Lunar Soil Depth Tracking Method for Lunar Surface Neutron Sources Based on Particle Transport Analysis

Abstract

A method for tracking the lunar regolith depth of the lunar surface neutron source based on particle transport analysis, comprising: obtaining the high-energy particle spectrum of the lunar surface; establishing a particle transport model; according to the high-energy particle spectrum and the particle transport model, emitting initial particles into the lunar regolith model, and forming events and tracks after interacting with the lunar regolith after entering the lunar regolith; first forming an initial trajectory record and transmitting it to the event record set; the neutron tracks are transported step by step, and the current event record is updated according to the property change of the neutrons caused by the interaction; the neutrons perform elastic collision motion in the lunar regolith, until the neutron transport ends, forming an end track record and transmitting it to the event record set; when all the events are transported, output all the information in the event record set; according to the high-energy particle spectrum statistics, obtain the lunar regolith depth from which neutrons of different energies on the lunar surface are sourced, providing a basis for the design of the drilling depth for water exploration on the lunar surface.

Description

Technical Field

[0001] The present invention belongs to the field of space science and technology, and particularly relates to a method for tracking the depth of lunar soil of the source of neutrons on the lunar surface based on particle transport analysis. Technical Background

[0002] There is a neutron environment on the lunar surface. This neutron does not exist naturally in space, but is generated by high-energy solar cosmic rays and galactic cosmic rays in space incident on the lunar soil. After interacting with the lunar soil, secondary neutrons are produced, and the secondary neutrons move from the lunar soil to the lunar surface, forming the neutron environment on the lunar surface.

[0003] The source mode of neutrons on the lunar surface can be used to detect whether there is water in the lunar soil. Since the hydrogen element in water has an obvious effect on neutron moderation and attenuation, when there is water in the lunar soil, the neutron flux on the lunar surface will change. By detecting the neutron flux on the lunar surface, it can be inferred whether there is water in the lunar soil. Currently, NASA has carried a neutron detector on the spacecraft orbiting the moon, realizing the detection of the distribution of lunar soil water on the entire moon.

[0004] There are two key parameters for using lunar surface neutron detection to realize the exploration of lunar soil water distribution: the first is the neutron energy, and the second is the depth of the lunar soil where the neutrons originate.

[0005] The first key parameter: neutron energy. When there is water in the lunar soil, different energy neutrons are affected differently. Among them, the low-energy neutron flux will increase, and the neutron fluxes of the remaining energies will decrease, especially the neutron flux in the energy range of 1 eV to 10 keV decreases more significantly. Therefore, by the different changes in the fluxes of neutrons with different energies, it can be inferred whether there is water in the lunar soil, especially the situation in the sensitive energy range of concern or the energy range that can be detected by the neutron detector.

[0006] The second key parameter: the depth of the lunar soil where the neutrons originate. When using the neutron detection method for lunar soil water exploration, the range of the lunar soil depth that can be reflected is limited. After neutrons are generated in the lunar soil, they will move outward until they reach the lunar surface. During the movement process, they will damage their energy through elastic collisions, and the longer the movement path, the greater the energy loss, and the lower the energy of the neutrons reaching the lunar surface. Therefore, neutrons with different energies on the lunar surface originate from different depths of the lunar soil. Low-energy neutrons often originate from deeper lunar soil, while high-energy neutrons often originate from shallower lunar soil. The parameter of the depth of the lunar soil where the neutrons in the sensitive energy range of concern originate not only determines the depth of the lunar soil that can be reached by the method of using neutron detection to search for water, but also affects the designed value of the drilling depth when searching for water by drilling on the lunar surface.

[0007] In summary, the lunar regolith source depths of neutrons with different energies on the lunar surface are important parameters for lunar regolith water exploration. Currently, the neutron energy information and lunar regolith depth information on the lunar surface can be analyzed, but the two parameters are isolated, and no relationship has been established between the lunar regolith source depth and the neutron energy.

[0008] To establish the relationship between the lunar regolith source depth and the neutron energy, it is necessary to continuously track the motion process of neutrons in the lunar regolith. However, due to the very complex process of the interaction between neutrons and the lunar regolith, neutron tracking is very difficult. Neutrons mainly experience the following two processes in the lunar regolith: (1) High-energy particles in space enter the lunar regolith and generate neutrons; (2) Neutrons move in the lunar regolith and interact with the lunar regolith to generate one or more secondary neutrons, and the secondary neutrons will further generate one or more sub-secondary neutrons. The generation of neutrons will continue until the neutrons disappear in the lunar regolith or escape to the lunar surface. The complex and changeable processes of neutron generation and disappearance make neutron tracking extremely difficult.

[0009] Therefore, it is necessary to establish a method for continuous neutron tracking to track various complex processes such as the generation, re-generation, and disappearance of neutrons in the lunar regolith, obtain the source depths of neutrons with different energies on the lunar surface in the lunar regolith, and provide a basis for the design of the drilling depth for water exploration on the lunar surface. Summary of the Invention

[0010] The technical problem to be solved by the present invention is: The present invention provides a method for tracking the lunar regolith depth of the lunar surface neutron source based on particle transport analysis. This method solves the problem that it is difficult to continuously track neutrons due to the complex process of the interaction between neutrons and the lunar regolith, and the source depths of lunar surface neutrons with different energies in the lunar regolith can be obtained by using this method.

[0011] The technical solution of the present invention is as follows:

[0012] A method for tracking the lunar regolith depth of the lunar surface neutron source based on particle transport analysis, including: obtaining the high-energy particle spectrum on the lunar surface; establishing a particle transport model; generating the weights of the initial particles emitted to the lunar regolith structure model according to the high-energy particle spectrum, generating initial particles with these weights, and starting particle transport by emitting the initial particles to the lunar regolith structure model based on the particle transport model; after the initial particles enter the lunar regolith structure model, they interact with the lunar regolith to generate secondary particles including neutrons.

[0013] Before the neutrons start to be transported, form an initial trajectory record and transfer it to the current event record set; the neutron tracks are transported step by step, interact with the lunar regolith, update the event record corresponding to the current step according to the property changes of the neutrons caused by this interaction, and transfer it to the current event record set; the neutrons perform elastic collision motion in the lunar regolith, part of the neutrons escape to the lunar surface, and part of the neutrons terminate in the lunar regolith. At this time, the neutron transport ends, form an end trajectory record and transfer it to the current event record set.

[0014] Based on all the information in the current event record set, the neutron energy emitted to the lunar surface and the maximum depth of the neutron history are obtained;

[0015] Repeat the particle transport process based on the particle transport model until all energies and all types of particles in the high-energy particle spectrum are transported;

[0016] According to the neutron energy and the maximum historical depth of neutrons, the number of neutrons in different neutron energy ranges and the maximum historical depth ranges of neutrons is counted, and then the neutron differential energy spectrum on the lunar surface is determined. Based on the high-energy particle spectrum statistics, the depth of the lunar soil from which neutrons of different energies on the lunar surface originate is obtained.

