unit 1009 also performs communication processing of analog or digital signals with other devices.

[0028] The input / output interface 1005 is also connected to a drive 1010 as needed, and, for example, a magnetic disk 1011, an optical disk 1012, a flexible disk 1013, or a semiconductor memory 1014 is appropriately attached, and computer programs read from these are installed in the memory unit 1008 as needed.

[0029] Next, the density estimation principle of the density estimation system according to this embodiment will be described. Fig. 5 is a diagram showing an example of the energy spectrum I(E, θ) when muons arriving at a zenith angle θ are directly incident on a detector. In general, the energy spectrum of cosmic ray muons has a maximum intensity at a certain energy, and the intensity decreases as the energy increases. Hereinafter, the intensity in the muon energy spectrum refers to the intensity of the measured muon flux.

[0030] When measuring an energy spectrum by counting muons with a detector, the measurement data is obtained as discrete data, and a discontinuous histogram-like spectrum in which the intensity changes stepwise is obtained due to the resolution of the detector, etc. Therefore, in this embodiment, an interpolation method such as spline interpolation is used to obtain a continuous energy spectrum from the discontinuous histogram-like energy spectrum. The interpolation method used at this time is not limited, and various interpolation methods may be used.

[0031] In this embodiment, the energy spectrum when a muon coming from a zenith angle θ directly enters the detector is compared with the energy spectrum when a muon coming from the same zenith angle θ passes through an object and then enters the detector. Hereinafter, the energy spectrum when a muon coming from a zenith angle θ directly enters the detector is referred to as the reference energy spectrum I. １ (E, θ). The energy spectrum of a muon coming from the zenith angle θ when it passes through the object and then enters the detector is called the estimated object energy spectrum I ２ (E, θ). In the following, the reference energy spectrum I １(E, θ) is also referred to as the first energy spectrum. ２ (E, θ) is also referred to as the second energy spectrum.

[0032] In this embodiment, the energy spectrum of the incoming muons depends only on the zenith angle θ and does not depend on the azimuth angle φ. Therefore, the estimated energy spectrum I ２ At the position where (E, θ) is measured, the energy spectrum of muons coming from the same zenith angle but different azimuthal angles is observed to obtain the reference energy spectrum I １ (E, θ) may be obtained.

[0033] Since the muon energy spectrum depends only on the zenith angle θ, the estimated target energy spectrum I ２ The position where (E, θ) was measured and the reference energy spectrum I １ The position where (E, θ) is measured does not need to be exactly the same. Therefore, the estimation target energy spectrum I ２ The reference energy spectrum I is at the same position as (E, θ). １ If (E, θ) cannot be measured, the position is changed and the estimated target energy spectrum I ２ The reference energy spectrum I measured for the same zenith angle as (E, θ) １ (E, θ) may also be used.

[0034] In addition, within a range that does not affect the measurement accuracy, the estimation target energy spectrum I ２ The timing of measuring (E, θ) and the reference energy spectrum I １ The timing for measuring (E, θ) may be different from the timing for measuring (E, θ). This allows the estimation target energy spectrum I ２ (E, θ) and the reference energy spectrum I １ (E, θ) can be measured in sequence. Two detectors can be provided, and one of the detectors can be used to measure the energy spectrum I ２ (E, θ) and simultaneously measure the reference energy spectrum I using the other detector. １(E, θ) may be measured.

[0035] In the above, the reference energy spectrum I １ Although the case where (E, θ) can be measured has been described, depending on the measurement location, the reference energy spectrum I １ It is also possible that (E, θ) cannot be measured properly. In this case, the existing theoretical model of the cosmic ray muon energy spectrum is used as the reference energy spectrum I １ (E, θ). This allows the spatial dependency due to the measurement point and the time dependency due to the measurement time to be calculated using the reference energy spectrum I １ Although it is not reflected in (E, θ), it is possible to estimate the density ρ of the object with a certain degree of accuracy.

