Muon detector for measuring soil moisture

Abstract

The invention provides a muon detector for measuring soil moisture, and belongs to the technical field of testing by utilizing wave or particle radiation. The muon detector comprises a tubular scintillator which is used for detecting muons in cosmic rays and emitting scintillation light, and at least two outer optical fibers which are equal in screw pitch and used for collecting and transmitting the scintillation light are spirally wound on the periphery of the tubular scintillator. At least two inner optical fibers which are equal in screw pitch and used for collecting and transmitting scintillation light are spirally arranged on the inner circumference of the tubular scintillator, and the rotation direction of each inner optical fiber is opposite to that of each outer optical fiber, so that the tubular scintillator is divided into a plurality of latticed detection units in the internal and external directions. Compared with the prior art, the latticed detection unit is smaller, the existing scintillation light signal can only be acquired by the outer optical fiber, the scintillation light signal can also be acquired by the inner optical fiber, the optical fiber closer to the optical fiber can be acquired by the optical fiber, and the inner optical fiber and the outer optical fiber form an acquisition network, so that the detection precision is higher.

Description

Technical Field

[0001] The invention relates to a muon detector for measuring soil moisture, belonging to the technical field of testing using wave or particle radiation. Background Art

[0002] Soil moisture is a key state parameter in the soil-crop-atmosphere continuum, playing a crucial role in the exchange of moisture and energy in the soil surface. The spatiotemporal distribution and variability of soil moisture significantly influence the heat balance between land and atmosphere, atmospheric circulation, and soil temperature variations. This has significant implications for scientific research, including improving regional and even global climates and predicting dry and wet conditions. Traditional soil moisture measurement methods, such as oven drying and neutron metering, typically only provide information on soil moisture within a small, localized area. Muon measurement, however, can cover larger areas, typically several square meters or even larger. This is crucial for monitoring soil moisture across large farmland or regions, providing a more comprehensive understanding of soil moisture distribution.

[0003] High-energy particles in cosmic rays rub against the atmosphere to produce secondary cosmic rays, one type of which is cosmic ray muons. When these secondary particles enter Earth, some penetrate the surface and reach the ground, where their intensity is reduced by absorption by the soil. The soil's ability to absorb muons is closely related to its moisture content. The higher the moisture content, the greater the energy loss of the muons in the soil, and the more they are absorbed. Therefore, by measuring the number of muons reaching different depths underground, the soil's moisture content can be inferred. Furthermore, this technique does not require the use of any radioactive isotopes or other external radiation sources, making it harmless to the environment and humans. Currently, research in this field by domestic and international researchers is still in its early stages, primarily focusing on theoretical studies.

[0004] Chinese invention patent application publication number CN112697815A discloses a method for monitoring soil moisture using cosmic ray muons. This method involves placing a primary detector underground and a secondary detector on the soil surface. The method processes the measured data from the primary and secondary detectors and uses the established relationship between soil moisture and the counts from the underground primary detector to infer the soil moisture content. Both the primary and secondary detectors are muon detectors, but the specific structures of the muon detectors are not disclosed.

[0005] Referring to other types of particle detectors, such as the neutron detector disclosed in the Chinese utility model patent with authorization publication number CN204945390U, the neutron detector includes an outer scintillator and an inner scintillator in a tubular structure. Several wave-shifted optical fibers are spirally wound around the outer surface of the inner scintillator, and the outer scintillator is wrapped around the outer circumference of the wave-shifted optical fiber to form a tubular sandwich structure. The end faces of the wave-shifted optical fiber can be coupled to a photoelectric converter via a light-conducting material or air. When neutrons are incident on the detector, they undergo nuclear reactions with certain nuclides in the outer and inner scintillators, respectively. The secondary particles produced lose energy in the scintillator matrix, causing the scintillator matrix to generate scintillation light. The scintillation light is collected by the nearest wave-shifted optical fiber, and wavelength conversion and transmission are achieved within the wave-shifted optical fiber. It eventually reaches the photoelectric converter at the end of the wave-shifted optical fiber, which converts the received scintillation light signal into an electrical signal for output.

