Vacuum system for precisely controlling gas density of nano dose detector

Abstract

The invention discloses a vacuum system for precisely controlling the gas density of a nano-dose detector, and belongs to the field of ionizing radiation nano-dose measurement. The system comprises a vacuum pump set unit, a vacuum degree detection unit and a logic control unit. According to the requirements of the nano dose detector for the vacuum degree and the gas concentration, the working air pressure is within 1 Torr and the air pressure control precision reaches 0.01 Torr through cooperation of a pump set in a vacuum system and PLC logic control and data monitoring. The system can provide gas for generating ionizing radiation and a low-vacuum environment for the nano-dose detector, and ensures that a measurement signal of the nano-dose detector is accurate and stable. The ionization degree of the nano dose detector depends on the vacuum degree in the cavity, and the vacuum degree of the cavity depends on the concentration of gas in the sensitive volume. The method has the advantages of high precision, high accuracy, high reliability and the like. According to the invention, the vacuum environment of the nano-dose detector is constant, the sensitive gas is single, and the precise measurement of the nano-dose detector can be supported.

Description

Technical Field

[0001] The invention relates to a vacuum system for precise control of gas density of a nanodose detector, belonging to the field of ionizing radiation nanodose measurement. Background Art

[0002] A deep understanding of the energy deposition and damage mechanism during the interaction between ionizing radiation and human tissue is the key to achieving precision radiotherapy. A nanodose detector is a detection device used to measure nanoscale dose characteristics during radiotherapy. The airtight chamber of the device needs to maintain a single type of sensitive gas with a constant concentration to achieve the detector's ion counting measurement, so as to understand the damage mechanism during the radiation beam. In practical applications, the vacuum degree in the cavity of the device needs to be kept constant at 1 Torr (the gas density is about 2.3×10-6g / cm3). However, the traditional gas concentration control method often uses a single vacuum pump to adjust the vacuum pressure, which makes it difficult to achieve quantitative and precise control of the gas concentration and meet the current measurement conditions of nanodose detectors. If the concentration of sensitive gas inside the cavity of the nanodose detector is too high or too low, the detection signal will be seriously deviated. How to control the vacuum degree and gas concentration inside the cavity within a reasonable range has become one of the research focuses of nanodose detectors. In order to solve this problem, it is urgent to systematically develop a vacuum system device with multiple vacuum pumps for precise control of gas density in nanodose detectors. Summary of the invention

[0003] In order to overcome the above-mentioned measurement difficulties of nanodose detectors, the purpose of the present invention is to provide a vacuum system for precise control of gas density of nanodose detectors. In view of the requirements of nanodose detectors for vacuum degree and gas concentration, the pump group and PLC logic control in the vacuum system are coordinated with data monitoring to achieve a working gas pressure within 1 Torr, and the gas pressure control accuracy reaches 0.01 Torr. The system can provide the nanodose detector with gas and a low vacuum environment that produce ionizing radiation, ensuring that the measurement signal of the nanodose detector is accurate and stable. The degree of ionization of the nanodose detector depends on the vacuum degree in the cavity, and the vacuum degree of the cavity depends on the concentration of the gas in the sensitive volume. The present invention has the advantages of high precision, high accuracy, and high reliability. Through the present invention, the vacuum environment of the nanodose detector can be constant and the sensitive gas can be single, which can support the precise measurement of the nanodose detector and help to establish the inline relationship between the nanodose quantity and the macroscopic water absorption dose.

[0004] The purpose of the present invention is achieved through the following technical solutions.

[0005] The invention discloses a vacuum system for precise control of gas density of a nanodose detector, comprising a vacuum pump unit, a vacuum degree detection unit and a logic control unit.

[0006] The vacuum pump unit consists of a molecular pump, a vortex pump a, a vortex pump b, a first high-pressure solenoid valve, and a second high-pressure solenoid valve. The air inlet of the vortex pump a is connected to the high-pressure solenoid valve through a vacuum pipe, the air inlet of the vortex pump b is connected to the air outlet of the molecular pump through a vacuum pipe, and the third high-pressure solenoid valve is connected to the air inlet of the molecular pump through a vacuum pipe. The high-pressure solenoid valve and the other side of the high-pressure solenoid valve are connected to the air outlet below the nanodose detector through a KF interface. The vortex pump a is used for pre-pumping to ensure that the vacuum inside the cavity drops below 20Pa. Since the vacuum degree when the molecular pump is started needs to be below 10Pa, the vortex pump b is installed as a drag pump of the molecular pump, thereby ensuring that the pressure on both sides of the molecular pump and the air inlet and outlet is less than 10Pa to complete the opening of the molecule. The stable operation of the molecular pump is ensured by the coordinated use of the pump group. If the molecular pump is turned on directly under atmospheric pressure, the blades in the pump will be damaged and the molecular pump will be damaged.

