A small-scale methane-moderated cold neutron cryogenic system for laboratory use and its application method

Abstract

This invention discloses a small-scale methane moderation cold neutron cryogenic system for laboratory use and its method of operation. The system includes a gas source, a moderator, a refrigerator fixed to the moderator, inlet and outlet gas pipelines, a buffer gas supply pipeline, and an evacuation pipeline. The moderator contains a vacuum chamber. The primary and secondary cold heads of the refrigerator extend into the vacuum chamber. A primary cold shield assembly with a sealed cavity is installed within the vacuum chamber, and the primary cold heads are fixedly connected to the primary cold shield assembly. In this invention, through the arrangement of the small-scale refrigerator, moderator, inlet and outlet gas pipelines, buffer gas supply pipeline, and evacuation pipeline, methane gas is slowly supplied to the methane chamber from the buffer pipeline based on the pressure difference caused by the temperature difference. This achieves low-temperature solidification of methane within the methane chamber, ensuring the supply of methane gas during low-temperature solidification or the release of methane gas pressure during low-temperature vaporization phase change, thus ensuring the safety of the equipment.

Description

Technical Field

[0001] This invention relates to the field of neutron cryogenic moderation technology, and more specifically to a small laboratory methane-moderated cold neutron cryogenic system and its usage method. Background Technology

[0002] The energy of a neutron is directly proportional to its temperature. Therefore, the energy level of a neutron is often expressed by its temperature, and it is classified into hot neutrons, thermal neutrons, cold neutrons, very cold neutrons, and ultracold neutrons.

[0003] Cold neutrons, with their low energy, long wavelength, and large scattering cross-section, can be used to analyze the scattered waves after penetrating a sample. This makes them a powerful tool for studying the structure of materials such as alloy clusters, polymers, and biomolecules, and is well-suited for application in the field of neutron scattering technology.

[0004] Obtaining cold neutrons requires a cryogenic moderation system that uses cryogenic moderators such as liquid hydrogen, liquid deuterium, and solid methane to slow down high-energy neutrons generated by neutron source devices such as reactors into low-energy cold neutrons.

[0005] Spallation pulse neutron sources and reactor neutron sources can produce high-flux cold neutrons through cryogenic moderation systems. However, as ultra-large scientific facilities, they can only be built as national projects by one or more countries. Moreover, the cryogenic moderation systems are also quite large. In addition, the refrigeration method used by these cryogenic moderation systems is a large-scale helium refrigeration system. This type of cold neutron cryogenic system is not suitable for small laboratories due to its different refrigeration method.

[0006] In addition, there are also some micro-pulsed neutron sources suitable for construction in colleges and universities and research institutes. Due to their advantages such as low cost, short construction period, low activation and radiation dose, and flexible structure, they have received increasing attention and application worldwide.

[0007] These laboratory-grade miniature neutron sources typically use solid methane, liquid hydrogen, or liquid deuterium as cryogenic moderators. Although solid methane has poor irradiation performance, it possesses excellent neutron moderation properties and can produce a higher flux of low-energy cold neutrons compared to cryogenic moderators such as liquid hydrogen and liquid deuterium, making it popular among many researchers.

[0008] However, currently, no company or researcher in China has provided detailed explanations of the devices for small-scale laboratory cryogenic moderation systems and the corresponding neutron cryogenic moderation operation methods and procedures.

[0009] Patent document CN113324345A discloses a 1.5K cryogenic system without liquid helium. This system includes a refrigerator, a cryostat cylinder, a refrigeration flow controller, a buffer tank, and a circulating pump. The cryostat cylinder houses a primary cold shield assembly; an adsorption cold trap is mounted on the primary cold shield assembly; a secondary cold shield assembly with a regenerating heat exchanger and a helium pool is located within the primary cold shield assembly; the adsorption cold trap inlet I is connected to the refrigeration flow controller outlet I, and the refrigeration flow controller inlet II is connected to the buffer tank and pipeline III; the buffer tank is connected to the make-up gas pipeline and the circulating gas pipeline; the regenerating heat exchanger's hot fluid side inlet III is connected to the adsorption cold trap outlet II, and the hot fluid side outlet III is connected to the helium pool inlet IV; the helium pool outlet IV is connected to the cold fluid side inlet V, and the cold fluid side outlet V is connected to pipeline III and the circulating pump; the circulating gas pipeline is connected to the exhaust pipeline. This solution also discloses a method for implementing the system, which features short evacuation time, thorough gas replacement, and resistance to blockage during the cooling process.