[0017] Furthermore, the particle transport model includes a lunar soil structure model, an initial particle source emission surface model, and a neutron collector model, wherein the emission surfaces and receiving surfaces of the three are parallel;

[0018] The lunar soil structure model includes: lunar soil density and distribution, composition, whether it contains water and its distribution, and lunar soil shape and size;

[0019] The initial particle source emission surface model emits particles from an emission point toward the lunar soil structure model based on the high-energy particle spectrum, with the emission direction being perpendicular to the lunar soil structure model and emitting downward, and the emission angle is determined by using a cosine distribution;

[0020] The collector model is a virtual cylinder, which is used to count the emitted neutrons.

[0021] Furthermore, the weights of the initial particles emitted to the lunar soil structure model are generated according to the high-energy particle spectrum, specifically including: determining the particle type as T0, the particle energy as E0, the number of particles emitted as N0, and the angle using a cosine distribution;

[0022] According to the spatial high-energy particle differential spectrum f(T0, E0), the weight W of the initial particle is:

[0023]

[0024] The unit of particle energy E0 is MeV / u; ΔE is the energy interval where E0 is located, in MeV; S 空间初始粒子源发射面 is the area of the emitting surface of the initial particle source in space, in cm 2 .

[0025] Furthermore, after the initial particle enters the lunar soil structure model, it interacts with the lunar soil to produce secondary particles including neutrons. The interaction and movement process of the initial particle and all its secondary particles in the lunar soil constitute an event. The movement process of each secondary particle in the lunar soil forms a track, and the weight of each secondary particle and its track is the same as the weight W of the initial particle.

[0026] Before the neutron starts to be transported, an initial track record is formed, and the neutron initial track record is as follows:

[0027] D 当前径迹 =[[ID 本代径迹_当前径迹 , ID 父代径迹_当前径迹 , E 粒子能量_当前径迹 , P 产生深度_当前径迹 , P 父代历史最大深度_当前径迹 , P 历史最大深度_当前径迹 , W(T0, E0, N0)]

[0028] Where: ID 本代径迹_当前径迹 is the track number of this generation, ID 父代径迹_当前径迹 is the track number of the parent generation, E 粒子能量_当前径迹 is the particle energy, P 产生深度_当前径迹 is the generation depth, P 父代最大历史深度_当前径迹 is the maximum historical depth variable of the parent generation, P 历史最大深度_当前径迹 is the maximum historical depth variable of the history, and W(T0, E0, N0) is the initial particle weight.

[0029] Furthermore, the transfer of the current initial track record to the event record set specifically includes:

[0030] The event record set is a set containing n track records, and each track record contains the parameters: the track number of this generation, the track number of the parent generation, the particle energy, the generation depth, the maximum historical depth variable of the parent generation, the maximum historical depth variable of the history, and the initial particle weight;

[0031] When the track number of the parent generation in the initial track record is the same as the track number of this generation of the kth record in the current event record set, update the track number of this generation and the track number of the parent generation of the kth record in the event record set to the track number of this generation and the track number of the parent generation of the current track respectively;

[0032] When the track number of the parent generation in the initial track record is not the same as the track numbers of this generation and the track numbers of the parent generation of all records in the event record set, add the initial track record to the event record set;

[0033] When it is shown that the track number of the parent generation in the initial track record is not the same as the track numbers of this generation of all records in the event record set, but is the same as the track number of the parent generation of the mth record in the event record set, update the maximum historical depth of the parent generation and the maximum historical depth of the history of the current track to the maximum historical depth of the parent generation of the mth record, and add the current track record to the event record set.

[0034] Furthermore, the neutron track is transported step by step, interacts with the lunar soil, and updates the current step record according to the property changes of the neutrons caused by this interaction, specifically including:

[0035] The current step record includes:

[0036] D 当前步 = [E 粒子能量_当前步 , P 历史最大深度_当前步 , B 经过收集体标志_当前步 , B 生存标志_当前步 , N 次级中子数目_当前步

[0037] where E 粒子能量_当前步 is the particle energy at the current step; P 历史最大深度_当前步 is the maximum historical depth at the current step; B 经过收集体标志_当前步 is the flag indicating passing through the collector at the current step; B 生存标志_当前步 is the flag indicating the survival status at the current step; N 次级中子数目_当前步 is the number of secondary particles at the current step;

[0038] According to the transport process, the step record update process is as follows:

[0039] E 粒子能量_当前步 = E 当前粒子能量

[0040]

[0041]

[0042]

[0043]

[0044] where E 当前粒子能量 is the current energy of the particle, and P 当前深度 is the current depth of the particle.

[0045] Furthermore, the neutrons undergo elastic collision motion in the lunar soil structure model. Some neutrons are emitted to the lunar surface, and some neutrons terminate in the lunar soil. At this time, the neutron transport ends, forming an end track record, and the end track record is passed to the current event record set, specifically including:

[0046] The processing methods for step records in various situations are as follows:

[0047] When a neutron is emitted outside the lunar soil structure model and the neutron has not passed through the neutron collector model, delete the current track record in the current event record set;

[0048] When a neutron is emitted outside the lunar soil structure model and the neutron passes through the neutron collector, update the maximum historical depth of the track record of this neutron in the current event record set to the maximum historical depth at the current step, and update the particle energy to the particle energy at the current step;

[0049] When a neutron terminates in the lunar soil and the neutron is absorbed and disappears, delete the current track record in the current event record set;​

[0050] When the neutron terminates in the lunar regolith and the neutron disappears through inelastic collision but generates secondary neutrons that continue to move in the lunar regolith, updating the track record of the neutron in the current event record set includes updating the maximum depth of the parent history to the current maximum depth of the parent history and updating the maximum depth of the history to the current maximum depth of the history.

[0051] Furthermore, the number of neutrons in different neutron energy ranges and neutron maximum history depth ranges is statistically calculated according to the neutron energy and the neutron maximum history depth. The statistical method is as follows:

[0052] ΔF(E i ~E j ,P m ~P n )=∑W(T0,E0,N0)×η(E i ~E j ,P m ~P n )

[0053]

[0054] where ΔF(E i ~E j ,P m ~P n ) is the star catalog neutron flux within the energy range [E i ,E j and within the maximum history depth range [P i ,P j , with the unit of cm -2 〃s -1 ; E i 、E j are the upper and lower limits of the neutron energy range [E i ,E j , with the unit of MeV; P i 、P j are the upper and lower limits of the neutron maximum history depth range [P i ,P j , with the unit of mm; η(E i ~E j ,P m ~P n ) is the selection factor when statistically calculating neutron information according to the neutron energy and the maximum history depth.

