Gas purification system and purification method for 3He neutron detector

Abstract

The invention relates to the technical field of neutron detection, and discloses a gas purification system and method for a He neutron detector. The system comprises a high-pressure cavity, a miniaturized high-pressure circulating pump, a multifunctional purification gas path system, a filter, a pressure gauge, a valve and the like, a dynamic purification circulation loop is constructed by integrating the high-efficiency filter and the miniaturized circulating pump, impurities such as H2O, O2 and organic volatile matters are effectively removed, and the gas purity is ensured. A metal corrugated pipe and metal sealing structure is adopted in the system, the extremely low leakage rate is achieved, and the pump body is small in size and convenient to integrate; the multifunctional gas circuit system is controlled through a valve time sequence, four-function switching is achieved, operation is simplified, and reliability is improved; the system performance can be optimized through switchable gas circuit design, and different working conditions are adapted; reliable technical support is provided for the He neutron detector, and technical development in related fields is promoted.

Description

Technical Field

[0001] This invention relates to the field of neutron detection technology, specifically to a method for... 3 The gas purification system and method for He neutron detectors are applicable to high-pressure environments in fields such as nuclear safety regulation, particle physics experiments, industrial non-destructive testing, and homeland security. 3 Long-term maintenance of gas purity in He detectors, high-pressure cycle drive, and system integration. Background Technology

[0002] Neutron detection technology plays a crucial supporting role in many key areas, including nuclear safety regulation, particle physics experiments, industrial non-destructive testing, and homeland security. Among these, neutron detection technology based on helium-3 (… 3 He's gas detector relies on 3 He nuclei have an ultra-high capture cross section for thermal neutrons (up to 5330 barns), and their reaction products (protons and tritium nuclei) have clear energies (total Q value 764 keV). They also have excellent gamma-ray discrimination capabilities and have long been regarded as the "gold standard" in the field of neutron detection.

[0003] To further improve detection efficiency, high-pressure ³He detectors have become a research hotspot. Increasing gas density can significantly increase the probability of neutron collisions with ³He nuclei, making them particularly suitable for low-flux neutron fields, such as long-distance monitoring of nuclear materials. However, ³He is primarily produced through tritium decay, resulting in extremely low natural abundance (only about 1.3 × 10⁻⁶). -6 The high purity of He (99.999% purity) results in its extremely high price, with He at a purity of 99.999% costing tens of thousands of US dollars per liter. This characteristic makes "reducing He loss and extending gas lifespan" a key prerequisite for the engineering application of high-pressure He detectors.

[0004] However, under high-pressure conditions, the detector's gas management system faces many challenges that have not yet been systematically resolved: First, maintaining gas purity over the long term presents a significant challenge. ³He detectors are extremely sensitive to gaseous impurities. Moisture can reduce the insulation of the GEM film surface, leading to increased dark current. Oxygen and volatile organic compounds (such as small molecules released from sealing materials) readily polymerize under plasma conditions, forming an insulating layer on the electrode surface, causing a continuous decrease in detector gain or even failure. Existing technologies often employ a "single-time purification before filling" approach, which cannot address the accumulation of impurities during long-term detector operation. For example, minute sputtering of electrode materials during GEM avalanches and slow venting from cavity seals continuously introduce impurities, and static purification systems cannot remove these contaminants in real time, ultimately leading to long-term degradation of detector stability.

[0005] Secondly, gas circulation under high pressure presents challenges. High-pressure He detectors require gas circulation to function. Traditional solutions often use commercial high-pressure circulation pumps, which, while achieving high-pressure sealing, are bulky and difficult to integrate into compact detector systems, such as portable radionuclide identification devices. Furthermore, some pump bodies use rubber seals, which are prone to fatigue failure and leakage during long-term high-pressure circulation. This not only results in the loss of expensive He gas but also introduces impurities, degrading detector performance.

[0006] Finally, the gas path system has a low degree of integration. The initial commissioning of the high-pressure³He detector requires three key steps: "vacuum replacement - helium purging - high-pressure charging". In traditional solutions, these three steps and the "gas circulation" during operation require independent pipelines and control units, which not only increases the complexity of the system, but also increases the risk of leakage due to the increased number of interfaces.