[0010] However, its structure, process and related operations are mainly used for low-temperature gas circulation cooling, and cannot be applied to the methane moderation cold neutron low-temperature system test. Summary of the Invention

[0011] The technical problem to be solved by this invention is how to provide a laboratory-grade methane-moderate cold neutron cryogenic system.

[0012] This invention solves the above-mentioned technical problems through the following technical means: a small-scale methane moderation cold neutron cryogenic system for laboratory use, comprising a gas source, a moderator, a refrigerator fixed on the moderator, inlet and outlet gas pipelines, a buffer gas supply pipeline, and an evacuation pipeline. The moderator has a vacuum chamber. The primary and secondary cold heads of the refrigerator extend into the vacuum chamber. A primary cold shield assembly with a sealed cavity is provided within the vacuum chamber, and the primary cold head is fixedly connected to the primary cold shield assembly. The secondary cold head extends into the inner cavity of the primary cold shield assembly. One end of the methane cooling rod is connected to a methane chamber. The methane chamber is connected to the inlet and outlet gas pipelines via connecting pipes. Downstream of the inlet and outlet gas pipelines are connected a buffer gas supply pipeline and a vacuum pipeline. Downstream of the buffer gas supply pipeline and the vacuum pipeline are connected an exhaust pipeline. The gas source is connected to the inlet and outlet gas pipelines. The gas in the buffer pipeline can be injected into the methane chamber, causing the test gas in the methane chamber to solidify at low temperature and fill the methane chamber. The methane cooling rod can ensure that the refrigerator and the methane chamber are not on the same horizontal neutron incident surface.

[0013] As a preferred technical solution, the methane cooling rod is Z-shaped, and the vertical incident surface of the methane cavity is offset from the refrigerator through the cooling rod. The methane cooling rod includes one end fixed to the bottom of the methane cavity and the other end fixedly connected to the secondary cold head.

[0014] As a preferred technical solution, the buffer gas supply pipeline is equipped with a buffer tank gas supply valve, a buffer tank, and a buffer tank evacuation valve. When the test gas in the methane chamber is solidified at low temperature, the methane gas can drive the gas in the buffer tank to be supplied into the methane chamber according to the pressure caused by its temperature difference.

[0015] As a preferred technical solution, it also includes an active emission pipeline, which is connected to the inlet and outlet gas pipelines. The active emission pipeline is equipped with a pipeline system vent valve, and the exhaust pipeline is equipped with a vacuum pump and a vacuum exhaust valve.

[0016] As a preferred technical solution, it also includes an overpressure relief pipeline, which includes a first relief pipeline and a second relief pipeline. The input end of the first relief pipeline is connected to the inlet and outlet gas pipelines, and the input end of the second relief pipeline is connected to the buffer gas supply pipeline. The output ends of both the first and second relief pipelines are connected to the exhaust pipeline. The first relief pipeline and the second relief pipeline are respectively equipped with a pipeline system safety valve and a buffer tank safety valve.

[0017] As a preferred technical solution, the gas source includes a methane gas source and a helium gas source. The methane gas source is connected to the inlet and outlet gas pipeline through a first gas source connecting pipeline, which is equipped with a methane pressure reducing valve and a methane valve. The helium gas source is connected to the inlet and outlet gas pipeline through a second gas source connecting pipeline, which is equipped with a helium pressure reducing valve and a helium valve.

