Inference device, and inference method and program

Abstract

Provided is an inference device (100) for inferring secondary neutron spectra produced within the atmosphere, said device comprising: an inference unit (11) that infers, with respect to a plurality of proton energies, atmospheric responses indicating interactions between protons and the atmosphere when monoenergetic protons have been radiated within the atmosphere; an approximation processing unit (12) that on the basis of the atmospheric responses of the different proton energies inferred by the inference unit (11), derives an approximation function for the atmospheric responses; a setting unit (21) that sets up a proton spectrum in an environment for secondary neutron spectrum measurement; and an arithmetic unit (22) that on the basis of the proton spectrum set up by the setting unit (21) and the approximation function, computes a secondary neutron spectrum in the measurement environment.

Description

Estimation device, estimation method, and program

[0001] The present disclosure relates to an estimation device, an estimation method, and a program for estimating a secondary neutron spectrum.

[0002] When a strong solar flare occurs, many protons arrive at the Earth, generating secondary neutrons in the atmosphere. These secondary neutrons can cause problems such as exposure of aircraft flying overhead and soft errors in semiconductor devices on the ground. For this reason, it is necessary to estimate the secondary neutron spectrum. Non-Patent Document 1 discloses a method for estimating the secondary neutron spectrum using atmospheric response.

[0003] EXPACS “https: / / phits.jaea.go.jp / expacs / jpn.html”

[0004] The spectrum Φn(En,d) for each energy En of secondary neutrons at a specific altitude d (hereinafter referred to as "secondary neutron spectrum Φn(En,d)") can be expressed by the following equation (1).

[0005]

[0006] In equation (1), Ep is the energy of cosmic rays (protons in this case), Φ(Ep) is the proton spectrum, En is the energy of secondary neutrons, and R(Ep,En,d) is the atmospheric response, which refers to the spectrum of secondary neutrons produced by the interaction of monoenergetic protons with the Earth's atmosphere.

[0007] That is, the secondary neutron spectrum Φn(En,d) can be calculated by the convolution integral of the proton spectrum Φp(Ep) and the atmospheric response Rair(Ep,En,d). It is difficult to analytically obtain the atmospheric response Rair(Ep,En,d) shown in equation (1). For this reason, Φn(En,d) shown in equation (1) is estimated by a "particle transport simulation" using the well-known Monte Carlo method. Specifically, the proton spectrum Φp(Ep) shown in equation (1) is set to galactic cosmic rays, and Φn(En,d) in equation (1) is directly estimated by particle transport simulation.

[0008] However, the proton spectrum generated by a solar flare varies greatly depending on the scale of the solar flare. The method disclosed in Non-Patent Document 1 requires that simulations be performed individually depending on the scale of the solar flare. That is, for each proton energy Ep, a proton spectrum Φp(Ep) must be set and a simulation must be performed for each proton spectrum Φp(Ep). This increases the computational load required to estimate the secondary neutron spectrum.

[0009] Furthermore, with the method disclosed in Non-Patent Document 1, it is difficult to estimate the secondary neutron spectrum generated by cosmic ray protons, which has a spectrum different from that of galactic cosmic rays. In order to estimate this secondary neutron spectrum, it is necessary to redo the simulation, which poses the problem of an even greater computational load.

[0010] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide an estimation device, an estimation method, and a program that are capable of estimating a secondary neutron spectrum from a cosmic ray spectrum with a small computational load, regardless of the scale of a solar flare or the magnitude of cosmic ray energy.

[0011] An estimation device according to one aspect of the present disclosure is an estimation device that estimates a secondary neutron spectrum generated in the atmosphere, and includes: an estimation unit that estimates, for a plurality of cosmic ray energies, atmospheric responses that indicate interactions between the cosmic rays and the atmosphere when the cosmic rays of a single energy are irradiated into the atmosphere; an approximation processing unit that derives an approximate function of the atmospheric response based on the atmospheric responses for each cosmic ray energy estimated by the estimation unit; a setting unit that sets a cosmic ray spectrum in a measurement environment for the secondary neutron spectrum; and a calculation unit that calculates the secondary neutron spectrum in the measurement environment based on the cosmic ray spectrum set by the setting unit and the approximate function.