[0007] Therefore, developing a gas purification system and method for a high-pressure He detector that can effectively solve the above problems is of great practical significance. Summary of the Invention

[0008] To address the above problems, the present invention aims to provide a method for 3 The gas purification system and method for He neutron detectors are applicable to high-pressure environments in fields such as nuclear safety regulation, particle physics experiments, industrial non-destructive testing, and homeland security. 3 Long-term maintenance of gas purity in He detectors, high-pressure cycle drive, and system integration.

[0009] The main technical solution adopted in this invention is: a method for 3 The gas purification system of the He neutron detector includes: The high-pressure chamber has an end cap made of high-strength 7075 aluminum alloy with a square groove as an entrance window. The interior has a cylindrical groove that fits into the chassis and encloses the detection components. The chassis is made of stainless steel and is welded to the detector's signal connector, high-voltage connector, and inlet / outlet pipes. This miniaturized high-pressure circulating pump, employing a metal bellows and metal seal structure, achieves a pressure of ≤1×10⁻⁶ at 7.5 atm. -With a leakage rate of ¹¹Pa·m³ / s, and a pump body volume that is 60% of similar commercial products, it consists of a pair of one-way valves, a pair of flanges, two-stage bellows, a drive cylinder, and metal seals. It achieves gas circulation drive through a positive displacement reciprocating pump principle, and connects the internal space of the upper flange to the high-pressure chamber via a balance conduit. The two-stage bellows design ensures long-term operational reliability under high pressure. The multi-functional purified gas circuit system allows for four functions—vacuum replacement, helium purging, high-pressure charging, and circulating purification—through valve timing control. A filter is used to purify impurities in the gas; a pressure gauge is used to monitor the gas pressure within the system; valves are used to control the gas flow direction; and 1 / 4" stainless steel tubing serves as the gas circuit connection component.

[0010] The working process of the miniaturized high-pressure circulating pump is as follows: a high-pressure gas source drives a cylinder push rod to reciprocate. The push rod is connected to a two-stage bellows, converting linear displacement into periodic changes in the bellows volume. When the bellows is stretched and expanded, the internal volume increases and the pressure decreases. When the pressure difference between the bellows and the cavity exceeds the opening threshold of the inlet check valve, the valve opens, drawing gas from the detector cavity into the bellows. During the compression stroke, the bellows volume decreases and the internal pressure increases, pushing the exhaust check valve to open and pressing the gas back into the cavity circuit, thus achieving the circulation drive of high-pressure gas in the sealed cavity.

[0011] The specific operation process of the multi-functional purified gas circuit system to achieve four-function switching is as follows: Vacuuming: Connect the working gas cylinder to the corresponding valve, close the cylinder valve, connect the combined pump to the corresponding valve, open some valves, and start the back pump for rough evacuation. After rough evacuation, change the connection position of the combined pump and perform rough evacuation again. Then, first remove the air between the valve and the interface, and then open the corresponding valve to start the molecular pump to evacuate the chamber to a high vacuum of 10. -2 Pa, after completion, maintain the cavity vacuum; Working gas replacement: Open the working gas cylinder valve and slowly introduce working gas to a certain pressure, then close the cylinder valve. After standing, open the corresponding valve to discharge the gas in the cavity. When the vacuum degree reaches the set value, turn on the molecular pump to evacuate the high vacuum. Repeat the operation to maintain the vacuum state of the cavity. Inflation: Before inflation, connect the combination pump to the corresponding valve end to evacuate the small cavity to a high vacuum, then close the valve and open the relevant valves to start filling the working gas to the working pressure. After completion, close some valves. Circulation: Connect the air source to the cylinder and start the circulation pump to drive the gas circulation and perform initial purification of the working gas.

[0012] The filter is an Entegris GPUS500FDZ04R00CA filter, which has a high efficiency in purifying H2O, O2 and organic impurities at 7.5 atm. It can stably control the H2O concentration below 10 ppm, the O2 concentration below 50 ppm, and rapidly reduce organic impurities such as toluene to below the detection limit.

[0013] It also includes a mass flow meter, connected in series between the circulation pump and the filter, used to monitor the gas flow rate in the loop and assess the flow stability of the circulation pump and the reliability of the circulation function.

[0014] The system employs a helium mass spectrometer leak detector with helium injection and a static pressure holding test for sealing testing. Helium mass spectrometry leak detection: Evacuate the entire detector cavity and gas path to 10. -3 Pa, use a leak detector to systematically purge all possible leak points with helium. If the leak detector reading exceeds the background noise value and alarms stably at a suspected leak point, the point is determined to be a leak point and needs to be tightened or resealed before testing again. Static pressure holding test: After confirming no leaks by helium testing, fill the cavity and gas path with high-purity helium to the design pressure of 8 atm, close the inlet and outlet valves, and put the system in a completely closed static pressure holding state. Record the pressure change continuously within a set time under constant temperature environment. Calculate the equivalent standard leak rate of the system by using the recorded pressure-temperature-time data.

