Test method for accurate detection of trace water in lunar soil under coupling of equivalent vacuum and ultralow temperature

Abstract

The invention relates to a lunar soil trace water accurate detection test method under equivalent vacuum and ultralow temperature coupling, and belongs to the technical field of extraterrestrial celestial body sampling detection. Aiming at the technical bottleneck that the existing lunar soil trace water detection technology in the earth environment is interfered by water vapor, the method comprises the following steps: placing lunar soil in a sample cabin in a nuclear magnetic probe; the temperature of the sample cabin is adjusted through liquid nitrogen refrigeration, and the ultralow-temperature lunar environment is simulated; the humidity condition of the sample cabin is adjusted, and lunar soil nuclear magnetic semaphores under different humidity are collected; establishing a relation curve of different humidity and nuclear magnetic signal increments; when the semaphore is different, deducting signal increment caused by environment humidity by taking a nuclear magnetic signal of unit humidity under a steady-state condition as a reference to obtain nuclear magnetic signal data under an equivalent vacuum environment; and inverting the semaphore under the equivalent vacuum to obtain the lunar soil water content. Compared with the prior art, the method has the advantages that the key technical problem in extraterrestrial sample earth environment detection is solved, and an important means is provided for moon water resource detection and sampling return sample analysis.

Description

Technical Field

[0001] The present invention relates to the technical field of extraterrestrial celestial body sampling and detection, and particularly relates to a precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature. Background Art

[0002] The lunar surface is under extreme space environmental conditions, and its environmental characteristics are essentially different from those of the Earth. Due to the lack of atmospheric protection, the lunar surface is directly exposed to cosmic space, resulting in an extreme fluctuation characteristic of the thermal environment. The highest temperature during the lunar day reaches 127°C, while the lowest temperature at night can drop to -183°C. Such drastic temperature fluctuations have a significant impact on the physical and chemical properties of lunar surface substances (such as soil). Through satellite remote sensing, lunar soil sampling and analysis, it can be inferred that the forms of water occurrence on the moon include structural water in mineral lattices and bound water on particle surfaces. Among them, the lunar soil samples collected by Chang'e-5 showed that the water content was less than 120 ppm (that is, about 120 grams of water in 1 ton of lunar soil). This indicates that there is trace water in lunar soil. However, there are two key challenges in detecting trace water in lunar soil in the Earth environment: First, the water content of the lunar soil sample itself is extremely low, and the air water vapor (humidity condition) in the Earth environment inevitably interacts with the sample, and this interference will seriously affect the repeatability and accuracy of the experimental results; Second, the traditional water content test methods (such as time domain reflectometry, differential scanning calorimetry, etc.) have obvious limitations: the measurement error is large, and the heat generated during the test may interfere with the test results. In contrast, the low-field nuclear magnetic resonance technology has significant advantages: this method does not require destroying the sample, can maximize the preservation of the original state of the soil sample, and can accurately obtain the true data of the water content in lunar soil under different temperature and humidity conditions. However, existing equipment for testing trace water in lunar soil, such as low-field nuclear magnetic resonance, is often distributed in different humidity regions. For example, when detecting the water content in lunar soil in Shanghai, the air humidity is relatively high, while when conducting tests in the northwest region, the air humidity is relatively low. And due to the vacuum environment of the moon, most tests also need to rely on professional equipment of the aerospace institute to carry out tests. This not only greatly increases the research cost but also raises the technical threshold of the research. In order to give full play to the versatility of the low-field nuclear magnetic resonance moisture detection instrument, there is an urgent need to propose a precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature. Summary of the Invention

[0003] The objective of the present invention is to propose a test method that can overcome environmental interference and achieve precise detection of trace water in lunar soil, so as to solve the problem of the influence of water vapor in the Earth's environment on the detection results. The core innovation of this method lies in the first proposal of the concept of "equivalent vacuum" - this system does not preset a fixed vacuum degree threshold, but realizes the intelligent discrimination of the test environment by establishing a dynamic correlation between the humidity gradient and the increment of nuclear magnetic resonance (NMR) signals: when the increment of NMR signals under specific humidity conditions approaches zero, it is determined that the current environment reaches the equivalent vacuum state, and the in-situ inversion analysis of the water content in lunar soil can be directly carried out; if there is a significant signal shift, the environmental moisture interference is deducted through a humidity compensation algorithm, and finally precise detection data of trace water equivalent to the lunar surface conditions are obtained. It breaks through the dependence on traditional mechanical vacuum pumping or high-precision and sophisticated equipment in spaceflight, but relies on relatively common low-field NMR moisture detection instruments.