[0012] An estimation method according to one aspect of the present disclosure is a method for estimating a secondary neutron spectrum generated in the atmosphere, in which an estimation unit estimates, for a plurality of cosmic ray energies, atmospheric responses indicating interactions between the cosmic rays and the atmosphere when the cosmic rays of a single energy are irradiated into the atmosphere, an approximation processing unit derives an approximation function of the atmospheric response based on the atmospheric responses for each cosmic ray energy estimated by the estimation unit, a setting unit sets a cosmic ray spectrum in a measurement environment for the secondary neutron spectrum, and a calculation unit calculates the secondary neutron spectrum in the measurement environment based on the cosmic ray spectrum set by the setting unit and the approximation function.

[0013] One aspect of the present disclosure is a program for causing a computer to function as the estimation device.

[0014] According to the present disclosure, it is possible to estimate a secondary neutron spectrum from a cosmic ray spectrum with a small computational load, regardless of the scale of a solar flare and the magnitude of cosmic ray energy.

[0015] FIG. 1 is a block diagram showing the configuration of an estimation device according to an embodiment. FIG. 2 is an explanatory diagram showing a simulation of secondary neutrons generated by monoenergetic protons with Ep = 10 [GeV]. FIG. 3 is a graph showing atmospheric response data obtained by the simulation shown in FIG. 2. FIG. 4 is a flowchart showing the processing procedure of the estimation device according to an embodiment. FIG. 5A is a graph showing protons of multiple energies and proton spectra according to a comparative example. FIG. 5B is an explanatory diagram showing a simulation of secondary neutrons generated by protons according to a comparative example. FIG. 5C is a graph showing the relationship between secondary neutron energy and secondary neutron spectrum generated by the simulation according to a comparative example. FIG. 6 is a block diagram showing the hardware configuration of this embodiment.

[0016] Hereinafter, an embodiment will be described with reference to the drawings. Fig. 1 is a block diagram showing the configuration of an estimation device 100 according to the embodiment. The estimation device 100 according to the embodiment approximates the atmospheric response R(Ep,En,d) shown on the right side of the above-mentioned equation (1) with an approximation function fair(Ep,En,d) formed from a general mathematical formula. That is, the estimation device 100 estimates the secondary neutron spectrum Φn(En,d) generated in the atmosphere using the following equation (2):

[0017]

[0018] In equation (2), Ep is the energy of protons (cosmic rays), En is the secondary neutron energy, Φp(Ep) is the proton spectrum (cosmic ray spectrum), and Rair(Ep,En,d) is the atmospheric response. Atmospheric response refers to the spectrum of secondary neutrons produced by the interaction of monoenergetic protons with the Earth's atmosphere. Rair(Ep,En,d) is an approximation function, and d is the altitude relative to the Earth's surface.

[0019] As shown in FIG. 1, the estimation device 100 includes a first calculation unit 1 that calculates the atmospheric response and a second calculation unit 2 that calculates the neutron spectrum.

[0020] The first calculation unit 1 includes an estimation unit 11, an approximation processing unit 12, and an approximate expression generation unit 13. The second calculation unit 2 includes a setting unit 21 and a calculation unit 22.

[0021] The estimation unit 11 estimates the atmospheric response R(Ep,En,d) shown in equation (2) based on simulations and theoretical values. For example, as shown in Fig. 2, a particle transport simulation is performed using monoenergetic protons P1 with a constant energy to estimate the atmospheric response R(Ep,En,d). That is, a particle transport simulation is performed using monoenergetic protons P1 (for example, Ep = 10 [GeV]) to estimate the energy and number of secondary neutrons N1 irradiating the Earth's surface 31.