[0015] In the static pressure holding test, the recorded air pressure is temperature-corrected based on the relationship between air pressure and temperature. Each recorded air pressure is converted to air pressure under the same temperature conditions. An exponential function is then used to fit the relative air pressure change under the same temperature conditions. , Where R is the relative air pressure value, P0 is the initial air pressure, and P i Let t be the air pressure value recorded for the i-th time, and t be the time. Using the obtained leakage rate model, predict the pressure loss of the detector after the set operating period and calculate the equivalent standard leakage rate.

[0016] A type of 3 The gas purification method for He neutron detectors includes the following steps: Vacuuming procedure: Follow the vacuuming operation process of the multi-functional purified gas path system to evacuate the detector cavity and gas path to a high vacuum state; Working gas replacement procedure: Following the working gas replacement operation process of the multi-functional purified gas circuit system, the cavity is replaced with gas multiple times while maintaining a vacuum state; Inflation procedure: Following the inflation operation process of the multi-functional purified air circuit system, inflate the cavity with working gas to the working pressure; Circulation and purification steps: Start the miniaturized high-pressure circulation pump to drive the gas to circulate in the circulation loop containing the filter, and continuously purify the gas through the filter; at the same time, the system can be tested for tightness by helium injection method and static pressure holding test method as needed using helium mass spectrometer leak detector.

[0017] In the circulation purification step, the gas flow rate in the loop is monitored by a mass flow meter to evaluate the flow stability of the circulation pump and the reliability of the circulation function; filtered gas samples are collected and sent to a professional testing institution to determine the impurity concentration in order to quantify the filter purification efficiency.

[0018] The gas purification method described herein is applicable to high-pressure applications in nuclear safety regulation, particle physics experiments, industrial non-destructive testing, and homeland security. 3 HeGEM neutron detector.

[0019] The present invention is used for 3 The gas purification system and method for He neutron detectors have many significant advantages over existing technologies and in practical applications, as detailed below: This invention integrates a high-efficiency filter (such as the Entegris GPUS500FDZ04R00CA filter) with a miniaturized high-pressure circulation pump to construct a dynamic and continuous purification circulation loop. At an operating pressure of 7.5 atm, the system effectively removes key impurities such as H2O, O2, and volatile organic compounds, stably controlling H2O concentration below 10 ppm, O2 concentration below 50 ppm, and rapidly reducing organic impurities such as toluene to below the detection limit. This fundamentally overcomes the shortcomings of traditional "single-cycle purification" modes in dealing with the continuous accumulation of impurities during operation, providing crucial assurance for the long-term stable operation and high gain maintenance of the detector, and significantly improving the accuracy and reliability of neutron detection.

[0020] This invention relates to a miniaturized high-pressure circulating pump independently developed, which employs a metal bellows and metal sealing structure, ensuring a pressure of ≤1×10⁻⁶. -10 With an extremely low leakage rate of Pa·m³ / s, the pump body volume is only 60% of that of commercially available similar products, allowing for direct integration into the detector cavity. This successfully solves the problem of bulky and difficult-to-integrate high-pressure circulating pumps. Performance testing confirms that the pump can provide a stable flow rate of 2 L / min at 7.5 atm, with fluctuations of less than ±3%, and the power output is sufficient to overcome system flow resistance. Its metal bellows and metal sealing structure effectively avoids the fatigue leakage risk of rubber seals under high-pressure circulation, significantly reducing the possibility of loss of expensive He³ gas and lowering operating costs.

[0021] This invention's multifunctional purified gas system, through sequential valve control, enables the same piping system to sequentially perform four core functions: vacuum replacement, helium purging, high-pressure charging, and circulating purification. This integrated design significantly reduces the number of independent valves, connectors, and pipes required by the system, simplifying the operation process and reducing potential leakage points at the physical level, thus improving the inherent reliability of the entire gas system. Verified by helium mass spectrometry leak detection and static pressure holding tests, the system achieves extremely high sealing levels at all static sealing interfaces, with an equivalent standard leak rate as low as 4.54 × 10⁻⁶. - 12 The Pa·m³ / s range is crucial for high-value, long-life He detector engineering applications, ensuring the stability and safety of the detector during long-term operation.