[0018] As a preferred technical solution, the gas source also includes a nitrogen source, which is connected to the exhaust pipeline through a third gas source connecting pipeline. The third gas source connecting pipeline is equipped with a nitrogen pressure reducing valve, a nitrogen valve, and a nitrogen mass flow controller.

[0019] As a preferred technical solution, the methane chamber is connected to the inlet and outlet gas pipelines through the methane pipeline inside the slower, and the slower is provided with a slower methane inlet flange that is compatible with the methane pipeline inside the slower.

[0020] A method for using a small laboratory-scale methane-moderated cold neutron cryogenic system includes the following steps:

[0021] S1. Evacuation: Evacuate the entire system's piping.

[0022] S2, Protective gas replacement: After the evacuation is completed, the methane chamber, inlet and outlet gas pipelines, buffer gas supply pipelines and evacuation pipelines are filled with protective gas. After the filling is completed, step S1 is repeated three times.

[0023] S3. Test gas replacement: Fill the methane chamber, inlet and outlet gas lines, buffer gas supply line and evacuation line with test gas and then discharge it. Then repeat step S1 three times.

[0024] S4. Test gas filling: Fill the methane chamber and buffer gas supply line with test gas, observe the pressure of the buffer gas supply line, and complete the methane filling process after reaching the working pressure.

[0025] S5. Cooling and curing: The test gas is filled and the refrigeration unit is turned on to cool and cure the test gas in the methane chamber;

[0026] S6. Reheating: Cold neutrons are generated by slowing down the test gas. After the test is completed, the refrigerator is turned off, and the temperature is restored by opening the inlet and outlet gas pipelines and the buffer gas supply pipeline system.

[0027] As a preferred technical solution, in step S3, when evacuating and discharging the test gas, the discharged test gas is diluted before discharge.

[0028] The advantages of this invention are:

[0029] (1) In this invention, by setting up a primary cold shield component and a vacuum chamber, the radiative heat leakage of the methane chamber is reduced, and the temperature of the methane chamber can be reduced to below the phase transition point of methane solid crystal. By setting up a small refrigerator, a moderator, inlet and outlet gas pipelines, a buffer gas supply pipeline and an evacuation pipeline, the methane gas is slowly supplied to the methane chamber from the buffer pipeline based on the pressure difference caused by the temperature difference, so as to achieve low-temperature solidification of methane in the methane chamber. On the one hand, it can ensure the stability of the pressure of instantaneous gas release, and on the other hand, it can ensure the pressure release of methane gas when the gas in the methane chamber is undergoing low-temperature solidification or when methane undergoes vaporization phase transition at low temperature, thus ensuring the safety of the equipment. This invention provides a laboratory methane cold neutron low-temperature system.

[0030] (2) In this invention, by adopting a Z-shaped structure for the cooling rod and connecting it to the secondary cold head of the refrigerator and the methane chamber, the refrigerator and the methane chamber are not on the same horizontal neutron incident surface, so that the refrigerator is as far away from the influence of neutron irradiation as possible.

[0031] (3) In this invention, by installing a pipeline system vent valve on the methane inlet and outlet pipelines, active and safe discharge can be carried out when the pressure of the methane inlet and outlet pipelines is too high and active pressure relief is required, thus ensuring system safety. By setting the outlet of the pipeline system safety valve and the outlet of the buffer tank safety valve to be connected to the exhaust check valve through a pipeline, when the safety valve is over-pressured, the methane gas can be over-pressured and discharged to a safe place, avoiding the safety hazards caused by local discharge.

[0032] (4) In this invention, by setting a evacuation valve for the pipeline system and a evacuation valve for the buffer tank, and by using the vacuum pumping capacity of the evacuation pump to evacuate and replace the gas in the pipeline system and the buffer tank, the purity of the gas in the system is ensured.