[0055] Furthermore, the determination of the neutron differential energy spectrum on the lunar surface includes:

[0056]

[0057] Where F is the neutron differential energy spectrum of the lunar surface, in cm -2 MeV -1 〃s -1 ;

[0058] The depths of the lunar soil from which neutrons of different energies originate on the lunar surface are obtained based on the high-energy particle spectrum.

[0059] The advantages of the present invention compared with the prior art are:

[0060] (1) The entire life cycle of neutrons is tracked. When using conventional particle transport methods for analysis, when neutrons are emitted from the lunar surface, they do not include information about the depth of the lunar soil they have traveled. This invention overcomes the fact that conventional particle transport methods do not pay attention to the intermediate processes and achieves the full tracking of neutrons from generation, action, destruction, and emission from the lunar soil.

[0061] (2) The source depth distribution of neutrons of different energies on the lunar surface can be obtained. By tracking the entire life cycle of neutrons, the source depth distribution data of neutrons of different energies on the lunar surface can be obtained, providing a basis for the design of drilling depth for water exploration on the lunar surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is a flow chart of the lunar soil depth tracking method for neutron sources of different energies on the lunar surface of the present invention.

[0063] Figure 2 It is a particle transport analysis model.

[0064] Figure 3 It is the movement process of neutrons.

[0065] Figure 4 It is the neutron tracking method.

[0066] Figure 5 It is the neutron flux on the lunar surface under the conditions of water and no water in the lunar soil.

[0067] Figure 6 It is the ratio of the neutron flux on the lunar surface under the conditions of water and no water in the lunar soil.

[0068] Figure 7 It is the source depth of neutrons of different energies on the lunar surface. DETAILED DESCRIPTION

[0069] This paper proposes a method for deep tracing of lunar surface neutron sources based on particle transport analysis. The method includes three main aspects: (1) analyzing the spectrum of high-energy particles in space, (2) establishing a particle transport analysis model, and (3) performing particle transport analysis and tracking the neutron history.

[0070] First, obtain the high-energy particle spectrum on the lunar surface, then establish a particle transport model, and generate particles emitted towards the lunar regolith structure model according to the high-energy particle spectrum.

[0071] Generate the weights of the initial particles emitted towards the lunar regolith structure model according to the high-energy particle spectrum, generate the initial particles with these weights, and start particle transport by emitting the initial particles towards the lunar regolith structure model based on the particle transport model; after the initial particles enter the lunar regolith structure model, they interact with the lunar regolith to generate secondary particles including neutrons; before the neutrons start to be transported, form an initial trajectory record; transfer the current initial track record to the current event record set; the neutron tracks are transported step by step, interact with the lunar regolith, update the event record corresponding to the current step according to the changes in the properties of the neutrons caused by this interaction, and transfer it to the current event record set; the neutrons perform elastic collision motion in the lunar regolith, some neutrons are emitted to the lunar surface, and some neutrons terminate in the lunar regolith. At this time, the neutron transport ends, form an end track record, and transfer the end track record to the current event record set; output all the information in the current event record set; obtain the neutron energy and the maximum depth of the neutron history emitted to the lunar surface; repeat the above-mentioned particle transport process until all energies and all types of particles are transported.

[0072] According to the neutron energy and the maximum depth of the neutron history, count the number of neutrons in different neutron energy ranges and different maximum depth ranges of the neutron history, and then determine the differential energy spectrum of neutrons on the lunar surface. According to the high-energy particle spectrum statistics, obtain the lunar regolith depth from which neutrons of different energies on the lunar surface originate.

[0073] The present invention will be described below in conjunction with the accompanying drawings and embodiments. As Figure 1 shown, the present invention mainly includes:

[0074] (1) Read and analyze the high-energy particle spectrum on the lunar surface, which includes three parameters: particle type, particle energy, and differential flux corresponding to particles of each energy.

[0075] (2) Establish a particle transport model as the input for neutron analysis. The particle transport analysis model includes three parts: a neutron collector, an initial particle source emission surface, and a lunar regolith model. The neutron collector is a virtual structure without substances inside, used to count the emitted neutrons. The initial particle source emission surface emits space high-energy particles towards the lunar regolith model. The parameters such as the particle type, energy, and flux of the high-energy particles adopt the results of step (1), and are emitted downward, and the angle adopts a cosine distribution. The lunar regolith model is the main part of particle transport, including two types of information: one is material information, including the density and distribution of the lunar regolith, composition, whether it contains water and water distribution; the other is size information, including the shape and size of the lunar regolith, etc.

[0076] (3) The movement process of neutrons in lunar soil is divided into four cases: (A) Neutrons are generated by the interaction between space particles and lunar soil; (B) Neutrons undergo elastic collisions with lunar soil, and only parameters such as energy, direction, and position change, while the two parameters of the current generation track number and the parent generation track number remain unchanged; (C) Neutrons are absorbed and disappear; (D) Neutrons undergo inelastic collisions with lunar soil, generating one or more secondary neutrons. In addition to changes in parameters such as energy, direction, and position, the two parameters of the current generation track number and the parent generation track number also change.

[0077] In this step, the method of particle transport analysis is used to trace the neutron process. Three data records, namely the step record, track record, and event record set of neutrons, are constructed. Through the parameter transfer from the step record to the track record and from the track record to the event record set, through the judgment and processing methods of parameters such as the number of secondary neutrons, the current generation track number, and the parent generation track number, and by constructing and transferring the parameter of "maximum depth of parent history", the continuous tracking of the entire life cycle of neutrons is realized, and the depth of lunar soil from which neutrons of different energies on the lunar surface originate can be obtained. This step includes four parts: particle transport, step record processing, track record processing, and event record processing.

[0078] The key points of this step are as follows:

[0079] (A) Three data records, namely the step record, track record, and event record set of neutrons, are constructed. Through the parameter transfer from the step record to the track record and from the track record to the event record set, the continuous tracking of the movement process of neutrons in lunar soil can be realized, and the binding of two key parameters, namely neutron energy and source depth, is achieved, so that the source depth of neutrons with different energies on the lunar surface can be obtained.

[0080] (B) In the step record, track record, and event record set, through the judgment and processing methods of parameters such as the number of secondary neutrons, the current generation track number, and the parent generation track number, the changes in neutron properties brought about by various complex interaction processes, such as neutron generation, neutron movement in lunar soil through elastic collisions, neutron absorption by lunar soil, and neutron generation of multiple neutrons in lunar soil through inelastic collisions, can be processed.