[0036] In this case, the reference energy spectrum I １ (E, θ) may be given to the spectrum acquisition unit 1 from the outside via an input means. １ (E, θ) may be stored in a storage unit (not shown) provided in the density estimation device 10, and the spectrum acquisition unit 1 may read it from the storage unit as needed. As the input means, for example, the input unit 1006 in FIG. 4 may be used. As the storage unit, for example, the storage unit 1008 in FIG. 4 may be used. In addition, the reference energy spectrum I １ (E, θ) and the transmission path length L may be stored in the storage unit 1008 via the communication unit 1009 or the drive 1010 .

[0037] FIG. 6 shows the reference energy spectrum I １ (E, θ) and the estimated energy spectrum I ２ (E, θ) is compared with the estimated target energy spectrum I ２ (E, θ) is the reference energy spectrum I １ Move relative to (E, θ).

[0038] Reference Energy Spectrum I １ In (E, θ), the value of energy at a certain intensity is E １The intensity at this time is I １ (E １ , θ). The energy spectrum to be estimated I ２ At (E, θ), the intensity is I １ (E １ , θ) is equal to E ２ The intensity at this time is I ２ (E ２ , θ) = I １ (E １ , θ). In this case, the energy E １ and energy E ２ The difference ΔE = E １ -E ２ is thought to be caused by the loss of muon energy as it passes through the object. In other words, the difference ΔE at this time is thought to contain information about the amount of material in the object through which the muon passed.

[0039] Fig. 7 is a graph showing the stopping power for muons that have passed through a material. Stopping power is generally also called stopping power and is understood as a quantity that indicates the degree to which particles are slowed down and lose energy due to the interaction between radiation such as a charged particle beam and a material.

[0040] When a muon passes through a substance, the stopping power is defined as the energy loss per unit amount of the substance that passes through. Here, the amount of substance is defined as the product of the density ρ of the substance and the transmission path length L. If the lost energy is E and the amount of substance is M, the stopping power S(E) is expressed by the following equation [1]: A specific expression for stopping power is explained in, for example, Non-Patent Document 1.

[0041] Using the definition of stopping power S(E), the reciprocal of stopping power S(E) is -dM / dE, which is E １ ≦E≦E ２ In other words, the amount of substance M(ΔE) corresponding to the above-mentioned energy loss ΔE can be expressed by the following equation [2]: Fig. 8 is a diagram showing an outline of calculation of the amount of substance by integration. By performing the above integration, the amount of substance M (ΔE) can be calculated as the area of ​​the hatched region shown in Fig. 8. Although it is difficult to analytically integrate equation [2], it is possible to calculate equation [2] by using various numerical integration methods such as the Gaussian quadrature method.

[0042] In this embodiment, it is assumed that when a muon passes through an object, the muon travels in a straight line through the object. In this case, the transmission path length L of a muon arriving at the zenith angle θ can be determined by using a drawing if the object is an artificial object such as a building, or by using topographical information if the object is a natural object such as a mountain. The transmission path length L may be provided to the estimation unit 3 from an external source via an input means, for example. The transmission path length L may also be stored in a memory unit (not shown) provided in the density estimation device 10, and the estimation unit 3 may read it from the memory unit as needed. The input means may be, for example, the input unit 1006 in FIG. 4 . The memory unit may be, for example, the memory unit 1008 in FIG. 4 . The transmission path length L may also be stored in the memory unit 1008 via the communication unit 1009 or the drive 1010.

[0043] By dividing the amount of substance M (ΔE) through which the muon has passed, calculated using equation [2], by the transmission path length L, the density ρ of the object along the muon's transmission path can be estimated as shown in the following equation [3].

[0044] As described above, it can be understood that the density estimation system according to this embodiment makes it possible to estimate the density of an object using the energy spectrum of muons.

[0045] It is known that the stopping power used to estimate the density of an object is less dependent on the material through which the radiation penetrates, provided that the type of radiation passing through is the same. Therefore, even when estimating the density of an unknown material, as in this embodiment, the density can be estimated with high accuracy by using the stopping power obtained for other materials.

[0046] In the above description, the density estimation system 100 is described as estimating the density of an object, but more specifically, the density estimation system 100 estimates the average density of the object. For example, if the density along the muon transmission path in the object is non-uniform or if there is a cavity along the transmission path, it can be understood that the estimated density value indicates the average density of the object along the transmission path.