[0007] The vacuum detection unit includes a low vacuum pressure sensor, a high vacuum pressure sensor, and a static vacuum pressure sensor. The vacuum detection unit is used to detect the vacuum degree inside the pipeline and the cavity. The low vacuum pressure sensor is installed on the sixth vacuum pipeline between the bottom air outlet and the third high-pressure solenoid valve, and is used to detect the vacuum degree of the sixth vacuum pipeline in real time. The high vacuum pressure sensor is installed on the seventh vacuum pipeline between the molecular pump and the high-pressure third high-pressure solenoid valve, and is used to detect the vacuum degree on the seventh pipeline to detect whether the pipeline vacuum degree reaches the molecular pump start-up condition. The static vacuum pressure is connected to the middle air outlet of the nanodose detector to detect the static vacuum degree in the nanodose detector cavity. The vacuum degree detection unit is used to ensure the detection of the vacuum degree of the pipeline and the cavity, and the PLC logic controller in the logic control unit is efficiently coordinated to judge the current vacuum state, and the high-pressure solenoid valve is controlled to operate, and then the MFC flow controller is coordinated to deliver effective gas to achieve the preset vacuum condition and gas concentration. The pipeline refers to the sixth vacuum pipeline and the seventh vacuum pipeline.

[0008] The logic control unit includes a PLC controller, an MFC flow controller, a gas cylinder A, a gas cylinder B, a fourth high-pressure solenoid valve, and a first high-pressure solenoid valve. The fourth high-pressure solenoid valve is connected to the gas cylinder A, and the fourth high-pressure solenoid valve is connected to the first high-pressure solenoid valve. One end of the MFC flow controller is connected to the gas cylinder B, and the other end is connected to the first high-pressure solenoid valve. The other side of the first high-pressure solenoid valve is connected to the air inlet at the top of the cavity. In addition, the PLC controller is connected to the first high-pressure solenoid valve, the second high-pressure solenoid valve, the third high-pressure solenoid valve, the fourth high-pressure solenoid valve, the MFC, and the static vacuum pressure sensor communication interface. The PLC logic control collects the branch vacuum value and the MFC flow meter state and flow information. Through the serial communication multi-device collaborative control, the PLC logic controller determines the current vacuum state, controls the high-pressure solenoid valve action, and then cooperates with the MFC flow controller to deliver effective gas to ensure that the concentration of the sensitive gas inside the nanodose detector cavity is constant and the negative pressure environment realizes the measurement environment of the nanodose detector, and reaches the preset vacuum condition and gas concentration requirements.

[0009] In order to ensure remote control accuracy and sensitivity, preferably, the first high-pressure solenoid valve, the second high-pressure solenoid valve, the third high-pressure solenoid valve, and the fourth high-pressure solenoid valve are all high-pressure solenoid valves.

[0010] The present invention discloses a working method of a vacuum system for precise control of gas density of a nanodose detector as follows:

[0011] Step 1: Start the vacuum pump unit. In order to ensure the stable startup of the molecular pump and the vortex pump, it is necessary to complete the entire startup process of the pump unit and the system self-test. Start the vortex pump a and the vortex pump b. Before starting, it is necessary to check whether the first high-pressure solenoid valve, the second high-pressure solenoid valve, the third high-pressure solenoid valve, the fourth high-pressure solenoid valve, and the MFC flow controller are closed to ensure that the pipes connecting the molecular pump and the vortex pump are in a sealed cover state to prevent damage to the molecular pump. When the high vacuum pressure sensor on the pipeline indicates below 20Pa, it means that the vacuum degree of the pipeline meets the startup conditions of the molecular pump. When the startup conditions are met, the molecular pump is started. When the molecular pump speed is stable, the vacuum pump unit startup is completed.