[0022] The switchable gas path designed in this invention allows the filter to be connected to the main circulation loop only when active purification is required. In normal operation, the filter is bypassed, forming a "micro-circulation" loop. This design ensures gas uniformity while minimizing dead volume and potential contamination risks, further optimizing system performance, improving system adaptability and flexibility, and meeting the needs of different operating conditions.

[0023] This invention is applicable to high-pressure³HeGEM neutron detectors in the fields of nuclear safety regulation, particle physics experiments, industrial non-destructive testing, and homeland security. It provides reliable technical support for neutron detection in these fields, helps promote the technological development and application expansion of related fields, and has significant economic and social benefits. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the exploded structure of the detector in this invention; Figure 2 This is a schematic diagram of the detector's main view structure in this invention; Figure 3 This is a schematic diagram of the circulating pump structure in this invention; Figure 4 This is a schematic diagram of the loop in this invention; Figure 5 This is the gas path diagram of the detector in this invention; Figure 6 This is the test gas path diagram in this invention; Figure 7 This is a schematic diagram of the cavity pressure holding record in this invention; Figure 8 This is a schematic diagram illustrating the relationship between air pressure and temperature in this invention; Figure 9 This is a schematic diagram of relative pressure changes under the same temperature conditions in this invention; Attached diagram labels: 1-Cylinder, 2-Cylinder push rod, 3-Lower flange, 4-Secondary bellows, 5-Primary bellows, 6-Upper flange, 7-Check valve, 8-O-ring, 9-Copper gasket, 10-Check valve, 11-Inlet window, 12-End cap, 13-GEM membrane, 14-Chassis, 15-Filter, 16-Circulation pump. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0026] like Figure 1-9 As shown, this embodiment is used for 3 The gas purification system of the He neutron detector mainly consists of a high-pressure chamber, a miniaturized high-pressure circulating pump 16, a multi-functional purification gas path system, a filter 15, pressure gauges, valves, 1 / 4" stainless steel tubing, and a mass flow meter. It is suitable for high-pressure applications in nuclear safety regulation, particle physics experiments, industrial non-destructive testing, and homeland security. 3 HeGEM neutron detector.

[0027] The high-pressure chamber in this embodiment features an end cap 12 made of high-strength 7075 aluminum alloy. Its outer surface has a square groove with an area of ​​204×204 mm², serving as the detector's entrance window 11. This entrance window 11 deforms by less than 0.6 mm under 7.5 atm pressure and has sufficiently high neutron transmittance. The end cap 12 has an internal cylindrical groove that, when engaged with the chassis 14, completely encloses the detector's components, such as the PCB board and GEM film 13. The chassis 14 is made of stainless steel and is used to weld to the detector's signal connectors, high-voltage connectors, and inlet / outlet pipes, ensuring a stable and airtight connection.

[0028] The miniaturized high-pressure circulating pump 16 in this embodiment adopts a metal bellows and metal sealing structure. Its core components include a pair of one-way valves (inlet one-way valve 7, exhaust one-way valve 10), a pair of flanges (upper flange 6 and lower flange 3), two-stage bellows (first-stage bellows 5 and second-stage bellows 4), a drive cylinder 1, and metal sealing rings (O-rings 8 and copper washers 9). Its maximum external dimension (flange diameter) is 70mm, and the pump body volume is only 60% of that of similar commercial products, effectively meeting the limited installation space requirements at the back end of the detector.

[0029] The working principle is based on the principle of a positive displacement reciprocating pump. A high-pressure air source drives the cylinder push rod 2 to reciprocate. The cylinder push rod 2 is connected to a two-stage bellows, thus converting the linear displacement of the cylinder push rod 2 into a periodic change in the volume of the bellows. When the bellows is stretched and expanded, its internal volume increases and the pressure decreases. When the pressure difference between the bellows and the cavity exceeds the opening threshold of the inlet check valve 7, the valve opens, drawing gas from the detector cavity into the bellows. Subsequently, during the compression stroke, the bellows volume decreases and the internal pressure increases, pushing the exhaust check valve 10 to open and pushing the gas back into the cavity circuit. Through this continuous action of suction and exhaust, the high-pressure gas in the sealed cavity is circulated and driven.