[0004] The relative characteristic of the "equivalent vacuum" concept is reflected in its environmental adaptation mechanism: under the conditions of an Earth laboratory, if the NMR response characteristics of lunar soil samples in different humidity regions (such as the arid region in northern China and the humid region in southern China) show a high degree of consistency, it indicates that the humidity fluctuation in the Earth's environment has not caused substantial interference to the test results, and at this time the test environment can be regarded as equivalent vacuum. On the contrary, when cross-regional signal differences are detected, identify the reference humidity conditions corresponding to the signal stability threshold, and calculate the signal correction amount under different humidity gradients. Finally, correct the measured data in the Earth's environment to the equivalent vacuum reference to ensure the comparability of the lunar soil moisture content measurement results with the in-situ measurement values on the moon.

[0005] To achieve the above objective, the present invention proposes a precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature, including the following steps: S1: Place the lunar soil in the sample chamber inside the NMR probe; S2: Adjust the temperature of the sample chamber through liquid nitrogen refrigeration to simulate the ultra-low temperature environment on the lunar surface; S3: Adjust the humidity conditions of the sample chamber and collect the NMR signal amounts of lunar soil under different humidity conditions; S4: Establish a quantitative relationship curve between different humidity gradients and the increment of NMR signals; S5: When there are differences in the increment of NMR signals, based on the NMR signal per unit humidity under steady-state conditions, deduct the signal increment caused by environmental humidity to obtain the NMR signal data in the equivalent vacuum environment; S6: Invert and calculate the trace water content of the lunar soil sample according to the NMR signal data in the true equivalent vacuum environment.

[0006] Further, in step S1, the lunar soil sample is selected from real lunar soil or a lunar soil simulant that meets the standards. The materials of the lunar soil simulant include at least one of volcanic ash, basalt, and ilmenite; the sample chamber is made of a fluorine-free material, including polyether ether ketone (PEEK) or polyimide. The sample chamber is cylindrical in shape, with a diameter of 5 mm and a height of 20 mm, geometrically matching the NMR probe.

[0007] Further, in step S2, the temperature of the sample chamber is reduced to the target temperature of -183 °C by liquid nitrogen refrigeration to freeze the temperature of the lunar soil body, so as to simulate the ultra-low temperature environment on the moon; the lowest temperature of the liquid nitrogen refrigeration is -193 °C, so as to simulate the real temperature experienced by the lunar soil (-183 °C, the temperature at night on the moon); it is judged whether the soil body reaches the target temperature according to the reading of the temperature sensor in the middle of the soil body in the sample chamber.

[0008] Further, in step S2, the liquid nitrogen refrigeration realizes precise temperature control through the PID temperature control algorithm, with a temperature control accuracy of ±0.1 °C, and thermocouples are arranged every 1 cm along the axial direction of the sample chamber for temperature monitoring to ensure that the overall temperature of the sample uniformly reaches the target value.

[0009] Further, in step S3, the humidity adjustment adopts the staged pressure reduction method. Using a humidity regulator, with 10%RH as the gradient unit, the humidity in the chamber is gradually reduced from 100%RH to 0%RH, and a humidity meter is used to obtain the real humidity conditions; combined with a molecular pump group, the pressure in the chamber is gradually reduced from atmospheric pressure to the order of 10-3 Pa; the NMR signal quantity includes the overall T2 spectrum and the layered T2 spectrum of the lunar soil sample under ultra-low temperature conditions, which are collected in real time by a low-field nuclear magnetic resonance device using the CPMG sequence.

[0010] Further, in step S3, the T2 spectrum and the layered T2 spectrum of the lunar soil sample under ultra-low temperature conditions at different humidity conditions are collected in real time by a low-field nuclear magnetic resonance device. The specific method for collecting the lunar soil NMR signal quantity under different humidity conditions is: fixing the temperature of the lunar soil sample at a constant -183 °C, and collecting the overall T2 spectrum and the layered T2 spectrum of the sample under different humidity conditions (from 0%RH to 100%RH) at this temperature; the overall T2 spectrum and the layered T2 spectrum respectively refer to the overall T2 spectrum of the soil sample and the layered T2 spectrum at different heights of the soil sample.