[0006] The above-mentioned wave-shifted optical fiber (i.e., optical fiber) is spirally wound on the outer surface of the inner scintillator and is sandwiched between the outer and inner scintillators. Since the lengths of the outer and inner scintillators are consistent and fixed, the pitch of a single optical fiber also determines its total length. In order to avoid excessive length and increased energy loss of light during optical fiber propagation, its pitch cannot be too small. The above-mentioned patent uses multiple optical fibers wound in parallel with equal spacing. However, the scintillation light is collected by the nearest optical fiber, and there is a distance between adjacent optical fibers. Therefore, even if the structure of the above-mentioned neutron detector is used for a muon detector, the detection accuracy is still low. Summary of the Invention

[0007] The object of the present invention is to provide a muon detector for measuring soil moisture, so as to solve the problem of low detection accuracy of existing detectors.

[0008] To achieve the above objectives, the muon detector for measuring soil moisture in the present invention adopts the following technical solutions: A muon detector for measuring soil moisture includes a tubular scintillator for detecting muons in cosmic rays and emitting scintillation light. The outer periphery of the tubular scintillator is spirally wound with at least two outer optical fibers with equal pitches for collecting and transmitting the scintillation light. The inner periphery of the tubular scintillator is spirally arranged with at least two inner optical fibers with equal pitches for collecting and transmitting the scintillation light. The handedness of each inner optical fiber is opposite to that of each outer optical fiber, so that the tubular scintillator is divided into a plurality of grid-shaped detection units in the inner and outer directions.

[0009] The beneficial effect of the above technical solution is that: the present invention is an improved invention, at least two inner optical fibers with equal pitch are spirally arranged on the inner circumference of the tubular scintillator for collecting and transmitting scintillation light, the rotation direction of each inner optical fiber is opposite to the rotation direction of each outer optical fiber, and the tubular scintillator is divided into multiple grid-shaped detection units in the inner and outer directions. Compared with the spiral detection units divided by multiple spirally wound optical fibers in the prior art, the grid-shaped detection units in the present invention are smaller. The existing scintillation light signals can only be collected by the outer optical fibers, but in the present invention, they can also be collected by the inner optical fibers. The optical fiber that is closer to the optical fiber will collect the light, and the inner and outer optical fibers form a "collection network", so the detection accuracy is higher.

[0010] Furthermore, the total number of the outer optical fibers is equal to the total number of the inner optical fibers, and the outer optical fibers and the inner optical fibers are arranged at equal intervals.

[0011] Furthermore, the helix angle of each inner optical fiber and each outer optical fiber is 45°.

[0012] Furthermore, outer spiral grooves corresponding to the outer optical fibers are provided on the outer peripheral surface of the tubular scintillator, and each outer optical fiber is embedded in the corresponding outer spiral groove.

[0013] Furthermore, the muon detector further includes a light-proof film covering the tubular scintillator and the outside of each outer optical fiber, and an outer protective tube sleeved on the outside of the light-proof film.

[0014] Furthermore, the muon detector further comprises an outer protective tube which is sleeved on the outside of the tubular scintillator and each outer optical fiber, and a light-shielding coating is provided on the inner wall of the outer protective tube.

[0015] Furthermore, inner spiral grooves corresponding to the inner optical fibers are provided on the inner circumferential surface of the tubular scintillator, and each inner optical fiber is embedded in the corresponding inner spiral groove.

[0016] Furthermore, the muon detector also includes a core rod inserted into the inner hole of the tubular scintillator. The core rod is a hollow or solid structure. A spiral hole is formed between the outer circumference of the core rod and the inner spiral groove for the inner optical fiber to pass through.

[0017] Furthermore, the core rod includes a core rod body and an opaque film covering the outer circumference of the core rod body.

[0018] Furthermore, the muon detector also includes an outer shell, which includes an upper shell for being exposed above the ground and an intermediate shell and a lower shell for being inserted below the ground. The intermediate shell is tubular for housing the tubular scintillator, and the lower shell includes a cone head. The upper ends of each inner optical fiber and each outer optical fiber are connected to a photoelectric converter, and the photoelectric converter is located inside the upper shell. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the composition of an embodiment of a muon detector for measuring soil moisture according to the present invention; Figure 2 A schematic front view of an embodiment of a muon detector for measuring soil moisture according to the present invention (the intermediate housing is not shown); Figure 3 A schematic cross-sectional view of a tubular scintillator in an embodiment of a muon detector for measuring soil moisture according to the present invention; Figure 4 Schematic cross-section of a tubular scintillator, an outer optical fiber, and an inner optical fiber in an embodiment of a muon detector for measuring soil moisture according to the present invention; Figure 5 Schematic diagram of the cooperation between the tubular scintillator and the core rod in an embodiment of the muon detector for measuring soil moisture of the present invention; Figure 6 This is a diagram showing the usage of a muon detector for measuring soil moisture according to an embodiment of the present invention.