[0012] Step 2: Through the PLC collaborative control, the second high-pressure solenoid valve is opened to complete the pipeline conduction between the nanodose detector cavity and the vortex pump. This process is a rough exhaust process of the nanodose detector cavity, and the vacuum degree inside the nanodose detector cavity is quickly reduced to below 20Pa. When the value of the low vacuum pressure sensor is ≤10Pa, it indicates that the vacuum degree of the pipeline has reached the limit of the vortex pump a, and the nanodose detector cavity is pre-evacuated. To completely extract the air in the nanodose detector cavity, a molecular pump with a stronger pumping speed is required. At this time, the second high-pressure solenoid valve is closed and the third high-pressure solenoid valve is opened to complete the pipeline conduction between the nanodose detector cavity and the molecular pump, so as to achieve precise exhaust of the nanodose detector cavity and extract the gas molecules more finely. The molecular pump has a stronger pumping speed to keep the nanodose detector cavity at a lower vacuum degree.

[0013] Step 3: In actual situations, due to the leakage rate of the nanodose detector cavity and pipelines and the dead volume problem inside the nanodose detector cavity, the nanodose detector cavity cannot be evacuated to an absolute vacuum. At this time, gas replacement is required to minimize the gas impurities inside the nanodose detector cavity. When the value of the low vacuum pressure sensor reaches 1-3Pa, close the second high-pressure solenoid valve and open the first and second high-pressure solenoid valves of the air inlet valve to transport the nitrogen in gas cylinder A to the interior of the nanodose detector cavity, so that the nitrogen molecules occupy space inside the nanodose detector cavity, thereby rapidly raising the vacuum degree in the cavity to atmospheric pressure. When the value of the low vacuum pressure sensor is ≥10 -5 When Pa, the first high-pressure solenoid valve and the second high-pressure solenoid valve are closed to complete the nitrogen intake process.

[0014] Step 4: Cycle steps 2 and 3, and control the content of other gases in the nanodose detector cavity except nitrogen to below 0.1% through nitrogen circulation washing. Cycle steps 2 and 3 15 to 20 times, and finally keep the nanodose detector cavity in a vacuum state and the first high-pressure solenoid valve, the second high-pressure solenoid valve, and the fourth high-pressure solenoid valve are all in a closed state. The vacuum state refers to a vacuum degree ≤ 1.2Pa.

[0015] Step 5: The effective gas in the gas cylinder B is introduced through the MFC flowmeter to establish the relationship between the vacuum pressure and the propane gas concentration. The flow rate of the MFC flowmeter is set to 0.01-0.1 mL / min. The PLC detects the value of the static vacuum gauge in real time. When the value is equal to the set value, the MFC flowmeter and the first high-pressure solenoid valve are closed, and the pressure of the nanodose detector cavity is completed. The actual vacuum degree in the nanodose detector cavity is guaranteed to be within 5% of the set value deviation, thereby ensuring that the measurement signal is accurate and stable. The source of the deviation within 5% is due to the dead volume inside the nanodose detector cavity and the adsorption of gas molecules by the deposited grease. The corresponding relationship between the actual vacuum degree and the set value deviation is determined by fitting. The vacuum degree is precisely controlled according to the corresponding relationship between the actual vacuum degree and the set value deviation after fitting, that is, the precise control of the gas density in the nanodose detector cavity is achieved.

[0016] Preferably, according to steps one to five, the vacuum degree of the nanodose detector cavity is controlled within the range of 1 Torr to 30 Torr to ensure that the measurement signal of the nanodose detector is accurate and stable, and the readout pole signal of the ionization avalanche event is counted by the nanodose detector, and an inline relationship between the nanodose quantity and the macroscopic water absorption dose is established based on the readout pole signal counting result.

[0017] As a further preferred embodiment, according to steps 1 to 5, the vacuum degree of the nanodose detector cavity is controlled within the range of 2 Torr to 8 Torr, so as to further improve the accuracy and stability of the nanodose detector measurement signal.

[0018] Beneficial effects:

[0019] 1. The present invention discloses a vacuum system for precise control of gas density of nanodose detectors, which is based on a gas precision extraction method combining a front-stage vortex pump and a molecular pump, and uses a PLC logic controller to collect pipeline vacuum values ​​through a serial port protocol to complete the start-up of a pump group consisting of a molecular pump and a vortex pump. Compared with a single vortex pump, the present invention can achieve rapid response and enable the nanodose detector cavity to reach a lower vacuum degree, and reduce the air content to a minimum by washing, thereby reducing the gas content in the nanodose detector cavity.