[0011] Further, in step S4, the quantitative relationship curve is established through a controllable humidity experiment from 0% RH to 100% RH, which is used to calibrate the interference of water vapor in the Earth's environment on the nuclear magnetic detection signal. This curve is obtained under the coupled environment of equivalent vacuum and ultra-low temperature, which truly matches the actual environment of lunar soil. If the slope of the curve is zero (i.e., the increment of the nuclear magnetic signal does not change with humidity), it indicates that the lunar soil sample has the characteristic of completely blocking water vapor adsorption, that is, the humidity condition does not affect the detection of trace water in the lunar soil sample. At this time, the nuclear magnetic signal directly reflects the true water content, and the water content is directly inverted from the nuclear magnetic signal amount. If the curve is linear or non-linear, it means that water vapor is adsorbed / absorbed by the lunar soil, resulting in the detection signal containing the contribution of additional moisture in the environmental humidity. At this time, the environmental humidity interference is eliminated by the reference subtraction method.

[0012] Further, the reference subtraction method specifically measures the increment of the nuclear magnetic signal of the lunar soil in adjacent humidity intervals with equal gradients through low-field nuclear magnetic resonance experiments in the reference humidity range. If the signal increment in adjacent humidity intervals is the same, at this time, the increment of the nuclear magnetic signal strictly corresponds to the amount of water vapor adsorption caused by humidity change. By calculation, the nuclear magnetic signal amount per unit humidity is obtained, and then the nuclear magnetic signal amounts under other humidity conditions are subtracted by the signal increment corresponding to the unit humidity, and the true nuclear magnetic signal data under the equivalent vacuum environment is obtained, which is the net signal amount of the inherent moisture of the lunar soil sample.

[0013] Further, in step S5, the steady state means that during the adjustment process of adjacent humidity intervals with equal gradients, when the relative deviation of the nuclear magnetic signal caused by three consecutive humidity changes ≤ 0.1%, it is considered that the system reaches a stable state. At this time, the increment of the nuclear magnetic signal strictly corresponds to the amount of water vapor adsorption caused by humidity change, and the water content of the lunar soil body remains constant. In the stable state, the increment of the nuclear magnetic signal and the humidity difference show a linear relationship with equal gradients. When determining the increment of the nuclear magnetic signal corresponding to a certain humidity range, the nuclear magnetic signal amounts under other humidity conditions are subtracted by the signal increment caused by the environmental humidity, and the true nuclear magnetic signal data under the equivalent vacuum environment is obtained.

[0014] Further, step S6 is specifically as follows: Normalize the nuclear magnetic signal data under the true equivalent vacuum environment to obtain the nuclear magnetic signal amount of the lunar soil sample per unit mass under the equivalent vacuum environment. Using a standard sample, pre-calibrate the water content corresponding to the unit nuclear magnetic signal amount of the nuclear magnetic resonance equipment and record it as the calibration coefficient. Based on the nuclear magnetic signal amount per unit mass of the lunar soil and the calibration coefficient, inversely analyze to obtain the trace water content corresponding to the lunar soil sample per unit mass, realizing high-precision quantitative analysis of the trace water content of the lunar soil sample.

[0015] Further, the inversion calculation formula for the trace water content of the lunar soil sample is: ; In the formula, w 1 is the water content of the lunar soil sample; w 0 is the water content corresponding to the unit signal quantity collected by the used nuclear magnetic resonance equipment; is the unit signal quantity collected by the used nuclear magnetic resonance equipment; F 1 is the nuclear magnetic signal quantity corresponding to the unit mass of the lunar soil.

[0016] Based on the data collected under ultra-low temperature and equivalent vacuum environment, the present invention establishes a relationship curve between different humidity and the increment of nuclear magnetic signal, scientifically evaluates the influence degree of environmental humidity on the detection of trace water in lunar soil, and obtains the nuclear magnetic signal data under equivalent vacuum environment by deducting the signal increment caused by environmental humidity. Using the water content corresponding to the unit signal quantity of different nuclear magnetic resonance equipment itself, the nuclear magnetic signal data collected under the true equivalent vacuum environment is solved and further inverted to obtain the trace water content of lunar soil, which not only provides important technical support for future human lunar immigration and deep space base construction, but also lays a key guarantee for the exploration and development of extraterrestrial celestial body resources.