[0020] In the figure: 10, muon detector; 1, tubular scintillator; 11, outer spiral groove; 12, inner spiral groove; 2, outer optical fiber; 3, inner optical fiber; 4, upper end shell; 5, lower end shell; 6, core rod. DETAILED DESCRIPTION

[0021] In response to the technical problems existing in the prior art, the basic concept of the present invention is to arrange spirally extended optical fibers on both the inner and outer circumferences of the tubular scintillator. The rotation direction of the inner optical fiber is opposite to that of the outer optical fiber. The tubular scintillator is divided into multiple grid-shaped detection units in the inner and outer directions. The inner and outer optical fibers form a "collection network" with higher detection accuracy.

[0022] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0023] Implementation of the muon detector for measuring soil moisture in the present invention: like Figure 1 、 Figure 2 、 Figure 6 As shown, the muon detector 10 of the present invention includes a housing, a sensing unit, a signal acquisition system, a data processing system, a communication system, a power supply system, and the like.

[0024] Combine Figure 2 、 Figure 3 、 Figure 4 As shown, the sensing unit is a tubular scintillator 1, which is usually made of plastic scintillator. The scintillator can detect muons in cosmic rays and emit scintillation light. The process is essentially a physical process in which high-energy charged particles lose energy through ionization and excite scintillator molecules to produce fluorescent radiation.

[0025] In the present invention, the outer periphery of the tubular scintillator 1 is spirally wound with at least two outer optical fibers 2 with equal pitch for collecting and transmitting scintillation light. At the same time, the inner periphery of the tubular scintillator 1 is spirally arranged with at least two inner optical fibers 3 with equal pitch for collecting and transmitting scintillation light. The rotation direction of each inner optical fiber 3 is opposite to that of each outer optical fiber 2. The tubular scintillator 1 is divided into multiple grid-shaped detection units in the inner and outer directions. Compared with the spiral detection units divided by multiple spirally wound optical fibers in the prior art, the grid-shaped detection units in the present invention are smaller. The existing scintillation light signals can only be collected by the outer optical fibers, but in the present invention, they can also be collected by the inner optical fibers. The optical fiber that is closer to it will be collected by that optical fiber. The inner and outer optical fibers form a "collection network", so the detection accuracy is higher.

[0026] Furthermore, the total number of outer optical fibers 2 is equal to the total number of inner optical fibers 3, and the outer optical fibers 2 and inner optical fibers 3 are arranged at equal intervals. This ensures that each grid is of equal size, the resulting detection units are of the same size, and the acquisition capabilities of each detection unit are balanced. The total number of outer optical fibers 2 and inner optical fibers 3 is determined based on the size of the tubular scintillator 1, the required measurement accuracy, and the optical fiber parameters.

[0027] Furthermore, the helix angle of each inner optical fiber 3 and each outer optical fiber 2 is 45°, so the grid divided is approximately a square. If the helix angle is at other angles, the grid divided is approximately a diamond. For two inner optical fibers 3 and two outer optical fibers 2 with a constant spacing, the square grid divided when the helix angle is 45° is the smallest compared to the diamond grids divided by various other helix angles. The detection unit is the smallest and the detection accuracy is the highest.

[0028] A 45° helix angle also means that the lengths of the inner and outer optical fibers 3 and 2 are moderate. A smaller helix angle and pitch increase the fiber length, which in turn increases the energy loss of the scintillation light during fiber propagation. While a larger helix angle and pitch shorten the fiber length, the area of ​​the resulting diamond-shaped grid increases, making the detection units larger and reducing detection accuracy. Therefore, a 45° helix angle balances detection accuracy and energy loss, offering the optimal compromise.

[0029] Of course, since the present invention uses inner and outer optical fibers to divide the detection units into a grid shape, the present invention already has obvious advantages under the same helix angle as the prior art. Therefore, in other embodiments, the helix angle can also be other degrees, such as 30°, 60°, or any value between 30° and 60° (except 45°).

[0030] In addition, in other embodiments, according to actual needs, the total number of outer optical fibers 2 and the total number of inner optical fibers 3 can also be designed to be unequal, and the outer optical fibers 2 and the inner optical fibers 3 can be arranged at non-equidistant distances. In this way, the sizes of the divided grids are different, and the collection capabilities of the detection units are different, so that different areas of the tubular scintillator 1 are designed to achieve the required detection effect.