[0020] 2. The present invention discloses a vacuum system for precise control of gas density in a nanodose detector. The vacuum detection unit ensures the detection of the vacuum degree of the pipeline and the nanodose detector cavity, and efficiently cooperates with the logic control unit to control the high-pressure solenoid valve to achieve precise control of the pressure inside the nanodose detector cavity, meeting the high standard requirements for vacuum degree and gas content when an ionization avalanche event occurs, that is, the vacuum degree is in the range of 1Torr to 30Torr.

[0021] 3. The vacuum system for precise control of gas density of nanodose detector disclosed in the present invention installs a vortex pump b as a drag pump of the molecular pump, thereby ensuring that the pressure on both sides of the molecular pump and the air inlet and the air outlet is less than 10Pa to complete the opening of the molecule. The stable operation of the molecular pump is ensured by the coordinated use of the pump group. If the molecular pump is directly opened under atmospheric pressure, the blades in the pump will be damaged and the molecular pump will be damaged.

[0022] 4. The present invention discloses a vacuum system for precise control of gas density of a nanodose detector. By setting the flow rate of the MFC flowmeter, the PLC detects the value of the static vacuum gauge in real time. When the value is equal to the set value, the MFC flowmeter and the first high-pressure solenoid valve are closed, and the pressure of the nanodose detector cavity is waited for to be equalized. This ensures that the actual vacuum degree in the nanodose detector cavity deviates from the set value by less than 5%, thereby achieving the ionization reaction conditions of the nanodose detector.

[0023] 5. The vacuum system for precise control of gas density of nanodose detector disclosed in the present invention, based on the realization of beneficial effects 1, 2, 3, 4, through a large number of experiments and theoretical analysis, determines that the vacuum degree of the nanodose detector cavity is controlled within the range of 1Torr to 30Torr, which can ensure that the nanodose detector has an ionization avalanche event, and ensure that the measurement signal of the nanodose detector is accurate and stable. The nanodose detector counts the readout pole signal of the ionization avalanche event, and establishes an inline relationship between the nanodose quantity and the macroscopic water absorption dose according to the count result of the readout pole signal of the ionization avalanche event. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a vacuum system for precise control of gas density of a nanodose detector of the present invention;

[0025] Figure 2 It is a logical control schematic diagram of the present invention.

[0026] Among them, 1-molecular pump, 2-vortex pump a, 3-vortex pump b, 4-gas cylinder A, 5-gas cylinder B, 6-MFC flow controller, 7-static vacuum pressure sensor, 8-low vacuum pressure sensor, 9-high vacuum pressure sensor, 10-first high-pressure solenoid valve, 11-second high-pressure solenoid valve, 12-third high-pressure solenoid valve, 13-fourth high-pressure solenoid valve, 14-PLC controller. DETAILED DESCRIPTION

[0027] like Figure 1 As shown, the present embodiment discloses a vacuum system for precise control of gas density of a nanodose detector, which is composed of a vacuum pump unit, a vacuum degree detection unit, and a logic control unit.

[0028] The vacuum pump unit consists of a molecular pump 1, a vortex pump a2, a vortex pump b3, a first high-pressure solenoid valve 10, and a second high-pressure solenoid valve 11. The air inlet of the vortex pump a2 is connected to the high-pressure solenoid valve through a vacuum pipe, the air inlet of the vortex pump b3 is connected to the air outlet of the molecular pump 1 through a vacuum pipe, and the third high-pressure solenoid valve 12 is connected to the air inlet of the molecular pump 1 through a vacuum pipe. The high-pressure solenoid valve and the other side of the high-pressure solenoid valve are connected to the air outlet below the nanodose detector through a KF interface. The vortex pump a2 is used for pre-pumping to ensure that the vacuum inside the cavity drops below 20Pa. Since the vacuum degree of the molecular pump 1 needs to be below 10Pa when it is started, the vortex pump b3 is installed as a drag pump of the molecular pump 1, thereby ensuring that the pressure on both sides of the molecular pump 1 and the air inlet and outlet is less than 10Pa to complete the opening of the molecule. The stable operation of the molecular pump 1 is ensured by the coordinated use of the pump group. If the molecular pump 1 is directly opened at atmospheric pressure, the blades in the pump will be damaged and the molecular pump 1 will be damaged.