[0047] Based on the above principles, the operation of estimating the density of an object by the density estimation system 100 will be described below. Fig. 9 is a flowchart of the operation of estimating the density of an object by the density estimation system according to one embodiment.

[0048] Step S1: The spectrum acquisition unit 1 acquires the reference energy spectrum I of muons that have not passed through the target and arrived at the zenith angle θ. １ As described above, the spectrum acquisition unit 1 measures muons with the detector 20 to obtain the reference energy spectrum I １ (E, θ). The spectrum acquisition unit 1 may also acquire a reference energy spectrum I １ (E, θ) may be obtained.

[0049] Step S2: The spectrum acquisition unit 1 calculates the estimated target energy spectrum I of muons that have traveled at the zenith angle θ and passed through the target. ２ As described above, the spectrum acquisition unit 1 measures muons with the detector 20 to obtain the estimation target energy spectrum I ２ (E, θ) can be obtained.

[0050] Step S3: The spectrum comparison unit 2 compares the reference energy spectrum I １ (E, θ) and the estimated energy spectrum I ２ (E, θ) and the reference energy spectrum I １ Energy E of (E, θ) １ and estimated target energy spectrum I ２ Energy E of (E, θ) ２ Identify the following.

[0051] 9, steps S2 and S3 are shown in parallel, but this is not intended to limit the execution of steps S2 and S3 to simultaneous parallel execution. Steps S2 and S3 may be executed simultaneously in parallel, or may be executed sequentially.

[0052] Step S4: The estimation unit 3 estimates the specified energy E １ and energy E ２ is applied to equation [2] to calculate the amount of substance M(ΔE) along the path of the object through which the muon has passed.

[0053] Step S5 The estimation unit 3 divides the calculated amount of substance M(ΔE) by the muon transmission path length L, as shown in equation [3], to obtain an estimate of the density ρ of the object.

[0054] As described above, by performing the above steps S1 to S5, the density estimation system can estimate the density of an object using the muon energy spectrum according to the principles described above.

[0055] Furthermore, the density estimation system according to this embodiment can also shorten the time required for density estimation compared to a general density measurement method. As described above, in a general density measurement method, if the muon measurement time is insufficient, the accuracy of estimating the density of the target object decreases. Therefore, in order to ensure estimation accuracy, it has been necessary to measure muons for a long period of time. For example, in a general density measurement method, if the sensitive area of ​​the detector is 2500 cm ２ Assume that the measurement was performed for 28,800 seconds (8 hours) under the condition of an effective solid angle of 0.025 sr. In this case, approximately 470 muons can be counted. The density estimation error in this case is ±0.1 g / cm within the statistical error range of 1 σ. ３ This becomes:

[0056] In contrast, the density estimation system according to this embodiment directly measures the muon energy spectrum. Therefore, even if the measurement time is set to 3600 seconds (1 hour), the overall trend of the energy spectrum is expected to remain unchanged. This shortens the measurement time of the energy spectrum, and allows the density of the object to be estimated with high accuracy, even in a shorter time than with general density measurement methods.

[0057] Next, a simulation result will be described as an example of density estimation of an object by the density estimation system according to the present embodiment. In this example, the density of an object present above the observation position is estimated by observing muons coming from a zenith angle of 0°.

[0058] In this example, the reference energy spectrum I of muons that have not passed through the object is １ As (E, θ), the energy spectrum using the EXPACS model described in Non-Patent Documents 2 and 3 was used.

[0059] In this example, the target is 2.0 g / cm ３ The path length of the virtual substance was assumed to be 10 m. The structure of the virtual substance was assumed to have a density of 2.65 g / cm ３ Inside the Standard Rcock, the density is 1.2 mg / cm ３ A structure in which a void of 100 μm exists was assumed. Regarding Standard Rcok, a model was constructed based on the one explained in Non-Patent Document 1. The estimated target energy spectrum I of muons that have passed through the above target object is ２ (E, θ) is the reference energy spectrum I １ Compared with (E, θ).