[0030] In this embodiment, a balanced conduit connects the internal space of the upper flange 6 to the high-pressure chamber, so that the bellows is always subjected to system pressure when it is stationary and working, thereby avoiding the bellows from deforming and failing due to the huge pressure difference in the initial state.

[0031] This embodiment employs a two-stage bellows design to isolate the dynamic seal (between the lower flange 3 and the cylinder push rod 2) from the static seal (between the upper flange 6 and the lower flange 3). The dynamic seal uses an O-ring 8 to seal the cylinder 1 and the lower flange 3, preventing gas from the pump from entering the atmosphere. The static seal uses a copper gasket 9, which seals the upper flange 6 and the lower flange 3, significantly improving the overall sealing integrity and achieving a sealing density of ≤1×10⁻⁶. -11 The extremely low leakage rate of Pa·m³ / s laid the mechanical foundation.

[0032] The multifunctional purified gas path system in this embodiment: This system enables the same gas path to switch between four functions: "vacuum replacement - helium purging - high-pressure charging - circulating purification" through valve timing control. The system mainly consists of key components such as detector cavity, filter 15, circulating pump 16, mass flow meter, pressure gauge, needle valve, and 1 / 4" stainless steel tubing.

[0033] The function switching process of the multi-functional purified gas circuit system in this embodiment is as follows: Vacuuming: Before evacuation, connect the working gas cylinder to valve 3, close the cylinder valve, connect the combined pump to valve 4, open valves 1, 2, 3, and 4, close valves 5 and 6, and start the backing pump for rough evacuation. After rough evacuation, close valve 4, connect the combined pump to valve 6, open valve 6, and start the backing pump to perform rough evacuation of the blue section of the cavity. After completion, close valve 6, and then connect the combined pump to valve 4. Due to a small amount of air between the valve and the interface, first keep valve 4 closed, start the backing pump to remove the air between the valve and the interface, then open valve 4 and start the molecular pump to evacuate the cavity to a high vacuum of 10. -2Pa, after completion, close valve 4 to maintain chamber vacuum, turn off molecular pump while keeping back pump on and combined pump connected.

[0034] Working gas replacement: Open the working gas cylinder valve and slowly introduce working gas to a pressure of 1.2 atm. After completion, close the cylinder valve and let it stand for 10 minutes. Then, open valve No. 4 to purge the gas from the chamber. When the vacuum reaches 0.1 Pa, turn on the molecular pump to evacuate to a high vacuum. Repeat the above operation 3-4 times, and finally maintain the vacuum state of the chamber.

[0035] Inflation: Before inflation, connect the combination pump to valve 6 to evacuate the small cavity in the blue part to a high vacuum. After completion, close valve 6 and open valve 5 to start filling the gas cylinder with working gas to the working pressure. After completion, close valves 3 and 5.

[0036] Circulation: Connect the air source to cylinder 1 to start the circulation pump 16, drive the gas circulation, and perform initial purification of the working gas.

[0037] In this embodiment, filter 15 is an Entegris GPUS500FDZ04R00CA filter 15. This filter 15 has a high purification capacity for H2O, O2, and organic impurities at 7.5 atm. Experimental verification shows that it can stably control the H2O concentration below 10 ppm, the O2 concentration below 50 ppm, and rapidly reduce organic impurities such as toluene to below the detection limit, thus meeting the requirements for maintaining the purity of 3He gas during long-term operation of the detector.

[0038] In this embodiment, the pressure gauge is installed in a suitable location within the system to monitor the gas pressure in real time, providing operators with accurate gas pressure information so that system operating parameters can be adjusted in a timely manner to ensure that the system operates within a safe pressure range.

[0039] In this embodiment, the valves used are needle valves or similar types. By precisely controlling the opening and closing of the valves, as well as the degree of opening, the direction and flow of gas can be accurately controlled, thereby ensuring that the multifunctional purified gas circuit system can smoothly switch between the four functions.

[0040] In this embodiment, the 1 / 4" stainless steel tube serves as a gas path connection component, used to connect various gas management components, such as the detector cavity, filter 15, circulation pump 16, pressure gauge, valve, etc., to form a complete gas flow loop, ensuring that the gas can flow smoothly within the system.

[0041] In this embodiment, the mass flow meter is connected in series between the circulating pump 16 and the filter 15 to monitor the gas flow rate in the circuit. By acquiring flow rate data in real time, the flow stability and reliability of the circulating pump 16 can be evaluated, providing important monitoring data for the normal operation of the system.