[0029] The vacuum detection unit includes a low vacuum pressure sensor 8, a high vacuum pressure sensor 9, and a static vacuum pressure sensor 7. The vacuum detection unit is used to detect the vacuum degree inside the pipeline and the cavity. The low vacuum pressure sensor 8 is installed on the sixth vacuum pipeline between the bottom air outlet and the third high-pressure solenoid valve 12, and is used to detect the vacuum degree of the sixth vacuum pipeline in real time. The high vacuum pressure sensor 9 is installed on the seventh vacuum pipeline between the molecular pump 1 and the high-pressure third high-pressure solenoid valve 12, and is used to detect the vacuum degree on the seventh pipeline to detect whether the pipeline vacuum degree reaches the start-up condition of the molecular pump 1. The static vacuum pressure is connected to the middle air outlet of the nanodose detector to detect the static vacuum degree in the cavity of the nanodose detector. The vacuum degree detection unit ensures the detection of the vacuum degree of the pipeline and the cavity, and efficiently cooperates with the PLC logic controller in the logic control unit to judge the current vacuum state, and control the action of the high-pressure solenoid valve, and then cooperates with the MFC flow controller to deliver effective gas to achieve the preset vacuum condition and gas concentration. The pipeline refers to the sixth vacuum pipeline and the seventh vacuum pipeline.

[0030] The logic control unit includes a PLC controller 14, an MFC flow control meter 6, a gas cylinder A4, a gas cylinder B5, a fourth high-pressure solenoid valve 13, and a first high-pressure solenoid valve 10. The fourth high-pressure solenoid valve 13 is connected to the gas cylinder A4, and the fourth high-pressure solenoid valve 13 is connected to the first high-pressure solenoid valve 10. One end of the MFC flow control meter 6 is connected to the gas cylinder B5, and the other end is connected to the first high-pressure solenoid valve 10. The other side of the first high-pressure solenoid valve 10 is connected to the air inlet at the top of the cavity. In addition, the PLC controller 14 is connected to the communication interface of the first high-pressure solenoid valve 10, the second high-pressure solenoid valve 11, the third high-pressure solenoid valve 12, the fourth high-pressure solenoid valve 13, the MFC, and the static vacuum pressure sensor 7. The branch vacuum value and the MFC flow meter status and flow information are collected through PLC logic control. Through serial communication and coordinated control of multiple devices, the PLC logic controller determines the current vacuum state and controls the action of the high-pressure solenoid valve, thereby coordinating with the MFC flow controller to deliver effective gas to ensure a constant concentration of sensitive gas inside the nanodose detector cavity and a negative pressure environment to achieve the measurement environment of the nanodose detector and achieve the preset vacuum conditions and gas concentration.

[0031] The working method of a vacuum system for precise control of gas density of a nanodose detector disclosed in this embodiment is as follows:

[0032] Step 1: Start the vacuum pump unit. In order to ensure the stable startup of molecular pump 1 and vortex pump, it is necessary to complete the entire startup process of the pump group and the system self-test. Start vortex pump a2 and vortex pump b3. Before starting, it is necessary to check whether the first high-pressure solenoid valve 10, the second high-pressure solenoid valve 11, the third high-pressure solenoid valve 12, the fourth high-pressure solenoid valve 13, and the MFC flow control meter 6 are closed to ensure that the pipeline connecting the molecular pump 1 vortex pump is in a sealed cover state to prevent damage to the molecular pump 1. When the high vacuum pressure sensor 9 on the pipeline reads below 20Pa, it means that the vacuum degree of the pipeline meets the startup conditions of molecular pump 1. When the startup conditions are met, start molecular pump 1. When the speed of molecular pump 1 is stable, the startup of the vacuum pump unit is completed.