[0017] Compared with the prior art, the advantages of the present invention are as follows: 1. Through extreme environment simulation, dynamic signal calibration, precise interference stripping and high-precision inversion model, the present invention realizes the interference-free and high-precision detection of trace water in lunar soil for the first time in an earth laboratory, solves the two major problems of "uncontrollable earth environment interference" and "insufficient detection accuracy" that have long troubled the industry, and provides key technical support for lunar resource development and deep space exploration.

[0018] 2. The present invention accurately reproduces the extreme environment of ultra-low temperature and equivalent vacuum on the moon in the laboratory, solves the problem of earth environment interference that cannot be avoided in traditional detection, combines the dynamic humidity gradient experimental design, systematically calibrates the quantitative relationship between humidity and the increment of nuclear magnetic signal, quantifies the influence of earth environmental humidity on the detection result, and provides necessary environmental conditions for subsequent interference elimination and precise detection.

[0019] 3. The present invention adopts the reference deduction method, takes the nuclear magnetic signal of unit humidity under steady state conditions as the reference, gradually strips the signal increment caused by environmental humidity, realizes the complete elimination of the interference of earth water vapor for the first time, combines the nuclear magnetic signal acquisition technology under ultra-low temperature, significantly improves the sensitivity and spatial resolution of the detection of trace water in lunar soil, effectively solves the technical problem that it is difficult to distinguish the humidity interference of the earth environment from the precise detection and characterization of trace water in lunar soil in the prior art, and provides reliable technical support and scientific basis for the evaluation of lunar water resource distribution, the analysis of sampling return samples and the construction of manned lunar bases.

[0020] 4. The present invention does not rely on special aerospace equipment, has compatibility with general-purpose equipment, can achieve standardized detection in different regions, and greatly reduces costs.

[0021] 5. In the process of calculating trace water in lunar soil, the present invention adopts a pre-calibration technique to pre-calibrate the calibration coefficient between the nuclear magnetic signal quantity and the water content through standard samples, solving the compatibility problem of signal quantity differences between different devices; combined with the inversion calculation formula model, the complex signal data is converted into an intuitive water content value, simplifying the process of quantitative analysis of trace water.

[0022] 6. The method of the present invention organically combines cross-field technologies such as nuclear magnetic resonance technology, liquid nitrogen refrigeration, vacuum control, and dynamic humidity control to form a systematic solution, providing a general method framework for the detection of extraterrestrial celestial body resources. This method is not only applicable to lunar soil, but also can be extended to the detection of trace water in other extraterrestrial samples such as Mars and asteroids, and has broad application prospects in deep space exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic flow chart of a method for accurately detecting trace water in lunar soil under an equivalent vacuum and ultra-low temperature coupling environment provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of a relationship curve in which the nuclear magnetic signal increment does not change with humidity (slope is zero) in an embodiment of the present invention; Figure 3 It is a schematic diagram of a relationship curve in which the nuclear magnetic signal increment changes linearly with humidity in an embodiment of the present invention; Figure 4 It is a schematic diagram of a relationship curve in which the nuclear magnetic signal increment changes non-linearly with humidity in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0025] This embodiment proposes a method for accurately detecting trace water in lunar soil under an equivalent vacuum and ultra-low temperature coupling environment, as Figure 1 shown, the method includes the following steps: S1: Place the lunar soil in the sample chamber of the nuclear magnetic probe; In this embodiment, referring to the provisions of the "Standard for Geotechnical Test Methods" (GBT 50123-2019), the lunar soil samples are selected from real lunar soil or standard-compliant lunar soil simulants (JSC-1A or CAS-1, earth materials for simulating lunar soil), and the materials of the lunar soil simulants include at least one of volcanic ash, basalt, and ilmenite; Among them, JSC-1A is a lunar regolith simulant developed by NASA's Johnson Space Center. It is processed from volcanic ash in Arizona, USA, and is similar to the lunar mare basalt soil brought back by the Apollo missions. Its composition (vitreous particles, plagioclase, etc.) and particle characteristics (particle size range 0.01–1000 μm, average about 100 μm, similar to lunar fine particle dust) can highly simulate real lunar regolith.

[0026] CAS-1 is a low-titanium basalt lunar regolith simulation material developed by the Chinese Academy of Sciences. The raw material is from the basalt of the Changbai Mountain volcanic group in Jilin Province, China. Its mineral composition highly coincides with that of the low-titanium lunar mare regolith obtained by the Apollo missions (including minerals such as plagioclase, pyroxene, and olivine), and its particle size is similar to that of JSC-1A.