[0081] (C) In the track record and event record set, the parameter of "maximum depth of parent history" is constructed. This parameter records the maximum depth of the history of the parent neutron that generates the neutron. Through the update and transfer process of this parameter, this data is finally assigned to the parameter of the maximum depth of neutron history. Therefore, the parameter of the maximum depth of neutron history not only reflects its own movement process but also reflects the movement process of the parent particle, making the information of the parameter of the maximum depth of neutron history accurate.

[0082] Using the initial particle source in step (1), the simulation model in step (2), and the method in step (3), neutrons with different energies emitted onto the lunar surface can be correlated with the lunar regolith depth parameters they have experienced, thereby obtaining the lunar regolith source depth data for neutrons with different energies on the lunar surface.

[0083] The specific implementation steps are as follows:

[0084] (1) Analyze the space high-energy particle spectrum

[0085] The interaction between space high-energy particles and lunar regolith generates neutrons, which is the source of neutrons on the lunar surface. Analyze the high-energy differential particle spectrum on the lunar surface, including three parameters: particle type, energy, and flux, as the input parameters for neutron analysis.

[0086] Taking galactic cosmic rays as an example, using the CREME96 model, analyze the differential flux of particles with atomic numbers from 1 to 92, as shown in the following table.

[0087] Table 1 Galactic cosmic ray differential spectrum

[0088]

[0089]

[0090]

[0091]

[0092] (2) Establish a particle transport analysis model

[0093] Establish a particle transport analysis model as the input for neutron analysis. The particle transport analysis model consists of three parts: a neutron collector, an initial particle source emission surface, and a lunar regolith structure model.

[0094] The initial particle source emission surface emits space high-energy particles towards the lunar regolith. The parameters of the high-energy particles, such as particle type, energy, and flux, adopt the results of step (1), and are emitted downward with an angle following a cosine distribution.

[0095] The neutron collector is a virtual structure without substances inside, used to count the emitted neutrons.

[0096] The lunar regolith structure model is the main part of particle transport, including two types of information: one is material information, including the density and distribution of lunar regolith, composition, whether it contains water and the water distribution; the other is size information, including the shape and size of lunar regolith, etc.

[0097] The lunar regolith material information can adopt the lunar regolith composition at the location of interest. Taking the Shackleton crater as an example, Table 2 gives the corresponding lunar regolith composition, Table 3 gives the lunar regolith density and distribution, and Table 4 gives the water content.

[0098] Table 2 Lunar soil composition

[0099] Component proportion Shackleton crater <![CDATA[SiO2 (wt%)]]> 44.51 <![CDATA[TiO2 (wt%)]]> 0.17 <![CDATA[Al2O3 (wt%)]]> 28.67 FeO (wt%) 4.94 MgO (wt%) 7.62 CaO (wt%) 15.63 <![CDATA[K2O (wt%)]]> 0.04

[0100] Table 3 Variation of lunar soil density with depth

[0101] Depth (cm) <![CDATA[Average bulk density ρ (g / cm 3 )]]> 0～15 1.50±0.05 15～30 1.58±0.05 30～60 1.74±0.05

[0102] Table 4 Lunar soil water content

[0103] Depth (cm) Water content (%) 3.17E+00 1.25E-04 4.14E+00 3.61E-04 5.16E+00 5.80E-04 6.15E+00 1.35E-03 7.18E+00 1.87E-03 8.22E+00 2.50E-03 9.20E+00 6.24E-03 1.02E+01 9.34E-03 2.16E+01 6.02E-01 3.21E+01 2.33E+00 4.17E+01 3.23E+00 5.13E+01 3.35E+00 6.19E+01 2.90E+00 7.05E+01 2.60E+00 8.75E+01 2.50E+00 9.07E+01 2.33E+00 1.01E+02 1.94E+00 2.02E+02 2.24E+00 3.00E+02 1.74E-02 4.02E+02 3.74E-04 4.53E+02 1.56E-04

[0104] The initial particle source emission surface is a circular surface, and the neutron collector and lunar soil are cylindrical, as shown in Figure 2 . To ensure factors such as neutron collection efficiency, collection angle, and sufficient interaction between space high-energy particles and lunar soil, the dimensions of the two structures are shown in Table 5.

[0105] Table 5 Simulation model dimensions

[0106] Initial particle source emission surface diameter (m) 3000 Initial particle source emission surface height from the lunar regolith surface (mm) 1 Neutron collector diameter (m) 2926 Neutron collector thickness (mm) 1 Neutron collector height from the lunar regolith surface (cm) 1 Lunar regolith diameter (m) 3000 Lunar regolith thickness (m) 5

[0107] (3) Conduct particle transport analysis and track the neutron history

[0108] The movement history of neutrons in lunar soil is divided into four cases: (A) Space particles interact with lunar soil to generate neutrons; (B) Neutrons undergo elastic collisions with lunar soil, and only parameters such as energy, direction, and position change, while the two parameters of the current track number and the parent track number remain unchanged; (C) Neutrons are absorbed and disappear; (D) Neutrons undergo inelastic collisions with lunar soil, generating one or more secondary neutrons. In addition to changes in parameters such as energy, direction, and position, the two parameters of the current track number and the parent track number also change. The neutron movement history is as shown in Figure 3 .

[0109] In this step, the method of particle transport analysis is used to track the neutron history and achieve continuous tracking of the entire life cycle of neutrons. It consists of four parts: neutron envelope particle transport, step record processing, track record processing, and event record processing. The steps are as follows, and the neutron tracking method is shown in Figure 4 :

[0110]

[01] . Vertically downward emit initial particles from the emission surface of the space initial particle source. The particle type is T0, the particle energy is E0, the number of emitted particles is N0, and the angle adopts a cosine distribution. Using the differential spectrum f(T0, E0) of space high-energy particles in step (1), the weight W of the initial particles is:

[0111]

[0112] Where W is the weight of each emitted particle; T0 is the particle type; E0 is the particle energy in MeV / u; ΔE is the energy interval where E0 is located in MeV; S 空间初始粒子源发射面 is the area of the emission surface of the initial particle source in space, in cm 2 ; N0 is the actual number of emitted particles.

[0113]

[02] . After the initial particles enter the lunar regolith, through interaction with the lunar regolith, various types of secondary particles such as electrons, gamma photons, and neutrons are generated. The secondary particles will continue to interact with the lunar regolith until they exit the lunar regolith model or terminate in the lunar regolith, at which point the transport ends. The interaction and movement processes of the initial particles and all their secondary particles in the lunar regolith constitute 1 event; the movement process of each secondary particle in the lunar regolith forms 1 track, and the weight of each secondary particle and its track is the same as that of the primary particle determined by formula (1). This invention analyzes the neutron environment, so all the following processes only involve the analysis and statistics of neutrons among the secondary particles.