[0033] Step 2: Through the PLC collaborative control, the second high-pressure solenoid valve 11 is opened to complete the pipeline conduction between the nanodose detector cavity and the vortex pump. This process is a rough air extraction process of the nanodose detector cavity, and the vacuum degree inside the nanodose detector cavity is quickly reduced to below 20Pa. When the value of the low vacuum pressure sensor 8 is ≤10Pa, it indicates that the vacuum degree of the pipeline has reached the limit of the vortex pump a2, and the nanodose detector cavity is pre-vacuumed. To completely extract the air in the nanodose detector cavity, a molecular pump 1 with a stronger pumping speed is required. At this time, the second high-pressure solenoid valve 11 is closed, and the third high-pressure solenoid valve 12 is opened to complete the pipeline conduction between the nanodose detector cavity and the molecular pump 1, so as to achieve precise air extraction of the nanodose detector cavity and extract the gas molecules more finely. The molecular pump 1 has a stronger pumping speed to keep the nanodose detector cavity at a lower vacuum degree.

[0034] Step 3: In actual situations, due to the leakage rate of the nanodose detector cavity and pipelines and the dead volume problem inside the nanodose detector cavity, the nanodose detector cavity cannot be evacuated to an absolute vacuum. At this time, gas replacement is required to minimize the gas impurities inside the nanodose detector cavity. When the value of the low vacuum pressure sensor 8 reaches 1.2Pa, close the second high-pressure solenoid valve 11 and open the intake valve. The first high-pressure solenoid valve 10 and the second high-pressure solenoid valve 11 transport the nitrogen in the gas cylinder A4 to the interior of the nanodose detector cavity, so that the nitrogen molecules occupy space inside the nanodose detector cavity, thereby rapidly raising the vacuum degree in the cavity to atmospheric pressure. When the value of the low vacuum pressure sensor 8 is ≥10 -5 When Pa, the first high-pressure solenoid valve 10 and the second high-pressure solenoid valve 11 are closed to complete the nitrogen intake process.

[0035] Step 4: Cycle steps 2 and 3, and control the content of other gases in the nanodose detector cavity except nitrogen to below 0.1% by circulating nitrogen gas washing. Cycle steps 2 and 3 16 times, and finally keep the nanodose detector cavity in a vacuum state and the first high-pressure solenoid valve 10, the second high-pressure solenoid valve 11, and the fourth high-pressure solenoid valve 13 in a closed state. The vacuum state refers to a vacuum degree ≤ 1.2Pa.

[0036] Step 5: The effective gas in the gas cylinder B5 is introduced through the MFC flowmeter to establish the relationship between the vacuum pressure and the propane gas concentration. The flow rate of the MFC flowmeter is set to 0.02mL / min. The PLC detects the value of the static vacuum gauge in real time. When the value is equal to the set value, the MFC flowmeter and the first high-pressure solenoid valve 10 are closed, and the pressure of the nanodose detector cavity is completed. The actual vacuum degree in the nanodose detector cavity is guaranteed to deviate from the set value by 5%, thereby achieving the ionization reaction conditions of the nanometer detector. The source of the 5% deviation is due to the dead volume inside the nanodose detector cavity and the adsorption of gas molecules by the deposited grease, which is a normal phenomenon. The corresponding relationship between the actual vacuum degree and the set value deviation is determined by fitting. The vacuum degree is precisely controlled according to the corresponding relationship between the actual vacuum degree and the set value deviation after fitting, that is, the precise control of the gas density in the nanodose detector cavity is achieved.

[0037] According to steps 1 to 5, the vacuum degree of the nanodose detector cavity is controlled at about 3Torr to ensure that the measurement signal of the nanodose detector is accurate and stable. The nanodose detector reads the pole signal count of the ionization avalanche event, and the inline relationship between the nanodose quantity and the macroscopic water absorption dose is established based on the readout pole signal count result.

[0038] When the vacuum degree of the nanodose detector cavity is less than 0.1 Pa, ionization avalanche events cannot occur due to the extremely low content of gas molecules inside the nanodose detector cavity.