[0033] (5) In this invention, by designing a helium replacement process, the impurities in the methane inlet and outlet pipelines and buffer tank can be replaced clean before the methane gas replacement and washing process, so as to avoid the danger of methane explosion caused by oxygen or other combustion-supporting gases, or the situation of other gases freezing and blocking ice during the low-temperature solidification process of methane. A nitrogen dilution process is designed for methane emission, which can dilute the methane gas to the lower explosive limit during methane gas emission, so as to facilitate the safe emission of methane gas. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure provided in an embodiment of the present invention;

[0035] Reference numerals: 11. Refrigeration unit; 12. Vacuum chamber; 13. First-stage cold head; 14. First-stage cold shield assembly; 15. Second-stage cold head; 16. Methane cooling rod; 17. Methane inlet flange of the moderator; 18. Methane pipeline inside the moderator; 19. Methane chamber; 21. Nitrogen source; 22. Nitrogen pressure reducing valve; 23. Nitrogen valve; 24. Nitrogen mass flow controller; 25. Helium source; 26. Helium pressure reducing valve; 27. Helium valve; 28. Methane source; 29. ​​Methane pressure reducing valve; 30. Methane valve; 31. Moderator inlet valve; 32. Piping system safety valve; 33. Piping system evacuation valve; 34. Piping system vent valve; 35. Buffer tank make-up valve; 36. Buffer tank safety valve; 37. Buffer tank; 38. Buffer tank evacuation valve; 39. Evacuation pump; 40. Evacuation and exhaust valve; 41. Exhaust check valve. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] See Figure 1 A small-scale methane moderation cold neutron cryogenic system for laboratory use includes a gas source, a moderator, a refrigerator 11 fixed on the moderator, inlet and outlet gas pipelines, a buffer gas supply pipeline, an evacuation pipeline, an active discharge pipeline, and an overpressure relief pipeline. The inlet and outlet gas pipelines are connected to the methane chamber 19 through a methane pipeline 18 inside the moderator. The inlet and outlet gas pipelines are equipped with a moderator inlet valve 31. The buffer gas supply pipeline and the evacuation pipeline are connected in parallel downstream of the inlet and outlet gas pipelines. The evacuation pipeline is connected downstream of the buffer gas supply pipeline and the evacuation pipeline. The evacuation pipeline is equipped with an evacuation pump 39, an evacuation and exhaust valve 40, and an exhaust check valve 41 in sequence. The evacuation pipeline is located downstream of the buffer gas supply pipeline and the evacuation pipeline so that they can be evacuated simultaneously by the evacuation pump 39.

[0038] The buffer gas supply line is used to share the pressure of the methane chamber 19 when the test gas is being filled, and to ensure the replenishment of methane gas during low-temperature solidification of the gas in the methane chamber 19 or the release of methane gas pressure when methane undergoes vaporization phase change at low temperature, thus ensuring the safety of the equipment. The active discharge line is connected to the inlet and outlet gas lines to ensure the system's need for active and safe discharge. The overpressure relief line ensures the emergency pressure relief needs when the inlet and outlet gas lines and the buffer gas supply line experience overpressure. The gas sources include methane gas source 28, helium gas source 25, and nitrogen gas source 21. Among them, methane gas source 28 is the gas source for the test gas, helium gas source 25 is the gas source for the protective gas, and nitrogen gas source 21 is the gas source for diluting the test gas. Both methane gas source 28 and helium gas source 25 can be connected to the inlet and outlet gas lines.

[0039] See Figure 1 The slower is equipped with a vacuum chamber 12. The first-stage cold head 13 and the second-stage cold head 15 of the refrigerator 11 extend into the vacuum chamber 12. The vacuum chamber 12 is equipped with a first-stage cold shield assembly 14, and the first-stage cold head 13 is fixedly connected to the first-stage cold shield assembly 14 to form a first-stage radiation shield cold shield assembly, which can be used to reduce the radiation heat leakage of each component inside the first-stage cold shield assembly 14.