[0114]

[03] . After neutrons are generated, before starting the transport movement, record their information to form an initial track record, which includes: (A) Generate and record the track number ID of the current generation 本代径迹_当前径迹 ; (B) Generate and record the track number ID of the parent generation 父代径迹_当前径迹 ; (C) Record the particle energy E 粒子能量_当前径迹 ; (D) Record the production depth P 产生深度_当前径迹 ; (E) Create a parent generation maximum historical depth variable P 父代最大历史深度_当前径迹 , and assign it the production depth P 产生深度_当前径迹 ; (F) Create a historical maximum depth variable P 历史最大深度_当前径迹 , and assign it the production depth P 产生深度_当前径迹 ; (G) Particle weight W(T0, E0, N0). As follows:

[0115] D 当前径迹 = [ID 本代径迹_当前径迹 , ID 父代径迹_当前径迹 , E 粒子能量_当前径迹 , P 产生深度_当前径迹 , P 父代历史最大深度_当前径迹 , P 历史最大深度_当前径迹 , W(T0, E0, N0)]

[0116] Formula (2)

[0117] Where: P 父代历史最大深度_当前径迹 = P 产生深度_当前径迹 , P 历史最大深度_当前径迹 = P 产生深度_当前径迹 , and W(T0, E0, N0) is determined by formula (1).

[0118]

[04] . Pass the current initial track record to the current event record set. The function of this step is to temporarily save the neutron record just generated. The judgment and processing methods are as follows:

[0119] The current event record set is a set containing n track records, and each track record contains 7 parameters, as shown in formula (2). The event record set is as follows:

[0120] D 当前事件 = {[ID 本代径迹_1 , ID 父代径迹_1 , E 粒子能量_1 , P 产生深度_1 , P 父代历史最大深度_1 , P 历史最大深度_1 , W(T0, E0, N0)],[ID 本代径迹_2 , ID 父代径迹_2 , E 粒子能量_2 , P 产生深度_2 , P 父代历史最大深度_2 , P 历史最大深度_2 , W(T0, E0, N0)],……[ID 本代径迹_n , ID 父代径迹_n , E 粒子能量_n , P 产生深度_n , P 父代历史最大深度_n , P 历史最大深度_n , W(T0, E0, N0)]}

[0121] Formula (3)

[0122] Among them, the last record, that is, the nth record, is the latest track record.

[0123] When there are different situations for the current initial track record, the processing methods are as follows:

[0124] Situation 1: ID 父代径迹_当前径迹 = ID 本代径迹_k It shows that the parent track number in the initial track record is the same as the current generation track number of the kth record in the event record set. This indicates that the neutron of the current track is generated by other neutrons. The processing method is: update the current generation track number and the parent track number of the kth record in the event record set to the current generation track number and the parent track number of the current track respectively, that is:

[0125] D 当前事件 = {[ID 本代径迹_1 , ID 父代径迹_1 , E 粒子能量_1 , P 产生深度_1 , P 父代历史最大深度_1 , P 历史最大深度_1 , W(T0, E0, N0)],[ID 本代径迹_2 , ID 父代径迹_2 , E 粒子能量_2,P 产生深度_2 ,P 父代历史最大深度_2 ,P 历史最大深度_2 ,W(T0,E0,N0)],……[ID 本代径迹_n ,ID 父代径迹_n ,E 粒子能量_n ,P 产生深度_n ,P 父代历史最大深度_n ,P 历史最大深度_n ,W(T0,E0,N0)]}(when ID 父代径迹_当前径迹 = ID 本代径迹_k )

[0126] Formula (4)

[0127] where ID 本代径迹_k = ID 本代径迹_当前径迹 , ID 父代径迹_k = ID 父代径迹_当前径迹 .

[0128] Case 2: ID 父代径迹_当前径迹 ≠ ID 本代径迹_k (k = 1 ~ n) and ID 父代径迹_当前径迹 ≠ ID 父代径迹_k (k = 1 ~ n), it shows that the parent track number in the initial track record is inconsistent with the current generation track numbers and parent track numbers of all records in the event record set. This indicates that the neutron of the current track is generated by other types of particles rather than neutrons. The processing method is: add the initial track record to the event record set, that is:

[0129] D 当前事件 = {D 当前事件 , D 当前径迹} = {[ID 本代径迹_1 , ID 父代径迹_1 , E 粒子能量_1 , P 产生深度_1 , P 父代历史最大深度_1 , P 历史最大深度_1 , W(T0,E0,N0)],[ID 本代径迹_2 , ID 父代径迹_2 , E 粒子能量_2 , P 产生深度_2 , P 父代历史最大深度_2 , P 历史最大深度_2 , W(T0,E0,N0)],……[ID 本代径迹_n , ID 父代径迹_n , E 粒子能量_n , P 产生深度_n , P 父代历史最大深度_n , P 历史最大深度_n , W(T0,E0,N0)],[ID 本代径迹_n+1 , ID 父代径迹_n+1 , E 粒子能量_n+1 , P 产生深度_n+1 , P父代历史最大深度_n+1 , P 历史最大深度_n+1 , W(T0, E0, N0)]} (when ID 父代径迹_当前径迹 ≠ ID 本代径迹_k and ID 父代径迹_当前径迹 ≠ ID 父代径迹_k , k = 1 to n)

[0130] Formula (5)

[0131] where [ID 本代径迹_n+1 , ID 父代径迹_n+1 , E 粒子能量_n+1 , P 产生深度_n+1 , P 父代历史最大深度_n+1 , P 历史最大深度_n+1 = D 当前径迹 .

[0132] Case 3: ID 父代径迹_当前径迹 ≠ ID 本代径迹_k (k = 1 to n) and ID 父代径迹_当前径迹 = ID 父代径迹_m , it shows that the parent track number in the initial track record is inconsistent with the current generation track numbers of all records in the event record set, but is consistent with the parent track number of the m-th record in the event record set. This means that the neutron of the current track is generated by other neutrons and has the same parent neutron as the m-th record in the event record set. The processing method is: update the maximum historical depth and the historical maximum depth of the parent of the current track to the maximum historical depth of the parent of the m-th record, that is, P 父代历史最大深度_当前径迹 = P 父代历史最大深度_m , P 历史最大深度_当前径迹 = P 父代历史最大深度_m , and add the current track record to the event record set, that is:

[0133] D 当前事件 = {D 当前事件 , D 当前径迹} = {[ID 本代径迹_1 , ID 父代径迹_1 , E 粒子能量_1 , P 产生深度_1 , P 父代历史最大深度_1 , P 历史最大深度_1 , W(T0, E0, N0)], [ID 本代径迹_2 , ID 父代径迹_2 , E 粒子能量_2 , P 产生深度_2 , P 父代历史最大深度_2 , P 历史最大深度_2 , W(T0, E0, N0)], …… [ID 本代径迹_n , ID 父代径迹_n , E 粒子能量_n , P 产生深度_n , P 父代历史最大深度_n , P 历史最大深度_n,W(T0,E0,N0)],[ID 本代径迹_n+1 ,ID 父代径迹_n+1 ,E 粒子能量_n+1 ,P 产生深度_n+1 ,P 父代历史最大深度_n+1 ,P 历史最大深度_n+1 ,W(T0,E0,N0)]}(when ID 父代径迹_当前径迹 ≠ID 本代径迹_k (k = 1 to n) and ID 父代径迹_当前径迹 =ID 父代径迹_m ))

[0134] Formula (6)

[0135] where [ID 本代径迹_n+1 ,ID 父代径迹_n+1 ,E 粒子能量_n+1 ,P 产生深度_n+1 ,P 父代历史最大深度_n+1 ,P 历史最大深度_n+1 = D 当前径迹 , and P 父代历史最大深度_当前径迹 =P 父代历史最大深度_m , and P 历史最大深度_当前径迹 =P 父代历史最大深度_m .

[0136]

[05] . The neutron track is transported step by step. At this time, the neutron will interact with the lunar soil through elastic and inelastic collisions, resulting in changes in the energy, position, state, etc. of the neutron. Update the current step record according to the changes, including five parameters: (A) particle energy; (B) historical maximum depth; (C) collection body flag passed; (D) survival state flag; (E) number of secondary particles.

[0137] The record of the current step is:

[0138] D 当前步 =[E 粒子能量_当前步 ,P 历史最大深度_当前步 ,B 经过收集体标志_当前步 ,B 生存标志_当前步 ,N 次级中子数目_当前步

[0139] Formula (7)

[0140] According to the transport process, update as follows:

[0141] E 粒子能量_当前步 =E 当前粒子能量 Formula (8)

[0142]

[0143]

[0144] ​

[0145]

[0146] Among them E 当前粒子能量 is the current energy of the particle, P 当前深度 is the current depth of the particle.

[0147]

[06] Neutrons continue to move through elastic collisions in the lunar soil until they are ejected from the lunar soil model, or terminate in the lunar soil by being absorbed or undergoing inelastic collisions. Neutron transport ends, forming a final track record, which is then passed to the event record set. The purpose of this step is to process the final neutron track record at the end of neutron transport based on the different states of the neutron's last step record. The judgment and processing method of this step is as follows:

[0148] When there are different situations in the step record of the last step of the neutron, the processing method is as follows:

[0149] Case 1: B 生存标志_当前步 =1 indicates that neutrons are emitted outside the lunar soil model, and B 经过收集体标志_当前步 =0 indicates that the neutron has not passed through the neutron collector. This indicates that the neutron is not the final record object. The processing method is: delete the current track record in the event record set, that is, the last track record, that is:

[0150] D 当前事件 ={[ID 本代径迹_1 ,ID 父代径迹_1 ,E 粒子能量_1 ,P 产生深度_1 ,P 父历史最大深度_1 ,P 历史最大深度_1 ,W(T0,E0,N0)],[ID 本代径迹_2 ,ID 父代径迹_2 ,E 粒子能量_2 ,P 产生深度_2 ,P 父历史最大深度_2 ,P 历史最大深度_2 ,W(T0,E0,N0)],……[ID 本代径迹_n-1 ,ID 父代径迹_n-1 ,E 粒子能量_n-1 ,P 产生深度_n-1 ,P 父历史最大深度_n-1 ,P 历史最大深度_n-1 ,W(T0,E0,N0)]}(When B 生存标志_当前步 =1 and B 经过收集体标志_当前步 =0 o'clock)

[0151] Formula (13)

[0152] Which deletes the nth record.

[0153] Case 2: B 生存标志_当前步 =1 indicates that neutrons are emitted outside the lunar soil model, and B经过收集体标志_当前步 = 1 indicates that the neutron passes through the neutron collector. At this time, it shows that the neutron is the final recording object, and the processing method is: update the track record of this neutron in the event record set, that is, the latest track record in the event record set, including depth and particle energy, that is:

[0154] D 当前事件 = {[ID 本代径迹_1 , ID 父代径迹_1 , E 粒子能量_1 , P 产生深度_1 , P 父代历史最大深度_1 , P 历史最大深度_1 , W(T0, E0, N0)],[ID 本代径迹_2 , ID 父代径迹_2 , E 粒子能量_2 , P 产生深度_2 , P 父代历史最大深度_2 , P 历史最大深度_2 , W(T0, E0, N0)],……[ID 本代径迹_n , ID 父代径迹_n , E 粒子能量_n , P 产生深度_n , P 父代历史最大深度_n , P 历史最大深度_n , W(T0, E0, N0)} (when B 生存标志_当前步 = 1 and B 经过收集体标志_当前步 = 1)

[0155] Formula (14)

[0156] where E 粒子能量_n = E 粒子能量_当前步 , P 历史最大深度_n = P 历史最大深度_当前步 .

[0157] Case 3: B 生存标志_当前步 = 2 indicates that the neutron terminates in the lunar soil, and N 次级中子数目_当前步 = 0 indicates that the neutron is absorbed and disappears. At this time, it shows that the neutron is not the final recording object, and the processing method is: delete the current track record in the event record set, that is, the last track record, that is:

[0158] D 当前事件 = {[ID 本代径迹_1 , ID 父代径迹_1 , E 粒子能量_1 , P 产生深度_1 , P 父代历史最大深度_1 , P 历史最大深度_1 , W(T0, E0, N0)],[ID 本代径迹_2 , ID 父代径迹_2 , E 粒子能量_2 , P 产生深度_2 , P 父代历史最大深度_2 , P 历史最大深度_2,W(T0,E0,N0)],……[ID 本代径迹_n-1 ,ID 父代径迹_n-1 ,E 粒子能量_n-1 ,P 产生深度_n-1 ,P 父代历史最大深度_n-1 ,P 历史最大深度_n-1 ,W(T0,E0,N0)]}(when B 生存标志_当前步 = 2 and B 经过收集体标志 = 0)

[0159] Formula (15)

[0160] Where the nth record is deleted.