[0039] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A vacuum system for precise control of gas density in a nanodose detector, characterized in that: It includes a vacuum pump unit, a vacuum degree detection unit, and a logic control unit; The vacuum pump group unit is composed of a molecular pump, a vortex pump a, a vortex pump b, a first high-pressure solenoid valve, and a second high-pressure solenoid valve; the air inlet of the vortex pump a is connected to the high-pressure solenoid valve through a vacuum pipe, the air inlet of the vortex pump b is connected to the air outlet of the molecular pump through a vacuum pipe, and the third high-pressure solenoid valve is connected to the air inlet of the molecular pump through a vacuum pipe; the high-pressure solenoid valve and the other side of the high-pressure solenoid valve are connected to the air outlet below the nanodose detector through a KF interface; the vortex pump a is used for pre-pumping to ensure that the vacuum degree inside the cavity drops below 20Pa. Since the vacuum degree when the molecular pump is started needs to be below 10Pa, the vortex pump b is installed as a drag pump of the molecular pump, thereby ensuring that the pressure on both sides of the molecular pump and the air inlet and outlet is less than 10Pa to complete the opening of the molecule; the stable operation of the molecular pump is ensured by the coordinated use of the pump group. If the molecular pump is turned on directly under atmospheric pressure, the blades in the pump will be damaged and the molecular pump will be damaged; The vacuum degree detection unit includes a low vacuum pressure sensor, a high vacuum pressure sensor, and a static vacuum pressure sensor. The vacuum degree detection unit is used to detect the vacuum degree inside the pipeline and the cavity; the low vacuum pressure sensor is installed on the sixth vacuum pipeline between the bottom air outlet and the third high-pressure solenoid valve, and is used to detect the vacuum degree of the sixth vacuum pipeline in real time; the high vacuum pressure sensor is installed on the seventh vacuum pipeline between the molecular pump and the high-pressure third high-pressure solenoid valve, and is used to detect the vacuum degree on the seventh pipeline to detect whether the pipeline vacuum degree reaches the molecular pump start-up condition; the static vacuum pressure is connected to the middle air outlet of the nanodose detector, and is used to detect the static vacuum degree in the nanodose detector cavity; the vacuum degree detection of the pipeline and the cavity is ensured by the vacuum degree detection unit, and the PLC logic controller in the logic control unit is efficiently coordinated to judge the current vacuum state, and the high-pressure solenoid valve is controlled to operate, and then the MFC flow controller is coordinated to deliver effective gas to achieve the preset vacuum condition and gas concentration. The pipeline refers to the sixth vacuum pipeline and the seventh vacuum pipeline; The logic control unit includes a PLC controller, an MFC flow control meter, a gas cylinder A, a gas cylinder B, a fourth high-pressure solenoid valve, and a first high-pressure solenoid valve; the fourth high-pressure solenoid valve is connected to the gas cylinder A, and the fourth high-pressure solenoid valve is connected to the first high-pressure solenoid valve; one end of the MFC flow control meter is connected to the gas cylinder B, and the other end is connected to the first high-pressure solenoid valve; the other side of the first high-pressure solenoid valve is connected to the air inlet at the top of the cavity; in addition, the PLC controller is connected to the first high-pressure solenoid valve, the second high-pressure solenoid valve, the third high-pressure solenoid valve, the fourth high-pressure solenoid valve, the MFC, and the static vacuum pressure sensor communication interface; the branch vacuum value and the MFC flow meter status and flow information are collected through the PLC logic control.

2. A vacuum system for precise control of gas density of a nanodose detector as claimed in claim 1, characterized in that: Through serial communication and coordinated control of multiple devices, the PLC logic controller determines the current vacuum state and controls the action of the high-pressure solenoid valve, and then cooperates with the MFC flow controller to deliver effective gas to ensure the constant concentration of sensitive gas inside the nanodose detector cavity and the negative pressure environment to achieve the measurement environment of the nanodose detector and meet the preset vacuum conditions and gas concentration requirements.