[0027] In addition, the sample chamber is precisely processed from polyetheretherketone (PEEK) or polyimide materials. The shape of the sample chamber is designed as a cylinder with a diameter of 5 mm and a height of 20 mm, geometrically matching the NMR probe. The sample chamber body is a hollow structure, and the central area of the chamber is the sample area. The soil sample is loaded through a polytetrafluoroethylene mold (cylindrical), and the area outside the mold is empty for circulating liquid to reduce the temperature of the soil sample. The working temperature range of the cylindrical sample chamber is -269°C to 200°C. The prepared sample is placed in the sample chamber, and then the sample chamber is placed in the NMR probe.

[0028] S2: Adjust the temperature of the sample chamber through liquid nitrogen refrigeration to simulate the ultra-low temperature environment on the lunar surface; In this embodiment, the liquid nitrogen freezing controller is connected to both sides of the sample chamber through the inlet and outlet pipelines, and the liquid nitrogen refrigeration system (cold end) and the resistance heating system (hot end) are connected and started to pre-cool to the target temperature (-183°C). Determine whether the soil body in the sample chamber reaches the target temperature according to the reading of the temperature sensor in the middle of the lunar regolith soil body. Set the PID temperature control algorithm to ensure the temperature control accuracy of ±0.1°C. Calibrate the thermocouple (type T or K, accuracy ±0.05°C) to ensure data reliability. Start the anti-frosting system to prevent frosting at the cold end from affecting temperature control. Enter the target temperature of -183°C in the control software, select the linear gradient mode, the system automatically calculates the heat flux distribution, and cooperatively regulates through the liquid nitrogen cold source (cold end) and the ceramic heating sheet (hot end) in the liquid nitrogen freezing controller. A thermocouple is arranged every 1 cm along the axial direction of the sample chamber (a total of N, depending on the sample length), fixed on the sample surface or embedded in the chamber wall. Use a standard temperature source (such as a platinum resistance thermometer) to in-situ calibrate all thermocouples to ensure data consistency. When the temperature stabilizes at -183°C, it is considered that the ultra-low temperature environment has been created.

[0029] S3: Adjust the humidity condition of the sample chamber and collect the lunar regolith NMR signal quantity under different humidity conditions; In this embodiment, a humidity meter is used to obtain the real humidity condition, and the humidity is adjusted by the staged pressure reduction method. The specific method is as follows: 1) Connect the high-precision humidity regulator to the sample chamber through a sealed interface to ensure the airtightness of the system; then set the initial humidity in the sample chamber to 100%RH (relative humidity) to simulate the Earth's atmospheric environment; adopt the staged pressure reduction method, with 10%RH as the gradient unit, gradually reduce the humidity in the chamber. When the humidity drops below 10%RH, switch to the molecular pump group and gradually reduce the pressure in the chamber from atmospheric pressure (101.325 kPa) to the order of 10-3 Pa; during this process, record the change curves of the humidity (accuracy ±0.1%RH) and pressure (accuracy ±0.1 Pa) in the chamber in real time.

[0030] 2) Turn on the low-field nuclear magnetic resonance instrument, preheat the magnet to a stable state, load the special probe for lunar soil samples, select the CPMG sequence, adjust nuclear magnetic parameters such as the 90° and 180° pulse widths and amplitudes, echo time, number of echoes, number and thickness of slice layers, etc., and use the low-field nuclear magnetic resonance instrument to collect the overall T2 spectrum and layered T2 spectrum of lunar soil samples at different humidities under normal temperature and ultra-low temperature conditions. Among them, the layered thickness can be determined according to the equipment accuracy and research requirements. Specifically: according to the spatial resolution of the nuclear magnetic resonance instrument (usually 0.1~1 mm), ensure that the layered thickness ≥ the minimum resolvable scale (such as 3 mm). In order to capture the moisture gradient change, a layered thickness of 5-10 mm (capturing the moisture gradient change) can be preferably recommended. In order to focus on analyzing the change of the solid-liquid interface effect, a thin layer of 3-5 mm can be preferably selected. The layered position is symmetrically layered (such as ±10 mm, ±20 mm) based on the central plane of the probe. Or determine the high signal gradient area through pre-scanning and encrypt the layering (such as at intervals of 3 mm).