[0042] To ensure the long-term safe storage and stable operation of expensive He gas, this system employs a helium mass spectrometer leak detector with helium injection and a static pressure holding test for sealing performance testing. The main steps are as follows: P1 Helium Mass Spectrometer Leak Detection: Evacuate the entire detector cavity and gas path to 10°C. -3 Pa, use a leak detector to systematically purge all possible leak points with helium. These leak points include the cavity welds, the sealing surfaces of the end cap 12 and chassis 14, all VCR joints, valve stems and seats, the bellows welds of the circulating pump 16, and dynamic sealing interfaces, etc. If the leak detector reading exceeds the background noise value and alarms stably at a suspected leak point, the location is determined to be a leak point, and tightening or resealing is required before retesting.

[0043] P2 Static Pressure Holding Test: After confirming no leaks with helium testing, the chamber and gas lines are filled with high-purity helium to the design pressure of 8 atm. The inlet and outlet valves are closed, placing the system in a completely closed static pressure holding state. Pressure changes are continuously recorded over 720 hours in a constant temperature environment (25±2℃). The equivalent standard leak rate of the system is calculated using the recorded pressure-temperature-time data. The specific calculation process is as follows: The recorded pressure is temperature-corrected based on the relationship between pressure and temperature. Each recorded pressure is converted to pressure under the same temperature conditions. An exponential function is used to fit the change in relative pressure (the ratio of each pressure to the initial pressure value) under the same temperature conditions, resulting in an exponential function: , Where R is the relative air pressure value, P0 is the initial air pressure, and P i Let t be the air pressure value recorded for the i-th time, and t be the time. Using the obtained leakage rate model, the pressure loss of the detector after 10 years of operation (87,600 hours) is predicted.

[0044] To further optimize the system and reduce the impact of filter 15 on the system during normal operation, this system also includes a switchable gas path design. By setting specific valve combinations, filter 15 is only connected to the main circulation loop when active purification is required (such as after system maintenance or when a decrease in purity is detected). During normal operation, filter 15 is bypassed, forming a shorter and cleaner "micro-circulation" loop, thereby minimizing dead volume and potential contamination risks while ensuring gas homogeneity.

[0045] The test results and analysis of this embodiment after multiple tests are as follows: Helium mass spectrometry leak detection results: Two rounds of comprehensive helium injection scans were performed on all sealed interfaces of the system. The first scan detected a weak leak at the static seal of flange 6 on circulating pump 16. After disassembly, replacement of metal gasket 9, and re-tightening, a second scan was performed. The results showed that the leak rate at all measuring points was below the effective detection limit of the leak detector (<5.0×10⁻⁶). -11 The Pa·m³ / s indicates that there is no detectable helium leak in the system.

[0046] Static pressure holding test results: After 792 hours of static pressure holding at an initial pressure of 8 bar, the pressure change curve over time is shown below. Figure 7 As shown, it exhibits good periodic fluctuations. Figure 8 To record the pressure and temperature of the high-pressure chamber, the relationship between pressure and temperature was obtained. The recorded pressure was then converted to pressure under the same temperature conditions based on this relationship. After temperature correction, the fluctuation range of the pressure data was significantly reduced, effectively eliminating the influence of temperature changes on the pressure readings and making the leakage trend more obvious. To obtain the change in relative pressure (i.e., the ratio of each pressure to the initial pressure value) under the same temperature conditions, the leakage rate of the high-pressure chamber was determined. The higher the pressure, the greater the leakage rate. The relative pressure obtained on the first day was 1, and the relative pressure after an infinitely long time was 0. Therefore, exponential fitting was used. Figure 9 The relative pressure change yields an exponential function: In the formula, R is the relative air pressure value, P0 is the initial air pressure, and P i Let t be the air pressure value recorded for the i-th time, and t be the time.

[0047] Using the obtained leakage rate model, the pressure loss of the detector after 10 years of operation (87,600 hours) is predicted: in, This is a prediction of relative air pressure 10 years from now.

[0048] Based on the above model, the predicted relative air pressure in 10 years is: The corresponding pressure value is Pressure loss is The equivalent standard leakage rate can be calculated using the formula. : in, For total pressure drop, atm is standard atmospheric pressure. L is the system volume. h represents the predicted lifetime. The equivalent standard leak rate is calculated after unit conversion. Pa·m³ / s.