[0022] That is, the estimation unit 11 estimates an atmospheric response that indicates an interaction between protons and the atmosphere when monoenergetic protons (cosmic rays) are irradiated into the atmosphere. The estimation unit 11 also performs a simulation for calculating a secondary neutron spectrum using monoenergetic protons for protons of multiple energies.

[0023] The approximation processing unit 12 performs approximation processing using a mathematical formula to fit the results of the simulation of the atmospheric response estimated by the estimation unit 11. Specifically, the approximation processing unit 12 simulates the spectrum of secondary neutrons N1 generated by monoenergetic protons P1 that have entered the atmosphere, and fits the obtained secondary neutron spectrum with a model function.

[0024] For example, when a simulation is performed in which protons with an energy of Ep = 10 [GeV] are irradiated, the data shown in Figure 3 is obtained. In Figure 3, the horizontal axis represents the energy of secondary neutrons, and the vertical axis represents the number of secondary neutrons. The curve s1 created from the data shown in Figure 3 is the secondary neutron spectrum Φn(En,d) generated in the process of protons with Ep = 10 [GeV] passing through the atmosphere.

[0025] The approximation processing unit 12 performs simulations by changing the proton energy Ep to various values ​​such as 1 [GeV], 10 [GeV], and 100 [GeV], and obtains the atmospheric response at each altitude d as a general mathematical formula.

[0026] That is, the approximation processing unit 12 derives an approximation function of the atmospheric response for a plurality of proton energies (cosmic ray energies) based on the respective atmospheric responses estimated by the estimation unit 11. The approximation processing unit 12 derives the approximation function by fitting the secondary neutron spectrum calculated by simulations performed for a plurality of energies with a model function.

[0027] The approximate equation generator 13 derives an approximate function fair (Ep, En, 0 km) of the atmospheric response from the particle transport simulation in the range of Ep = 0.3 to 500 [GeV]. The approximate equation generator 13 generates the approximate function shown in the following equation (3).

[0028]

[0029] The parameters shown in equation (3) are as follows:

[0030]

[0031] That is, the approximate equation generator 13 approximates the atmospheric response R(Ep,En,d) with an approximate function fair(Ep,En,d) consisting of a general mathematical expression, and by limiting the integration range, generates an approximate equation that approximately calculates the secondary neutron spectrum Φn(En,d) produced by an arbitrary proton spectrum Φp(Ep) using only numerical integration. As a result, the approximate equation shown in the above-mentioned equation (2) is obtained.

[0032] 1 sets a proton spectrum indicating the distribution of proton energy Ep (cosmic ray energy) generated due to a solar flare. That is, the setting unit 21 sets a proton spectrum (cosmic ray spectrum) in the measurement environment for the secondary neutron spectrum.

[0033] The calculation unit 22 calculates the secondary neutron spectrum Φn(En,d) due to cosmic rays based on the approximate equation generated by the approximate equation generation unit 13. That is, the calculation unit 22 executes a calculation to calculate the secondary neutron spectrum in the measurement environment based on the proton spectrum set by the setting unit 21 and the approximate function.

[0034] Next, the operation of the estimation device 100 according to this embodiment configured as described above will be described with reference to the flowchart shown in FIG.

[0035] First, in step S11 of Fig. 4, the estimation unit 11 estimates the atmospheric response Rair(Ep, En, d) shown in the above-mentioned equation (2) based on simulations and theoretical values, etc., with the proton energy Ep set to a constant value. As a result, the estimation unit 11 obtains the graph showing the relationship between neutron energy and the number of neutrons shown in Fig. 3. This process is performed for a plurality of proton energies.

[0036] In step S12, the approximation processing unit 12 approximates the simulation result of the atmospheric response estimated in the process of step S11 using a general mathematical formula.

[0037] In step S13, the approximate expression generator 13 obtains an approximate function f(Ep, En, d) based on the approximation process in step S12. The approximate expression generator 13 generates a function in which the atmospheric response Rair(Ep, En, d) is replaced with the approximate function f(Ep, En, d), i.e., the approximate expression of the above-mentioned equation (2).