[0031] 3) Open the nuclear magnetic resonance imaging software, adjust parameters such as resonance frequency, sampling bandwidth, echo position, etc., and collect nuclear magnetic resonance images of lunar soil samples under different humidities under normal temperature and ultra-low temperature conditions in different directions (XYZ).

[0032] S4: Establish a quantitative relationship curve between different humidity gradients and the increment of nuclear magnetic signals; In this embodiment, a quantitative relationship curve between the increment of nuclear magnetic signals and humidity is established through a controllable humidity experiment (0%RH~100%RH gradient) to calibrate the interference of water vapor in the Earth environment on the detection signal. This curve is obtained in an equivalent vacuum and ultra-low temperature coupling environment and can truly match the actual environment of lunar soil. If the increment of nuclear magnetic signals does not change with humidity (the slope is zero), as Figure 2 shown, it indicates that the lunar soil sample has the characteristic of completely blocking water vapor adsorption, that is, the humidity condition does not affect the detection of trace water in the lunar soil sample. At this time, the nuclear magnetic signal directly reflects the true moisture content, and the moisture content is directly inverted from this nuclear magnetic signal amount.

[0033] S5: When the nuclear magnetic signal response shows humidity dependence, a dynamic reference correction strategy is adopted: taking the nuclear magnetic response amount per unit humidity change under steady-state conditions as the reference, subtracting the signal increment caused by environmental humidity, so as to decouple the intrinsic nuclear magnetic signal of trace water in lunar soil under an equivalent vacuum environment; Among them, the steady-state condition means that during the adjustment process in adjacent humidity intervals with equal gradients, when the relative deviation of the nuclear magnetic signal caused by three consecutive humidity changes ≤ 0.1%, it is considered that the system reaches a stable state. At this time, the nuclear magnetic signal increment strictly corresponds to the water vapor adsorption amount caused by humidity change, and the water content of the lunar soil body remains constant. Under the stable state, the nuclear magnetic signal increment has a linear relationship with the humidity difference (equal gradient change). When determining the nuclear magnetic signal increment corresponding to a certain humidity range, subtracting the signal increment caused by environmental humidity from the nuclear magnetic signal amounts under other humidity conditions will obtain the true nuclear magnetic signal data under an equivalent vacuum environment.

[0034] In this embodiment, as Figure 3 and Figure 4 shown, when the magnetic signal increment changes linearly or non-linearly with humidity, it indicates that water vapor is adsorbed / absorbed by the lunar soil, resulting in the detection signal containing the contribution of moisture in the additional earth environment. At this time, it is necessary to eliminate the interference of environmental humidity through the reference subtraction method and subtract the water vapor entering the soil.

[0035] The specific method of this reference subtraction method is as follows: 1) Calibrate the reference increment Under the reference humidity range, measure the nuclear magnetic signal increment of lunar soil through low-field nuclear magnetic resonance experiments . For example: if the signal increases when the humidity rises from 10% to 20% .

[0036] Verification in other humidity ranges: In the range of 20% → 30%, the signal increment is still . Then the signal amount corresponding to unit humidity (1%) is / 10. If the measured increment deviates from , it is necessary to check the system error, first check the system drift (temperature / magnetic field stability), then verify the sample homogeneity, and if necessary, expand the calibration humidity range to reconstruct the response model.

[0037] 2) Subtract the influence of air water vapor Record the nuclear magnetic signals at each humidity point (such as 15%, 25%) as (measured value). According to the calibrated signal amount per unit humidity ( / 10%), calculate the signal of trace water in lunar soil corresponding to the current humidity. The formula for subtracting the nuclear magnetic signal of water vapor in the air is: = - (current humidity × / 10).

[0038] Example: = 1000, the nuclear magnetic resonance signal amount corresponding to 1% humidity is 100, the nuclear magnetic resonance signal amount at 25% humidity is 4000, and the lunar soil trace water signal = 4000 - (25 * 100) = 1500.

[0039] When the humidity drops to the equivalent vacuum condition (the relative deviation of the nuclear magnetic resonance signal caused by three consecutive humidity changes ≤ 0.1%, deducting the difference in the unit nuclear magnetic resonance signal of water vapor in the air), the true nuclear magnetic resonance signal data in the equivalent vacuum environment can be obtained. This remaining signal is the net nuclear magnetic resonance signal of the inherent water content characteristics of the lunar soil sample, realizing the accurate detection of the trace water in the lunar soil sample itself.