[0049] The sealing test results of this embodiment fully verify the superiority of the gas management system design. Helium mass spectrometry leak detection confirms that, after fine-tuning, the system achieved an extremely high sealing level (leakage rate <5.0 × 10⁻⁶) at all static sealing interfaces. - ¹¹Pa·m³ / s), far exceeding the sealing requirements of typical high vacuum / high pressure systems (usually 10). -10 (on the order of Pa·m³ / s).

[0050] A static pressure test lasting 792 hours showed that the system's equivalent standard leak rate at a design pressure of 8 atm was as low as 4.54 × 10⁻⁶. -12 The result is on the order of Pa·m³ / s. This result corroborates the helium injection detection results, proving the sealing reliability of the system under long-term static conditions. The small pressure drop is likely due to temperature fluctuations or weak adsorption / desorption effects of the material, rather than actual leakage. This leakage rate means that the annual loss rate of He gas is extremely low, fully meeting the stringent requirements for gas retention during the detector's long operating cycle of several years. This fundamentally solves the core challenge of high-pressure He detectors, which suffer from performance degradation and high operating costs due to gas leakage.

[0051] In summary, the Entegris GPU S500FDZ04R00CA filter 15 demonstrates highly efficient purification capabilities for H2O, O2, and organic impurities at 7.5 atm, with consistently stable purification performance over long periods, meeting the requirements for long-term detector operation. 3 Maintaining the purity of He gas is required; at the same time, combined with the stable circulation function of the circulation pump 16, the purification system can achieve closed-loop operation of "continuous circulation - high-efficiency purification - accurate gas sampling verification", which ensures the long-term reliability of the detector.

[0052] Through the detailed embodiments described above, those skilled in the art can implement the present invention according to actual needs and conditions. 3 The gas purification system of the He neutron detector effectively solves the problem of high gas pressure. 3 The core challenges facing He detectors are maintaining gas purity over long periods, high-pressure cyclic drive, and system integration.

Claims

1. A method for 3 The gas purification system of the He neutron detector is characterized by... include: The high-pressure chamber has an end cap made of high-strength 7075 aluminum alloy, with a square groove as an entrance window, and a cylindrical groove inside that fits with the chassis to enclose the detection component. The chassis is made of stainless steel and is welded to the detector's signal connector, high-voltage connector, and air inlet / outlet pipes. This miniaturized high-pressure circulating pump, employing a metal bellows and metal seal structure, achieves a pressure of ≤1×10⁻⁶ at 7.5 atm. - With a leakage rate of ¹¹Pa·m³ / s, the pump body volume is 60% of that of similar commercial products. It consists of a pair of check valves, a pair of flanges, two-stage bellows, a drive cylinder, and a metal seal ring. It achieves gas circulation drive through the principle of positive displacement reciprocating pump. Furthermore, it connects the internal space of the upper flange with the high-pressure chamber through a balance conduit and adopts a two-stage bellows design to ensure long-term operational reliability under high pressure. The multi-functional purified gas circuit system enables the same gas circuit to switch between four functions: "vacuum replacement - helium purging - high-pressure charging - circulation purification" through valve timing control. A filter is used to purify impurities from a gas. Pressure gauges are used to monitor gas pressure within a system; Valves are used to control the direction of gas flow; A 1 / 4" stainless steel tube is used as a gas connection component.

2. The method for use according to claim 1 3 The gas purification system of the He neutron detector is characterized by... The working process of the miniaturized high-pressure circulating pump is as follows: a high-pressure gas source drives a cylinder push rod to reciprocate. The push rod is connected to a two-stage bellows, converting linear displacement into periodic changes in the bellows volume. When the bellows is stretched and expanded, the internal volume increases and the pressure decreases. When the pressure difference between the bellows and the cavity exceeds the opening threshold of the inlet check valve, the valve opens, drawing gas from the detector cavity into the bellows. During the compression stroke, the bellows volume decreases and the internal pressure increases, pushing the exhaust check valve to open and pressing the gas back into the cavity circuit, thus achieving the circulation drive of high-pressure gas in the sealed cavity.