[0040] One end of the secondary cold head 15 extends into the inner cavity of the primary cold shield assembly 14 and is connected to the methane chamber 19 via one end of the methane cooling rod 16. The methane chamber 19 is connected to the inlet and outlet gas pipelines via connecting pipes. In this embodiment, the connecting pipe is the methane pipeline 18 inside the moderator. The moderator is provided with a moderator methane inlet flange 17 that is adapted to the methane pipeline 18 inside the moderator. The methane gas is transported to the methane chamber 19 from inside and outside the vacuum insulation cavity through the moderator methane inlet flange 17. The methane cooling rod 16 can ensure that the refrigerator 11 and the methane chamber 19 are not on the same horizontal neutron incident surface, while also ensuring the realization of the low-temperature curing temperature of methane.

[0041] The methane cooling rod 16 is Z-shaped, and the vertical incident surface of the methane cavity 19 is offset from the refrigerator 11 by the cooling rod 16. The methane cooling rod 16 includes an integrally formed first horizontal connecting part, a first vertical connecting part, and a second horizontal connecting part. One end of the first horizontal connecting part is fixedly connected to the secondary cold head 15, and the other end is vertically fixed to one end of the first vertical connecting part. The other end of the first vertical connecting part is fixedly connected to the second horizontal connecting part. The second horizontal connecting part is fixed to the bottom of the methane cavity 19. The lowest temperature at the secondary cold head 15 of the refrigerator 11 can be conducted to the bottom of the methane cavity 19 through the methane cooling rod 16, which facilitates the low-temperature solidification of methane inside the methane cavity 19.

[0042] After the methane gas source 28 is reduced to a suitable methane gas pressure by the methane pressure reducing valve 29, it then enters the methane pipeline 18 inside the moderator through the methane valve 30, the moderator inlet valve 31 and the moderator methane inlet flange 17 in sequence, and flows to the methane chamber 19, forming the inlet and outlet gas lines for methane, ensuring that the gas in the methane chamber 19 can be supplied by the methane gas source 28.

[0043] See Figure 1 The buffer gas supply pipeline is sequentially equipped with a buffer tank gas supply valve 35, a buffer tank 37, and a buffer tank evacuation valve 38. The outlet of the methane valve 30 is connected to the buffer tank 37 through the buffer tank gas supply valve 35 for gas pressure stabilization. Since the volume of the methane chamber 19 is much smaller than that of the buffer tank 37, the volume of methane gas in the buffer tank 37 is greater than that in the methane chamber 19 during the gas filling process, which can reduce the pressure impact on the methane chamber 19. When the methane chamber 19 is solidified at low temperature, the methane gas is slowly replenished from the buffer tank 37 to the methane chamber 19 based on the pressure difference caused by the temperature difference, so as to achieve complete filling of the methane chamber 19 with solidified methane gas. When methane undergoes vaporization phase change at low temperature, the pressure of the methane gas can also be released to ensure the safety of the equipment.

[0044] The active emission pipeline is equipped with a pipeline system vent valve 34, and then through an exhaust check valve 41, the pipeline gas can be discharged to a safe location, forming an active gas emission pipeline to ensure the system's need for active safety emission. The overpressure relief pipeline includes a first relief pipeline and a second relief pipeline. The inlet end of the first relief pipeline is connected to the inlet and outlet gas pipelines, and the inlet end of the second relief pipeline is connected to the buffer gas supply pipeline. The outlet ends of both the first and second relief pipelines are connected to the exhaust pipeline. The first and second relief pipelines are respectively equipped with a pipeline system safety valve 32 and a buffer tank safety valve 36. The inlet of the pipeline system safety valve 32 is connected to the outlet of the methane valve 30, and its outlet and the outlet of the buffer tank safety valve 36 are both connected to the exhaust check valve 41 through pipelines and discharged to a safe location, forming an overpressure safety relief pipeline to ensure the emergency pressure relief needs when the methane inlet and outlet gas pipelines and the buffer tank 37 experience overpressure.