[0161] Case 4: B 生存标志_当前步 = 2 indicates that the neutron terminates in the lunar regolith, and N 次级中子数目_当前步 ≥ 1 indicates that the neutron disappears through inelastic collision but produces one or more secondary neutrons, and the secondary neutrons will continue to move in the lunar regolith. This neutron is not the object of the final record, but this record needs to be retained to save the maximum depth of the parent history. This neutron record will be replaced during the movement of the secondary particles. The processing method is: update the track record of this neutron in the event record set, that is, the latest track record in the event record set, including the maximum depth of the parent history and the maximum depth of history, that is:

[0162] D 当前事件 = {[ID 本代径迹_1 ,ID 父代径迹_1 ,E 粒子能量_1 ,P 产生深度_1 ,P 父代历史最大深度_1 ,P 历史最大深度_1 ,W(T0,E0,N0)],[ID 本代径迹_2 ,ID 父代径迹_2 ,E 粒子能量_2 ,P 产生深度_2 ,P 父代历史最大深度_2 ,P 历史最大深度_2 ,W(T0,E0,N0)],……[ID 本代径迹_n ,ID 父代径迹_n ,E 粒子能量_n ,P 产生深度_n ,P 父代历史最大深度_n ,P 历史最大深度_n ,W(T0,E0,N0)]}(when B 生存标志_当前步 = 2 and N 次级中子数目_当前步 ≥ 1)

[0163] Formula (16)

[0164] Where P 父代历史最大深度_n = P 父代历史最大深度_当前径迹 ,P 历史最大深度_n = P 历史最大深度_当前步 .

[0165]

[07] . When all the transports of this event are completed, all the information in the event record set is output. Thus, the information of the neutrons emitted to the lunar surface can be obtained, including key information such as neutron energy, maximum depth of neutron history, and neutron weight.

[0166]

[08] . Repeat steps

[01] to

[08] until the transports of all energies and all types of particles are completed.

[0167]

[09] . According to the neutron energy and the maximum depth of neutron history, count the number of neutrons in different neutron energy ranges and maximum depth ranges of neutron history. The statistical processing method is as follows:

[0168] ΔF(E i ~E j ,P m ~P n )=∑W(T0,E0,N0)×η(E i ~E j ,P m ~P n ) Formula (17)

[0169]

[0170] where ΔF(E i ~E j ,P m ~P n ) is the star catalog neutron flux within the energy range [E i ,E j and within the maximum depth range of neutron history [P i ,P j , with the unit of cm -2 〃s -1 ; Ei, Ej are neutron energies, with the unit of MeV; Pi, Pj are the maximum depths of neutron history, with the unit of mm; η(E i ~E j ,P m ~P n ) is the selection factor when counting neutron information according to neutron energy and maximum depth of neutron history.

[0171] Dividing the result of formula (16) by the energy interval, the differential energy spectrum of neutrons on the lunar surface can be obtained, that is:

[0172]

[0173] where F is the differential energy spectrum of neutrons on the lunar surface, with the unit of cm -2 〃MeV -1 〃s -1 .

[0174] Using the data from Step 2, an analysis model is established, which consists of a neutron collector, an initial particle source emission surface, and lunar regolith. The lunar regolith is cylindrical, with a diameter of 3000 m and a thickness of 5 m. The composition of the lunar regolith is shown in Table 2, and the density of the lunar regolith at different depths is shown in Table 2. First, a lunar regolith model without water is established; the initial particle source emission surface is a circular surface with a diameter of 3000 m and a distance of 1 mm from the surface of the lunar regolith model; the neutron collector is cylindrical, with a diameter of 2926 m and a thickness of 1 mm, and the distance between the lower surface of the neutron collector and the surface of the lunar regolith model is 1 cm.

[0175] Using the data from Step 1, initial space particles are emitted vertically downward from the initial particle source emission surface. The space particles are evenly distributed on the initial particle source emission surface, and the angle follows the cosine law. First, H particles are emitted, with energies of 1.0E+00 MeV / u, 1.0E+01 MeV / u, 1.0E+02 MeV / u,

[0176] 1.0E+03 MeV / u, 1.0E+04 MeV / u, 1.0E+05 MeV / u respectively. 1000 H particles of each energy are emitted, that is, N0 = 1000 in formula (1). Each H particle enters the lunar regolith and moves in the lunar regolith. During the movement, the H particle generates neutrons through interaction with the lunar regolith. Use Step (3) to analyze and record the information of the neutrons. After the emission of H particles is completed, all the particles and all their energies in Table 1 are emitted, and use Step (3) to analyze and record the information of the neutrons.

[0177] After all particle simulations are completed, the depth information of the lunar regolith source of neutrons with different energies on the lunar surface can be obtained under the condition that the lunar regolith does not contain water.

[0178] The soil without water is established above. Next, using the data in Table 4, a water-containing model is established, and the above process is repeated. Then the depth information of the lunar regolith source of neutrons with different energies on the lunar surface can be obtained under the condition that the lunar regolith contains water., as and Figure 5 shown. When there is water in the lunar regolith, it will cause the neutron flux above 0.08 eV to decrease and the neutron flux below 0.08 eV to increase. For neutrons in the energy range of 0.65 eV - 8 keV, the reduction ratio is the largest and the reduction ratios are close under the condition of having water, which is less than 40% of the condition without water.

[0179] This analysis also obtains the depth distribution of the sources of neutrons with different energies on the lunar surface in the lunar regolith, as Figure 6 shown. Figure 7 Figure 7 The depth source of 50% neutron flux is given, where 0.65 eV - 8 keV mainly comes from 500 mm - 700 mm. When searching for water on the lunar surface according to the neutron detection results, the drilling depth on the lunar surface can be designed with reference to this data.

Claims

1. A method for tracking the lunar regolith depth of the lunar surface neutron source based on particle transport analysis, characterized in that, Comprising: Obtaining the high-energy particle spectrum on the lunar surface; Establishing a particle transport model; Generating the weights of the initial particles emitted towards the lunar regolith structure model according to the high-energy particle spectrum, generating initial particles with these weights, and starting particle transport by emitting the initial particles towards the lunar regolith structure model based on the particle transport model; after the initial particles enter the lunar regolith structure model, they interact with the lunar regolith to generate secondary particles including neutrons; Before the neutrons start to be transported, forming an initial track record and transmitting it to the current event record set; the neutron tracks are transported step by step, interact with the lunar regolith, update the event record corresponding to the current step according to the property changes of the neutrons caused by this interaction and transmit it to the current event record set; the neutrons perform elastic collision motion in the lunar regolith, some neutrons are emitted to the lunar surface, and some neutrons terminate in the lunar regolith. At this time, the neutron transport ends, forming an end track record and transmitting it to the current event record set; Obtaining the neutron energy and the maximum neutron history depth that are emitted to the lunar surface according to all the information in the current event record set; Repeating the particle transport process based on the particle transport model until all the particles with all energies and all types in the high-energy particle spectrum are transported; Counting the number of neutrons in different neutron energy ranges and different maximum neutron history depth ranges according to the neutron energy and the maximum neutron history depth, and then determining the differential neutron energy spectrum on the lunar surface, and statistically obtaining the lunar regolith depth from which the neutrons with different energies on the lunar surface originate according to the high-energy particle spectrum.