[0060] 10 is a diagram showing an example of a reference energy spectrum and a measurement target energy spectrum of a muon arriving at a zenith angle of 0° in an embodiment. The energy spectrum shown in FIG. 10 shows the intensity at the average energy of muons measured as discrete data points, which are converted into continuous data by cubic spline interpolation. In FIG. 10, the unit of intensity on the vertical axis is cm－２ ・sr －１ ・s －１ ・MeV －１ The horizontal axis shows the muon energy in MeV.

[0061] In FIG. 10, the intensity I １ and intensity I ２ is 3 x 10 －７ cm －２ ・sr －１ ・s －１ ・MeV －１ When we focus on the energy at １ Energy E at (E, θ) １ is 5000 MeV, estimated target energy spectrum I ２ Energy E at (E, θ) ２ is 1000 MeV. Therefore, the energy loss ΔE is 5000-1000=4000 MeV.

[0062] 11 is a graph showing the stopping power of Standard Rcok used in the examples. For reference, FIG. 11 also shows the stopping power of Standard Rcok described in Non-Patent Document 1. １ and E ２ Applying this to the above equation [2], the curve showing the stopping power in Figure 11 is integrated over the energy range of 1000 MeV to 5000 MeV. In this case, the amount of material M (ΔE) transmitted by the muon is 19 hg / cm ２ This value is the density of the assumed virtual material, 2.0 g / cm ３ is multiplied by the transmission path length of 10 m to obtain 20 hg / cm ２ It roughly coincides with.

[0063] Next, the calculated amount of substance M (ΔE) = 19 hg / cm ２ By dividing by the transmission path length L = 10 m, the density ρ of the object is 1.9 g / cm ３ It can be estimated that:

[0064] The estimated density ρ = 1.9 g / cm ３ is the density of the assumed virtual substance ρ = 2.0 g / cm ３0.1 g / cm ３ However, this is thought to be an error due to interpolation. This error can be improved by selecting a more appropriate interpolation method.

[0065] As described above, in this example, it is possible to estimate the density of the object as a value that is close to the density of the assumed object. Therefore, it can be understood that the density estimation system 100 according to this embodiment can accurately estimate the density of the object.

[0066] Other Embodiments The present disclosure is not limited to the above-described embodiments and can be modified as appropriate without departing from the spirit and scope of the present disclosure. For example, in the above-described embodiments, the density of an object is estimated using cosmic ray muons that have passed through the object. However, the cosmic rays used are not limited to muons. For example, other types of cosmic rays, such as electron beams, may also be used. In this case, by applying a stopping power appropriate to the type of cosmic ray used, the density of the object can be suitably estimated, as in the case of muons.

[0067] In the above embodiment, the density estimation device 10 has been described as a single device, but this is merely an example. The spectrum acquisition unit 1, the spectrum comparison unit 2, and the estimation unit 3 may be configured as a density estimation system having the same functions as the density estimation device 10, with the spectrum acquisition unit 1, the spectrum comparison unit 2, and the estimation unit 3 being distributed among multiple entities. Also, in the above density estimation system 100, the spectrum acquisition unit 1, the spectrum comparison unit 2, and the estimation unit 3 may be distributed among multiple entities.

[0068] In the above embodiment, the density estimation device 10 and the detector 20 have been described as separate entities, but this is merely an example. For example, the density estimation device 10 and the detector 20 may be configured as an integrated device as long as they can perform similar functions as the density estimation system 100. Furthermore, the detector 20 may have some of the functions of the density estimation device 10 as long as they can perform similar functions as the density estimation system 100. In this case, the density estimation device may have functions of the density estimation device 10 other than those of the detector 20.

[0069] In the above-described embodiment, the density estimation device has been described as having a hardware configuration, but this is not limiting, and any process can be realized by having a CPU (Central Processing Unit) execute a computer program. In this case, the computer program can be stored using various types of non-transitory computer-readable medium and supplied to the computer. Non-transitory computer-readable medium includes various types of tangible storage medium. Examples of non-transitory computer-readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memories (e.g., mask ROMs, programmable ROMs (PROMs), erasable PROMs (EPROMs), flash ROMs, and random access memories (RAMs)). The program may also be supplied to a computer by various types of transient computer-readable media. Examples of transient computer-readable media include electric signals, optical signals, and electromagnetic waves. The transient computer-readable medium can supply the program to a computer via a wired communication path such as an electric wire or optical fiber, or via a wireless communication path.