[0031] Further, if Figure 3 and Figure 4 As shown, the present invention provides an outer spiral groove 11 on the outer circumference of the tubular scintillator 1, corresponding one-to-one with the outer optical fibers 2. Each outer optical fiber 2 is embedded in the corresponding outer spiral groove 11. This provides a good positioning effect for the outer optical fibers 2, ensuring that the pitch of the outer optical fibers 2 is fixed and the spacing between adjacent outer optical fibers 2 is also fixed. Furthermore, each outer optical fiber 2 can be wound along the corresponding outer spiral groove 11, facilitating the assembly and manufacture of the muon detector. During actual manufacturing, to prevent the outer optical fibers 2 from slipping out of the outer spiral groove 11, after the outer optical fibers 2 are wound, the outer spiral groove 11 can be filled with a liquid high-transparency silicone optical coupling agent. After solidification, the optical fibers are fixed and ensured to be tightly bonded to the tubular scintillator 1.

[0032] Furthermore, as an embodiment, the muon detector further includes a light-proof film (not shown) covering the tubular scintillator 1 and each outer optical fiber 2, and an outer protective tube disposed over the light-proof film to protect the muon detector and prevent interference from external stray light on the tubular scintillator 1. Of course, in other embodiments, the muon detector may include an outer protective tube disposed over the tubular scintillator 1 and each outer optical fiber 2 to protect the muon detector. In this embodiment, the light-proof film is omitted, and instead, a light-shielding coating is provided on the inner wall of the outer protective tube to prevent interference from external stray light on the tubular scintillator 1.

[0033] In the two embodiments described above, the outer protective tube is in close contact with the opaque film or directly with the outer circumference of the tubular scintillator 1, limiting and securing the tubular scintillator 1. Furthermore, the outer optical fiber 2 is embedded in the outer spiral groove 11 and does not protrude beyond the outer circumference of the tubular scintillator 1, thus preventing damage to the outer optical fiber 2 during assembly. This also means that the present invention comprises only one tubular scintillator. Compared to conventional scintillators with two inner and outer layers, the present invention has a simpler structure, is more convenient to manufacture, and offers lower costs.

[0034] Further, if Figure 3 and Figure 4As shown, the present invention provides inner spiral grooves 12 corresponding to the inner optical fibers 3 on the inner circumference of the tubular scintillator 1, and each inner optical fiber 3 is embedded in the corresponding inner spiral groove 12. The inner spiral groove 12 can position the inner optical fiber 3 so that the inner optical fiber 3 maintains a spiral shape, ensuring that the pitch of the inner optical fiber 3 is determined and the spacing between adjacent inner optical fibers 3 is also determined, thereby ensuring the detection effect.

[0035] Since the inner spiral groove 12 is located on the inner circumference of the tubular scintillator 1, in order to facilitate the installation of the inner optical fiber 3, as shown in FIG. Figure 5 As shown, the muon detector of the present invention also includes a core rod 6 inserted into the inner bore of the tubular scintillator 1. The core rod 6 can be hollow or solid and is made of high-strength plastic to ensure its strength. The length of the core rod 6 is the same as that of the tubular scintillator 1, and its outer diameter matches the inner diameter of the tubular scintillator 1. During assembly, the core rod 6 is first inserted into the inner bore of the tubular scintillator 1, aligning its ends with those of the tubular scintillator 1. This creates multiple spiral holes between the outer circumference of the core rod 6 and the inner spiral groove 12. The inner optical fiber 3 is then inserted along one end of the spiral hole until it exits at the other end. After all inner optical fibers 3 have been inserted into their corresponding spiral holes, the inner spiral groove 12 is filled with a liquid, highly transparent silicone optical coupling agent to eliminate any gaps between the inner optical fiber 3 and the inner spiral groove 12, ensuring a tight bond between the inner optical fiber 3 and the tubular scintillator 1.

[0036] Furthermore, the core rod 6 in this embodiment includes a core rod body and a light-proof film covering the outer circumference of the core rod body to prevent interference from other light on the tubular scintillator 1. In other embodiments, a light-shielding coating may be provided on the outer circumference of the core rod body, eliminating the need for a light-shielding film. Of course, in other embodiments, the core rod body itself can be made of a light-shielding material, eliminating the need for a light-shielding film or light-shielding coating. In this case, the outer circumference of the core rod body directly forms a spiral hole with the inner spiral groove.