3. A vacuum system for precise control of gas density of a nanodose detector as claimed in claim 1 or 2, characterized in that: The working method is: Step 1: Start the vacuum pump unit; in order to ensure the stable startup of the molecular pump and the vortex pump, it is necessary to complete the entire startup process of the pump unit and the system self-check; start the vortex pump a and the vortex pump b. Before starting, it is necessary to check whether the first high-pressure solenoid valve, the second high-pressure solenoid valve, the third high-pressure solenoid valve, the fourth high-pressure solenoid valve, and the MFC flow control meter are closed to ensure that the pipeline connecting the molecular pump and the vortex pump is in a sealed cover state to prevent damage to the molecular pump; when the high vacuum pressure sensor on the pipeline indicates below 20Pa, it means that the vacuum degree of the pipeline meets the startup conditions of the molecular pump. When the startup conditions are met, the molecular pump is started. When the molecular pump speed is stable, the vacuum pump unit startup is completed; Step 2: The second high-pressure solenoid valve is opened through PLC collaborative control to complete the pipeline conduction between the nanodose detector cavity and the vortex pump. This process is a rough air extraction process of the nanodose detector cavity, and the vacuum degree inside the nanodose detector cavity is quickly reduced to below 20Pa; when the value of the low vacuum pressure sensor is ≤10Pa, it indicates that the vacuum degree of the pipeline has reached the limit of the vortex pump a, and the nanodose detector cavity is pre-vacuumed; to completely extract the air in the nanodose detector cavity, a molecular pump with a stronger pumping speed is required. At this time, the second high-pressure solenoid valve is closed and the third high-pressure solenoid valve is opened to complete the pipeline conduction between the nanodose detector cavity and the molecular pump, so as to achieve precise air extraction of the nanodose detector cavity and extract the gas molecules more finely. The molecular pump has a stronger pumping speed to keep the nanodose detector cavity at a lower vacuum degree; Step 3: In actual situations, the cavity and pipeline of the nanodose detector have leakage rates, and there is a dead volume problem inside the cavity of the nanodose detector, which makes it impossible to evacuate the cavity of the nanodose detector to an absolute vacuum. At this time, it is necessary to reduce the gas impurities inside the cavity of the nanodose detector to a minimum through gas replacement; when the value of the low vacuum pressure sensor reaches 1-3Pa, close the second high-pressure solenoid valve and open the first and second high-pressure solenoid valves of the inlet valve to transport the nitrogen in the gas cylinder A to the cavity of the nanodose detector, so that the nitrogen molecules occupy space inside the cavity of the nanodose detector, thereby rapidly raising the vacuum degree in the cavity to atmospheric pressure; when the value of the low vacuum pressure sensor is ≥10 -5 When Pa, the first high-pressure solenoid valve and the second high-pressure solenoid valve are closed to complete the nitrogen intake process; Step 4: Cycle step 2 and step 3, and control the content of other gases in the nanodose detector cavity except nitrogen to be reduced to less than 0.1% by circulating nitrogen gas washing, and cycle step 2 and step 3 15 to 20 times, and finally keep the nanodose detector cavity in a vacuum state and the first high-pressure solenoid valve, the second high-pressure solenoid valve, and the fourth high-pressure solenoid valve are all in a closed state; the vacuum state refers to a vacuum degree ≤ 1.2Pa; Step 5: The effective gas in the gas cylinder B is introduced through the MFC flowmeter to establish the relationship between the vacuum pressure and the propane gas concentration; the flow rate of the MFC flowmeter is set to 0.01-0.1 mL / min, and the PLC detects the value of the static vacuum gauge in real time. When the value is equal to the set value, the MFC flowmeter and the first high-pressure solenoid valve are closed, and the pressure equalization of the nanodose detector cavity is completed, which ensures that the deviation between the actual vacuum degree and the set value in the nanodose detector cavity is within 5%, thereby ensuring that the measurement signal is accurate and stable; the corresponding relationship between the actual vacuum degree and the set value deviation is determined by fitting, and the vacuum degree is precisely controlled according to the corresponding relationship between the actual vacuum degree and the set value deviation after fitting, that is, the precise control of the gas density in the nanodose detector cavity is achieved.

4. A vacuum system for precise control of gas density of a nanodose detector as claimed in claim 3, characterized in that: According to steps 1 to 5, the vacuum degree of the nanodose detector cavity is controlled within the range of 1 Torr to 30 Torr to ensure that the measurement signal of the nanodose detector is accurate and stable. The nanodose detector reads out the pole signal count of the ionization avalanche event, and the inline relationship between the nanodose quantity and the macroscopic water absorption dose is established based on the readout pole signal counting result.

5. A vacuum system for precise control of gas density of a nanodose detector as claimed in claim 4, characterized in that: According to step 1 to step 5, the vacuum degree of the nanodose detector cavity is controlled within the range of 2 Torr to 8 Torr.

6. A vacuum system for precise control of gas density of a nanodose detector as claimed in claim 3, characterized in that: The source of the deviation within 5% is due to the dead volume inside the nanodose detector cavity and the adsorption of gas molecules by deposited grease.

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