[0045] See Figure 1 The evacuation pipeline is equipped with a pipeline system evacuation valve 33, which is connected to the inlet of the moderator inlet valve 31 in the methane inlet pipeline. The inlet of the buffer tank evacuation valve 38 is connected to the buffer tank 37. The outlets of the pipeline system evacuation valve 33 and the buffer tank evacuation valve 38 are both connected to the inlet of the evacuation pump 39 through pipelines. The outlet of the evacuation pump 39 is connected to the exhaust check valve 41 through the evacuation exhaust valve 40, so that it can be discharged to a safe place. This allows the evacuation pump 39 to evacuate and replace the methane inlet and outlet pipelines and the buffer tank 37, ensuring that the gas in the pipeline is methane gas before cooling.

[0046] See Figure 1 Methane source 28 is connected to the inlet and outlet gas pipelines through a first gas source connection pipeline. The first gas source connection pipeline is equipped with a methane pressure reducing valve 29 and a methane valve 30. Helium source 25 is connected to the inlet and outlet gas pipelines through a second gas source connection pipeline. The second gas source connection pipeline is equipped with a helium pressure reducing valve 26 and a helium valve 27. After the helium source 25 is reduced to a suitable helium gas pressure by the helium pressure reducing valve 26, it then enters the methane pipeline 18 inside the moderator through the helium valve 27, the moderator inlet valve 31 and the moderator methane inlet flange 17 in sequence, and flows to the methane chamber 19, forming helium protection. Before the methane gas replacement and flushing, the impurities in the methane inlet and outlet gas pipelines and the buffer tank 37 can be replaced cleanly to avoid the danger of methane explosion caused by oxygen or other combustion-supporting gases.

[0047] Nitrogen source 21 is connected to exhaust pipeline via third gas source connection pipeline. The third gas source connection pipeline is equipped with nitrogen pressure reducing valve 22, nitrogen valve 23, and nitrogen mass flow controller 24. After nitrogen source 21 is reduced to a suitable nitrogen pressure by nitrogen pressure reducing valve 22, it is then connected to the outlet of exhaust one-way valve 41 in sequence through nitrogen valve 23 and nitrogen mass flow controller 24, forming a safe dilution pipeline for methane emission. This allows nitrogen to be diluted to the lower explosive limit of methane gas during methane emission for safe methane emission.

[0048] The usage method includes the following steps:

[0049] S1. Evacuation: First, confirm that the evacuation and exhaust valve 40 is open and the pipeline system evacuation valve 34 is closed. Then, close the nitrogen valve 23, helium valve 27, and methane valve 30 in sequence. Then, open the evacuation pump 39, the moderator inlet valve 31, and the buffer tank replenishment valve 35 in sequence. Slowly open the pipeline system evacuation valve 33 and the buffer tank evacuation valve 38 to evacuate the buffer replenishment pipeline system, methane chamber 19, inlet and outlet pipelines, and evacuation pipeline to avoid safety hazards from combustion-supporting or other flammable gases in the pipelines or buffer tank 37.

[0050] S2. Protective gas replacement: After the pipeline and buffer tank 37 are evacuated, the pipeline system evacuation valve 33, the buffer tank evacuation valve 38 and the evacuation pump 39 are closed in sequence. Then, the helium valve 27 at the helium source 25 is opened, the corresponding helium pressure reducing valve 26 is adjusted, and the moderator inlet valve 31 is opened to fill the methane pipeline 18, methane chamber 19 and buffer tank 37 in the moderator with helium. After the filling is completed, step 1 is repeated three times to complete the replacement gas with helium. This avoids the solidification and blockage of the pipeline by other impurities in the pipeline or buffer tank 37 when they are cooled, which would affect the methane gas supply during methane solidification.