[0070] The figures referred to in this disclosure and each element and operation shown in the figures should not be construed as relating to only one embodiment, but may be related to one or more embodiments.

[0071] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0072] Each drawing is merely an example for describing one or more embodiments. Each drawing may relate not only to one particular embodiment, but also to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0073] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes.

[0074] (Supplementary Note 1) A density estimation device comprising: a spectrum acquisition unit that acquires a first energy spectrum of a first cosmic ray that has traveled without passing through an object at a predetermined zenith angle, and acquires a second energy spectrum based on measurement results of a second cosmic ray that has traveled after passing through the object at the predetermined zenith angle; a spectrum comparison unit that compares the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object; and an estimation unit that calculates an amount of matter in a path that the second cosmic ray has traveled through the object based on the analysis results of the energy loss, and calculates an estimated value of the density of the object by dividing the amount of matter by the length of the path.

[0075] (Supplementary Note 2) The density estimation device described in Supplementary Note 1, wherein the spectrum comparison unit identifies a first energy having a predetermined intensity in the first energy spectrum, identifies a second energy having the predetermined intensity in the second energy spectrum, and calculates the amount of substance by integrating the reciprocal of the stopping power when the second cosmic ray passes through a substance with respect to energy in a range between the first energy and the second energy.

[0076] (Supplementary Note 3) The density estimation device described in Supplementary Note 1 or 2, wherein the first energy spectrum is acquired based on the results of measuring the first cosmic ray, which arrives at an azimuth angle different from that of the second cosmic ray, using a detector.

[0077] (Supplementary Note 4) The density estimation device according to Supplementary Note 3, wherein the first energy spectrum is obtained based on the results of measuring the first cosmic ray by the detector.

[0078] (Supplementary Note 5) The density estimation device according to Supplementary Note 3, wherein the one energy spectrum is an energy spectrum prepared in advance for a predetermined substance.

[0079] (Supplementary Note 6) The density estimation device according to any one of Supplementary Notes 1 to 5, wherein the first and second cosmic rays are cosmic ray muons.

[0080] (Supplementary Note 7) The density estimation device according to Supplementary Note 4, wherein the first and second energy spectra are continuous data obtained by interpolating the measurement results obtained as discrete data.

[0081] (Supplementary Note 8) A density estimation method comprising: acquiring a first energy spectrum of a first cosmic ray that has traveled without passing through an object at a predetermined zenith angle; acquiring a second energy spectrum based on a measurement result of a second cosmic ray that has traveled after passing through the object at the predetermined zenith angle; comparing the first and second energy spectra to analyze an energy loss of the second cosmic ray due to passing through the object; calculating an amount of matter in a path that the second cosmic ray has traveled through the object based on an analysis result of the energy loss; and calculating an estimated value of the density of the object by dividing the amount of matter by the length of the path.

[0082] (Supplementary Note 9) A density estimation system comprising: a detector that measures second cosmic rays that have passed through an object at a predetermined zenith angle and then arrived; and a density estimation device that estimates the density of the object based on the detection results of the detector, wherein the density estimation device comprises: a spectrum acquisition unit that acquires a first energy spectrum of a first cosmic ray that has passed through the object at the predetermined zenith angle without passing through the object, and acquires a second energy spectrum based on the measurement results of the second cosmic ray; a spectrum comparison unit that compares the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object; and an estimation unit that calculates an amount of substance along a path that the second cosmic ray has passed through the object based on the analysis results of the energy loss, and calculates an estimated value of the density of the object by dividing the amount of substance by the length of the path.

[0083] (Supplementary Note 10) A program causing a computer to execute the following steps: acquiring a first energy spectrum of a first cosmic ray that has traveled without passing through an object at a predetermined zenith angle; acquiring a second energy spectrum based on measurement results of a second cosmic ray that has traveled after passing through the object at the predetermined zenith angle; comparing the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object; calculating an amount of substance along a path that the second cosmic ray has traveled through the object based on the analysis results of the energy loss; and calculating an estimated value of the density of the object by dividing the amount of substance by the length of the path.