2. The method according to claim 1, wherein The particle transport model includes a lunar regolith structure model, an initial particle source emission surface model, and a neutron collector model, and the emission surfaces and receiving surfaces of the three are parallel; The lunar regolith structure model includes: the density and distribution of the lunar regolith, the composition, whether it contains water and the water distribution, as well as the shape and size of the lunar regolith; The initial particle source emission surface model, based on the high-energy particle spectrum, emits particles from the emission point towards the lunar regolith structure model, and the emission direction is vertically downward towards the lunar regolith structure model, and the emission angle is determined by a cosine distribution; The neutron collector model is a virtual cylinder for counting the emitted neutrons.

3. The method according to claim 2, wherein The generating of the weights of the initial particles emitted towards the lunar regolith structure model according to the high-energy particle spectrum specifically includes: determining that the particle type is T0, the particle energy is E0, the number of emitted particles is N0, and the angle is determined by a cosine distribution; According to the spatial high-energy particle differential spectrum f(T0, E0), the weight W of the initial particles is: Among them, the unit of the particle energy E0 is MeV / u; ΔE is the energy interval where E0 is located, and the unit is MeV; S 空间初始粒子源发射面 is the area of the emission surface of the initial particle source in space, and the unit is cm 2 .

4. The method according to claim 3, wherein After the initial particles enter the lunar regolith structure model, they interact with the lunar regolith to generate secondary particles including neutrons. The interaction and movement process of the initial particles and all their secondary particles in the lunar regolith constitute 1 event, the movement process of each secondary particle in the lunar regolith forms 1 track, and the weight of each secondary particle and its track is the same as the weight W of the initial particles.

5. The method according to claim 4, wherein Forming an initial track record before the neutrons start to be transported, and the neutron initial track record is as follows: D 当前径迹 = 本代径迹_当前径迹 , ID 父代径迹_当前径迹 , E 粒子能量_当前径迹 , P 产生深度_当前径迹 , P 父代历史最大深度_当前径迹 , P 历史最大深度_当前径迹 , W(T0, E0, N0)] Where: ID 本代径迹_当前径迹 is the track number of this generation, ID 父代径迹_当前径迹 is the track number of the parent generation, E 粒子能量_当前径迹 is the particle energy, P 产生深度_当前径迹 is the production depth, P 父代最大历史深度_当前径迹 is the maximum historical depth variable of the parent generation, P 历史最大深度_当前径迹 is the maximum historical depth variable, and W(T0, E0, N0) is the initial particle weight.

6. The method according to claim 5, wherein Transmitting the current initial track record to the event record set, specifically including: The event record set is a set containing n track records, and each track record contains parameters: the current generation track number, the parent track number, the particle energy, the generation depth, the parent maximum history depth variable, the history maximum depth variable, and the initial particle weight. When the parent track number in the initial track record is the same as the progeny track number of the k-th record in the current event record set, update the progeny track number and the parent track number of the k-th record in the event record set to the progeny track number and the parent track number of the current track, respectively; When the parent track number in the initial track record is different from both the progeny track numbers and the parent track numbers of all records in the event record set, add the initial track record to the event record set; When the parent track number in the initial track record is different from the progeny track numbers of all records in the event record set but is the same as the parent track number of the m-th record in the event record set, update both the maximum historical depth of the parent generation and the maximum historical depth of the current track to the maximum historical depth of the parent generation of the m-th record, and add the current track record to the event record set.

7. The method according to claim 6, characterized in that, The neutron track is transported step by step and interacts with the lunar regolith. Update the current step record according to the property changes of neutrons caused by this interaction, specifically including: The current step record includes: D 当前步 = [E 粒子能量_当前步 , P 历史最大深度_当前步 , B 经过收集体标志_当前步 , B 生存标志_当前步 , N 次级中子数目_当前步 ​ Among them, E 粒子能量_当前步 is the particle energy at the current step; P 历史最大深度_当前步 is the maximum historical depth at the current step; B 经过收集体标志_当前步 is the collection body flag passed at the current step; B 生存标志_当前步 is the survival status flag at the current step; N 次级中子数目_当前步 is the number of secondary particles at the current step; According to the transport process, the step record is updated as follows: E 粒子能量_当前步 = E 当前粒子能量 where E 当前粒子能量 is the current energy of the particle, and P 当前深度 is the current depth of the particle.

8. The method according to claim 7, wherein The neutrons perform elastic collision motion in the lunar regolith structure model. Some neutrons are emitted to the lunar surface, and some neutrons terminate in the lunar regolith. At this time, the neutron transport ends, forming an end track record, and passing the end track record to the current event record set, specifically including: The processing methods for step records in various situations are as follows: When a neutron is emitted outside the lunar regolith structure model and the neutron does not pass through the neutron collector model, delete the current track record in the current event record set; When a neutron is emitted outside the lunar regolith structure model and the neutron passes through the neutron collector, update the maximum historical depth of the track record of this neutron in the current event record set to the maximum historical depth of the current step, and update the particle energy to the particle energy of the current step; When a neutron terminates in the lunar regolith and the neutron is absorbed and disappears, delete the current track record in the current event record set; When a neutron terminates in the lunar regolith and the neutron disappears through inelastic collision but generates secondary neutrons that continue to move in the lunar regolith, update the track record of this neutron in the current event record set, including updating the maximum historical depth of the parent generation to the current maximum historical depth of the parent generation and updating the maximum historical depth to the current maximum historical depth.

9. The method according to claim 8, wherein The method for counting the number of neutrons in different neutron energy ranges and different maximum historical depth ranges of neutrons according to neutron energy and the maximum historical depth of neutrons is as follows: ΔF(E i ~E j ,P m ~P n ) = ∑W(T0, E0, N0) × η(E i ~E j ,P m ~P n ) where ΔF(E i ~E j ,P m ~P n ) is the neutron flux in the star catalog within the energy range [E i ,E j and within the historical maximum depth range [P i ,P j , with the unit of cm -2 ·s -1 ; E i and E j are the upper and lower limits of the neutron energy range [E i ,E j , with the unit of MeV; P i and P j are the upper and lower limits of the neutron historical maximum depth range [P i ,P j , with the unit of mm; η(E i ~E j ,P m ~P n ) is the selection factor when counting neutron information according to neutron energy and historical maximum depth.

10. The method according to claim 9, wherein The determination of the neutron differential energy spectrum on the lunar surface includes: where F is the neutron differential energy spectrum of the lunar surface, with the unit of cm -2 ·MeV -1 ·s -1 ; Obtain the lunar regolith depth from which neutrons of different energies on the lunar surface originate according to the high-energy particle spectrum statistics.

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