[0040] S6: Invert and calculate the trace water content of the lunar soil sample according to the nuclear magnetic resonance signal data in the true equivalent vacuum environment.

[0041] In this embodiment, the specific operations are as follows: 1) Normalize the nuclear magnetic resonance signal data in the true equivalent vacuum environment obtained through the above steps to obtain the nuclear magnetic resonance signal amount of the lunar soil sample per unit mass in the equivalent vacuum environment; 2) Use a standard sample with a known water content (such as pure water or water-containing minerals) to pre-calibrate the water content corresponding to the unit nuclear magnetic resonance signal amount of the nuclear magnetic resonance equipment, and record it as the calibration coefficient; For example: When calibrating with pure water, the nuclear magnetic resonance signal amount corresponding to 100% water content (1 g of water / g of sample) is 1000, then the water content corresponding to the unit signal amount 1 is 0.1% (i.e., the calibration coefficient k = 0.1% / unit signal); 3) Based on the nuclear magnetic resonance signal amount per unit mass of the lunar soil and the calibration coefficient, inversely analyze to obtain the trace water content corresponding to the lunar soil sample per unit mass, realizing the high-precision quantitative analysis of the trace water content of the lunar soil sample.

[0042] The inversion calculation formula for the trace water content of the lunar soil sample is: ; In the formula, w 1 is the water content of the lunar soil sample; w 0 is the water content corresponding to the unit signal amount collected by the used nuclear magnetic resonance equipment; is the unit signal amount collected by the used nuclear magnetic resonance equipment; F 1 is the nuclear magnetic resonance signal amount per unit mass of the lunar soil.

[0043] In this embodiment, when the nuclear magnetic resonance signal amount of the lunar soil sample is 50, then the water content of the lunar soil sample .

[0044] Through the method of this embodiment, the interference-free and high-precision detection of trace water in lunar soil has been successfully achieved in the Earth laboratory.

[0045] The above are only the preferred embodiments of the present invention and do not impose any limitation on the present invention. Any person skilled in the art within the technical field, without departing from the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed by the present invention, which are all within the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature, characterized in that, It includes the following steps: S1: Place the lunar soil in the sample chamber inside the nuclear magnetic probe; S2: Adjust the temperature of the sample chamber through liquid nitrogen refrigeration to simulate the ultra-low temperature environment on the lunar surface; S3: Adjust the humidity condition of the sample chamber and collect the nuclear magnetic signal quantity of the lunar soil under different humidity conditions; S4: Establish a quantitative relationship curve between different humidity gradients and the nuclear magnetic signal increment; S5: When there are differences in the nuclear magnetic signal increment, based on the nuclear magnetic signal per unit humidity under steady-state conditions, deduct the signal increment caused by environmental humidity to obtain the nuclear magnetic signal data under an equivalent vacuum environment; S6: According to the nuclear magnetic signal data under the true equivalent vacuum environment and combined with the pre-calibrated calibration coefficient of the nuclear magnetic signal quantity and water content, inversely calculate the trace water content of the lunar soil sample.

2. The precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature according to claim 1, characterized in that, In step S1, the lunar soil sample is selected from real lunar soil or lunar soil simulants that meet the standards. The materials of the lunar soil simulants include at least one of volcanic ash, basalt, and ilmenite. The sample chamber is made of fluorine-free materials, including polyether ether ketone (PEEK) or polyimide. The shape of the sample chamber is cylindrical, with a diameter of 5 mm and a height of 20 mm, geometrically matching the nuclear magnetic probe.

3. The precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature according to claim 1, wherein In step S2, the temperature of the sample chamber is reduced to the target temperature of -183 °C through liquid nitrogen refrigeration to freeze the soil body temperature to simulate the ultra-low temperature environment on the moon. Determine whether the soil body reaches the target temperature according to the reading of the temperature sensor in the middle of the soil body in the sample chamber.

4. The precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature according to claim 1, wherein In step S2, the liquid nitrogen refrigeration realizes precise temperature control through the PID temperature control algorithm, with a temperature control accuracy of ±0.1 °C. Thermocouples are arranged every 1 cm along the axial direction of the sample chamber for temperature monitoring to ensure that the overall temperature of the sample uniformly reaches the target value.