[0051] S3. Test Gas Replacement: After the helium replacement process is completed, close the helium valve 27, and then close the pipeline system evacuation valve 33, the buffer tank evacuation valve 38, and the evacuation pump 39 in sequence. Then open the methane valve 30 at the methane source 28, adjust the corresponding methane pressure reducing valve 29, and fill the methane pipeline 18, methane chamber 19, and buffer tank 37 in the moderator with methane. After the filling is completed, repeat step 1. However, before repeating step 1 after the methane filling is completed, open the nitrogen valve 23 at the nitrogen source 21, adjust the corresponding nitrogen pressure reducing valve 22 and nitrogen mass flow controller 24, and dilute the methane discharged by evacuation to ensure that the methane emission ratio is lower than the explosion limit. Repeat the methane filling and evacuation three times to complete the methane gas replacement, thereby determining the methane purity of the system and buffer tank 37.

[0052] S4. Test gas filling: After the methane replacement process is completed, the pipeline system evacuation valve 33, the buffer tank evacuation valve 38, and the evacuation pump 39 are closed in sequence. At the same time, the nitrogen valve 23 and the nitrogen pressure reducing valve 22 at the nitrogen source 21 are closed. The methane valve 30 at the methane source 28 is opened, and the corresponding methane pressure reducing valve 29 is adjusted to fill the methane pipeline 18, methane chamber 19, and buffer tank 37 in the slower with methane. The pressure at the buffer tank 37 is observed. After the working pressure is reached, the methane valve 30 is closed to complete the methane filling process.

[0053] S5. Cooling and solidification: After the methane is filled, ensure that the slower inlet valve 31 and the buffer tank replenishment valve 35 are open. At this time, the pipeline system evacuation valve 33, the buffer tank evacuation valve 38, and the evacuation pump 39 are all closed. Then, the refrigerator 11 can be turned on to cool and solidify the methane gas in the methane chamber 19 to the target temperature for the generation of cold neutrons. During this process, the methane gas is slowly replenished from the buffer tank 37 to the methane chamber 19 based on the pressure difference caused by the temperature difference.

[0054] S6. Temperature recovery: After generating cold neutrons through the slowing down of solid methane and completing the corresponding tests, shut down the refrigerator 11 while ensuring that the slowing inlet valve 31 and the buffer tank gas supply valve 35 are open to allow the system to recover temperature.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A small-scale methane-moderated cold neutron cryogenic system for laboratory use, characterized in that, The system includes a gas source, a slower, a refrigerator (11) fixed on the slower, inlet and outlet gas pipelines, a buffer gas supply pipeline, and an evacuation pipeline. The slower is equipped with a vacuum chamber (12). The primary cold head (13) and the secondary cold head (15) of the refrigerator (11) extend into the vacuum chamber (12). The vacuum chamber (12) is equipped with a primary cold shield assembly (14) with a sealed cavity. The primary cold head (13) is fixedly connected to the primary cold shield assembly (14). One end of the secondary cold head (15) extends into the inner cavity of the primary cold shield assembly (14) through one end of a methane cooling rod (16). A methane chamber (19) is connected, and the methane chamber (19) is connected to the inlet and outlet gas pipelines through a connecting pipe. A buffer gas supply pipeline and an evacuation pipeline are connected in parallel downstream of the inlet and outlet gas pipelines. An exhaust pipeline is connected downstream of the buffer gas supply pipeline and the evacuation pipeline. The gas source is connected to the inlet and outlet gas pipelines. The gas in the buffer gas supply pipeline can be supplied into the methane chamber (19) and cause the test gas in the methane chamber (19) to solidify at low temperature and fill the methane chamber (19). The methane cooling rod (16) can cause the refrigerator (11) and the methane chamber (19) to be not on the same horizontal neutron incident surface.

2. The laboratory-scale methane-moderated cold neutron cryogenic system according to claim 1, characterized in that, The methane cooling rod (16) is Z-shaped. The vertical incident surface of the methane cavity (19) is offset from the refrigerator (11) through the cooling rod. The methane cooling rod (16) includes one end fixed to the bottom of the methane cavity (19) and the other end fixedly connected to the secondary cold head (15).