[0038] In step S14, the setting unit 21 determines the proton spectrum Φp(Ep) that occurs when estimating the neutron spectrum.

[0039] In step S15, the calculation unit 22 substitutes the proton spectrum Φp(Ep) into the approximate formula shown in equation (2), and further uses the approximate function f(Ep,En,d) to calculate the secondary neutron spectrum Φn(En,d) generated due to cosmic rays.

[0040] In step S16, the calculation unit 22 outputs the calculated secondary neutron spectrum Φ(E,d) to a downstream device. In this way, it becomes possible to easily calculate the secondary neutron spectrum caused by protons (cosmic rays) of a solar flare with a small calculation load.

[0041] 5A, 5B, and 5C are explanatory diagrams schematically showing a comparative example for comparison with the estimation device according to this embodiment. In the comparative example, a particle transport simulation is performed without using a single energy to generate a graph showing the relationship between the secondary neutron energy E and the secondary neutron spectrum Φ. In the comparative example, this graph is used to directly estimate the secondary neutron spectrum. In other words, the comparative example does not use an approximation function.

[0042] Fig. 5A is a graph showing the relationship between proton energy Ep and proton spectrum Φp(Ep). Here, graphs s11, s12, and s13 of proton spectra with different energy distributions are assumed. Fig. 5B is an explanatory diagram that schematically shows how secondary neutrons N2 irradiating the Earth's surface 31 are measured by particle transport simulation for proton spectra with each energy distribution. Fig. 5C is a graph showing the relationship between secondary neutron energy En and secondary neutron spectrum Φn(En) for each proton spectrum. Curve s21 corresponds to s11, curve s22 corresponds to s12, and curve s23 corresponds to s13.

[0043] As shown in Figure 5A, a proton spectrum Φ(Ep) is set for each of a plurality of proton energies Ep. Furthermore, a particle transport simulation is performed as shown in Figure 5B. As a result, a graph showing the relationship between secondary neutron energy En and secondary neutron spectrum Φ(En,d) is obtained as shown in Figure 5C. If the comparative example method shown in Figures 5A to 5C is adopted, it is not possible to estimate the secondary neutron spectrum Φ(En,d) when a proton energy Ep with a spectrum different from that of galactic cosmic rays is generated.

[0044] In this embodiment, an approximation formula using an approximation function f(Ep,En,d) of the atmospheric response R(Ep,En,d), i.e., the above-mentioned formula (2), is used. Therefore, even if the proton energy Ep changes, it is possible to easily estimate the corresponding secondary neutron spectrum Φn(En,d) with a small calculation load.

[0045] As described above, the estimation device 100 according to this embodiment is an estimation device 100 for estimating the secondary neutron spectrum generated in the atmosphere, and includes an estimation unit 11 that estimates the atmospheric response indicating the interaction between protons and the atmosphere when monoenergetic protons (cosmic rays) are irradiated into the atmosphere for a plurality of proton energies (cosmic ray energies), an approximation processing unit 12 that derives an approximate function of the atmospheric response based on the atmospheric response for each proton energy estimated by the estimation unit 11, a setting unit 21 that sets the proton spectrum (cosmic ray spectrum) in the measurement environment for the secondary neutron spectrum, and a calculation unit 22 that calculates the secondary neutron spectrum in the measurement environment based on the proton spectrum set by the setting unit 21 and the approximate function.

[0046] In this embodiment, by using an approximate function f(Ep,En,d) that replaces the atmospheric response R(Ep,En,d), which requires computer simulation, with a mathematical expression, the computational load when estimating the secondary neutron spectrum can be reduced and the secondary neutron spectrum can be estimated with high accuracy. Also, it becomes possible to quickly calculate the energy spectrum of secondary neutrons generated by cosmic ray protons, which have diverse spectra.