3. The method for use according to claim 1 3 The gas purification system of the He neutron detector is characterized by... The specific operation process of the multi-functional purified gas circuit system to achieve four-function switching is as follows: Vacuuming: Connect the working gas cylinder to the corresponding valve, close the cylinder valve, connect the combined pump to the corresponding valve, open some valves, and start the back pump for rough evacuation. After rough evacuation, change the connection position of the combined pump and perform rough evacuation again. Then, first remove the air between the valve and the interface, and then open the corresponding valve to start the molecular pump to evacuate the chamber to a high vacuum of 10. -2 Pa, after completion, maintain the cavity vacuum; Working gas replacement: Open the working gas cylinder valve and slowly introduce working gas to a certain pressure, then close the cylinder valve. After standing, open the corresponding valve to discharge the gas in the cavity. When the vacuum degree reaches the set value, turn on the molecular pump to evacuate the high vacuum. Repeat the operation to maintain the vacuum state of the cavity. Inflation: Before inflation, connect the combination pump to the corresponding valve end to evacuate the small cavity to a high vacuum, then close the valve and open the relevant valves to start filling the working gas to the working pressure. After completion, close some valves. Circulation: Connect the air source to the cylinder and start the circulation pump to drive the gas circulation and perform initial purification of the working gas.

4. The method for use according to claim 1 3 The gas purification system of the He neutron detector is characterized by... The filter is an Entegris GPUS500FDZ04R00CA filter, which has a high purification capacity for H2O, O2 and organic impurities at 7.5 atm. It can stably control the H2O concentration below 10 ppm, the O2 concentration below 50 ppm, and rapidly reduce organic impurities such as toluene to below the detection limit.

5. The method for use according to claim 1 3 The gas purification system of the He neutron detector is characterized by... It also includes a mass flow meter, connected in series between the circulation pump and the filter, used to monitor the gas flow rate in the loop and assess the flow stability of the circulation pump and the reliability of the circulation function.

6. The method for use according to claim 1 3 The gas purification system of the He neutron detector is characterized by... The system employs a helium mass spectrometer leak detector with helium injection and a static pressure holding test for sealing testing. Helium mass spectrometry leak detection: Evacuate the entire detector cavity and gas path to 10. -3 Pa, use a leak detector to systematically purge all possible leak points with helium. If the leak detector reading exceeds the background noise value and alarms stably at a suspected leak point, the point is determined to be a leak point and needs to be tightened or resealed before testing again. Static pressure holding test: After confirming no leaks by helium testing, fill the cavity and gas path with high-purity helium to the design pressure of 8 atm, close the inlet and outlet valves, and put the system in a completely closed static pressure holding state. Record the pressure change continuously within a set time under constant temperature environment. Calculate the equivalent standard leak rate of the system by using the recorded pressure-temperature-time data.

7. The method for use according to claim 6 3 The gas purification system of the He neutron detector is characterized by... In the static pressure holding test, the recorded air pressure is temperature-corrected based on the relationship between air pressure and temperature. Each recorded air pressure is converted to air pressure under the same temperature conditions. An exponential function is then used to fit the relative air pressure change under the same temperature conditions. ， Where R is the relative air pressure value, P0 is the initial air pressure, and P i Let t be the air pressure value recorded for the i-th time, and t be the time. Using the obtained leakage rate model, predict the pressure loss of the detector after the set operating period and calculate the equivalent standard leakage rate.

8. A method for 3 The gas purification method for a He neutron detector is characterized by... Using any one of claims 1-7 for 3 The gas purification system for the He neutron detector includes the following steps: Vacuuming procedure: Follow the vacuuming operation process of the multi-functional purified gas path system to evacuate the detector cavity and gas path to a high vacuum state; Working gas replacement procedure: Following the working gas replacement operation process of the multi-functional purified gas circuit system, the cavity is replaced with gas multiple times while maintaining a vacuum state; Inflation procedure: Following the inflation operation process of the multi-functional purified air circuit system, inflate the cavity with working gas to the working pressure; Circulation and purification steps: Start the miniaturized high-pressure circulation pump to drive the gas to circulate in the circulation loop containing the filter, and continuously purify the gas through the filter; at the same time, the system can be tested for tightness by helium injection method and static pressure holding test method as needed using helium mass spectrometer leak detector.

9. The method for use according to claim 8 3 The gas purification method for a He neutron detector is characterized by... In the circulation purification step, the gas flow rate in the loop is monitored by a mass flow meter to evaluate the flow stability of the circulation pump and the reliability of the circulation function; filtered gas samples are collected and sent to a professional testing institution to determine the impurity concentration in order to quantify the filter purification efficiency.

10. The method for use according to claim 8 3 The gas purification method for a He neutron detector is characterized by... The gas purification method described herein is applicable to high-pressure applications in nuclear safety regulation, particle physics experiments, industrial non-destructive testing, and homeland security. 3 HeGEM neutron detector.

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