[0037] Of course, in other embodiments, the inner optical fibers 3 can be arranged helically around the inner circumference of the tubular scintillator 1 by first helically winding the inner optical fibers 3 around a core rod, and then inserting the core rod and the inner optical fibers 3 into the inner hole of the tubular scintillator 1. In this case, to ensure that the inner optical fibers 3 are not tangled during the insertion of the core rod, an optical coupling agent can be used to bond the inner optical fibers 3 to the outer circumference of the core rod after the inner optical fibers 3 are wound. In this case, the inner wall of the tubular scintillator 1 can be smooth, and no inner spiral groove is provided. The inner optical fibers 3 can directly contact the inner wall of the tubular scintillator 1. Of course, the inner spiral groove can still be provided on the inner wall of the tubular scintillator 1. In this case, the inner optical fibers 3 are rotated along the corresponding inner spiral groove to achieve the effect similar to the connection between internal and external threads.

[0038] Of course, this method is also applicable to the winding of each external optical fiber 2, that is, the outer spiral groove is no longer provided on the outer peripheral surface of the tubular scintillator 1. At this time, each external optical fiber 2 is directly wound on the outer peripheral surface of the tubular scintillator 1. In order to ensure the positioning effect, an optical coupling agent can be used to bond and fix it.

[0039] In other embodiments, the inner optical fibers 3 can be arranged helically on the inner circumference of the tubular scintillator 1 by integrally forming a plurality of spiral holes on the inner circumference of the tubular scintillator 1, close to the inner circumference. In this case, the inner optical fibers 3 can be directly inserted into the spiral holes, without the need for a core rod. Alternatively, a spiral groove can be formed on the inner circumference of the tubular scintillator 1, with a major arc cross-section, i.e., a circular groove larger than half a circle. As long as the groove opening is larger than the size of the optical fiber, the optical fiber can be prevented from slipping out. In this case, the inner optical fibers 3 can also be directly inserted into the holes, without the need for a core rod.

[0040] Furthermore, the muon detector also includes a shell, combined with Figure 2 and Figure 6 As shown, the housing includes an upper shell 4 for being exposed above the ground D and an intermediate shell ( Figure 2 and Figure 6 To facilitate visualization of the optical fiber arrangement, the intermediate housing and lower housing 5 are hidden. The intermediate housing is tubular and accommodates the tubular scintillator 1; it also constitutes the aforementioned outer protective tube. The lower housing 5 includes a tapered tip, facilitating insertion of the muon detector into the soil. The maximum outer diameter of the lower housing 5 is consistent with that of the intermediate housing and the upper housing 4. Externally, the muon detector appears as a slender cylinder with a uniform outer diameter.

[0041] In this embodiment, the upper ends of each inner optical fiber 3 and each outer optical fiber 2 are connected to a photoelectric converter, which constitutes the above-mentioned signal acquisition system. The photoelectric converter is used to convert optical signals into electrical signals. Specifically, silicon photomultiplier tubes (SiPMs), traditional photomultiplier tubes (PMTs), avalanche photodiodes (APDs), single-photon avalanche diodes (SPADs), charge-coupled devices (CCDs), etc. can be used.

[0042] The data processing system is used to process electrical signals, the communication system is responsible for data transmission and reception, and the power supply system is responsible for providing power to the electrical components. The corresponding components of the data processing system, communication system, and power supply system, as well as the photoelectric converters connected to each optical fiber, are all located within the upper housing 4. In other embodiments, photoelectric converters can be connected to both the upper and lower ends of each optical fiber, as in the prior art. In other embodiments, the muon detector may not integrate a data processing system, communication system, or power supply system, but may only perform signal acquisition and data storage, with an external power supply providing power to the various electrical components.

[0043] In a specific embodiment of the present invention, the muon detector has a total length of 120 cm, the electronic unit (i.e., the upper housing 4) is 40 cm long, and the sensitive scintillator (i.e., the tubular scintillator 1) is 80 cm long. The tubular scintillator 1 has a wall thickness of 1 cm, an outer diameter of 10 cm, and an inner diameter of 8 cm. Twenty-five external spiral grooves 11 are formed on the outer circumference of the tubular scintillator 1 at a 45° spiral angle. Similarly, twenty-five internal spiral grooves 12 are formed on the inner circumference of the tubular scintillator 1 at a 45° counter-spiral angle (the number of spiral grooves shown in the drawings is much smaller than the actual number to facilitate visualization of the arrangement of the spiral grooves). After the inner and outer optical fibers 3 and 2 are installed, each outer optical fiber 2 corresponds to the adjacent inner optical fiber 3, ensuring that the tubular scintillator 1 is divided into several small sensing units on the same diameter of the inner and outer concentric circles.