3. The laboratory-scale methane-moderated cold neutron cryogenic system according to claim 1, characterized in that, The buffer gas supply pipeline is equipped with a buffer tank gas supply valve (35), a buffer tank (37), and a buffer tank evacuation valve (38). When the test gas in the methane chamber (19) is solidified at low temperature, the test gas can drive the gas in the buffer tank (37) to be supplied to the methane chamber (19) according to the pressure caused by its temperature difference.

4. A laboratory-scale methane-moderate cold neutron cryogenic system according to claim 1, characterized in that, It also includes an active exhaust pipeline, which is connected to the inlet and outlet gas pipelines. The active exhaust pipeline is equipped with a pipeline system vent valve (34), and the exhaust pipeline is equipped with a vacuum pump (39) and a vacuum exhaust valve (40).

5. A laboratory-scale methane-moderated cold neutron cryogenic system according to claim 1, characterized in that, It also includes an overpressure relief pipeline, which includes a first relief pipeline and a second relief pipeline. The input end of the first relief pipeline is connected to the inlet and outlet gas pipeline, and the input end of the second relief pipeline is connected to the buffer gas supply pipeline. The output ends of the first relief pipeline and the second relief pipeline are both connected to the exhaust pipeline. The first relief pipeline and the second relief pipeline are respectively equipped with a pipeline system safety valve (32) and a buffer tank safety valve (36).

6. A laboratory-scale methane-moderated cold neutron cryogenic system according to claim 1, characterized in that, The gas sources include a methane gas source (28) and a helium gas source (25). The methane gas source (28) is connected to the inlet and outlet gas pipelines through a first gas source connecting pipeline. The first gas source connecting pipeline is equipped with a methane pressure reducing valve (29) and a methane valve (30). The helium gas source (25) is connected to the inlet and outlet gas pipelines through a second gas source connecting pipeline. The second gas source connecting pipeline is equipped with a helium pressure reducing valve (26) and a helium valve (27).

7. A small-scale methane-moderate cold neutron cryogenic system for laboratory use according to claim 6, characterized in that, The gas source also includes a nitrogen source (21), which is connected to the exhaust pipe through a third gas source connection pipe. The third gas source connection pipe is equipped with a nitrogen pressure reducing valve, a nitrogen valve, and a nitrogen mass flow controller.

8. A small-scale laboratory methane-moderate cold neutron cryogenic system according to claim 1, characterized in that, The methane chamber (19) is connected to the inlet and outlet gas pipelines through the methane pipeline (18) inside the moderator. The moderator is provided with a moderator methane inlet flange (17) that is compatible with the methane pipeline (18) inside the moderator.

9. A method of using a small laboratory methane-moderated cold neutron cryogenic system according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Evacuation: Evacuate the entire system's piping. S2, protective gas replacement: After the evacuation is completed, the methane chamber (19), inlet and outlet gas pipelines, buffer gas supply pipelines and evacuation pipelines are filled with protective gas. After the filling is completed, step S1 is repeated three times. S3, Test gas replacement: Test gas is filled into the methane chamber (19), inlet and outlet gas pipelines, buffer gas supply pipelines and evacuation pipelines, and then discharged. Then step S1 is repeated three times. S4. Test gas filling: Test gas is filled into the methane chamber (19) and the buffer gas supply line. The pressure of the buffer gas supply line is observed. After the working pressure is reached, the methane filling process is completed. S5, Cooling and curing: The test gas is filled and the refrigeration unit (11) is turned on to cool and cure the test gas in the methane chamber (19); S6. Warm-up: Cold neutrons are generated by slowing down the test gas. After the test is completed, the refrigerator (11) is turned off, and the temperature is restored by opening the inlet and outlet gas pipelines and the buffer gas supply pipeline system.

10. The method of using a small laboratory methane-moderated cold neutron cryogenic system according to claim 9, characterized in that, In step S3, when the test gas is evacuated and discharged, the discharged test gas is diluted and discharged.

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