5. The precise detection test method for trace lunar water under the coupling of equivalent vacuum and ultra-low temperature according to claim 1, characterized in that, In step S3, the humidity is adjusted by the method of stepwise pressure reduction. Using a humidity regulator, with a gradient unit of 10%RH, the humidity in the chamber is gradually reduced from 100%RH to 0%RH; combined with a molecular pump set, the pressure in the chamber is gradually reduced from atmospheric pressure to the order of 10 -3 Pa; the nuclear magnetic signal quantity includes the overall T2 spectrum and the layered T2 spectrum of the lunar soil sample under ultra-low temperature conditions, which are collected in real time by a low-field nuclear magnetic resonance device using the CPMG sequence.

6. The precise detection test method for trace lunar water under the coupling of equivalent vacuum and ultra-low temperature according to claim 5, wherein In step S3, the specific method for collecting the nuclear magnetic signal quantity of the lunar soil under different humidity conditions is as follows: Fix the temperature of the lunar soil sample at a constant -183 °C, and collect the overall T2 spectrum and the layered T2 spectrum of the sample under different humidity conditions at this temperature. The overall T2 spectrum and the layered T2 spectrum respectively refer to the overall T2 spectrum of the soil sample and the layered T2 spectrum at different heights of the soil sample.

7. The precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature according to claim 1, characterized in that, In step S4, the quantitative relationship curve is established through a controllable humidity experiment from 0% RH to 100% RH to calibrate the interference of water vapor in the earth environment on the nuclear magnetic detection signal. If the slope of the curve is zero, directly inversely calculate the water content based on the nuclear magnetic signal quantity. If the curve is linear or non-linear, eliminate the environmental humidity interference through the reference deduction method.

8. The precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature according to claim 7, characterized in that The specific benchmark deduction method is as follows: in the benchmark humidity range, the nuclear magnetic signal increment of lunar soil in adjacent humidity intervals with equal gradients is measured through low-field nuclear magnetic resonance experiments. ; If the signal increments in adjacent humidity intervals are the same, at this time, the nuclear magnetic signal increment strictly corresponds to the water vapor adsorption amount caused by humidity changes. By calculation, the nuclear magnetic signal amount per unit humidity is obtained, and then the nuclear magnetic signal amount under other humidity conditions is deducted from the signal increment corresponding to the unit humidity, and the true nuclear magnetic signal data in an equivalent vacuum environment is obtained, which is the net signal amount of the inherent moisture of the lunar soil sample.

9. The precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature according to claim 1, wherein, In step S5, the steady-state condition means that during the adjustment process in adjacent humidity intervals with equal gradients, when the relative deviation of the nuclear magnetic signal caused by three consecutive humidity changes ≤ 0.1%, it is considered that the system reaches a stable state. At this time, the nuclear magnetic signal increment strictly corresponds to the water vapor adsorption amount caused by humidity changes, and the water content of the lunar soil body remains constant. Under the stable state, the nuclear magnetic signal increment and the humidity difference show a linear relationship with equal gradients. When determining the nuclear magnetic signal increment corresponding to a certain humidity range, deduct the signal increment caused by environmental humidity from the nuclear magnetic signal quantities under other humidity conditions to obtain the true nuclear magnetic signal data under an equivalent vacuum environment.

10. The precise detection test method for trace lunar soil water under the coupling of equivalent vacuum and ultra-low temperature according to claim 1, characterized in that Step S6 is specifically as follows: Normalize the nuclear magnetic resonance signal data in the true equivalent vacuum environment to obtain the nuclear magnetic resonance signal amount of the lunar soil sample per unit mass in the equivalent vacuum environment; Using a standard sample, pre-calibrate the water content corresponding to the nuclear magnetic resonance signal amount per unit of the nuclear magnetic resonance equipment, and record it as the calibration coefficient; Based on the nuclear magnetic resonance signal amount per unit mass of the lunar soil and the calibration coefficient, inversely analyze to obtain the trace water content corresponding to the lunar soil sample per unit mass.

11. The precise detection test method for trace water in lunar soil under the coupling of equivalent vacuum and ultra-low temperature according to claim 10, characterized in that, The inversion calculation formula for the trace water content of the lunar soil sample is: ； Wherein, w 1 is the water content of the lunar soil sample; w 0 is the water content corresponding to the unit signal quantity collected by the used nuclear magnetic resonance equipment, i.e., the calibration coefficient; is the unit signal quantity collected by the used nuclear magnetic resonance equipment; F 1 is the nuclear magnetic signal quantity corresponding to the unit mass of the lunar soil.

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