[0047] In this embodiment, when a huge solar flare occurs or is expected to occur, it becomes possible to calculate the secondary neutron spectrum at the Earth's surface with a small computational load based on the proton energy spectrum, and to estimate the probability of semiconductor soft errors occurring.

[0048] In this embodiment, when a huge solar flare occurs or when the occurrence of a huge solar flare is expected, it becomes possible to calculate the secondary neutron spectrum at aircraft altitude based on the proton energy spectrum with a small computational load, and to calculate the amount of radiation exposure inside the aircraft.

[0049] Furthermore, since the neutron spectrum at the Earth's surface can be calculated quickly, it will be possible to report changes in the amount of neutrons at the Earth's surface as early as possible when a solar flare occurs.

[0050] In the above-described embodiment, protons are used as cosmic rays, but the present disclosure can also be applied to cosmic rays other than protons.

[0051] The estimating device 100 of the present embodiment described above can be, for example, a general-purpose computer system including a CPU (Central Processing Unit, processor) 901, a memory 902, a storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), a communication device 904, an input device 905, and an output device 906, as shown in Fig. 6. The memory 902 and the storage 903 are storage devices. In this computer system, the CPU 901 executes a predetermined program loaded on the memory 902, thereby realizing each function of the estimating device 100.

[0052] The estimation device 100 may be implemented by one computer or by multiple computers. Furthermore, the estimation device 100 may be a virtual machine implemented on a computer.

[0053] The program for the estimation device 100 can be stored in a computer-readable recording medium such as a HDD, an SSD, a Universal Serial Bus (USB) memory, a Compact Disc (CD), or a Digital Versatile Disc (DVD), or can be distributed via a network. The computer-readable recording medium is, for example, a non-transitory recording medium.

[0054] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure.

[0055] REFERENCE SIGNS LIST 1 First calculation unit 2 Second calculation unit 11 Estimation unit 12 Approximation processing unit 13 Approximation formula generation unit 21 Setting unit 22 Calculation unit 31 Earth's surface 100 Estimation device d Altitude En Secondary neutron energy Ep Proton energy (cosmic ray energy) Φn Secondary neutron spectrum Φp Proton spectrum

Claims

1. An estimation device for estimating a secondary neutron spectrum generated in the atmosphere, comprising: an estimation unit that estimates, for a plurality of cosmic ray energies, atmospheric responses that indicate interactions between the cosmic rays and the atmosphere when the atmosphere is irradiated with monoenergetic cosmic rays; an approximation processing unit that derives an approximation function of the atmospheric response based on the atmospheric responses for each cosmic ray energy estimated by the estimation unit; a setting unit that sets the cosmic ray spectrum in a measurement environment for the secondary neutron spectrum; and a calculation unit that calculates the secondary neutron spectrum in the measurement environment based on the cosmic ray spectrum set by the setting unit and the approximation function.

2. The estimation device according to claim 1, wherein the cosmic rays are protons, the estimation unit performs a simulation for a plurality of proton energies to calculate a secondary neutron spectrum using monoenergetic protons, and the approximation processing unit derives the approximation function by fitting the secondary neutron spectrum calculated by the simulation performed for the plurality of proton energies with a model function.

3. A method for estimating a secondary neutron spectrum generated in the atmosphere, comprising: an estimation unit estimating, for a plurality of cosmic ray energies, atmospheric responses indicating interactions between the cosmic rays and the atmosphere when the cosmic rays of a single energy are irradiated into the atmosphere; an approximation processing unit deriving an approximation function of the atmospheric response based on the atmospheric responses for each cosmic ray energy estimated by the estimation unit; a setting unit setting a cosmic ray spectrum in a measurement environment for the secondary neutron spectrum; and a calculation unit calculating a secondary neutron spectrum in the measurement environment based on the cosmic ray spectrum set by the setting unit and the approximation function.

4. A program that causes a computer to function as the estimation device according to claim 1 or 2.

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