[0084] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

[0085] This application claims priority based on Japanese Patent Application No. 2023-142217, filed September 1, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0086] REFERENCE SIGNS LIST 1 spectrum acquisition unit 2 spectrum comparison unit 3 estimation unit 10 density estimation device 20 detector 100 density estimation system 1000 computer 1001 CPU 1002 ROM 1003 RAM 1004 bus 1005 input / output interface 1006 input unit 1007 output unit 1008 storage unit 1009 communication unit 1010 drive 1011 magnetic disk 1012 optical disk 1013 flexible disk 1014 semiconductor memory

Claims

1. A density estimation device comprising: a spectrum acquisition unit that acquires a first energy spectrum of a first cosmic ray that arrives at a specified zenith angle without passing through an object, and acquires a second energy spectrum based on measurement results of a second cosmic ray that arrives after passing through the object at the specified zenith angle; a spectrum comparison unit that compares the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object; and an estimation unit that calculates an amount of matter of the path that the second cosmic ray passed through in the object based on the analysis results of the energy loss, and calculates an estimate of the density of the object by dividing the amount of matter by the length of the path.

2. The density estimation device of claim 1, wherein the spectrum comparison unit: identifies a first energy having a predetermined intensity in the first energy spectrum; identifies a second energy having the predetermined intensity in the second energy spectrum; and calculates the amount of substance by integrating the inverse of the stopping power of the second cosmic ray when it passes through a substance, with respect to energy, in the range between the first energy and the second energy.

3. A density estimation device as described in claim 1 or 2, wherein the second energy spectrum is obtained based on the results of measuring the second cosmic ray coming from an azimuth angle different from that of the first cosmic ray by a detector.

4. The density estimation device according to claim 3, wherein the first energy spectrum is obtained based on the result of measuring the first cosmic ray by the detector.

5. The density estimation device according to claim 3, wherein the one energy spectrum is an energy spectrum prepared in advance for a predetermined material.

6. The density estimation device according to claim 1 or 2, wherein the first and second cosmic rays are cosmic ray muons.

7. The density estimation device according to claim 4, wherein the first and second energy spectra are continuous data obtained by interpolating the measurement results obtained as discrete data.

8. A density estimation method comprising: acquiring a first energy spectrum of a first cosmic ray that arrives at a specified zenith angle without passing through an object; acquiring a second energy spectrum based on measurement results of a second cosmic ray that arrives after passing through the object at the specified zenith angle; comparing the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object; calculating the amount of matter of the path that the second cosmic ray passed through in the object based on the analysis results of the energy loss; and calculating an estimate of the density of the object by dividing the amount of matter by the length of the path.

9. A density estimation system comprising: a detector that measures a second cosmic ray that has passed through an object at a predetermined zenith angle and then arrived; and a density estimation device that estimates the density of the object based on the detection results of the detector, wherein the density estimation device comprises: a spectrum acquisition unit that acquires a first energy spectrum of a first cosmic ray that has passed through an object at the predetermined zenith angle without passing through the object, and acquires a second energy spectrum based on the measurement results of the second cosmic ray; a spectrum comparison unit that compares the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object; and an estimation unit that calculates an amount of matter of the path that the second cosmic ray has passed through in the object based on the analysis results of the energy loss, and calculates an estimate of the density of the object by dividing the amount of matter by the length of the path.

10. A program that causes a computer to execute the following processes: acquiring a first energy spectrum of a first cosmic ray that arrives at a specified zenith angle without passing through an object; acquiring a second energy spectrum based on measurement results of a second cosmic ray that arrives after passing through the object at the specified zenith angle; comparing the first and second energy spectra to analyze the energy loss of the second cosmic ray due to passing through the object; calculating the amount of substance along the path that the second cosmic ray passed through in the object based on the analysis results of the energy loss; and calculating an estimate of the density of the object by dividing the amount of substance by the length of the path.

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