[0044] When using, such as Figure 6 As shown, the muon detector 10 is inserted into the soil. Muons from cosmic rays pass through the soil and enter the sensitive area. The location and angle of the muon ingress are confirmed by the inner and outer optical fibers. The number of muons ingress is recorded, and the soil moisture is calculated based on the relationship between the number of muons and soil moisture (using a known formula). The soil moisture measurement radius can be calculated based on the muon incidence angle, thereby obtaining the soil moisture content and the detector measurement radius. Figure 6 The F position marked in the middle is the measuring radius of the detector.

[0045] In practice, the sensing area can be divided into 10-cm sections, and the sensitive scintillator can be equally divided into eight sections. Corresponding to the soil depth, the soil measurement can be divided into eight layers. Based on the muon measurement position, the muon content in each of the eight layers can be determined. The soil moisture content W1 of the first layer (the first 10 cm) is calculated based on the muon content. The soil moisture content W2 of the second layer is calculated based on the muon content of the second layer. Similarly, the soil moisture content of each of the eight layers can be calculated.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be based on the claims. Any equivalent structural changes made using the description and drawings of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A muon detector for measuring soil moisture, comprising a tubular scintillator for detecting muons in cosmic rays and emitting scintillation light, wherein at least two outer optical fibers with equal pitches for collecting and transmitting the scintillation light are spirally wound around the outer periphery of the tubular scintillator, characterized in that: At least two inner optical fibers with equal pitch are spirally arranged on the inner circumference of the tubular scintillator for collecting and transmitting scintillation light. The rotation direction of each inner optical fiber is opposite to that of each outer optical fiber, so as to divide the tubular scintillator into multiple grid-shaped detection units in the inner and outer directions.

2. The muon detector for measuring soil moisture according to claim 1, characterized in that: The total number of the outer optical fibers is equal to the total number of the inner optical fibers, and the outer optical fibers and the inner optical fibers are arranged at equal intervals.

3. The muon detector for measuring soil moisture according to claim 2, characterized in that: The helix angle of each inner optical fiber and each outer optical fiber is 45°.

4. The muon detector for measuring soil moisture according to any one of claims 1 to 3, characterized in that: The outer peripheral surface of the tubular scintillator is provided with outer spiral grooves corresponding to the outer optical fibers one by one, and each outer optical fiber is embedded in the corresponding outer spiral groove.

5. The muon detector for measuring soil moisture according to claim 4, characterized in that: The muon detector further comprises a light-proof film covering the outside of the tubular scintillator and each outer optical fiber, and an outer protective tube sleeved on the outside of the light-proof film.

6. The muon detector for measuring soil moisture according to claim 4, characterized in that: The muon detector further comprises an outer protective tube which is sleeved on the outside of the tubular scintillator and each outer optical fiber, and a light-shielding coating is provided on the inner wall of the outer protective tube.

7. The muon detector for measuring soil moisture according to any one of claims 1 to 3, characterized in that: The inner circumference of the tubular scintillator is provided with inner spiral grooves corresponding to the inner optical fibers one by one, and each inner optical fiber is embedded in the corresponding inner spiral groove.

8. The muon detector for measuring soil moisture according to claim 7, characterized in that: The muon detector also includes a core rod inserted into the inner hole of the tubular scintillator. The core rod is a hollow or solid structure. A spiral hole is formed between the outer circumference of the core rod and the inner spiral groove for the inner optical fiber to pass through.

9. The muon detector for measuring soil moisture according to claim 8, characterized in that: The core rod comprises a core rod body and a light-proof film covering the outer peripheral surface of the core rod body.

10. The muon detector for measuring soil moisture according to any one of claims 1 to 3, characterized in that: The muon detector also includes an outer shell, which includes an upper shell for being exposed above the ground, an intermediate shell for being inserted below the ground, and a lower shell. The intermediate shell is tubular for housing a tubular scintillator, and the lower shell includes a cone head. The upper ends of each inner optical fiber and each outer optical fiber are connected to a photoelectric converter, which is located inside the upper shell.

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